The specificity of any protein is determined by its primary structure. 20 proteinogenic amino acids must be encoded in nucleic acids, and information about them can be recorded only in the variable part of nucleic acids using nitrogenous bases.
Both DNA and RNA contain four basic nitrogenous bases. Only four different amino acids can be encrypted with one nitrogenous base. With two - 16 (42 \u003d 16). With a combination of four nitrogenous bases of three, 64 combinations can be made (43 \u003d 64). This is more than enough to encrypt all 20 amino acids.
A group of three nitrogenous bases (or nucleotides) in the polynucleotide chain, encoding one amino acid, is called a triplet.
In the course of decoding the nucleotide-amino acid code, the semantic meaning of each triplet was established. Of the 64 possible triplets, amino acids codes for 61. These triplets are called significant. The three remaining triplets do not code for amino acids. These triplets are called "meaningless".
The nucleotide-amino acid code is degenerate. This means that more than one significant triplet can correspond to the same amino acid. At the same time, each triplet encodes only one amino acid, which indicates that the code is unambiguous.
The nucleotide-amino acid code is universal, since the semantic meaning of triplets is the same for all living organisms. The code is written in the RNA language. It has the following structure: gli - GGA, GGG, GGU, GGTs; acha - HCA, HCG, HCU, HCTs; ser - ASU, AGC, UCA, UCG, UCU, UCTs; tre - ACA, ACG, ACU, ACC; cis - USU, UGTs; met - AUG; shaft - GUA, GUG, GUU, GUTs; lei - UUA, UUG, CUA, CUG, CUU, CUTS; those - AUA, AUU, AUC; fairies - UUU, UUC; shooting gallery - UAU, UAC; three - UGG; about - ЦЦЦ, ЦЦГ, ЦЦУ, ЦЦЦ; gis - CAU. CAC; lys - AAA, AAH; arg - AGA, AGG, TsGA, TsGG, TsGU, TsGTs; asp - GAU, GAC; glu - GAA, GAG; asn - AAU, AAC; gln - TsAA, TsAG.
Many thousands of different proteins are synthesized in cells throughout life. The unique amino acid sequence in the polypeptide chain of any protein molecule is given by the sequence of triplets in the polynucleotide chain.
The storage of information about the primary structure of all cell proteins is carried out by DNA molecules. A piece of DNA, which contains information about the primary structure of one protein, is called a gene (Greek "genos" - genus, origin), the information stored in DNA is genetic, and the nucleotide-amino acid code is called a genetic code.
DNA is a material carrier of genetic information. One of the features of genetic information is that it can be inherited, that is, passed down from generation to generation.
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Encodes the amino acid sequence of proteins using the nucleotide sequence of nucleic acids. There are only four nucleotides and twenty amino acids. If each amino acid were encoded by one nucleotide, then only 4 amino acids could be encoded. If there were two nucleotides, then only 16 amino acids could be encoded. Therefore, in order to be able to encode all the necessary amino acids, each amino acid is encoded by a combination of three nucleotides, which is called a triplet or codon.
However, there can be 64 triplets, and only 20 amino acids (plus a stop codon). Therefore, redundancy occurs in the genetic code - a situation when several different triplets can encode one amino acid.
A task
What do you think, for what this redundancy can be used, what kind does it give additional advantages?
hint
The more correct spellings of a word there are, the less chance of a mistake.
Decision
The very first and most obvious answer to this question is the word "stability". If there are several similar triplets per amino acid, then the likelihood that with a point mutation in this triplet we get the wrong amino acid in the protein decreases. Therefore, most of the codons encoding the same amino acid differ from each other by only one nucleotide "letter". The more codons a given amino acid encodes, the higher its stability; therefore, the largest number of codons encodes the most common amino acids, such as leucine and arginine; rare amino acids, for example tryptophan, on the contrary, are encoded by a single codon.
It is difficult to understand what is the cause and what is the consequence: whether the most needed amino acids began to be encoded b abouta larger number of codons (that is, the need for stability led to this very stability), or, conversely, the more codons an amino acid had (that is, the more stable it was), the more often it began to occur. Obviously, the answer to this fundamental question is akin to the answer to the question "which came before - a chicken or an egg?" and is rooted in those prehistoric and hard-to-investigate times, when the genetic code was just created and optimized.
In addition, looking at the frequency distribution of amino acids (Fig. 1), one can notice that, in general, the simpler the structure of an amino acid, the more often it occurs (for example, the same tryptophan, which has one of the most "complex" structures, is the least common). This is also understandable, since a simple structure usually means stability; A “simple” amino acid is easier to synthesize and harder to “spoil” than a “complex” one.
However, stability and resistance to mutations are not the only benefits of the redundancy of the genetic code. By playing with alternative codons, you can fine-tune various parameters related to the work of nucleic acids. And first of all, here it is necessary to mention the so-called "codon bias" (Codon usage bias).
"Codon skew" is a situation in which only one or two of the several synonymous codons in a given organism are preferred (Fig. 2). Although it has been repeatedly shown that for many organisms such a bias is a common situation, why it occurs is still not really clear. The most accepted explanation for this mysterious phenomenon in the scientific community is as follows.
As is known, each codon coding for an amino acid has its own tRNA. Some organisms have something like "favorites" tRNA, that is, there is much more tRNA for one of the synonymous codons than for the rest. If we want this protein to be synthesized quickly and correctly, we'd better not experiment with rare codons, but assemble its sequence from the most "pop" codons, for which tRNAs are more likely to float past the ribosome and will not delay translation.
The "skew" in various tRNAs is observed primarily in fast-growing organisms that require "industrial" synthesis of certain proteins. Moreover, the codon skew is observed primarily for proteins that are expressed at a high level, that is, for those for which the speed and quality of synthesis is especially important. At the same time, the nature of the occurrence of the tRNA skew is not completely clear, and what arose earlier - the codon skew or tRNA skew - is also completely incomprehensible.
However, despite all the grace, this explanation can be justly criticized. The fact is that the level of protein translation is determined primarily at the initiation stage (when the mRNA only sits on the ribosome), and not elongation (when new amino acids are attached to the protein chain). And since elongation is not a limiting stage of protein synthesis, then fussing with the selection of hundreds of optimal codons to accelerate it seems not entirely justified.
Another version of the existence of the skew is associated with the secondary structures formed by mRNA. The complementary regions of the mRNA fold into sections of the double helix - hairpins. Sometimes these hairpins play an important role in the regulation of various intracellular processes (more about this is described in the problem "Form and content"). However, on the whole, such hairpins strongly poison the existence of the protein synthesis apparatus and slow down translation. Moreover, it is easy to guess that hairpins rich in GC-pairs (guanine-cytosine pairs) will cling to each other tighter and unwind worse than AU (adenine-uracil) rich hairpins (because guanine and cytosine are linked to each other by three hydrogen bonds , and adenine and uracil - only two).
Therefore, a possible reason for the preference of certain codons is such an optimization of the mRNA, in which as few hairpins as possible will be formed on it (or, possibly, the necessary hairpins will be formed in strategic places). It is especially important that the region coding for the beginning of the protein, near which translation initiation occurs, remains "hairless", since disturbances in initiation are detrimental to translation in general (see the very recent article by Daniel B. Goodman, George M. Church, Sriram Kosuri, 2013. Causes and Effects of N-Terminal Codon Bias in Bacterial Genes).
Another mystery of codon bias is related to the fact that in some cases a clear preference is given to rare codons, usually uncharacteristic for a given species. One of the versions to explain this strange pattern is that rare codons appear where it is necessary to slow down translation (for example, where the border of protein domains passes, so that the previous domain has time to fold before the next one begins to be synthesized). However, as far as I understand, there is no serious evidence for this version yet. It should be noted that the regions encoding the very beginning, N-terminus, of the protein are usually very rich in rare codons; why is also not yet fully understood.
Finally, another interesting work suggests that for at least one organism, cyanobacteria Synechococcus elongate, in the group of circadian (circadian rhythm) genes, on the contrary, non-optimal codon skew is used - that is, not the most popular codons are used to encode these genes (Yao Xu et al., 2013. Non-optimal codon usage is a mechanism to achieve circadian clock conditionality). The authors suggest that in this way, with the help of certain molecular mechanisms, the expression of these genes is disrupted in cold conditions, when it is more profitable for a given cyanobacterium to do without circadian rhythms.
Afterword
The practical application of codon skew is primarily in the field of biotechnology. The fact is that very often sad incidents occur among biotechnologists: some gene, carefully inserted into a given organism using a biotechnological method, flatly refuses to be expressed there or is expressed too sluggishly. The reason is often that researchers do not take into account the inconsistency of the codon skew characteristic of the donor organism (from which the gene is taken) and the recipient organism (into which this gene is inserted). By changing the sequence of the gene in the right way, by inserting codons that are popular in the recipient organism, this situation can be corrected and a high level of expression can be achieved.
This can be useful in a wide range of applications - from growing proteins in bacterial cells to gene therapy, in which the correct version of the gene is inserted into the body instead of a broken, mutant version of the gene.
Independent work on the topic: "Protein biosynthesis".
Choose one of the answer options ... For each correct answer 1 point:
A1. The material carrier of hereditary information in a eukaryotic cell is:
1) i-RNA 2) t-RNA 3) DNA 4) chromosome
A2. The species of an organism can be established by analysis:
1) amino acids 2) nucleotides 3) DNA fragment 4) carbohydrates
A3. The gene encodes information about:
1) the structure of proteins, fats and carbohydrates
2) the sequence of nucleotides in DNA
3) the primary structure of the protein
4) amino acid sequences in two or more protein molecules
3) one triplet encodes a sequence of amino acids in a protein molecule
4) the code is degenerate, since amino acids can be encoded by several codons
5) the code is redundant, can encode more than 20 amino acids
6) the code is characteristic only for eukaryotic cells
AT 2. Relate the substances and structures involved in protein synthesis with their functions by putting the necessary letters next to the numbers.
OT. Build a sequence of reactions of protein biosynthesis by writing out the numbers in the required order.
1) removing information from DNA
2) recognition by the t-RNA anticodon of its codon on u - RNA
3) cleavage of amino acids from t-RNA
4) the supply of i-RNA to ribosomes
5) attachment of amino acids to the protein chain using an enzyme
AT 4. Build a sequence of translation reactions by writing out the numbers in the correct order.
1) attachment of amino acids to t-RNA
2) the beginning of the synthesis of the polypeptide chain on the ribosome
3) attachment of i-RNA to the ribosome
4) the end of protein synthesis
5) lengthening the polypeptide chain
C1.A region of one of two chains of nucleotides with thymine (T), 150 nucleotides with guanine (G) and 200 nucleotides with cytosine (C). How many nucleotides with A, T, G and C are contained in a double-stranded DNA molecule? How many amino acids
C2.It is known that all types of RNA are synthesized on a DNA template. A fragment of a DNA molecule, on which a region of the central loop of tRNA is synthesized, has the following nucleotide sequence: ATAGCTGAACGGATT. Establish the nucleotide sequence of the tRNA region that is synthesized on this fragment, and the amino acid that this tRNA will carry in the process of protein biosynthesis, if the third triplet corresponds to the tRNA anticodon. Explain the answer. Use the genetic code table to solve the problem.
Genetic code (mRNA)
Rules for using the table
The first nucleotide in the triplet is taken from the left vertical row, the second from the upper horizontal row, and the third from the right vertical row. Where the lines from all three nucleotides intersect, and the desired amino acid is located.
Hereditary information is information about the structure of a protein (information about how what amino acids in what order combine during the synthesis of the primary structure of the protein).
Information about the structure of proteins is encoded in DNA, which in eukaryotes is part of the chromosomes and is located in the nucleus. The section of DNA (chromosome) in which information about one protein is encoded is called gene.
Transcription is the rewriting of information from DNA to mRNA (messenger RNA). mRNA transfers information from the nucleus to the cytoplasm, to the site of protein synthesis (to the ribosome).
Broadcast is the process of protein biosynthesis. Inside the ribosome, tRNA anticodons are attached to the mRNA codons according to the principle of complementarity. The ribosome connects the amino acids brought by tRNA with a peptide bond, resulting in a protein.
Transcription, translation, and replication (DNA doubling) reactions are reactions matrix synthesis... DNA serves as a template for mRNA synthesis, mRNA serves as a template for protein synthesis.
Genetic code is the way in which information about the structure of a protein is recorded in DNA.
Gencode properties
1) Tripletness: one amino acid is encoded by three nucleotides. These 3 nucleotides in DNA are called a triplet, in mRNA - a codon, in tRNA - an anticodon (but in the USE there can be a "code triplet", etc.)
2) Redundancy (degeneracy): there are only 20 amino acids, and the triplets encoding amino acids - 61, so each amino acid is encoded by several triplets.
3) Unambiguity: each triplet (codon) encodes only one amino acid.
4) Versatility: the genetic code is the same for all living organisms on Earth.
Tasks
Nucleotide / Amino Acid Tasks
3 nucleotides \u003d 1 triplet \u003d 1 amino acid \u003d 1 tRNA
Tasks at ATGC
DNA mRNA tRNA
A U A
T A U
G C G
C G C
Choose the one that is most correct. mRNA is a copy
1) one gene or a group of genes
2) chains of a protein molecule
3) one protein molecule
4) parts of the plasma membrane
Answer
Choose the one that is most correct. The primary structure of a protein molecule, given by the sequence of mRNA nucleotides, is formed in the process
1) broadcasts
2) transcriptions
3) reduplications
4) denaturation
Answer
Choose the one that is most correct. What sequence correctly reflects the path of genetic information realization?
1) gene -\u003e mRNA -\u003e protein -\u003e trait
2) trait -\u003e protein -\u003e mRNA -\u003e gene -\u003e DNA
3) mRNA -\u003e gene -\u003e protein -\u003e trait
4) gene -\u003e DNA -\u003e trait -\u003e protein
Answer
Choose the one that is most correct. Choose the correct sequence of information transmission in the process of protein synthesis in the cell
1) DNA -\u003e messenger RNA -\u003e protein
2) DNA -\u003e transport RNA -\u003e protein
3) ribosomal RNA -\u003e transport RNA -\u003e protein
4) ribosomal RNA -\u003e DNA -\u003e transport RNA -\u003e protein
Answer
Choose the one that is most correct. The same amino acid corresponds to the CAA anticodon on the transport RNA and the triplet on the DNA
1) CAA
2) CUU
3) GTT
4) GAA
Answer
Choose the one that is most correct. Anticodon AAU on the transport RNA corresponds to a triplet on DNA
1) TTA
2) AAT
3) AAA
4) TTT
Answer
Choose the one that is most correct. Each amino acid in the cell is encoded
1) one molecule of DNA
2) several triplets
3) multiple genes
4) one nucleotide
Answer
Choose the one that is most correct. Functional unit of the genetic code
1) nucleotide
2) triplet
3) amino acid
4) tRNA
Answer
Choose three options. As a result of matrix-type reactions, molecules are synthesized
1) polysaccharides
2) DNA
3) monosaccharides
4) mRNA
5) lipids
6) squirrel
Answer
1. Determine the sequence of processes providing protein biosynthesis. Write down the corresponding sequence of numbers.
1) the formation of peptide bonds between amino acids
2) attachment of the tRNA anticodon to the complementary codon of the mRNA
3) synthesis of mRNA molecules on DNA
4) movement of mRNA in the cytoplasm and its location on the ribosome
5) delivery by tRNA of amino acids to the ribosome
Answer
2. Establish the sequence of the processes of protein biosynthesis in the cell. Write down the corresponding sequence of numbers.
1) the formation of a peptide bond between amino acids
2) the interaction of the mRNA codon and the tRNA anticodon
3) release of tRNA from the ribosome
4) the connection of mRNA with the ribosome
5) release of mRNA from the nucleus into the cytoplasm
6) mRNA synthesis
Answer
3. Establish the sequence of processes in protein biosynthesis. Write down the corresponding sequence of numbers.
1) synthesis of mRNA on DNA
2) delivery of amino acids to the ribosome
3) the formation of a peptide bond between amino acids
4) attachment of amino acids to tRNA
5) the connection of mRNA with two ribosome subunits
Answer
4. Establish the sequence of steps of protein biosynthesis. Write down the corresponding sequence of numbers.
1) separation of the protein molecule from the ribosome
2) attachment of tRNA to the start codon
3) transcription
4) lengthening the polypeptide chain
5) release of mRNA from the nucleus into the cytoplasm
Answer
5. Establish the correct sequence of protein biosynthesis processes. Write down the corresponding sequence of numbers.
1) attachment of amino acid to peptide
2) synthesis of mRNA on DNA
3) recognition by the codon of the anticodon
4) combining mRNA with ribosome
5) release of mRNA into the cytoplasm
Answer
Choose the one that is most correct. Which anticodon of the transport RNA corresponds to the TGA triplet in the DNA molecule?
1) ACU
2) CUG
3) CAA
4) AHA
Answer
Choose the one that is most correct. The genetic code is universal, since
1) each amino acid is encoded by three nucleotides
2) the place of an amino acid in a protein molecule is determined by different triplets
3) it is the same for all creatures living on Earth
4) several triplets encode one amino acid
Answer
Choose the one that is most correct. A piece of DNA containing information about one polypeptide chain is called
1) chromosome
2) triplet
3) genome
4) code
Answer
Choose the one that is most correct. Broadcasting is a process by which
1) the number of DNA strands is doubled
2) mRNA is synthesized on the DNA matrix
3) proteins are synthesized on the mRNA matrix in the ribosome
4) hydrogen bonds between DNA molecules are broken
Answer
Choose three options. Protein biosynthesis, in contrast to photosynthesis, occurs
1) in chloroplasts
2) in mitochondria
3) in reactions of plastic exchange
4) in reactions of the matrix type
5) in lysosomes
6) in leukoplasts
Answer
Choose the one that is most correct. The translation matrix is \u200b\u200ba molecule
1) tRNA
2) DNA
3) rRNA
4) mRNA
Answer
All but two of the following traits can be used to describe the functions of nucleic acids in a cell. Identify two signs that "fall out" from the general list, and write down the numbers under which they are indicated in the table.
1) carry out homeostasis
2) transfer hereditary information from the nucleus to the ribosome
3) participate in protein biosynthesis
4) are part of the cell membrane
5) transport amino acids
Answer
AMINO ACIDS - IRNA CODONS
How many mRNA codons encode information about 20 amino acids? In the answer, write down only the corresponding number.
Answer
AMINO ACIDS - NUCLEOTIDES IRNA
1. A region of a polypeptide consists of 28 amino acid residues. Determine the number of nucleotides in the mRNA region that contains information about the primary structure of the protein.
Answer
2. How many nucleotides does mRNA contain if the protein synthesized from it consists of 180 amino acid residues? In the answer, write down only the corresponding number.
Answer
3. How many nucleotides does mRNA contain if the protein synthesized from it consists of 250 amino acid residues? In the answer, write down only the corresponding number.
Answer
4. Protein consists of 220 amino acid units (residues). Set the number of nucleotides of the region of the mRNA molecule encoding the given protein In the answer, write down only the corresponding number.
Answer
AMINO ACIDS - DNA NUCLEOTIDES
1. Protein consists of 140 amino acid residues. How many nucleotides are there in the region of the gene that encodes the primary structure of this protein?
Answer
2. Protein consists of 180 amino acid residues. How many nucleotides are there in the gene that encodes the amino acid sequence in this protein. In the answer, write down only the corresponding number.
Answer
3. A fragment of a DNA molecule encodes 36 amino acids. How many nucleotides does this fragment of the DNA molecule contain? Write down the corresponding number in your answer.
Answer
4. The polypeptide consists of 20 amino acid units. Determine the number of nucleotides in the gene region that encode these amino acids in the polypeptide. Write your answer as a number.
Answer
5. How many nucleotides in the gene region encode a protein fragment of 25 amino acid residues? In response, write down only the corresponding number.
Answer
6. How many nucleotides in a fragment of the template DNA chain encode 55 amino acids in a fragment of a polypeptide? In the answer, write down only the corresponding number.
Answer
AMINO ACIDS - tRNA
1. How many tRNAs took part in protein synthesis, which includes 130 amino acids? Write the appropriate number in your answer.
Answer
2. A fragment of a protein molecule consists of 25 amino acids. How many tRNA molecules were involved in its creation? In the answer, write down only the corresponding number.
Answer
3. How many molecules of transport RNAs were involved in translation if the gene region contains 300 nucleotide residues? In the answer, write down only the corresponding number.
Answer
4. Protein consists of 220 amino acid units (residues). Establish the number of tRNA molecules required to transport amino acids to the site of protein synthesis. In the answer, write down only the corresponding number.
Answer
AMINO ACIDS - TRIPLETS
1. How many triplets does a DNA fragment encoding 36 amino acids contain? Write down the corresponding number in your answer.
Answer
2. How many triplets do 32 amino acids code? In response, write down only the corresponding number.
Answer
NUCLEOTIDES - AMINO ACIDS
1. What is the number of amino acids encoded in the region of the gene containing 129 nucleotide residues?
Answer
2. How many amino acids are encoded by 900 nucleotides? In response, write down only the corresponding number.
Answer
3. What is the number of amino acids in a protein if its coding gene consists of 600 nucleotides? In response, write down only the corresponding number.
Answer
4. How many amino acids does 1203 nucleotides code for? In response, write down only the number of amino acids.
Answer
5. How many amino acids are needed for the synthesis of a polypeptide if the coding part of the mRNA contains 108 nucleotides? In the answer, write down only the corresponding number.
Answer
MRNA NUCLEOTIDES - DNA NUCLEOTIDES
An mRNA molecule takes part in protein synthesis, a fragment of which contains 33 nucleotide residues. Determine the number of nucleotide residues in the region of the template DNA chain.
Answer
NUCLEOTIDES - tRNA
How many RNA transport molecules were involved in translation if the gene region contains 930 nucleotide residues?
Answer
TRIPLETS - IRNA NUCLEOTIDES
How many nucleotides are there in a fragment of an mRNA molecule if a fragment of the coding DNA strand contains 130 triplets? In the answer, write down only the corresponding number.
Answer
tRNA - AMINO ACIDS
Determine the number of amino acids in the protein if 150 t-RNA molecules participated in the translation process. In the answer, write down only the corresponding number.
Answer
JUST
How many nucleotides are there in one mRNA codon?
Answer
How many nucleotides are there in one mRNA stop codon?
Answer
How many nucleotides are there in the tRNA anticodon?
Answer
COMPLICATED
A protein has a relative molecular weight of 6000. Determine the number of amino acids in a protein molecule if the relative molecular weight of one amino acid residue is 120. In your answer, write down only the corresponding number.
Answer
There are 3000 nucleotides in two strands of the DNA molecule. Information about the structure of a protein is encoded on one of the strands. Count how many amino acids are encoded on one DNA strand. In response, write down only the number corresponding to the number of amino acids.
Answer
Choose the one that is most correct. The same amino acid corresponds to the UCA anticodon on the transport RNA and the triplet in the gene on DNA
1) GTA
2) ACA
3) TGT
4) TCA
Answer
Choose the one that is most correct. The synthesis of hemoglobin in the cell controls a certain segment of the DNA molecule, which is called
1) codon
2) triplet
3) genetic code
4) genome
Answer
In which of the listed organelles of the cell occur matrix synthesis reactions? Identify three true statements from the general list, and write down the numbers under which they are indicated.
1) centrioles
2) lysosomes
3) Golgi apparatus
4) ribosomes
5) mitochondria
6) chloroplasts
Answer
Consider the picture depicting the processes taking place in the cell, and indicate A) the name of the process indicated by the letter A, B) the name of the process indicated by the letter B, C) the name of the type of chemical reactions. For each letter, select the appropriate term from the list provided.
1) replication
2) transcription
3) broadcast
4) denaturation
5) exothermic reactions
6) substitution reactions
7) reactions of matrix synthesis
8) cleavage reactions
Answer
Review the figure and indicate (A) the name of process 1, (B) the name of process 2, (c) the final product of process 2. For each letter, select the appropriate term or the corresponding concept from the list provided.
1) tRNA
2) polypeptide
3) ribosome
4) replication
5) broadcast
6) conjugation
7) ATP
8) transcription
Answer
1. Establish a correspondence between the processes and stages of protein synthesis: 1) transcription, 2) translation. Write down the numbers 1 and 2 in the correct order.
A) transfer of amino acids to t-RNA
B) DNA is involved
C) synthesis of i-RNA
D) formation of a polypeptide chain
D) occurs on the ribosome
Answer
2. Establish a correspondence between characteristics and processes: 1) transcription, 2) translation. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) three types of RNA are synthesized
B) occurs with the help of ribosomes
C) a peptide bond is formed between monomers
D) in eukaryotes occurs in the nucleus
E) DNA is used as a matrix
E) carried out by the enzyme RNA polymerase
Answer
Establish a correspondence between the characteristics and types of matrix reactions: 1) replication, 2) transcription, 3) translation. Write down the numbers 1-3 in the order corresponding to the letters.
A) Reactions take place on ribosomes.
B) RNA serves as a matrix.
C) A biopolymer is formed containing nucleotides with thymine.
D) The synthesized polymer contains deoxyribose.
E) A polypeptide is synthesized.
E) RNA molecules are synthesized.
Answer
All but two of the following attributes are used to describe the process depicted in the figure. Identify two signs that "fall out" from the general list, and write down the numbers under which they are indicated.
1) according to the principle of complementarity, the nucleotide sequence of a DNA molecule is translated into a sequence of nucleotides of molecules of various types of RNA
2) the process of translating a nucleotide sequence into an amino acid sequence
3) the process of transferring genetic information from the nucleus to the site of protein synthesis
4) the process takes place in ribosomes
5) the result of the process is the synthesis of RNA
Answer
The molecular weight of the polypeptide is 30,000 cu. Determine the length of the gene encoding it if the average molecular weight of one amino acid is 100, and the distance between nucleotides in DNA is 0.34 nm. In the answer, write down only the corresponding number.
Answer
Choose from the following reactions two related to reactions of the matrix synthesis. Write down the numbers under which they are indicated.
1) cellulose synthesis
2) synthesis of ATP
3) protein biosynthesis
4) oxidation of glucose
5) DNA replication
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated in the table. Matrix reactions in the cell include
1) DNA replication
2) photolysis of water
3) RNA synthesis
4) chemosynthesis
5) protein biosynthesis
6) synthesis of ATP
Answer
All but two of the features below can be used to describe the process of protein biosynthesis in a cell. Identify two signs that "fall out" from the general list, and write in the answer the numbers under which they are indicated.
1) The process takes place in the presence of enzymes.
2) The central role in the process belongs to RNA molecules.
3) The process is accompanied by the synthesis of ATP.
4) Amino acids serve as monomers for the formation of molecules.
5) The assembly of protein molecules is carried out in lysosomes.
Answer
Find three mistakes in the above text. Indicate the numbers of the proposals in which they are made. (1) In protein biosynthesis, matrix synthesis reactions occur. (2) Matrix synthesis reactions include only replication and transcription reactions. (3) As a result of transcription, mRNA is synthesized, the template for which is the entire DNA molecule. (4) After passing through the pores of the nucleus, mRNA enters the cytoplasm. (5) Messenger RNA is involved in the synthesis of tRNA. (6) Transport RNA provides the delivery of amino acids for protein assembly. (7) The energy of ATP molecules is expended to combine each of the amino acids with tRNA.
Answer
All but two of the following concepts are used to describe a broadcast. Identify two signs that "fall out" from the general list, and write down the numbers under which they are indicated.
1) matrix synthesis
2) mitotic spindle
3) polysome
4) peptide bond
5) higher fatty acids
Answer
All but two of the features listed below are used to describe the processes required for the synthesis of a polypeptide chain. Identify two signs that "fall out" from the general list, and write down the numbers under which they are indicated.
1) transcription of messenger RNA in the nucleus
2) transport of amino acids from the cytoplasm to the ribosome
3) DNA replication
4) the formation of pyruvic acid
5) compound of amino acids
Answer
© D.V. Pozdnyakov, 2009-2019
Basic concepts and keywords to the topic:
Nucleic acid Nucleotide
Nitrogen bases Replication
Genetic information Gene
Transcription Genetic code
Codon, genetic anticodon Broadcast
Amino Acid Protein Biosynthesis
Polymerase
DNA - deoxyribonucleic acid is a biological macromolecule, a carrier of genetic information in all eukaryotic and prokaryotic cells and in many viruses.
In 1928 F. Griffith discovered in pneumococci the phenomenon of transformation (transformation of the properties of bacteria). The nature of the transforming agent was established by Avery, McLeod, and McCarthy in 1944 and turned out to be DNA. Thus, the discovery and study of transformation proved the role of DNA as a material carrier of hereditary information.
A three-dimensional model of the spatial structure of double-stranded DNA was described in the Aperlian journal Nature in 1953 by J. Watson, Francis Crick and Maurice Wilkins. These studies formed the basis of molecular biology, which studies the basic properties and manifestations of life at the molecular level.
The structure of DNA is a polymer, the structural unit of which is a nucleotide.
The nucleotide consists of a purine nitrogenous base: adenine (A) or guanine (G) or pyrimidine: cytonine (C) or thymine (T), a deoxyribose carbohydrate (five-carbon sugar ring) and a phosphoric acid residue (HPO-3). The double helix of DNA is right-handed. 10 base pairs make up a full 360 ° rotation, therefore, each base pair is rotated 36 degrees around the spiral relative to the next pair. Phosphate groups are located outside the spirals, while the bases are inside and are located at intervals of 34 nm. The chains are held together by hydrogen bonds between the bases and are twisted around each other and around a common axis.
An important role in the development of the DNA model was played by the observations of Chargaff (1949) that the quantitative ratios of gaunine are always equal to the content of cytosine, and the content of adenine corresponds to the content of thymine. This provision has been called the "Chargaff rule":
A \u003d T; G \u003d C or A + G / C + T \u003d 1
The nucleotides are linked in a polynucleotide chain by bonds between the 5 'position of one pentose end and the 3' position of the next pentose ring through a phosphate group to form phosphodiester bridges, i.e. the sugar-phosphate backbone of DNA consists of 5 '- 3' bonds. Genetic information is written in a sequence of nucleotides from the 5 'end to the 3' end - this strand is called sense DNA, where the genes are located. The second strand of direction 3'-5 'is considered antisense, but it is a necessary “standard” for storing genetic information. The antisense strand plays an important role in the processes of replication and repair (restoration of the structure of damaged DNA). Bases in antiparallel threads form complementary pairs due to hydrogen bonds: A + T; G + C. Thus, the structure of one strand determines the nucleotide sequence of the other strand. Therefore, the base sequences in DNA strands are always antiparallel and complementary.
The principle of complementarity is universal for replication and transcription processes.
Several modifications of the DNA molecule are currently described. DNA polymorphism is the ability of a molecule to take on various configurations.
Knowledge of the structure and function of DNA is necessary to understand the essence of some genetic processes, which are matrix. It was clear that DNA itself cannot play the role of a matrix in the synthesis of proteins from amino acids, since almost all of it is found in the chromosomes located in the nucleus, while most, if not all, cellular proteins are synthesized in the cytoplasm. Thus, the genetic information contained in DNA must be transferred to some intermediate molecule that would be transported into the cytoplasm and participate in the synthesis of polypeptide chains. The assumption that such an intermediate molecule could be RNA began to be seriously considered as soon as the structure of the DNA double helix was discovered. First, cells that synthesize a large amount of protein contained a lot of RNA. Second, it seemed even more important that the sugar-phosphate "skeletons" of DNA and RNA are extremely similar and it would be easy to imagine how the synthesis of single RNA strands on single-stranded DNA occurs with the formation of unstable hybrid molecules, one strand of which is represented by DNA, and the other RNA. The relationship between DNA, RNA and protein in 1953 was presented in the following diagram:
transcription broadcast
DNA replication --------- → RNA --------- → protein,
where single strands of DNA serve as templates for the synthesis of complementary DNA molecules (replication). In turn, RNA molecules serve as templates for the sequential connection of amino acids with the formation of polypeptide chains of proteins in a process so named because the “text” written in the “language” of nucleotides is translated (translated) into the “language” of amino acids. A group of nucleotides encoding one amino acid is called codon.
RNA - ribonucleic acid, has much in common with the structure of DNA, but differs from it in a number of features:
q RNA carbohydrate, to which purine or pyrimidine bases and phosphate groups are attached, is ribose;
q RNA, like DNA, contains nitrogenous bases adenine, guanine and cytosine. But RNA does not contain thymine, its place in the RNA molecule is occupied by uracil;
q RNA is a single-stranded molecule;
q since the RNA molecule is single-stranded, the Chargaff rule established for DNA may not be fulfilled due to the equality of the base content.
Ribonucleic acids (RNA), present in both pro- and eukaryotic cells, are of three main types: messenger RNA (mRNA), ribosomal RNA (rRNA), and transport RNA (tRNA).
The nucleus of eukaryotic cells contains RNA of the fourth type, heterogeneous nuclear RNA (hnRNA), which is an exact copy (transcript) of the corresponding DNA.
The tRNA molecules recognize the corresponding triplet (codon in mRNA) in the cytoplasm and transfer the required amino acid to the growing polypeptide chain. Recognition of a codon in mRNA is carried out using three consecutive bases in tRNA, called anticodons. It is believed that there is at least one tRNA for each amino acid.
Genetic code- a unified system for recording hereditary information in nucleic acid molecules in the form of a sequence of nucleotides. The genetic code is based on the use of an alphabet consisting of only four letters - nucleotides, differing in nitrogenous bases: A, T, C, G. Attempts to decipher the genetic code were undertaken in 1954 by G. Gamov. the basic properties of the code, tripletness and degeneracy, were revealed in 1961 by F. Crick and S. Brenner.
In 1961, the first triplet sequence was deciphered for the first time. The system containing artificial mRNA, consisting only of uracil nucleotides, synthesized a polypeptide chain, consisting only of phenylalanine (in the DNA the code for it must be a complementary triplet of nucleotides - AAA). By 1965, the entire genetic code was deciphered. Out of 64 codons, three codons UAH, UAA, and UGA do not encode amino acids; they were named nonsense codons. They were later shown to be termination codons.
Currently, the determination of the nucleotide sequences of DNA and RNA is carried out using a special method - sequencing.
Properties of the genetic code.
1. The genetic code is triplet. Triplet (codon) - a sequence of three nucleotides that encodes one amino acid.
2. The degeneracy of the genetic code is due to the fact that one amino acid can be encoded by several triplets (amino acids - 20, and triplets - 64), with the exception of methionine and tryptophan, which are encoded by only one triplet. Three triplets of UAA, UAH, UGA are stop signals (termination codons) that stop the synthesis of the polypeptide chain. The triplet corresponding to methionine (AUG) performs the function of initiation (excitation) of reading and does not encode an amino acid if it is at the beginning of the DNA chain.
3. Unambiguity - each given codon corresponds to one and only one definite amino acid.
4. The genetic code is not overlapping - the process of reading the genetic code does not allow for the possibility of overlapping codons. Starting at a certain codon, the next reading goes without gaps up to nonsense codons.
5. The genetic code is universal; all information in nuclear genes for all organisms with different levels of organization is encoded in the same way.
Matrix processes in the cell.
There are three types of matrix processes in cells: replication, transcription, and translation.
The main functional significance of the DNA replication process is to supply the offspring with genetic information that must be transmitted completely and with very high accuracy.
Replication is the duplication of DNA that occurs at the synthetic (S) stage of interphase before each cell division.
Conservative replication. The original double-stranded DNA molecule serves as a template for the formation of a completely new double-stranded molecule, which is completely completed on the original.
Semi-conservative replication. Two strands of DNA unravel (like a zipper). Each chain serves as a matrix for the formation of a new one. During replication, the DNA molecule is gradually divided by a special enzyme into two halves in the longitudinal direction. As the nucleotides of the molecule to be separated are opened, free nucleotides previously synthesized in the cytoplasm are immediately attached to them. As a result, each half helix becomes whole again, and instead of one molecule, two are obtained, as a result of which the chromosome becomes dichromatid.
Dispersion replication. The original DNA breaks down into short fragments of different lengths, used as templates for constructing fragments of two new double helices, which are then reconstituted into a single molecule structure. The formed DNA molecules contain old and new fragments.
M. Meselson and F. Stahl, using the autoradiographic method, showed that the semi-conservative replication method is characteristic of all eukaryotes and most prokaryotes.
In 1955 A. Kornberg and his colleagues at Stanford University discovered an enzyme that ensures DNA replication, and named it polymerase.
At the present stage, among the enzymes participating in DNA synthesis, DNA polymerases I, II, IIIhaving 5 '→ 3' polymerase activity.
Since DNA polymerases catalyze replication only in the 5 '→ 3' direction, and the parental DNA strands are antiparallel, only one of the new strands is synthesized continuously. This chain is called leading. The second chain called lagging behind synthesized in the form of DNA fragments - fragments of Okazaki, which in eukaryotes have a sequence of 100-200 nucleotides. These fragments are ligated (stitched) by polynucleotide ligases, and a continuous chain is formed. This process is called maturation. The synthesis of each Okazaki fragment (3 '→ 5') begins on a small RNA fragment (about 10-60 nucleotides), which is removed before the end of the fragment reading. This is the so-called seed, or primer.
In any human cell, under the influence of various factors, thousands of random changes occur in DNA every day, and during the year only a very small number of stable changes in the DNA nucleotide sequence accumulates in each cell. Among the multiple random base substitutions in DNA, only one in a thousand leads to a mutation. All other damage is very effectively eliminated in the process reparations DNA. The mechanism of repair ("healing" of DNA damage) is based on the fact that a DNA molecule has two copies of genetic information - one in each of the strands of the molecule. The main pathway of repair includes three stages:
1. The altered portion of the damaged DNA strand is recognized and removed using DNA-repairing nucleases. There is a gap in the DNA helix at this point;
2. DNA-polymerase and glycosylases fill this gap by attaching nucleotides one after another, copying information from an integral strand;
3. DNA ligase "sutures" the breaks and completes the restoration of the molecule.
Transcription (rewriting) is the synthesis of mRNA (the primary product of the gene) on the DNA template, which is carried out in the nucleus on a sense DNA strand in a relaxed state. This is the first step in protein synthesis. Messenger RNA (mRNA) contains genetic instructions for the synthesis of a specific polypeptide and transfers it to the protein-synthesizing apparatus of the cell, which is located in the ribosomes of the cytoplasm of cells.
To initiate transcription, a special region in the DNA called promoter... When RNA polymerase binds to a promoter, local unwinding of the DNA double helix occurs and an open promoter region is formed.
Elongation (elongation) of the RNA strand is the stage of transcription that occurs after the attachment of 8 ribonucleotides. In this case, the moving RNA polymerase along the DNA chain acts like a zipper, opening a double helix that closes behind the enzyme as the corresponding RNA bases pair with DNA bases.
Termination(cessation of growth) of an mRNA strand occurs at specific regions of DNA called terminators.
The process of forming mature RNA molecules from precursors is called processing, as a result of which the molecules undergo modification at the 5 '→ 3' ends and splicing. Splicing heterogeneous nuclear RNA is the removal of RNA sequences corresponding to DNA introns and the connection of regions with transcribed exon sequences.
Broadcast (translation) - the process of translating mRNA genetic information into a polypeptide structure. This is the second stage of protein synthesis, carried out by sequential polycondensation of individual amino acid residues, starting from the amino terminus of the polypeptide chain to the carboxyl terminus.
Mature messenger RNA enters the cytoplasm, where the translation process is carried out - decoding of mRNA into the amino acid sequence of the protein. The decoding process is carried out from 5 '→ 3' and takes place in the ribosomes. The complex of mRNA and ribosomes is called polysome.
Translation begins with the old codon AUG, which, when localized in the sense part of the structural gene, encodes the amino acid methionine. Each amino acid is delivered to the polysome by a transport RNA (tRNA) specific to that amino acid. tRNA acts as an intermediary between the mRNA codon and the amino acid. The tRNA molecules recognize the corresponding triplet (codon in mRNA) in the cytoplasm according to the principle of pairing of complementary nitrogenous bases. tRNA, which approaches the small subunit, forms a codon-anticodon bond, while simultaneously transferring its amino acid to the aminoacyl site (A-site) of the large subunit. The anticodon of only the tRNA that carries methionine "fits" to the AUG codon. Therefore, first of all, methionine is delivered to the ribosome. Then the AUG codon passes to the peptidyl region of the large subunit (P-region). As a result of these processes, a translating ribosome is formed - an initiating complex.
Termination(completion of synthesis) occurs at the command of the codons UAA, UAG, UGA. In nature, there are no tRNA molecules whose anticodons would correspond to these codons.
Polymerase chain reaction (PCR) was discovered in 1984 by Carey
B. Mullis. It is based on the fact that newly synthesized nucleic acid chains can serve as templates in the following replication cycles:
q double-stranded DNA, when heated, is divided into composing single-stranded chains and in this state can serve as a template for replication;
q single-stranded DNA strands are incubated in the presence of DNA polymerase and a solution containing a mixture of all 4 nucleotides, as well as specific DNA sequences (primers), which leads to the synthesis of copies of two DNA molecules.
Then the procedures are repeated from the beginning, and copying of both old and new single-stranded chains occurs with the formation of the third and fourth DNA molecules, then all four are copied again, and so on. As a result, 20-30 cycles amplified(copy number increases) effective amount of DNA. A single cycle takes about 5 minutes, while cell-free molecular cloning of a DNA fragment takes only a few hours.
The PCR method is very sensitive: it allows detecting only one DNA molecule present in the sample. The method has been widely used in prenatal diagnosis of hereditary diseases, detection of viral infections, as well as in forensic medicine, since it makes it possible to carry out genetic "fingerprinting" even on a single cell.
