RNA most often consists of. Template RNA

Assembly of an RNA molecule from nucleotides occurs under the action of RNA polymerase. This enzyme is a large protein that has a number of properties necessary at different stages of the synthesis of the RNA molecule.
1. On a DNA strand At the very beginning of each gene lies a nucleotide sequence called a promoter. The RNA polymerase enzyme carries recognition and complementary binding sites to the promoter. The binding of this enzyme to this site is necessary to initiate the assembly of the RNA molecule.

2. After linking with RNA polymerase promoter unwinds the DNA helix in a section occupying approximately two turns, which leads to the divergence of DNA chains in this section.

3. RNA polymerase begins to move along the DNA chain, causing temporary unwinding and divergence of its two chains. As this movement progresses, at each stage a new activated nucleotide is added to the end of the growing RNA chain. The process goes like this:
a) first, a hydrogen bond is formed between the nitrogenous base of the terminal DNA nucleotide and the nitrogenous base of the RNA nucleotide coming from the karyoplasm;
b) then RNA polymerase sequentially cleaves off two phosphates from each RNA nucleotide, releasing them when high-energy phosphate bonds are broken large number energy that immediately goes to education covalent bond between the remaining phosphate of the RNA nucleotide and the terminal ribose of the growing RNA strand;

c) when RNA polymerase reaches the end of the gene along the DNA chain, it interacts with a sequence of nucleotides, which is called the termination sequence; As a result of this interaction, RNA polymerase and the newly synthesized RNA molecule are detached from the DNA chain. After this, RNA polymerase can be used again to synthesize new RNA molecules;
d) weak hydrogen bonds between the newly synthesized RNA molecule and the DNA template are broken, and the connection between complementary DNA strands is restored, since the affinity between them is higher than between DNA and RNA. Thus, the RNA chain is separated from the DNA, remaining in the karyoplasm.

Thus genetic code, « recorded"on DNA, is complementarily transferred to the RNA strand. In this case, ribonucleotides can form only the following combinations with deoxyribonucleotides.

Attachment of a ribonucleotide to a DNA chain during the assembly of RNA, which carries the genetic code from genes into the cytoplasm.
The enzyme RNA polymerase moves along the DNA strand and ensures the assembly of RNA.

Types and types of RNA cells

There are three types of RNA, each of which plays a specific role in protein synthesis.
1. Messenger RNA transfers the genetic code from the nucleus to the cytoplasm, thus determining the synthesis of various proteins.
2. Transfer RNA carries activated amino acids to ribosomes for the synthesis of polypeptide molecules.
3. Ribosomal RNA in complex with approximately 75 different proteins forms ribosomes - cellular organelles on which polypeptide molecules are assembled.

It is a long single-chain molecule present in the cytoplasm. This RNA molecule contains from several hundred to several thousand RNA nucleotides, forming codons strictly complementary to DNA triplets.

A fragment of an RNA molecule containing three codons - CCG, UCU and GAA,
which ensure the attachment of three amino acids - proline, serine and glutamic acid, respectively, to the growing protein molecule.

Movement of a messenger RNA molecule along two ribosomes.
As the codon passes along the surface of the ribosome, the corresponding amino acid is attached to the growing polypeptide chain (shown near the right ribosome).
Transfer RNAs deliver amino acids to the growing polypeptide chain.

Another type of RNA, which plays a critical role in protein synthesis, is called transport RNA because it transports amino acids to the protein molecule under construction. Each transfer RNA specifically binds to only one of the 20 amino acids that make up protein molecules. Transfer RNAs act as carriers of specific amino acids, delivering them to ribosomes on which polypeptide molecules are assembled.

Each specific transfer RNA recognizes “its” codon of the messenger RNA attached to the ribosome and delivers the corresponding amino acid to the appropriate position in the synthesized polypeptide chain.

Transfer RNA strand much shorter than messenger RNA, containing only about 80 nucleotides and packaged in a cloverleaf shape. At one end of the transfer RNA there is always adenosine monophosphate (AMP), to which the transported amino acid is attached through the hydroxyl group of ribose.

Transfer RNAs serve to attach specific amino acids to the polypeptide molecule under construction, therefore it is necessary that each transfer RNA has specificity for the corresponding codons of the messenger RNA. The code by which transfer RNA recognizes the corresponding codon on the messenger RNA is also a triplet and is called an anticodon. The anticodon is located approximately in the middle of the transfer RNA molecule.

During protein synthesis, the nitrogenous bases of the anticodon transfer RNA are attached using hydrogen bonds to the nitrogenous bases of the messenger RNA codon. Thus, on the messenger RNA they line up in in a certain order different amino acids one after another, forming the corresponding amino acid sequence of the synthesized protein.

January 12, 2018

In the article presented to your attention, we propose to study and build a comparative table of DNA and RNA. To begin with, it must be said that there is a special section of biology that deals with the storage, implementation and transmission of hereditary information, its name is molecular biology. It is this area that we will touch upon next.

We will talk about polymers (high molecular weight organic compounds) formed from nucleotides, which are called nucleic acids. These connections perform very important functions, one of which is storing information about the body. In order to compare DNA and RNA (the table will be presented at the very end of the article), you need to know that there are two types in total nucleic acids involved in protein biosynthesis:

deoxyribonucleic acid, which we often see as an abbreviation - DNA;
ribonucleic acid (or RNA for short)

Nucleic acid: what is it?

In order to create a table comparing DNA and RNA, it is necessary to become more familiar with these polynucleotides. Let's start with general issue. Both DNA and RNA are nucleic acids. As mentioned earlier, they are formed from nucleotide residues.

These polymers can be found in absolutely any cell of the body, since it is on their shoulders that a great responsibility is entrusted, namely:

storage;
broadcast;
implementation of heredity.

Now we will very briefly highlight their main chemical properties:

dissolves well in water;
practically insoluble in organic solvents;
sensitive to temperature changes;
if a DNA molecule is isolated in any possible way from natural source, then fragmentation can be observed during mechanical actions;
fragmentation occurs by enzymes called nucleases.

Similarities and differences between DNA and RNA: pentoses

In the table comparing DNA and RNA, it is important to note one very important similarity between them - the presence of monosaccharides. It is important to note that each nucleic acid has its own distinct form. The division of nucleic acids into DNA and RNA occurs as a result of the fact that they have different pentoses.

For example, we can find deoxyribose in DNA, and ribose in RNA. Note the fact that there is no oxygen at the second carbon atom in deoxyribose. Scientists have made the following assumption - the absence of oxygen has the following meaning:

it shortens the C 2 and C 3 bonds;
adds strength to the DNA molecule;
creates conditions for the placement of a massive molecule in the nucleus.

Comparison of nitrogenous bases

So, there are five nitrogenous bases in total:

A (adenine);
G (guanine);
C (cytosine);
T (thymine);
U (uracil).

It is important to note that these tiny particles are the building blocks of our molecules. It is in them that all genetic information is contained, and to be more precise, in their sequence. In DNA we can find: A, G, C and T, and in RNA - A, G, C and U.

Nitrogen bases are the majority of nucleic acids. In addition to the five listed, there are others, but this is extremely rare.

Principles of DNA structure

Another important feature is the presence of four levels of organization (you can see this in the picture). As has already become clear, the primary structure is a chain of nucleotides, and the ratio of nitrogenous bases obeys certain laws.

The secondary structure is a double helix, the composition of each chain being species specific. We can find phosphoric acid residues on the outside of the helix, and nitrogenous bases are located inside.

The last level is the chromosome. Imagine that the Eiffel Tower is placed in a matchbox, this is how the DNA molecule is arranged in a chromosome. It is also important to note that a chromosome can consist of one chromatid or two.

Before we create a table comparing DNA and RNA, let's talk about the structure of RNA.

Types and structural features of RNA

To compare the similarities between DNA and RNA (you can see the table in the last paragraph of the article), let’s look at the varieties of the latter:

First of all, tRNA (or transport) is a single-stranded molecule that performs the functions of amino acid transport and protein synthesis. Its secondary structure is a “clover leaf”, and its tertiary structure has been studied very little.
Information or matrix (mRNA) - transfer of information from a DNA molecule to the site of protein synthesis.
And the last one is rRNA (ribosomal). As the name already makes clear, it is found in ribosomes.

What functions does DNA perform?

When comparing DNA and RNA, it is impossible to miss the question of the functions performed. This information will certainly be reflected in the final table.

So, without doubting for a second, we can say that in a small DNA molecule all the genetic information is programmed, capable of controlling our every step. These include:

health;
development;
life expectancy;
hereditary diseases;
cardiovascular diseases, etc.

Imagine that we isolated all the DNA molecules from one cell of the human body and arranged them in a row. How long do you think the chain will be? Many will think that it is millimeters, but this is not so. The length of this chain will be as much as 7.5 centimeters. It’s incredible, but why can’t we see the cell without a powerful microscope? The thing is that the molecules are very tightly compressed. Remember, in the article we already talked about the size of the Eiffel Tower.

But what functions does DNA perform?

Are carriers genetic information.
Reproduce and transmit information.

What functions does RNA perform?

For a more accurate comparison of DNA and RNA, we suggest considering the functions performed by the latter. It was previously said that there are three types of RNA:

RRNA serves as the structural basis of the ribosome; in addition, they interact with other types of RNA during protein synthesis and take part in the assembly of the polypeptide chain.
The function of mRNA is as a template for protein biosynthesis.
TRNAs bind amino acids and transfer them to the ribosome for protein synthesis, encode amino acids, and decipher the genetic code.

Conclusions and comparison table

Often, schoolchildren are given an assignment in biology or chemistry - to compare DNA and RNA. In this case, the table will be a necessary assistant. Everything that was said earlier in the article can be seen here in a condensed form.

Comparison of DNA and RNA (conclusions)

Sign	DNA	RNA
Structure	Two chains.	One chain.
Polynucleotide chain	The chains are right-handed relative to each other.	May have various shapes, it all depends on the type. For example, let's take a tRNA that has the shape of a maple leaf.
Localization	99% localized in the nucleus, but can be found in chloroplasts and mitochondria.	Nucleoli, ribosomes, chloroplasts, mitochondria, cytoplasm.
Monomer	Deoxyribonucleotides.	Ribonucleotides.
Nucleotides	A, T, G, C.	A, G, C, U.
Functions	Storage of hereditary information.	mRNA carries hereditary information, rRNA performs a structural function, mRNA, tRNA and rRNA are involved in protein synthesis.

Despite the fact that our comparative characteristics turned out to be very brief, we were able to cover all aspects of the structure and functions of the compounds in question. This table can serve as a good cheat sheet for the exam or just a reminder.

three main types of RNA: informational(mRNA), or matrix(mRNA), ribosomal(rRNA), and transport(tRNA). They vary in molecular size and function. All types of RNA are synthesized on DNA with the participation of enzymes - RNA polymerases. Messenger RNA makes up 2-3% of all cellular RNA, ribosomal RNA - 80-85, transport - about 15%.

mRNA. it reads hereditary information from a section of DNA and, in the form of a copied sequence of nitrogenous bases, transfers it to ribosomes, where the synthesis of a specific protein occurs. Each of the mRNA molecules corresponds in the order of nucleotides and in size to the gene in the DNA from which it was transcribed. On average, mRNA contains 1500 nucleotides (75-3000). Each triplet (three nucleotides) on an mRNA is called a codon. The codon determines which amino acid will appear at a given location during protein synthesis.

(tRNA) has a relatively low molecular weight about 24-29 thousand D and contains from 75 to 90 nucleotides in the molecule. Up to 10% of all tRNA nucleotides are minor bases, which apparently protects it from the action of hydrolytic enzymes. The role of tRNA is that they transfer amino acids to ribosomes and participate in the process of protein synthesis. Each amino acid is attached to a specific tRNA. A number of amino acids have more than one tRNA. To date, more than 60 tRNAs have been discovered that differ from each other in their primary structure (base sequence). The secondary structure of all tRNAs is presented in the form of a cloverleaf with a double-stranded stem and three single-stranded ones). At the end of one of the chains there is an acceptor site - a CCA triplet, to the adenine of which a specific amino acid is attached.

(rRNA). They contain 120-3100 nucleotides. Ribosomal RNA accumulates in the nucleus, in the nucleoli. Ribosomal proteins are transported into the nucleoli from the cytoplasm, and there the spontaneous formation of ribosomal subparticles occurs by combining proteins with the corresponding rRNA. Ribosomal subparticles, together or separately, are transported through the pores of the nuclear membrane into the cytoplasm. Ribosomes They are organelles 20-30 nm in size. They are built from two subparticles different sizes and shapes. At certain stages of protein synthesis in the cell, ribosomes are divided into subparticles. Ribosomal RNA serves as a framework for ribosomes and facilitates the initial binding of mRNA to the ribosome during protein biosynthesis.

The genetic code is a method of encoding the amino acid sequence of proteins using a sequence of nucleotides, characteristic of all living organisms.

Properties: 1) genetic code triplet(each amino acid is encoded by three nucleotides); 2) non-overlapping(neighboring triplets do not have common nucleotides); 3) degenerate(with the exception of methionine and tryptophan, all amino acids have more than one codon); 4) universal(basically the same for all living organisms); 5) in codons for one amino acid, the first two nucleotides are usually the same, but the third varies; 6) has a linear reading order and is characterized by colinearity, i.e., the coincidence of the order of codons in mRNA with the order of amino acids in the synthesized polypeptide chain.

Structure of nucleic acids

Nucleic acids – phosphorus-containing biopolymers of living organisms, ensuring the preservation and transmission of hereditary information.

Macromolecules of nucleic acids were discovered in 1869 by the Swiss chemist F. Miescher in the nuclei of leukocytes found in manure. Later, nucleic acids were identified in all cells of plants and animals, fungi, bacteria and viruses.

Note 1

There are two types of nucleic acids – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

As the names indicate, the DNA molecule contains the pentose sugar deoxyribose, and the RNA molecule contains ribose.

A large number of varieties of DNA and RNA are now known, which differ from each other in structure and importance in metabolism.

Example 1

IN bacterial cell Escherichia coli contains about 1000 varieties of nucleic acids, and animals and plants have even more.

Each type of organism has its own set of these acids. DNA is localized primarily in the chromosomes of the cell nucleus (% of the total DNA of the cell), as well as in chloroplasts and mitochondria. RNA is found in the cytoplasm, nucleoli, ribosomes, mitochondria, and plastids.

The DNA molecule consists of two polynucleotide chains, helically twisted relative to each other. The chains are arranged antiparallel, that is, the 3-end and the 5-end.

The structural components (monomers) of each such chain are nucleotides. In nucleic acid molecules, the number of nucleotides varies - from 80 in transfer RNA molecules to several tens of thousands in DNA.

Any DNA nucleotide contains one of four nitrogenous bases ( adenine, thymine, cytosine and guanine), deoxyribose And phosphoric acid residue.

Note 2

Nucleotides differ only in their nitrogenous bases, between which there are family ties. Thymine, cytosine and uracil are pyrimidine bases, while adenine and guanine are purine bases.

Adjacent nucleotides in a polynucleotide chain are linked by covalent bonds formed between the deoxyribose of a DNA molecule (or ribose of RNA) of one nucleotide and the phosphoric acid residue of another.

Note 3

Although there are only four types of nucleotides in a DNA molecule, due to changes in the sequence of their location in a long chain, DNA molecules achieve enormous diversity.

Two polynucleotide chains are combined into a single DNA molecule using hydrogen bonds, which are formed between the nitrogenous bases of nucleotides of different chains.

In this case, adenine (A) can only combine with thymine (T), and guanine (G) can only combine with cytosine (C). As a result, various organisms the number of adenyl nucleotides is equal to the number of thymidyl nucleotides, and the number of guanyl nucleotides is equal to the number of cytidyl nucleotides. This pattern is called "Chargaff's rule". In this way, the sequence of nucleotides in one chain is determined according to their sequence in the other.

This ability of nucleotides to selectively combine is called complementarity, and this property ensures the formation of new DNA molecules based on the original molecule (replication).

Note 4

The double helix is stabilized by numerous hydrogen bonds(two are formed between A and T, three - between G and C) and hydrophobic interactions.

The DNA diameter is 2 nm, the helix pitch is 3.4 nm, and each turn contains 10 nucleotide pairs.

The length of a nucleic acid molecule reaches hundreds of thousands of nanometers. This significantly exceeds the largest protein macromolecule, the length of which, when unfolded, is no more than 100–200 nm.

Self duplication of a DNA molecule

Each cell division, provided that the nucleotide sequence is strictly observed, is preceded by the replication of a DNA molecule.

It begins with the DNA double helix temporarily unwinding. This occurs under the action of the enzymes DNA topoisomerase and DNA helicase. DNA polymerase and DNA primase catalyze the polymerization of nucleoside triphosphates and the formation of a new chain.

The accuracy of replication is ensured by the complementary (A - T, G - C) interaction of the nitrogenous bases of the template chain that is being built.

Note 5

Each polynucleotide chain is a template for a new complementary chain. As a result, two DNA molecules are formed, one half of each of which comes from the mother molecule, and the other is newly synthesized.

Moreover, new chains are synthesized first in the form of short fragments, and then these fragments are “stitched” into long chains by a special enzyme.

The two new DNA molecules formed are an exact copy the original molecule due to replication.

This process is the basis for the transmission of hereditary information, which takes place at the cellular and organismal levels.

Note 6

Key Feature DNA replication - its high accuracy, which is ensured by a special complex of proteins - the “replication machine”.

Functions of the “replication machine”:

produces carbohydrates that form a complementary pair with the nucleotides of the mother matrix chain;
acts as a catalyst in the formation of a covalent bond between the end of the growing chain and each new nucleotide;
corrects the chain by removing nucleotides that are incorrectly incorporated.

The number of errors in the “replication machine” is very small, less than one error per 1 billion nucleotides.

However, there are cases when the “replication machine” can skip or insert several extra bases, insert a C instead of a T or an A instead of a G. Each such replacement of a nucleotide sequence in a DNA molecule is a genetic error and is called mutation. In all subsequent generations of cells, such errors will be reproduced again, which can lead to noticeable negative consequences.

Types of RNA and their functions

RNA is a single polynucleotide chain (some viruses have two chains).

Monomers are ribonucleotides.

Nitrogen bases in nucleotides:

adenine (A);*
guanine (G);
cytosine (C);
uracil (U).*

Monosaccharide – ribose.

In the cell it is localized in the nucleus (nucleolus), mitochondria, chloroplasts, ribosomes, and cytoplasm.

It is synthesized by template synthesis according to the principle of complementarity on one of the DNA strands, is not capable of replication (self-duplication), and is labile.

There are various types RNA, which differ in molecular size, structure, location in the cell and functions.

Low molecular weight transfer RNAs (tRNAs) make up about 10% total number cellular RNA.

In the process of transmitting genetic information, each tRNA can attach and transfer only a certain amino acid (for example, lysine) to ribosomes, the site of protein synthesis. But for each amino acid there is more than one tRNA. Therefore, there are many more than 20 different tRNAs, which differ in their primary structure (have a different nucleotide sequence).

Ribosomal RNAs (rRNAs) make up up to 85% of all RNA cells. Being part of ribosomes, they thereby perform a structural function. rRNA also takes part in the formation of the active center of the ribosome, where peptide bonds are formed between amino acid molecules during the process of protein biosynthesis.

Featuring messenger or messenger RNA (mRNA) the synthesis of proteins in the cell is programmed. Although their content in the cell is relatively low - about 5% - of total mass Of all RNA cells, mRNA comes first in importance, since they directly transfer the DNA code for protein synthesis. In this case, each cell protein is encoded by a specific mRNA. This is explained by the fact that RNA, during its synthesis, receives information from DNA about the structure of the protein in the form of a copied nucleotide sequence and transfers it to the ribosome for processing and implementation.

Note 7

The significance of all types of RNA is that they are a functionally unified system aimed at carrying out the synthesis of cell-specific proteins in the cell.

Chemical structure and role of ATP in energy metabolism

Adenosine triphosphoric acid (ATP ) is contained in every cell - in the hyaloplasm (the soluble fraction of the cytoplasm), mitochondria, chloroplasts and the nucleus.

It provides energy for most of the reactions occurring in the cell. With the help of ATP, the cell is able to move, synthesize new molecules of proteins, fats and carbohydrates, get rid of breakdown products, carry out active transport, etc.

The ATP molecule is formed by a nitrogenous base, the five-carbon sugar ribose and three phosphoric acid residues. The phosphate groups in the ATP molecule are connected to each other by high-energy (macroergic) bonds.

As a result of hydrolytic elimination of the final phosphate group, adenosine diphosphoric acid (ADP) and energy is released.

After the elimination of the second phosphate group, adenosine monophosphoric acid (AMP) and another portion of energy is released.

ATP is formed from ADP and inorganic phosphate due to the energy that is released during oxidation organic matter and during the process of photosynthesis. This process is called phosphorylation. In this case, at least 40 kJ/mol of ATP accumulated in its high-energy bonds must be used.

This means that the main significance of the processes of respiration and photosynthesis is that they supply energy for the synthesis of ATP, with the participation of which a significant number of different processes occur in the cell.

ATP is restored extremely quickly. Example In humans, each ATP molecule is broken down and renewed again 2400 times a day, therefore its average lifespan is less than 1 minute.

ATP synthesis occurs mainly in mitochondria and chloroplasts. ATP, which is formed, enters through the channels of the endoplasmic reticullum to those parts of the cell where energy is needed.

Any type of cellular activity occurs due to the energy that is released during ATP hydrolysis. The remaining energy (about 50%) that is released during the breakdown of molecules of proteins, fats, carbohydrates and others organic compounds, dissipates in the form of heat, dissipates and has no practically significant significance for the life of the cell.

There are three types of RNA: ribosomal, transport and messenger ribonucleic RNA. Everything depends on the structure, size of molecules, and functions performed.

What are the characteristics of ribosomal RNA (rRNA)

Ribosomal RNAs make up 85% of all RNA in a cell. They are synthesized in the nucleolus. Ribosomal RNAs are structural component ribosomes and are directly involved in protein biosynthesis.

Ribosomes are cell organelles consisting of four rRNAs and several dozen proteins. Their main function is protein synthesis.

Why are transfer RNAs needed?

Transfer RNAs (tRNAs) are the smallest ribonucleic acids in the cell. They make up 10% of all cellular RNAs. Transfer RNAs are formed in the nucleus on DNA and then move into the cytoplasm. Each tRNA carries specific amino acids to the ribosomes, where they are joined by peptide bonds in a specific sequence specified by the messenger RNA.

The transfer RNA molecule has two active sites: the triplet anticodon and the acceptor end. The acceptor end is the “landing pad” for the amino acid. The anticodon at the other end of the molecule is a triplet of nucleotides complementary to the corresponding messenger RNA codon.

Each amino acid corresponds to a sequence of three nucleotides - a triplet. A nucleotide is a nucleic acid monomer consisting of a phosphate group, a pentose group, and a nitrogenous base.

The anticodon is different for tRNAs transporting different amino acids. The triplet encodes information about exactly the amino acid that is carried by this molecule.

Where are messenger RNAs synthesized and what is their role?

Information, or messenger RNA (mRNA, mRNA) is synthesized on a section of one of the two DNA chains under the action of the enzyme RNA polymerase. They make up 5% of the cell's RNA. The sequence of the nitrogenous bases of mRNA is strictly complementary to the sequence of the bases of the DNA section: uracil mRNA corresponds to adenine in DNA, adenine to thymine, cytosine to guanine, and guanine to cytosine.

Messenger RNA reads hereditary information from chromosomal DNA and transfers it to ribosomes, where this information is implemented. The nucleotide sequence of mRNA contains information about the structure of the protein.

RNA molecules can be found in the nucleus, cytoplasm, ribosomes, mitochondria and plastids. From different types RNA develops into a single functional system, aimed through protein synthesis at the implementation of hereditary information.