Every living organism in our world is different. Not only people differ from each other. Animals and plants of the same species also have differences. The reason for this is not only different living conditions and life experience. The individuality of each organism is laid down in it with the help of genetic material.
Important and interesting questions about nucleic acids
Even before being born, each organism has its own set of genes, which determines absolutely all structural features. It's not just the color of the coat or the shape of the leaves, for example. More important characteristics are laid down in genes. After all, a hamster cannot be born to a cat, and a baobab cannot grow from wheat seeds.
And nucleic acids - RNA and DNA molecules - are responsible for all this huge amount of information. Their importance is very difficult to overestimate. After all, they not only retain information throughout life, they help to realize it with the help of proteins, and besides this, they pass it on to the next generation. How do they do it, how complex are the structure of the DNA and RNA molecules? How are they similar and what are their differences? In all this weand we will figure it out in the next chapters of the article.
We will analyze all the information piece by piece, starting with the very basics. First, we will learn what nucleic acids are, how they were discovered, then we will talk about their structure and functions. At the end of the article, we are waiting for a comparative table of RNA and DNA, which you can refer to at any time.
What are nucleic acids
Nucleic acids are organic compounds with a high molecular weight, are polymers. In 1869 they were first described by Friedrich Miescher, a Swiss biochemist. He isolated a substance, which includes phosphorus and nitrogen, from pus cells. Assuming that it is located only in the nuclei, the scientist called it nuclein. But what was left after the separation of proteins was called nucleic acid.
Its monomers are nucleotides. Their number in an acid molecule is individual for each species. Nucleotides are molecules made up of three parts:
- monosaccharide (pentose), can be of two types - ribose and deoxyribose;
- nitrogenous base (one of four);
- phosphoric acid residue.
Next, we will look at the differences and similarities between DNA and RNA, the table at the very end of the article will summarize.
Structural features: pentoses
The very first similarity between DNA and RNA is that they contain monosaccharides. But for each acid they are different. Depending on which pentose is in the molecule, nucleic acids are divided into DNA and RNA. DNA contains deoxyribose, while RNA containsribose. Both pentoses occur in acids only in the β-form.
Deoxyribose has no oxygen at the second carbon atom (denoted as 2'). Scientists suggest that its absence:
- shortens the link between C2 and C3;
- makes the DNA molecule stronger;
- creates the conditions for compact DNA packing in the nucleus.
Building Comparison: Nitrogenous Bases
Comparative characterization of DNA and RNA is not easy. But the differences are visible from the very beginning. Nitrogenous bases are the most important building blocks in our molecules. They carry the genetic information. More precisely, not the bases themselves, but their order in the chain. They are purine and pyrimidine.
The composition of DNA and RNA differs already at the level of monomers: in deoxyribonucleic acid we can find adenine, guanine, cytosine and thymine. But RNA contains uracil instead of thymine.
These five bases are the main (major), they make up most of the nucleic acids. But besides them, there are others. This happens very rarely, such bases are called minor. Both are found in both acids - this is another similarity between DNA and RNA.
The sequence of these nitrogenous bases (and, accordingly, nucleotides) in the DNA chain determines which proteins a given cell can synthesize. Which molecules will be created at a given moment depends on the needs of the organism.
Go tolevels of organization of nucleic acids. In order for the comparative characteristics of DNA and RNA to be as complete and objective as possible, we will consider the structure of each. DNA has four of them, and the number of levels of organization in RNA depends on its type.
Discovery of the structure of DNA, principles of structure
All organisms are divided into prokaryotes and eukaryotes. This classification is based on the design of the core. Both have DNA in the cell in the form of chromosomes. These are special structures in which deoxyribonucleic acid molecules are associated with proteins. DNA has four levels of organization.
The primary structure is represented by a chain of nucleotides, the sequence of which is strictly observed for each individual organism and which are interconnected by phosphodiester bonds. Enormous successes in the study of the DNA strand structure were achieved by Chargaff and his collaborators. They determined that the ratios of nitrogenous bases obey certain laws.
They were called the Chargaff rules. The first of these states that the sum of the purine bases must be equal to the sum of the pyrimidines. This will become clear after getting acquainted with the secondary structure of DNA. The second rule follows from its features: the molar ratios A / T and G / C are equal to one. The same rule is true for the second nucleic acid - this is another similarity between DNA and RNA. Only the second has uracil instead of thymine everywhere.
Also, many scientists began to classify the DNA of different species according to a larger number of bases. If the sum is "A+T"more than "G + C", such DNA is called AT-type. If it is the other way around, then we are dealing with the GC type of DNA.
The secondary structure model was proposed in 1953 by scientists Watson and Crick, and it is still generally accepted today. The model is a double helix, which consists of two antiparallel chains. The main characteristics of the secondary structure are:
- the composition of each DNA strand is strictly specific to the species;
- the bond between the chains is hydrogen, formed according to the principle of complementarity of nitrogenous bases;
- polynucleotide chains wrap around each other, forming a right-handed helix called "helix";
- phosphoric acid residues are located outside the helix, nitrogenous bases are inside.
Further, denser, harder
The tertiary structure of DNA is a supercoiled structure. That is, not only do two chains twist with each other in a molecule, for greater compactness, DNA is wound around special proteins - histones. They are divided into five classes depending on the content of lysine and arginine in them.
The last level of DNA is the chromosome. To understand how tightly the carrier of genetic information is packed in it, imagine the following: if the Eiffel Tower went through all the stages of compaction, like DNA, it could be placed in a matchbox.
Chromosomes are single (consist of one chromatid) and double (consist of two chromatids). They provide secure storagegenetic information, and if necessary, they can turn around and open access to the desired area.
Types of RNA, structural features
In addition to the fact that any RNA differs from DNA in its primary structure (lack of thymine, presence of uracil), the following levels of organization also differ:
- Transfer RNA (tRNA) is a single-stranded molecule. In order to fulfill its function of transporting amino acids to the site of protein synthesis, it has a very unusual secondary structure. It's called "cloverleaf". Each of its loops performs its own function, but the most important are the acceptor stem (an amino acid clings to it) and the anticodon (which must match the codon on messenger RNA). The tertiary structure of tRNA has been little studied, because it is very difficult to isolate such a molecule without disturbing the high level of organization. But scientists have some information. For example, in yeast, the transfer RNA is shaped like the letter L.
- Messenger RNA (also called informational) performs the function of transferring information from DNA to the site of protein synthesis. She tells what kind of protein will turn out in the end, ribosomes move along it in the process of synthesis. Its primary structure is a single-stranded molecule. The secondary structure is very complex, necessary for the correct determination of the start of protein synthesis. mRNA is folded in the form of hairpins, at the ends of which there are sites for the beginning and end of protein processing.
- Ribosomal RNA is found in ribosomes. These organelles consist of two subparticles, each of whichhosts its own rRNA. This nucleic acid determines the placement of all ribosomal proteins and functional centers of this organelle. The primary structure of rRNA is represented by a sequence of nucleotides, as in previous varieties of acid. It is known that the final stage of rRNA folding is the pairing of the terminal sections of one strand. The formation of such petioles makes an additional contribution to the compaction of the entire structure.
DNA functions
Deoxyribonucleic acid acts as a repository of genetic information. It is in the sequence of its nucleotides that all the proteins of our body are “hidden”. In DNA, they are not only stored, but also well protected. And even if an error occurs during copying, it will be corrected. Thus, all genetic material will be preserved and will reach the offspring.
In order to transmit information to descendants, DNA has the ability to double. This process is called replication. A comparative table of RNA and DNA will show us that another nucleic acid cannot do this. But it has many other functions.
RNA Functions
Each type of RNA has its own function:
- Transport ribonucleic acid delivers amino acids to ribosomes, where they are made into proteins. tRNA not only brings building material, it is also involved in codon recognition. And how correctly the protein will be built depends on its work.
- Message RNA reads information fromDNA and carries it to the site of protein synthesis. There, it attaches to the ribosome and dictates the order of the amino acids in the protein.
- Ribosomal RNA ensures the integrity of the structure of the organelle, regulates the work of all functional centers.
Here's another similarity between DNA and RNA: they both take care of the genetic information that the cell carries.
Comparison of DNA and RNA
To organize all the above information, let's write it all down in a table.
| DNA | RNA | |
| Cage location | Nucleus, chloroplasts, mitochondria | Nucleus, chloroplasts, mitochondria, ribosomes, cytoplasm |
| Monomer | Deoxyribonucleotides | Ribonucleotides |
| Structure | Double-stranded helix | Single chain |
| Nucleotides | A, T, G, C | A, U, G, C |
| Features | Stable, capable of replication | Labile, cannot double |
| Functions | Storage and transmission of genetic information | Transfer of hereditary information (mRNA), structural function (rRNA, mitochondrial RNA), participation in protein synthesis (mRNA, tRNA, rRNA) |
Thus, we briefly talked about the similarities between DNA and RNA. The table will be an indispensable assistant in the exam or a simple reminder.
In addition to what we already learned earlier, several facts appeared in the table. For example, the ability of DNAduplication is necessary for cell division so that both cells receive the correct genetic material in full. While for RNA, doubling makes no sense. If a cell needs another molecule, it synthesizes it from the DNA template.
The characteristics of DNA and RNA turned out to be brief, but we covered all the features of the structure and functions. The process of translation - protein synthesis - is very interesting. After getting acquainted with it, it becomes clear how big a role RNA plays in the life of a cell. And the process of DNA duplication is very exciting. What is worth breaking the double helix and reading each nucleotide!
Learn something new every day. Especially if this new thing happens in every cell of your body.
