Nucleic acids play a large role in ensuring the vital activity of cells of living organisms. An important representative of this group of organic compounds is DNA, which carries all the genetic information and is responsible for the manifestation of the necessary traits.
What is replication?
In the process of cell division, it is necessary to increase the number of nucleic acids in the nucleus so that there is no loss of genetic information in the process. In biology, replication is the doubling of DNA through the synthesis of new chains.
The main goal of this process is to transfer genetic information to daughter cells unchanged without any mutations.
Enzymes and Replication Proteins
Doubling a DNA molecule can be compared with any metabolic process in a cell that requires the appropriate proteins. Since in biology replication is an important component of cell division, accordingly, many auxiliary peptides are involved here.
- DNA polymerase is the most important reduction enzyme that is responsible for the synthesis of the deoxyribonucleic acid daughter chain . In the cell cytoplasm during replication, the presence of nucleic triphosphates, which bring all nucleic bases, is mandatory.
These bases are nucleic acid monomers; therefore, the entire chain of the molecule is built from them. DNA polymerase is responsible for the assembly process in the correct order, otherwise the appearance of all kinds of mutations is inevitable.
- Primase is a protein that is responsible for seed formation on the DNA template chain. This seed is also called a primer, it has the structure of RNA. For the DNA polymerase enzyme, the presence of initial monomers from which further synthesis of the entire polynucleotide chain is possible is important. This function is performed by the primer and its corresponding enzyme.
- Helicase (helicase) forms a replication fork, which is the divergence of matrix chains by breaking hydrogen bonds. So polymerase easier to approach the molecule and start the synthesis.
- Topoisomerase. If you imagine a DNA molecule in the form of a twisted rope, as the polymerase advances along the chain, a positive tension will form due to strong twisting. This problem is solved by topoisomerase, an enzyme that breaks the chain for a short time and unfolds the entire molecule. After that, the damaged site is stitched again, and the DNA does not experience stress.
- Ssb proteins, like clusters, attach to DNA chains in a replication fork to prevent the re-formation of hydrogen bonds before the end of the reduction process.
- Ligase. The function of the enzyme is to crosslink Okazaki fragments on the lagging strand of a DNA molecule. This happens by cutting primers and embedding in their place the native monomers of deoxyribonucleic acid.
In biology, replication is a complex multi-step process that is extremely important in cell division. Therefore, the use of various proteins and enzymes is necessary for effective and proper synthesis.
Reduction mechanism
There are 3 theories that explain the process of DNA doubling:
- Conservative claims that one daughter nucleic acid molecule has a matrix nature, and the second is completely synthesized from scratch.
- The semi-conservative was proposed by Watson and Crick and confirmed in 1957 in experiments on E. Coli. This theory says that both daughter DNA molecules have one old chain and one newly synthesized.
- The dispersive mechanism is based on the theory that daughter molecules have alternating sections along the entire length, consisting of both old and new monomers.
A semi-conservative model is now scientifically proven. What is molecular level replication? At the beginning, helicase breaks the hydrogen bonds of the DNA molecule, thereby opening both chains to the polymerase enzyme. The latter, after the formation of seeds, begin the synthesis of new chains in the direction of 5'-3 '.
The DNA antiparallel property is the main reason for the formation of leading and lagging chains. DNA polymerase moves continuously on the leading chain, and on the lagging chain it forms Okazaki fragments, which in the future will be connected using ligase.
Replication Features
How many DNA molecules are in the nucleus after replication? The process itself involves doubling the genetic set of cells, therefore, in the synthetic period of mitosis, the diploid set has twice as many DNA molecules. Such a record is usually marked as 2n 4c.
In addition to the biological meaning of replication, scientists have found application of the process in various fields of medicine and science. If in biology replication is a doubling of DNA, then in laboratory conditions the reproduction of nucleic acid molecules is used to create several thousand copies.
This method is called polymerase chain reaction (PCR). The mechanism of this process is similar to in vivo replication, therefore, similar enzymes and buffer systems are used for its course.
conclusions
Replication is of great biological importance to living organisms. The transfer of genetic information during cell division does not do without doubling the DNA molecules, therefore, coordinated work of enzymes is important at all stages.