Скачать или смотреть Types of DNA Replication

The replication of double-stranded (duplex) DNA is a highly coordinated and complex biological process. It involves multiple enzyme systems working together. The process happens in three main stages: initiation, elongation, and termination. However, before replication can even begin, the DNA, usually in a tightly wound, supercoiled form, must be unwound. This unwinding starts at a specific location on the chromosome called the origin of replication. An enzyme called topoisomerase helps in relaxing the supercoiled DNA by making small cuts, allowing the tension to be released. Replication cannot take place unless the DNA is in a relaxed state.

The Semi-Conservative Nature of DNA Replication
DNA replication follows a semi-conservative model, meaning that each of the two resulting DNA molecules will contain one strand from the original DNA and one newly made strand. The two strands in the original DNA are held together by hydrogen bonds, which can be easily broken, allowing the strands to separate. Once separated, each original strand acts as a template for building a new strand.

Conservative Model of Replication (Hypothetical)
The conservative model was a hypothetical alternative to the semi-conservative model. In this method, the original double-stranded DNA remains completely intact, and a wholly new DNA molecule is synthesized from it. After one round of replication, there would be one DNA molecule with both old strands and another DNA molecule with two entirely new strands. However, this model was proven incorrect through experimental evidence.

Dispersive Model of Replication (Hypothetical)
Another proposed model was the dispersive model, in which the original DNA is broken into segments, and these segments are randomly distributed in the newly formed DNA molecules. This would result in both new DNA strands being a mix of old and new parts. While an interesting idea, this model was also rejected based on experimental data, as it doesn’t accurately reflect how DNA replication occurs in cells.

Rolling Circle DNA Replication
Rolling circle replication is a specialized form of DNA replication used mainly by viruses and plasmids (small, circular DNA molecules). It is unidirectional and allows rapid production of multiple copies. Here's how it works:
I) A nick (cut) is made in one strand of the circular DNA.
II) The 3' end of the nicked strand is extended using the intact strand as a template. This becomes the leading strand.
III) The 5' end of the nicked strand is displaced and acts as the lagging strand.
IV) The displaced strand is also replicated to form a new complementary DNA strand.
The result is a new circular DNA and a single-stranded DNA, which can later become double-stranded.

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