9.2 DNA Replication

9.2 DNA Replication

• When a cell divides, it is important that each daughter cell has the same copy of the DNA.
• The process of DNA replication is used to accomplish this.
• The S phase of the cell cycle is where the replication of DNA occurs.

• The structure of the double helix gave a clue as to how it is copied.
• The adenine nucleotides pair with the other two.
• The two strands are related.

• A strand of DNA with a sequence of AGTCATGA will have a strand with the same sequence.

• The sequence of bases in one strand can be used to create the correct sequence of bases in the other strand.

• It is possible to recreate the other strand if you have one strand.

• The model suggests that the two strands of the double helix separate during replication, and each strand serves as a template from which the new strand is copied.

• The model of DNA replication is semiconservative.
• The original strands of DNA are shown in gray and the newly synthesized strands are shown in blue.

• Each of the two strands that make up the double helix serves as a template from which new strands are copied.
• The new strand will complement the old strand.
• There are two strands of new double strand, one parental and one daughter strand.
• Two DNA copies have the same sequence of bases and are divided into two daughter cells.

• The process of DNA replication is very complex because of the complexity of the genomes.
• It occurs in three stages.

• To form structures called nucleosomes, histones are bound to eukaryotic DNA.
• The replication process involves the accessibility of the DNA to the relevant genes.
• The origin of replication is a specific sequence of nucleotides.
• Two replication forks are formed at the beginning of replication, and they are extended in both directions as replication proceeds.
• Multiple origins of replication can be found on the chromosomes, and can occur at the same time.

• The primer is removed and replaced with a new one.
• One strand, which is similar to the parental strand, is synthesised continuously toward the fork so the polymerase can add more nucleotides.
• Each fragment requires a primer made ofRNA to start the synthesis.

• There are new bases added to the parental strands.
• One strand is made continuously, while the other strand is made in pieces.

• Primers are removed, new DNA nucleotides are put in place, and the backbone is sealed.

• The opening of the origin of replication leads to the formation of a replication fork.
• A primer is formed by the synthesis of an RNA molecule.
• The leading strand and lagging strand have different ways of making DNA.
• The fragments are joined by ligase.

• You have isolated a cell strain in which the joining together of the fragments is impaired and you suspect that there is a change in the activity of the replication fork.

• The end of a line in eukaryotic chromosomes is the reason for the linearity of the chromosomes.
• You have learned that the polymerase can add only one direction.
• The lagging strand has no place for a primer to be made for the DNA fragment to be copied at the end of the chromosomes.
• The ends of the cell are unpaired and get shorter as the cells divide.
• Each round of DNA replication shortens the telomeres, which are the ends of the chromosomes.
• A six base-pair sequence is repeated 100 to 1000 times in humans.
• The telomerase is attached to the end of the chromosomes and the bases of the RNA template are added on the end of the DNA strand.
• Once the lagging strand template is sufficiently long, DNA polymerase can add nucleotides to the ends of the chromosomes.
• The ends of the chromosomes are duplicated.

• The ends of linear chromosomes are maintained by telomerase.

• Germ cells, adult stem cells, and some cancer cells are some of the cells that telomerase is found to be active in.
• The discovery of telomerase and its action was made by Elizabeth Blackburn.

• The scientist who discovered how telomerase works is Elizabeth Blackburn.

• Adult cells that go through cell division have their telomeres shortened.

• These studies used mice that were deficient in telomerase.
• The function of the testes, spleen, and intestines were improved by the telomerase reactivation in these mice.
• Treatment of age-related diseases in humans may be possible with the reactivation of the telomeres.

• The prokaryotic chromosome has a less extensive coiling structure than the eukaryotic chromosomes.
• The chromosomes are coiled around the proteins.
• Structural differences necessitate some differences in the DNA replication process in two life forms.

• The small size of the genome and large number of variant available make DNA replication very well-studied in prokaryotes.
• 1000 nucleotides are added per second.
• The process is much quicker than in otheryotes.
• There are differences between prokaryotic and eukaryotic replications.

• Mistakes can be made while adding nucleotides.
• Every newly added base is edited by it.
• Incorrect bases are removed and replaced with the correct ones.

• The wrongly incorporated base is excised from the DNA and replaced with the correct base.
• It's important to correct thymine dimers, which are caused by ultraviolet light.
• The two thymine nucleotides on one strand are covalently bonding to each other.

• If the dimer is not removed and repaired, it will lead to a change.
• Individuals with flaws in their nucleotide excision repair genes are more likely to develop skin cancer early in life.

• Proofreading corrects errors during replication.
• The incorrect base is detected after replication.
• This base is detected by the mismatch repair proteins and removed by nuclease action.
• The correct base has filled the gap.
• The repair of thymine dimers is done by the nucleotide excision.
• When exposed to the sun's UV rays, thyemine can form thyemine dimers.
• They are excised and replaced in normal cells.

• A permanent change in the DNA sequence is what it is.
• Cancer can be caused by defects in repair genes.