DNA replication, the cell cycle and mitosis Flashcards
Explain semi-conservative DNA replcation
Each strand forms a template for a new strand of DNA
What enzyme unwounds the DNA helix before replication can occur?
This is done by a DNA helicase, an enzyme that uses ATP as source of energy to break hydrogen bonds between base pairs.
What does DNA polymerase do?
DNA polymerases add nucleotides to the 3’ end of a growing chain.
What does DNA polymerase require?
a template strand an oligonucleotide primer a supply of deoxynucleotide triphosphates (dNTPs) add pic
In what direction does DNA replication occur?
5’ to 3’ direction add pic
What drives the reaction for DNA replication?
DNA synthesis is driven by the release of energy from the hydrolysis of the triphosphates. add pic
What is required on the deoxyribose for DNA replication to occur?
A free 3’ hydoxyl group is required. add pic
What is the name of the discrete points on the DNA molecule wher replication begins?
Origins of Replication
What is the site of DNA synthesis called?
Replication fork add pic
What enzyme synthesizes the primer?
RNA polymerase called DNA primase
List the steps for DNA synthesis on the Lagging strand
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Why is DNA synthesis discontinous on the lagging strand?
it requires a series of DNA primers add pic
Explain the steps which joins the okazaki fragments?
A special ribonuclease removes the RNA primer using a 5’ to 3’ exonuclease activity. DNA polymerase then synthesises DNA through the RNA primer region DNA ligase joins the two adjacent strands of DNA together using ATP. add pic
What removes the RNA primer?
A special ribonuclease removes RNA primer using a 5’ to 3’ exonuclease activity
Describe the proof-reading mechanism of DNA?
Before a new nucleotide is added, the previous nucleotide is checked for correct base-pairing. Any incorrect bases are removed by 3’ to 5’ exonuclease activity of DNA polymerase. A new, correct nucleotide is then added. add pic
Describe the replication of a E.coli chromosome by drawing a diagram?
In E.coli, replication starts at a unique origin, OriC. Two replication forks proceed simultaneously in opposite directions. The two forks meet at the other side of the circular chromosome. add pic
Eukaryotic chromosomes are linear and very long. How does the cell manage to replicate the whole DNA molecule?
Each replication origin gives bi-directional replication forks. Replication is finished when all the forks have met. add pic
Define the different stages of the cell cycle?
G0: cells which have stopped dividing
G1: DNA of each chromosome present as a single linear double helix of DNA
S phase: the DNA is replicated
G2: each chromosome has two identical sister chromatids
Mitosis: the two chromatids separate to the daughter cells
Explain how chromosomes segregate at metaphase by drawing a diagram?
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