DNA replication Flashcards
DNA has two principal functions
Template for DNA replication
Template for RNA replication
Why is DNA considered semi conservative
One new daughter strand is synthesised with each round of DNA replication so it is reused
What is a replication fork
Both strands of the template DNA are replicated at the same time. So split
What is leading strand
Synthesised continuously in direction of the fork
What is the lagging strand
Synthesised discontinously against the replication fork
DNA replication process
- Helicases unwind the parental double helix
- Single strand binding proteins stabilise the unwound parental DNA
- The leading strand is synthesised continuously by DNA polymerase
- The lagging strand is synthesised discontinously formed by Okazaki fragment
- After the RNA primer is replaced by DNA. DNA ligase joins the Okazaki fragment to the growing strand
What does DNA polymerase do
Synthesise the DNA in the 5-3 direction
Needs a primer to start
What does DNA polymerase use to add nucelotides
3 OH groups
DNA polymerase creates new strand in what direction
3-5 direction
What are the DNA fragments called
Okazaki fragments
What enzyme removes the RNA primers
Exonuclease enzyme
Are both strands synthesised at the same time
Yes
What contributes to telomere shortening
Short segment of DNA
Endogenous damaging agents
Errors in replication
Reactive oxygen species
UV radiation from the sun
X-rays and gamma rays
Mutagenic chemicals
Healthy cells are able to respond to DNA damage by
Repairing the DNA using cells DNA repair mechanism
Apoptosis
Gene mutations will arise when
DNA damage
Silent mutations definition
Will have no effect on the protein
Missense mutation definition
Result in the incorporation of the wrong amino acid
Nonsense mutation definition
Results in a stop codon hence a premature codon
Frameshift mutation definition
Changes the frame of protein translation
Endogenous DNA damage results in
Base loss
The glycosyl bond linking DNA bases with deoxyribose is labile
When DNA is replicated causes by deletions, can cause breaks
Base modifications involve
Deamination
Oxidation by ROS
Deamination is when
Amino groups of nucleic acid bases are unstable and are lost
Oxidation by ROS is when
Reactive oxygen species result from oxidative metabolism and ionising radiation
Produces hyperactive oxygen can modify nucleotides
Causes point mutations when replicated
Common one is G-T