DNA replication in Eukaryotes Flashcards
What is the function of telomeres?
Protects the ends of DNA
What is a chromatid?
Newly copied chromosome paired with the original chromosome
What is the function of the centromere?
Promotes microtuble attachment during mitotic chromosome segregation
What kind of proteins are histones?
Highly basic
How many subunits is a histone protein made up of?
8
What is a nucleosome?
A segment of DNA wrapped around a histone complex
What is the effect of heterochromatin on gene expression?
Reduces gene expression
What is the effect of euchromatin on gene expression?
Increases gene expression
What is the effect of acetylation of chromatin on gene expression?
Produces euchromatin which Increases gene expression
How are pre-mRNA introns removed?
By splicing involving the spliceosome
What does initiation require?
An RNA primer
Compare eukaryotic and prokaryotic origins of replication
- Prokaryotes have a single origin of replication site
- Eukaryotes have many origins of replication
What is the function of topoisomerase I and II in eukaryotic DNA replication?
Relieves torsional stress ahead of the fork
What is the function of single-stranded DNA binding proteins in eukaryotic DNA replication?
Stabilise the fork
Which enzyme is responsible for lagging strand elongation in eukaryotic DNA replication?
DNA polymerase delta
Which enzyme is responsible for leading strand elongation in eukaryotic DNA replication?
DNA polymerase epsilon
Which enzyme is responsible for synthesis of okazaki fragments?
DNA polymerase alpha complexed with primase
What is processivity?
The ability of DNA polymerase to continuously synthesise DNA without frequent dissociation from template
Which type of DNA polymerase lack proofreading?
Alpha
What is the function of the RFC clamp loader?
Recruits PCNA clamp at the junction between RNA/DNA primer and template
What is the function of the PCNA clamp?
Forms a ring which displaces DNA polymerase alpha and recruits DNA polymerase delta and epsilon
Outline how RNA primers are removed on the lagging strand
- DNA polymerase delta elongates Okazaki fragments
- When polymerase delta encounters an RNA primer it is pushed aside to form a flap
- FEN1 cuts flap at branch point
- DNA ligase I seals gap
What is the function of FEN1?
It is an endonuclease involved in the removal of DNA primers
What is the problem with synthesising DNA at the telomeric ends of lagging strand?
At the lagging strand, unable to add or remove RNA primers at telomeric ends
What is the relationship between Chromosome length and replication?
Chromosome ends shorten after each round of replication
What are the 2 parts of telomerase?
- RNA template complementary to telomeric sequence
- Reverse transcriptase
What is the repeated sequence at telomeric ends?
TTAGGG
What is the link between telomerase and cancer?
Telomerase is often reactivated in human cancers
In what kind of cells is telomerase:
a) inactive
b) active?
a) Somatic cells
b) Stem cells
How many RNA polymerases do eukaryotes have?
3
At which point in the cell cycle does DNA replication occur?
S phase
