Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
23 Cards in this Set
- Front
- Back
|
What are the 4 fundamental features of DNA replication in all organisms? |
- It is semiconservative - bidirectional (two replications folks per origin) - semi-discontinuous (lagging strand - Okazaki) - dependent on RNA primers |
|
|
What does DNA polymerase need in order to synthesise DNA? |
- All four deoxynucleoside triphosphates - A template - A primer |
|
|
What is a primer? |
- a short piece of nucleic acid base-paired to template - acts as a start point - must have 3'-OH group attached to a nucleotide base-paired to the template |
|
|
In what direction is DNA synthesised? |
- 5' to 3' |
|
|
What is the role of Mg2+ ions in DNA replication? |
- they are found at the active side of DNA polymerase - one Mg2+ dissociation of the H from 3-OH to generate a nucleophilic O- - the other neutralises the charge on the incoming triphosphatase |
|
|
What does DNA polymerase resemble? |
- a hand |
|
|
What allows DNA polymerase to proofread? |
- Most of them have an inbuilt 3'->5' exonuclease - some cant - e.g. Taq DNA polymerase |
|
|
How often does DNA polymerase incorporate an incorrect nucleotide? |
- approximately once per 10^5 nucleotides - proofreading removes 99% of those - after replication mismatch repair removes 99.9% of the remaining ones |
|
|
Why are there no DNA polymerases that synthesise from 3' to 5'? |
- Once the mis-matched nucleotide is removed there is no triphosphate to form the next phosphodiester bond |
|
|
What mechanism does RNA polymerase use? |
- uses same Mg2+ dependent mechanism, but are structurally dissimilar and appear to have evolved separately |
|
|
What is a steric gate? |
- Amino acid that prevents bulkier rNTPs from entering so that the enzyme cannot synthesise RNA; - found at the active site of DNA polymerase |
|
|
What happens if you change the staric gate AA for a smaller one - tyr to gly? |
- together with one other AA change alteration in "thumb" region allows DNA polymerases to synthesise RNA |
|
|
The main DNA polymerases in both euk and prok utilise a sliding clamp: |
- able to repeatedly add nucleotides to a DNA molecule without dissociating from template - mediated by enzymes being attached to a sliding clamp - β-subunites of DNA polymerase III in E. coli and proliferating cell antigen (PCNA) in eukaryotes |
|
|
What are the primers synthesised by? |
- In E. coli - primase - in Eukaryoes - primase and DNA polymerase |
|
|
What is leading strand synthesised by> |
- In E. coli - DNA polymerase III
- In eukaryotes - DNA polymerase ε |
|
|
What is the lagging strand synthesised by? |
- In E. coli - DNA polymerase III - in Eukaryotes - DNA polymerase δ |
|
|
What removes the RNA primers and replaces them with DNA? |
- In E. coli - DNA polymerase I - in Eukaryotes - RNAse and DNA polymerase δ |
|
|
What is the difference in speed of synthesis between eukaryotes and prokaryotes? |
- prokaryotes are 10-20 times faster |
|
|
What is the difference in nuber of Ori between prokaryotes and eukaryotes? |
- In E. coli - 1 - in eukaryotes - 10 000 - 100 000 |
|
|
How many times is replication initiated per cell division in prok and euk? |
- 1 in both (although in prok could be more than once) |
|
|
What are the characteristics of the Ori sequence? |
- In E. coli - AT rich - in eukaryotes - no obvious consensus in mammals |
|
|
When are different DNA segment of eukaryotic DNA replicated? |
= they are not all activated simultaneously - housekeeping genes are first - heterochromatin is late - tissue specific genes may replicate early in tissues where they are active and late where they are repressed |
|
|
What is the "Window of opportunity" model? |
- different proteins are present in the nucleus early and late during S-phase of the cell cycle - e.g. acetylated histones - early - deacetylated histones - late |
