Lecture 20: DNA Replication Flashcards
Who discovered that the specific pairing in DNA suggests a possible copying mechanism for genetic material?
Watson and Crick
What results would you expect for the gen 2 sample of the pulse-chase experiment if DNA replication was conservative?
3/4 of the sample would be low density and 1/4 high density
What results would you expect for the gen 2 sample of the pulse-chase experiment if DNA replication was dispersive?
100% would be of intermediate density
What are the by-products of polymerization using activated nucleotides?
pyrophosphate, H2O and energy
What is the function of DNA polymerase?
catalyzes DNA synthesis
Does only one type of DNA polymerase exist in organisms?
No, DNA Polymerases are a family of enzymes with specialized functions in DNA synthesis during replication and repair
How many types of DNA polymerases exist in E.coli versus in humans?
5 versus a dozen
Three properties of DNA polymerization contribute to
fidelity
- H-bonding between A and T and G and C are stable
interactions. - Active site of DNA polymerase is unlikely to catalyze
bond formation if mismatched base pair is formed. - DNA polymerase can proofread.
How does DNA polymerase proofread?
- If the enzyme finds a mismatch, it pauses and removes the mismatched base that was just added.
- DNA polymerase III can do this because its e (epsilon) subunit acts as an exonuclease that removes a mismatched deoxyribonucleotides from DNA.
When does DNA replication happen in the cell cycle?
Synthesis phase
What makes a DNA
sequence an origin of
replication?
AT-Rich Regions: Origins of replication often have sequences rich in adenine (A) and thymine (T) because A-T base pairs are easier to separate than G-C pairs.
How does DNA replication proceed?
What is the difference between the number of origins of replication in a bacterial chromosome vs. a eukaryotic chromosome?
What are the leading and lagging strands?
leading strand builds a new strand towards the replication fork (5’ to 3’ direction)
lagging strand builds a new strand in the opposite direction as the replication fork (5’ to 3’ direction)
What’s the function of helicase?
What’s the function of single-strand -DNA-binding proteins?
What’s the function of topoisomerase?
What’s the function of primase? (leading strand vs lagging strand)
leading strand: catalyzes the synthesis of an RNA primer
lagging strand: catalyzes the synthesis of RNA primer of an okazaki fragment
What’s the function of DNA polymerase III? (leading strand vs lagging strand)
leading strand: extends leading strand in the 5’ to 3’ direction
lagging strand: extends okazaki fragements
What’s the function of the sliding clamp?
Holds DNA polymerase in place during extension
What’s the function of DNA polymerase I? Which strand synthesis needs it?
the lagging strand needs it to remove RNA primers et replace it with DNA
What’s the function of DNA ligase? Which strand synthesis needs it?
catalyzes the joining of okazaki fragments together in the lagging strand
makes a continuous strand of new DNA
Which three proteins in DNA replication require ATP to function? Which one can use other types of energy?
helicase, topoisomerase and DNA ligase
DNA ligase joins the fragments through a covalent bond between nucleotides and closes gap in sugar-phosphate backbone.
What is the name of this covalent bond formed by ligase?
phosphodiester bond
What is the replisome
