ALL THE THINGS Flashcards
DNA replication is described by what model?
Semiconservative Model
What do DNA polymerases do?
read DNA templates (parent strands) in the 3’-5’ direction
Synthesized a complementary DNA strand in the 5’-3’ direction
The Replication Fork is made of what two strands?
Leading and Lagging strand
What direction is the leading strand synthesized?
5’-3’ in the same direction as the rep fork
What direction is the lagging strand synthesized?
5’-3’ in the opposite direction of the replication fork
Can the lagging strand be synthesized continuously?
NO! synthesized as small fragments called Okazaki fragments which are later ligated
DNA replication can only begin at what specific sequences?
Origins of replication
How many replication forks begin from ever origin?
2 in opposite directions
DNA polymerases require an existing what?
3’-OH to add nucleotides to
provided by a Primer; cant synthesize using a naked strand
What is primase?
DNA-dependent RNA polymerase
What does primase do?
synthesizes a short RNA primer complementary to the template strand; provide the necessary 3’OH; do not require primers
What are the substrates for DNA chain elongation?
deoxynucleotidetriphosphates (dNTPs)
What is the reaction mechanism for DNA chain elongation?
nucleophilic attack by 3’-OH of primer on first phosphate (alpha) of the incoming dNTP
Is a transesterification rxn
What happens to the other 2 phosphates in DNA chain elongation?
released as inorganic phosphate (PPi)
Is the DNA chain elongation reaction reversible?
NO! irreversible
Most enzymes are what?
distributive; dissociate from substrate and product after catalyzing their reaction
What is processivity?
ability of an ezyme to catalyze multiple reactions without releasing its substrate
For DNA polymerases, processivity is what?
the number of nucleotides added before the polymerase dissociates
DNA Poly III has what kind of processivity?
High
DNA Poly I has what kind of processivity?
Low
What do highly processive DNA polys use to remain associated with their templates?
sliding clamps loaded via ATP hydrolysis
DNA Polys make a mistake every —
10,000 — 100,000
What does proofreading do?
removes incorrect, mispaired nucleotides introduced by errors
What kind of activity do proofreaders show?
3’-5’ exoneclease activty in most but not all DNA polys
