Molecular Biology Flashcards
1
Q
Pyrimidine bases
A
C,T,U
2
Q
Nucleosides are
A
Base + sugar
3
Q
Nucleotides are
A
Nucleoside + phosphate
4
Q
DNA is polymerized in the _ to _ direction
A
5’ to 3’
5
Q
Phosphodiester linkage
A
5’ PO4- to 3’ OH
6
Q
3 types of DNA
A
A,B and Z
7
Q
Differences in types of DNA
A
- Handedness: A-R, B-R, Z-L
- Condition: A-rel. humidity, B- high humidity, C-high salt
- BP/turn: A-11, B-10, C-12
- Vertical rise -B
- Helical Diameter -A
8
Q
Replication is:
A
- Semi-conservative
2. Bidirectional (2 replication forks)
9
Q
Mechanism of replication:
A
- Starts at origin of replication
- Local separation of duplex DNA
- Helicase unwinds the DNA at the fork
- SSB proteins keep duplex strands apart
- Primase synthesizes a short RNA primer
- DNA polymerase 3 extends this
- Topoisomerases maintain proper helical density
- Lagging strand synthesis involves Okazaki fragments
- DNA polymerase 1 removes RNA primers and fills the gaps
- Ligase seals the gaps
10
Q
DNA polymerases can’t
A
- Melt or unwind duplex DNA
2. Initiate chains, can only extend a pre-existing DNA or RNA strand
11
Q
Type 1 topoisomerases
A
Relax DNA by nicking and closing one strand of duplex DNA
12
Q
Type 2 topoisomerases
A
Change DNA topology by breaking and rejoining double stranded DNA
13
Q
Why is DNA replication accurate?
A
- Base pairing
- Proofreading by DNA polymerase
- Post-polymerase repair systems
14
Q
How does DNA polymerase proofread?
A
- Senses the distortion of the double helix from insertion of incorrect bases
- Closes ‘fingers’ of hand
- Move DNA from polymerase domain to exonuclease domain where incorrect base is removed
- Opens fingers of hand
- DNA strand moves back to polymerase domain
15
Q
Mismatch repair
A
Before replication finishes
