Lecture 11 Flashcards
1
Q
The parent DNA double helix
A
- The two strands of the DNA double helix possess complementary sequence
- Each strand can serve as a template strand
2
Q
DNA replication
A
the process by which a copy of DNA is made
3
Q
Models of replication
A
- Semiconservative: each daughter molecule posses one parental strand
- Dispersive: daughter molecules have patches of old and new DNA
- Conservative: one daughter DNA is completely new DNA while parental strand remains intact
4
Q
DNA replication begin at:
A
- The origin which is rich in A-Ts
- DNA double helix opened with the aid of initiator proteins including helicase, single stranded binding (SSB) proteins, topoisomerases
5
Q
Replication origins
A
- Number of replication origins vary by species
- Example: Ecoli have 1, but humans have 103-104 per cell
- Having more can speed up DNA replication which is important for humans because they have much larger genomes
- E. coli can speed up DNA replication by initiating a new round of replication before completing the previous replication
6
Q
DNA replication requirements:
A
- DNA template
- Deoxyribonucleotide triphosphates
- A protein complex involving DNA polymerase enzyme
- RNA or DNA primer
- Mg 2+ ions (as a cofactor)
7
Q
In what direction does DNA replicate in
A
- DNA is replicated in a 5’ to 3’ direction
- Oncoming deoxyribonucleoside triphosphate provide the energy required for polymerization:
- The 3’ OH attacks the a-phosphate of the incoming dNTP. Pyrophosphate is released which is further hydrolyzed to two molecules of in organic phosphate
8
Q
Leading strand:
A
- One newly synthesized strand made continuously
9
Q
Lagging strand
A
- One strand is made discontinuously in short fragments known as Okazaki fragments
10
Q
What is DNA polymerase
A
- Enzyme responsible for catalyzing the addition of nucleotides to the 3’ end of a growing nucleic acid (there are several different DNA polymerase)
- Very accurate
- Requires an existing 3’ end to function (cannot begin a brand new strand)
11
Q
What are 4 contributing factors to polymerase accuracy
A
- Hydrogen bonding of complementary base pairs
- DNA polymerase monitors the base pairing before catalyzing the addition of the nucleotide
* Active site only fits correct pairs
* Correct base pairs form noncovalent bonds with DNA polymerase - Cell maintain roughly equal concentrations of deoxyribonucleoside triphosphates (dNTPs)
- Proof reading: DNA polymerase can correct error using an 3’ to 5’ exonuclease
12
Q
Exonuclease:
A
Degrade nucleic acids from the end
13
Q
Endonuclease:
A
Cleave nucleic acids within a sequence
14
Q
Does DNA polymerase have separate sites for polymerization and error correcting?
A
- Yes there is a P and E site
- When an error occurs the incorrect nucleotide is pushed into the E site
15
Q
What is the function of primers:
A
- Dna polymerase cannot synthesize a new strand without a primer