Dna Replication

Question 1

What direction does bacterial dna replication occur

Answer 1

Bidirectional and from single origin

If relocation is unidirectional, termination and initiation will occur at the same site

Question 2

What direction does eukaryotic Dna replication proceed

Answer 2

Bifurcation and from several fixed or digits

Forms advance until they meet another fork traveling in the same direction

Question 3

Discuss DNA polymerase reaction

Answer 3

DNA polymerase catalyzes the nicleophillic attack by the 3’-OH

Question 4

What substrates does DNA polymerase require

Answer 4

Dna template, an rna or dna primer and dNTPs

In addition DNA polymerase one has both 3’ and 5’ endonuclease activity

Question 5

What is the major replicative polymerase in bacteria

Answer 5

DNA polymerase III

Question 6

How does dna proofreading work

Answer 6

3’ exonucleolytic proofreading delays the extension from a mismatch allowing for duplex unwinding at the primer terminus, placing the mismatched 3’ nucleotide in the exonuclease site

Question 7

Characteristics of DNA polymerase I

Answer 7

• 5’ to 3’
• 3’ exonuclease activity (proofreading)
• 5’ exonuclease activity (rna primer removal and dna repair)
• low polymerase processivity

Question 8

Characteristics of DNA polymerase III

Answer 8

• 5’ to 3’ activity
• 3’ exonuclease activity (proofreading)
• High polymerase processivity

Question 9

5 steps of dna replication involving discontinuous synthesis on the lagging strand

Answer 9

1. Unwinding of parental duplex by helicase and elongation of leading strand by polymerase III expose single stranded region infront of lagging strand
2. Primate synthesizes primer
3. Polymerase 3 extends DNA Okazaki fragment from primer
4. Polymerase I eliminates downstream rna primer by nick translation
5. Dna Logan legates Okazaki fragment to rest of lagging strand

Question 10

Action of e. Coli. Clamp loader

Answer 10

Exchange of ADP for ATP increases the affinity of the loader for the clamp

Upon binding the loader opens the clamp

Binding of the template primer dna to atp hydrolysis closure and clamp and release of loader

Question 11

How does topoisomerase work in the termination of dna replication

Answer 11

Topoisomerase IV allows the duplicates circular dna to decatenage through 2 mechanisms

Question 12

4 steps of extension of telomeres dna by telomerase

Answer 12

1. Telomerase binds to hexanucleotide telomere sequence via complementarity with telomerase dna
2. Telomerase reverse transcribed the hexanucleotide telomere tequence through incorporating dNTPs at the 3’-OH of telomere sequence
3. Telomerase Carrie’s out rna templates dna synthesis
4. Telomerase either translocated or dissociates and rebinds to post it Jon itself for a second round of nucleotide incorporation and the cycle repeats

Question 13

Huntingtons disease

Answer 13

• autosomal dominant neurological disease
• brain protein Huntingtin contains stretch of glutamine residues
• normal = 6-31 CAG repeats
• diseased = 80
• number of repeats increases if dna product slips out forming a loop during replication