chapter 7 part 2

Question 1

leading strand synthesis

Answer 1

1 copy of pol III synthesizes daughter strand continuously in same direction as fork progression

Question 2

lagging strand synthesis

Answer 2

other copy of pol III elongates daughter strand discontinuously in opposing direction to fork progression
- creates Okazaki fragments

Question 3

DNA polymerase I function

Answer 3

• 5’ to 3’ exonuclease activity (removes RNA primers)
• 5’ to 3’ polymerase activity (adds DNA nucleotides to 3’ end)
• 3’ to 5’ exonuclease activity

Question 4

DNA ligase function

Answer 4

seals gap between DNA segments by catalyzing formation of new phosphodiester bonds between neighboring nucleotides

Question 5

composition of DNA pol III holoenzyme

Answer 5

11 protein subunits:
- 2 pol III core polymerases
- copes of tau protein
- clamp loader
- sliding clamp

Question 6

what do tau proteins join

Answer 6

DNA polymerase III and clamp loader

Question 7

sliding clamp function

Answer 7

• anchors DNA pol III core enzyme to template
• required for high level of pol III activity

Question 8

DNA proofreading

Answer 8

maintains accuracy in DNA replication, corrects occasional erros

Question 9

what do replication errors produce

Answer 9

DNA mismatch

Question 10

DNA mismatch

Answer 10

inability of mismatched bases to form appropriate H-bonds

Question 11

what happens when DNA becomes mismatched

Answer 11

• 3’ OH fits into 3’ to 5’ exonuclease site of enzyme
• several nucleotides removed and new nucleotides incorporated

Question 12

can the leading strand of linear chromosomes be completely replicated?

Answer 12

yes all the way to the end

Question 13

can the lagging strand of linear chromosomes be completely replicated?

Answer 13

can’t be completely replicated because of primer
- primer leaves small gap
- solved by telomeres

Question 14

telomeres

Answer 14

repetitive sequences at ends of chromosomes

Question 15

purpose of telomeres

Answer 15

ensures incomplete chromosome replication doesn’t affect vital genes

Question 16

what are telomere sequences synthesized by

Answer 16

ribonucleoprotein Telomerase

Question 17

who discovered telomerase and telomeres

Answer 17

• Blackburn
• Greider
• Szostak
• Nobel Prize 2009

Question 18

telomerase is an _____-dependent ______- polymerase

Answer 18

RNA, DNA

Question 19

what does telomerase carry to make new DNA sequences

Answer 19

RNA template
- (like reverse transcriptase)

Question 20

a polymerase (primase in prokaryotes)

Answer 20

once telomeres sufficiently elongated, this synthesizes additional RNA primers to allow for DNA replication not by telomerase

Question 21

structure of telomeres

Answer 21

• repetitive DNA sequences
• T loop
• sheltering protein complex

Question 22

T loop

Answer 22

DNA sequences that forms a knotted fold in telomeres

Question 23

what does the T loop bind

Answer 23

sheltering protein complex

Question 24

shelterin protein complex

Answer 24

protects telomeres from degradation

Question 25

what happens when telomeres eventually shorten

Answer 25

apoptosis

Question 26

Hayflick limit

Answer 26

number of cell cycles of a vertebrate cell before the cell succumbs to apoptosis

Question 27

what is telomerase inactivity associated with

Answer 27

normal aging of cells

Question 28

Werner syndrome

Answer 28

• causes early onset of aging features
• caused by mutation in RECQL2

Question 29

RECQL2

Answer 29

gene encoding helices required for telomerase activity

Question 30

Dyskeratosis congenita

Answer 30

disorder associated with loss of function of a gene (DKC1)

Question 31

DKC1

Answer 31

gene that encodes a protein needed for normal telomerase function

Question 32

symptoms of dyskeratosis congenita

Answer 32

• skin/nail abnormalities
• loss of vision/hearing
• abnormal blood cell formation

Question 33

where is telomerase normally turned off

Answer 33

somatic cells

Question 34

what can reactivation of telomerase lead to

Answer 34

aging cells that continue to proliferate
- feature of many types of cancer

Question 35

TERT reactivation

Answer 35

one of most common mutations in cancers of all types

Question 36

TERT

Answer 36

encodes reverse transcriptase function of telomerase