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Biology > Molecular basis of inheritance part 2 > Flashcards

Molecular basis of inheritance part 2 Flashcards

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1
Q

What does helicase do

A

unwinds dna strands at the replication fork by breaking H-bonds

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2
Q

What does DNA polymerase do (4)

A
  • Synthesizes new DNA strand by adding nucleotides to free 3’-OH grp of pre-existing DNA strand or RNA primer
  • Uses parental strand as template
  • Makes DNA in 5’ –> 3’ direction (links 5’ phosphate grp of new nucleotide to 3’-OH of growing strand)
  • Reads template strand from 3’–> 5’
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3
Q

What does topoisomerase do

A

Relieves “overwinding” ahead of replication fork

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4
Q

what does primase do (2)

A
  • RNA polymerase that synthesizes an RNA primer complementary to the DNA strand
  • Provides a 3’ end for DNA polymerase
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5
Q

What does ligase do (2)

A
  • glues together nicks in DNA sugar-phosphate backbone (forms phosphodiester bond)
  • needed after RNA primers are replaced by DNA and for Okazi fragments
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6
Q

What do single-stranded binding proteins do

A

stabilizes single stranded DNA

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7
Q

Circular double stranded DNA (like in E. coli cell) has how many origins of replication and how many replication bubbles

A
  • 1 origin of replication
  • 1 replication bubble
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8
Q

Linear double stranded DNA (eukaryotic cell) has __ origins of replication and ____ replication bubbles

A
  • Many origins of replication (100s-1000s)
  • Many replication bubbles
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9
Q

What is the first step of DNA replication

A

initiation

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10
Q

where does initiation begin

A

origins of replication, which are short specific sequences of DNA

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11
Q

What 3 proteins bind to the origin of replication during initiation

A
  1. helicases (unzipping of DNA)
  2. single stranded binding proteins (stabilizes ss DNA)
  3. topoisomerase (relieves strain of unwinding)
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12
Q

in a replication bubble, how many replication forks

A

2 (Y-shaped region)

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13
Q

What enzyme does elongation involve

A

DNA polymerase III

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14
Q

What is elongation in DNA replication (4)

A
  • synthesizes new strand of DNA using parental strand as template
  • adds nucleotides according to base pairing rules
  • links nucleotides in growing DNA strand
  • requires free 3’ OH grp
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15
Q

What end does DNA polymerase add nucleotides to

A

3’end of existing nucleotide => primer needed for synthesis

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16
Q

in what direction does synthesis occur

A

5’ to 3’ direction

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17
Q

DNA polymerase reads template in what direction

A

3’ to 5’ direction

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18
Q

template dna containing a 3’ to 5’ strand and a 5’ to 3’ strand means replication is…

A

bidirectional

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19
Q

in dna leading strand:
DNA polymerase III synthesizes dna in what direction

A

same direction as dna unwinding= 5’ to 3’ toward replication fork

20
Q

in what direction is template read in leading strand ?

A

3’ to 5’

21
Q

how many rna primers needed in leading strand

A

1

22
Q

what is a lagging strand

A

from discontinuous dna synthesis

23
Q

in what direction does dna polymerase III synthesize DNA for lagging strands

A

opposite direction of DNA unwinding (5’ to 3’ away from replication fork)

24
Q

in what direction is the template read in lagging strands

A

3’ to 5’

25
Q

how many rna primers for lagging strands

A

many

26
Q

what are the fragments linked by in lagging strands

A

DNA ligase

27
Q

what is the problem on lagging strands

A

new DNA sequence is being built away from the fork (bc being built from 5’ to 3’)

28
Q

what are RNA primers replaced with on Okazaki fragments

A

DNA pol I

29
Q

what is the cause of the end replication problem

A

removal of rna primer from beginning of lagging strand leaves gap & fee 5’- PO4 grp

30
Q

Why can’t the gap left by the removal of rna primer on lagging strand be filled by DNA pol

A

bc there is no free 3’-OH grp, only 5’

31
Q

what is the consequence of the end-replication prob (gap from rna primer removal can’t be filled by DNA pol) (3)

A
  • each replication results in shorter DNA
  • can lead in possible deletion of genes
  • factor that limits life span of cells
32
Q

what comes to solve end-replication problem

A

telomeres

33
Q

what are telomeres

A

repeats of noncoding nucleotide sequences

34
Q

what is the sequence of nucleotides of telomeres

A

TTAGGG
AATCCC

35
Q

what are telomeres added by and when

A
  • added by telomerase enzyme
  • added during early development
36
Q

what happens to telomeres as cell ages

A

shortens

37
Q

in what type of cell is telomerase active

A

germ cells (not somatic cells)

38
Q

what happens if telomerase turned on in somatic cells

A

cancer

39
Q

do telomeres prevent dna shortening

A

no

40
Q

why do prokaryotes not have the dna shortening problem

A

they have circular chromosomes

41
Q

DNA id a highly accurate process. How does DNA polymerase have a role in this

A

it proofreads each nucleotide added

42
Q

when DNA pol is proofreading, what happens if incorrect pairing occurs (2)

A
  • incorrect nucleotide will be removed
  • synthesis resumes once error corrected
43
Q

what happened to errors not caught by DNA pol DURING DNA replication

A

repaired by mismatch repair

44
Q

what happened to errors/changes in existing DNA AFTER DNA replication

A

REPAIRED BY NUCLEOTIDE EXCISION REPAIR

45
Q

how does nucleotide excision repair work

A
  • a nuclease removes changed nucleotides
  • DNA pol fills gap & DNA ligase glues together backbone
46
Q

what can changes in DNA be caused by

A
  • chemicals, radioactivity, ultraviolet

Biology (6 decks)

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