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Bio 302 > Chapter 6 > Flashcards

Chapter 6 Flashcards

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Biology 101 flashcards
1
Q

when does DNA replication occur?

A

before a cell can produce two genetically identical daughter cells

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2
Q

what do replication initiator proteins do?

A

recognize sequences of DNA at replication origins and pry apart the two strand of double helix

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3
Q

the exposed single strand can serve as what for copying DNA?

A

templates

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4
Q

replication forks move in what direction?

A

move away in opposite directions from multiple replications origins in eukaryotic chromosome

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5
Q

what direction is DNA synthesized?

A

5’ to 3’

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6
Q

the addition of what to the 3’-hydroxyl end of a polynucleotide chain is the fundamental reaction by which DNA is synthesized?

A

deoxyribonucleotide

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7
Q

the nucleotides enter the reaction as ______

A

nucleoside triphosphates

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8
Q

what does DNA polymerase do?

A

catalyzes the addition of nucleotides to the free 3’ hydroxyl on the growing DNA strand

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9
Q

what does the breakage of a phosphoanhydride bond in the incoming nucleoside triphosphate do?

A

release a large amount of free energy and thus provides the energy for the polymerization reaction

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10
Q

at the replication fork, the two new synthesized DNA strands are of _____

A

opposite polarities

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11
Q

the lagging strand of DNA must be made initially as……

A

a series of short DNA strands called Okazaki fragments that are later joined together

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12
Q

the DNA strand that is synthesized discontinuously is called?

A

the lagging strand

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13
Q

the DNA strand that is synthesized continuously is called?

A

the leading strand

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14
Q

can DNA polymerase proofread its own work?

A

yes

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15
Q

if an incorrect nucleotide is added to a growing strand, the DNA polymerase will do what?

A

cleave it from the strand and replace it with the correct nucleotide before continuing

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16
Q

true or false? DNA polymerase contains separate sites for DNA synthesis and proofreading?

A

true

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17
Q

why does proofreading explain why DNAs are synthesized in 5’ to 3’ direction?

A

growth in 5’ to 3’ direction allows chain to continue to be elongated when incorrect nucleotide has been added then removed

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18
Q

how is RNA primers made?

A

at intervals of about 200 nucleotides on lagging strand by primase

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19
Q

how long are RNA primers

A

10 nucleotides long

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20
Q

how are primers removed?

A

by nucleases that recognize an RNA strand in and RNA/DNA helix and degrade it

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21
Q

removing a primer leaves a gap, how is it filled?

A

filled by a DNA repair polymerase that can proofread as it fills in the gaps

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22
Q

how are the completed fragments joined together?

A

by DNA ligase

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23
Q

what does DNA ligase do?

A

catalyze the formation of phosphodiester bond between 3’ OH end of fragment and 5’ phosphate end of the next-linking up sugar phosphate backbone

24
Q

where are DNA polymerase located when DNA is replicating?

A

one on leading strand and other on lagging strand

25
Q

how is DNA polymerase held on to DNA?

A

by a circular protein clamp that allow the polymerase to slide

26
Q

what does DNA helicase do?

A

uses the energy from ATP hydrolysis to move forward and separate strands of the parental DNA double helix

27
Q

what helps the two strands stay separated to provide access for primase and polymerase?

A

single-strand DNA-binding proteins

28
Q

why is the DNA on the lagging strand folded?

A

to bring the lagging-strand DNA polymerase in contact with the leading strand DNA polymerase

29
Q

the folding also does what?

A

brings the 3’ end of each completed O fragment close to the start side for next O fragments

30
Q

the lagging strand DNA polymerase can be reused for what?

A

to synthesize successive O fragments

31
Q

to synthesize the lagging strand at the end of a chromosome, the DNA replication machinery requires what?

A

requires the length of template DNA extending beyond the DNA that is to be copied

32
Q

what does telomerase do?

A

adds a series of repeats of a DNA sequence to the 3’ end of the template strand, which allows lagging strand to be completed by DNA polymerase

33
Q

what are mutations?

A

permanent changes of DNA caused by copying error and accidental damage

34
Q

how is colon cancer caused?

A

accumulation of multiple mutations

35
Q

what will happen if the mutation is uncorrected?

A

the mismatch will lead to permanent mutation in 1 of the 2 DNA molecules produced in next replication

36
Q

what will happen is the mismatch is repaired using new DNA strand as template?

A

both DNA molecules produced in next replication will contain mutation

37
Q

what will happen if the mismatch is correct using original template strand as the template?

A

the mutation is eliminated

38
Q

why are newly replicated DNA strand preferentially nicked?

A

nicks provide signal that directs the mismatch repair machinery to appropriate strand

39
Q

what does DNA mismatch do to the geometry of the DNA?

A

distorts it

40
Q

the DNA mismatch repair protein recognizes the distortion and does what?

A

removes the newly synthesized DNA

41
Q

the gap in the newly synthesized DNA is replaced by what?

A

by a DNA polymerase, which proofreads as it synthesize and sealed by DNA ligase

42
Q

where are these nicks known to occur?

A

in the lagging strand, less observed in leading strand

43
Q

what are the most frequent chemical reactions that cause serious DNA damage in cells?

A

depurination and deamination

44
Q

what is depurination?

A

purine bases lost from DNA in cells

45
Q

what is deamination?

A

loss of amino group from cytosine in DNA to produce uracil

46
Q

what happens if deamination of cytosine is uncorrected?

A

results in the substitution of one base fro another when DNA is replicated

47
Q

in deamination, what does uracil pair with?

A

adenine

48
Q

what does UV radiation from sunlight cause?

A

DNA damage

49
Q

What does UV radiation do to thymine bases?

A

2 adjacent thymine bases become covalently attached to one another to form thymine dimer

50
Q

what is the 1st step of DNA repair?

A

excision- damage DNA cut out by nucleases

51
Q

what is the 2nd step of DNA repair?

A

resynthesis- orig DNA sequence is restored by DNA polymerase, fills in the gap

52
Q

what is the 3rd step of DNA repair?

A

ligation- DNA ligase seals the nick.

53
Q

what energy does nick sealing require?

A

energy from ATP hydrolysis to remake broken phosphodiester bond

54
Q

what can cells use to repair double-strand breaks?

A

nonhomologous end-joining “quick and dirty”

55
Q

what allows for flawless repair of DNA double-strand breaks?

A

homologous recombination

56
Q

when is homologous recombination initiated?

A

when a double strand break occurs shortly after a stretch of DNA has been replicated

Bio 302 (7 decks)

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