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molecular cell biology > chapter 5.3 > Flashcards

chapter 5.3 Flashcards

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1
Q

colon cancer

A

mismatch repair

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2
Q

skin cancer

A

nucleotide excision repair

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3
Q

what are two most frequent spontaneous chemical reactions that cause serious DNA damage in cells

A

depurination and deamination

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4
Q

deamination of adenine

A

hypoxathine

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5
Q

deamination of guanine

A

xanthine

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6
Q

deamination of cytosine

A

uracil

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7
Q

deamination of thymine

A

NONE

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8
Q

what is deamination (for dummies)

A

the removal of an amine group from a base

note: if the normal C is paired with a G and is then deaminated, it will become a U. then, this U will be replicated and paired with an A and then this sequence is mutated

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9
Q

is deamination spontaneous

A

yes!

note: it is estimated to occur 100 times per day in every human cell

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10
Q

deamination can lead to……

A

point mutations if not corrected

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11
Q

how is deamination fixed

A

base-excision repair

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12
Q

what is depurination (for dummies)

A

the loss of a purine base (A or G)

the A or G is cleaved out at AP (apurinic) sites

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13
Q

what usually happens as a result of depurination

A

transversions! the missing base is normally replaced with a T

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14
Q

is depurination spontaneous

A

yes!

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15
Q

when does base excision repair occur

A

prior to DNA replication

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16
Q

when does mismatch excision repair occur

A

mainly post DNA replication

17
Q

when does nucleotide excision repair occur

A

prior to DNA replication

18
Q

when does proofreading by DNA polymerase occur

A

during DNA replication

19
Q

what does non-homologous end joining and homologous recombination fix

A

double stranded DNA breaks

20
Q

what are the main enzymes in base excision repair

A

DNA glycosylase - cut out wrong base (chop it out)
APEI endonuclease + AP lyase- cut out backbone
DNA Pol Beta + DNA ligase - add the correct base back in and repair the backbone (sew everything back up together and make it look cute again)

21
Q

what enzyme recognizes the unusual nucleotides and how does it do this

A

DNA glycosylases and base flipping

22
Q

what is base flipping (for dummies)

A

DNA glycosylase flips a base completely out of the double helix to check it out when it thinks it’s the wrong base paired into the helix

23
Q

what does mismatch excision repair fix

A

errors that remain in DNA after proofreading by DNA polymerase

24
Q

what are the steps of mismatch excision repair

A
  1. removal of the mutation by a nuclease
  2. gap filling by DNA polymerase
  3. sealing of the nick by DNA ligase
25
Q

what kind of damage does UV radiation cause

A

pyrimidine dimers

26
Q

what are thymine dimers + how do they happen (for dummies)

A

UV radiation gets thymine overly excited and makes it want to bond with its friends so it creates a C-C bond between itself and an adjacent thymine (its friend)

27
Q

what do T-T dimers interfere with

A

replication and transcription

28
Q

what mechanism fixes T-T dimers

A

excision repair

29
Q

what does nucleotide excision repair fix

A

DNA regions containing chemically modified bases that distort the normal shape of DNA

30
Q

how does DNA synthesis get around DNA lesions

A

DNA lesions cause DNA replication to stall so DNA polymerase delta or epsilon are momentarily switched out for an error-prone DNA polymerase that simply overlooks the bump in the DNA and moves right along and the lesion is bypassed!

after, the polymerases switch back

this is called translesion synthesis

31
Q

what is the difference between base excision repair and nucleotide excision repair

A

BER - one single base
NER - often chunks of the backbone to fix pyrimidine dimers

32
Q

nonhomologous end joining

A
  1. synapse forms at the broken ends of the double-stranded break by DNAPK
  2. nucleases remove bases from the DNA ends
  3. the two molecules are ligated together with several base pairs missing

note: error prone because base loss causes genetic mutation and incorrect rejoining can cause chromosomal rearrangment

33
Q

nonhomologous end joining (for dummies)

A

at the double stranded break, DNAPK (“dna pick”) comes and PICKS the two molecules up, cuts the torn ends so they line up, and sews them together without caring what is cut off (error prone)

34
Q

homologous recombination

A

genetic exchange at equivalent positions along two chromosomes with substantial DNA sequence homology

35
Q

how does homologous recombination fix DNA damage

A

causing the exchange of large regions of chromosomes between the maternal and paternal pair of homologous chromosomes

molecular cell biology (14 decks)

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