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MolBio and Genetics I > 7. Variations in DNA > Flashcards

7. Variations in DNA Flashcards

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1
Q

What effects can DNA mutations have?

A
  • nonsense mutation
  • missense mutation
  • framshift mutation
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2
Q

what is a non sense mutation

A

premature termination of protein translation from nonsynonymous mutations

(stop codon)

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3
Q

What are non synonymous mutations

A

codon information is changed to another amino acid or stop

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4
Q

what are synonymous mutations

A

no change to codon information same amino acid is incoporated

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5
Q

what are missense mutations

A

incoporation of a different amino acid

  • conservative substituition: exchange with amino acid of similar properties
  • radical replacement exchange with amino acid of different properties
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6
Q

What are polymorphic mutations

A

acceptable variations to DNA sequence

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7
Q

what types of mutations are usually polymorphic

A
  • synonymous/silent mutations
  • intronic mutations
  • intergenic mutations
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8
Q

What are copy number variations (CNVs)

A

large specifc regions of some chromosomes can be deleted/amplified (thus gene dosage) without any obvious ill effects.

  • resulting variation in gene dosage os CNVs
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9
Q

what are potential phenotypic consequences of DNA mutations

A
  • lethal mutation
  • conditional mutation loss of function mutation
  • loss of function mutation
  • null mutation gain of function mutation
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10
Q

How does DNA slippage occur

A

highly repetitive streches of DNA sequence (often non-protein coding regions) can be problematic for DNApol

  • slipping causes the deletion or insertion of nucleotides
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11
Q

which nitrogenous base mutations are most frequent

A

C to T

  • occur disproportionally on X chromsome due to cytosine mediated X-inactivation
  • responsible for many X linked disorders
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12
Q

Guanine and Adenine deamination is very rare and ledas to?

A

non-Watson& crick base pairing during DNA replication

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13
Q

What happens if depurination occurs (removal of purine base)

A
  • normally recognized and repaired when in double stranded DNA by cellular repair mechanisms
  • if present in single stranded can lead to mutation
  • catalyzed by nitrous acid
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14
Q

Is depyrimidnation or depurination more frequent

A

depurination

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15
Q

What is the effect of high energy ionizing radiation (Xray &gamma rays)

A
  • formation of free radical species
  • direct interaction with DNA
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16
Q

What is the effect of non-ionizing radiation (UV light)

A
  • DNA bases efficiently absorb UV
  • abdorb energy to promote electrons
  • exited pyrimidines form covalent bonds (form pyrimidine dimers)
  • pyrimidine dimers are mutagenic (repaired incorrectly
17
Q

What can base pair analogs/intercaltors do?

A

can squeeze between genuine base pairs of DNA causing distortions

18
Q

What do alkylating agents do

A

electrophilic chemicals that add alkyl groups to various positions of DNA bases

  • inhibit DNA helicase
  • can cause indirect mutagenises if replaced incorrectly
19
Q

Where are Reactive Oxygen Species derived from

A

ROS derive from both endogenous and exogenous sources

20
Q

What does ROS do to DNA

A

cause oxidative damage by breaking base/nucleotide destruction and modification

21
Q

Where do mispaired nucleotides that cause structional distortions come from

A
  • inappropriate H bonding (wrong pairing)
  • base analogs
  • chemically modified bases
22
Q

How are parental and template and newly synthesized DNA strands be determined in prokaryotes?

A

DNA hemi methaltion

23
Q

How can DNA hemi methylation determine parental and newly synthesized DNA strand

A

specific A and C nucleotides are methylated at palindromic sequences

  • (immidiately after replication they exist as hemi methylated state
24
Q

How does nucleotide existion repair work

A

removal of bulky DNA lesions

  • structural distorions in DNA detected and endonuclease enzymes cut DNA a
  • oglionucleotide containing the mutation is then removed leaving a relatively large gap
  • gap is filled with DNApol I
25
Q

How does base existion repair work

A

associated with removal of chemically modified bases

  • modified bases are recognized by DNA glycosylases
  • cleaves glycosylic bond attaching base to deoxyribose sugar
  • apruinic/apyrimidinic site generated
  • endonuclease recognized and makes gap
  • gap filled by DNApol I
26
Q

What does MutS in DNA repair system do

A

detects and binds to distorted DNA region

27
Q

What does MutH in the DNA repair system do

A

MutH locates teh nearest hemi-methylated adenosine andnicks the non-methylated strand

28
Q

What does MutL in the DNA repair system do

A

MutL provides structure to complex loop DNA

29
Q

Does Synthesis dependent strand annealing (SDSA) or Double strand break repair (DSBR/ Double Holliday junction model) involve crossover?

A

DSBR

MolBio and Genetics I (9 decks)

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