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MCAT Nucleic Acids, DNA, and RNA > Mutations > Flashcards

Mutations Flashcards

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1
Q

What are the 3 main mutation effects that polymerase errors can have on DNA?

A

point mutations
small repeats
insertions/deletions (small, frameshift)

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2
Q

What are the 3 types of point mutations?

A

missense, nonsense, and silent

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3
Q

What is a missense point mutation?

A

When the codon for an AA becomes a new codon for a new AA, resulting in a change of that AA

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4
Q

What is a nonsense point mutation?

A

When the codon for an AA becomes a stop codon, which results in a shortened protein

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5
Q

What is a silent point mutation?

A

When the codon for an AA becomes a new codon for the same AA. This has no effect on the genetic level of the protein, but can have a physiological effect i.e. even though it’s the same AA, your body may not produce as many tRNA for that particular codon, which means the production of that protein is slowed down, and there is less of that protein available for your body

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6
Q

What is a frameshift mutation?

A
  • Mutations that cause a change in the reading frame, which will result in a completely different, malfunctioning protein. -Occurs when one or more base pairs are inserted or deleted into the RNA sequence.
  • Also results in the loss of the stop codon.
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7
Q

What is the only way that an insertion or deletion will not cause a frameshift mutation?

A

The only type of insertion/deletion that will not cause a frameshift mutation is if you insert or delete 3 (or multiples of 3) base pairs. Note it could cause another type of mutation, but will not cause a frameshift mutation.

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8
Q

What causes endogenous damage?

A

reactive oxygen species and physical damage to the cell and DNA

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9
Q

What 4 types of mutation effects can endogenous damage have on DNA?

A

1) oxidized DNA
2) crosslinked bases
3) double or single stranded breaks
4) polymerase errors

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10
Q

What causes exogenous damage?

A

radiation or chemicals

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11
Q

What 3 types of mutation effects can exogenous damage (UV, Xray, and chemical damage) have on DNA?

A

1) UV radiation cause pyrimidine dimers
2) X rays cause double stranded breaks on DNA molecules that can lead to translocations
3) chemical damage can lead to physical damage or can cause intercalation and thus polymerase errors

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12
Q

What is a translocation?

A

refers to joining together the incorrect base pairs when trying to repair damaged DNA

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13
Q

What are transposons?

A

mobile genetic components (“jumping genes”) which can lead to massive insertions, deletions, inversions, and duplications of genetic material

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14
Q

What is transposase?

A

the “cut and paste” enzyme portion of the transposon, which is flanked by inverted repeats

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15
Q

What are the different types of transposons?

A

IS transposon
Complex transposon
Composite transposon

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16
Q

What is an IS transposon?

A

simply composed of a transposase gene flanked by inverted repeat sequences

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17
Q

What is a complex transposon?

A

a transposon that contains additional genes (genes are situated in between the transposase and the inverted repeat(s).

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18
Q

What is a composite transposon?

A

Has 2 similar or identical IS transposon elements with a central region in between.

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19
Q

What are the 3 mutation effects transposons can have on DNA?

A

1) insertions/deletions
2) inversions
3) duplications

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20
Q

If a transposon jumps into a promoter, how will this affect gene expression?

A

it can turn the gene expression off

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21
Q

transposons can jump into ____ parts of the genome and ramp up gene expression at a nearby site

A

regulatory

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22
Q

What does chromosomal rearrangement refer to?

A

one chunk of the chromosome has moved to a new location of the genome

23
Q

For a composite transposon that has 2 inverted transposons, the DNA segment between them will become _____

A

inverted

24
Q

For a composite transposon that has 2 transposons in the same direction, the DNA segment between them will become _____

A

deleted (and then can be inserted into another part of the genome)

25
Q

Describe the mismatch repair pathway

A
  • The replicated DNA strand is compared to the original DNA strand. The mutation is digested, along with additional bases both upstream and downstream from the mutation, and then the correct bases are filled in.
  • pathway can only be activated during or shortly after DNA replication because this pathway can only occur if replicated strand is not yet methylated (in prokaryotes), or still contains a free 3’ terminus or gaps between Okazaki fragments (in eukaryotes)
26
Q

Describe the base/nucleotide excision repair pathway

A
  • if DNA is found defective, the excision repair removes that base and replaces it (it doesn’t replace additional bases both upstream and downstream)
  • this pathway can occur at any time during the cell cycle
27
Q

Describe homology directed repair pathway

A
  • activated when there is a double stranded break in the DNA molecule
  • only activated after replication because a sister chromatid is used as a template to repair the broken strand
  • the broken bases/strands are digested away, along with some additional bases both upstream and downstream. The “sticky ends” then interweave themselves into corrresponding strands of the sister chromatid. The correct bases are then filled in. Enzymes will then disconnect the sister chromatids. Recombination does take place, as the swapped strands will stay on each sister chromatid.
28
Q

Describe the non-homologous end-joining repair pathway.

A
  • can occur at any time
  • broken ends are simply ligated together, but this can cause mutagenic DNA strands, as the broken pieces are not replaced, they are only put back together. These broken pieces can either be translocated or deleted
29
Q

Translocation can occur d/t faulty DNA repair like _____1______, or recombination between ______2_______ chromosomes

A

1) non-homologous end-joining

2) non-homologous

30
Q

What is gene fusion?

A

refers to translocation of genes between non-homologous chromosomes

31
Q

What is the direct reversal pathway to repair pyrimidine dimers (caused by UV radiation)? What are the limitations of this type of repair mechanism?

A
  • photoreactivation: enzymes can repair UV-induced pyrimidine photodimers using white/visible light
  • this can be done in a lab or by bacteria and many plants, but not in a real patients because there is not way to directly expose all DNA in the body to white light
32
Q

Do transposons generally lead to repair mechanisms?

A

No

33
Q

What is the main mechanism of DNA repair in humans?

A

Nucleotide Excision Repair

34
Q

If left unrepaired, pyrimidine dimers in humans may lead to ______

A

melanoma

35
Q

Repair pathways that rely on repairing the damaged DNA strand by comparing it to the undamaged strand of DNA is called ______ repair pathways

A

homology-dependent repair pathways

36
Q

Does excision repair pathway happen before, during, and/or after DNA replication?

A

before

37
Q

Does the mismatch repair pathway happen before, during, and/or after DNA replication?

A

during or shortly after

38
Q

In the mismatch repair pathway, how is the original DNA strand identified in prokaryotes and eukaryotes?

A
  • prokaryotes identifies the mutation by comparing the original methylated DNA strand and comparing it to the replicated unmethylated DNA strand.
  • eukaryotes recognized the replicated strand by the free 3’ end terminus on the leading strand, or by the presence of gaps between the Okazaki fragments on the lagging strand.
39
Q

List 4 things that can lead to double stranded breaks in DNA

A

overall occurs by either by exogenous or endogenous damage

1) reactive oxygen species
2) ionizing radiation (i.e. Xrays)
3) UV light
4) chemical agents

40
Q

What does intercalating DNA refer to?

A

Refers to mutagens that look like purines and pyrimidines that insert themselves between base pairs, thereby causing errors in DNA replication.

41
Q

What are point mutations?

A

single base pair substitutions, includes transitions (replacing a purine for another purine, or a pyrimidine for another pyrimidine) and transversions (substituting a purine for a pyrimdine or vice versa

42
Q

What does an inversion refer to?

A

when a segment of a chromosome is reversed end to end.

43
Q

What 4 types of mutations can occur from transposons?

A

insertions, deletions, inversions, and rearrangements

44
Q

What is chromosome amplification?

A

refers to when a segment of a chromosome is duplicated.

45
Q

What are translocations?

A

recombination between non-homologous chromosomes

46
Q

What is gene fusion and what is it caused by?

A
  • it is where a new gene product is made from parts of 2 genes that were not previously connected
  • caused by translocations
47
Q

What is balanced vs unbalanced translocation?

A
  • balanced translocation is recombination between non-homolgous chromosomes, but does not result in loss of genetic material
  • unbalanced translocation is the recombination between non-homologous chromosomes, and does result in the loss or gain of genetic material
48
Q

All transposons contain a gene that codes for a protein called ______. This enzyme has “cut and paste” activity, where is catalyzes mobilization of the transposon and integration into a new genetic location.

A

transposase

49
Q

When will the mobilization of a transposon not result in a mutation and when will it result in a mutation?

A
  • will not cause a mutation if it mobilizes to a relatively unimportant part of the genome i.e. part of the genome that doesn’t code for any proteins
  • will cause a mutation if it mobilizes to an important part of the genome i.e. part of the genome that is used for gene expression or transcription of proteins.
50
Q

Do mutations generally have greater affect of sex chromosomes or autosomes and why?

A

greater affect on sex chromosomes because male sex chromosomes only have one copy, whereas autosomes (and female sex chromosomes) are present in double copies.

51
Q

Haploid expression in a diploid organism is referred to as ________

A

hemizygosity

52
Q

What does loss of heterozygosity refer to in regards to mutations?

A
  • If a diploid organism has one normal gene and one mutated gene, deletion/loss of this normal gene means that the only gene left is the mutated one. Thus, there is no longer normal function of that gene because only the mutated one is expressed.
  • This can occur if a transposon deletes alleles off of the only normal gene.
53
Q

What is haploinsufficiency?

A

-Refers to a diploid organism having only one functional copy of a gene, and this single copy is not enough to support a normal state.
(Many times, expressing a gene is not enough. You must express enough of the gene to maintain good health).

MCAT Nucleic Acids, DNA, and RNA (5 decks)

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