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Genetics > BK Genetics Exam 3: DNA Mutation and Repair > Flashcards

BK Genetics Exam 3: DNA Mutation and Repair Flashcards

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1
Q

What do Loss-of-function mutations do?

A

Impair the function of a protein and is detrimental

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2
Q

What do Gain-of-function mutations do?

A

Cause the protein to be expressed at a higher level than it is supposed to be
AND
In tissues where it isn’t supposed to be expressed

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3
Q

What are germline mutations?

A

Present in either (or both) the sperm or the egg that made the individual

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4
Q

What are somatic mutations?

A

Arise after fertilization, during cell replication/division/differentiation/migration, therefore only present in a subset of the individual’s cells

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5
Q

How do cells become more specialized?

A

As your cells replicate

and divide, they also differentiate into different types of tissues

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6
Q

What happens when a somatic mutation arises?

A

It gets passed down to one fourth of the descendants of the cell in which it arose

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7
Q

Do somatic mutations occur in meiosis or mitoses?

A

Mitosis. Somatic=Diploid

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8
Q

How do somatic mutations get passed down To one fourth of the descendants of the original cell? (ESSAY QUESTION)

A
  • When you start out with two normal chromosomes in S phase, the new chromosomes have the mutation and split.
  • Now those 2 cells has one normal and one mutated chromosome and replicates again during S phase
  • When those split one of them has 2 mutated chromosomes and the other has 2 normal chromosomes (SLIDE 5)
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9
Q

How can somatic mutations be passed down to offspring?

A
  • If the mutation exists in the cells that make sperm (spermatogonia) or eggs (oogonia), the mutation can be packaged into a gamete
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10
Q

From the offsprings perspective, why are some somatic mutations considered germ line mutations?

A

(REMEMBER GERMLINE- Present in either (or both) the sperm or the egg that made the individual)
- It was present in one of the gametes that made the child, and it will exist in every cell the child has

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11
Q

What is a conditional mutation?

A

Some mutations only cause consequences under certain conditions

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12
Q

Give an example of a conditional mutation

A

Many people who have a glucose-6-phosphate dehydrogenase deficiency (an X-linked recessive disease) will experience “flare-ups” (main symptom = hemolytic anemia) if they eat fava beans

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13
Q

Most mutations occur from…

A

Substitutions, Insertions And

Deletions

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14
Q

The ribosome reads mRNA…

A

In 3 base codons

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15
Q

What does not shift the ribosomes reading frame?

A

An insertion or deletion when the ribosome is reading a nucleotide with a multiple of 3

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16
Q

Deletion of a codon results in…

A

a loss of one amino acid

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17
Q

Insertions And Deletions May

Arise Through…

A

Strand Slippage

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18
Q

How does strand slippage occur?

A
  • When a newly synthesized strand loops out and that nucleotide is placed on the new strand
  • When the template strand loops out and puts a nucleotide on the new strand
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19
Q

Repeated sequences may cause…

A

Insertions and deletions through unequal crossovers. This happens when chromosome misalign too far during cross over and take too much material of the other. One has an insertion and the other has a deletion (SLIDE 11)

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20
Q

Define Transition

A

Purine-purine substitution or pyrimidine-pyrimidine substitution

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21
Q

Define Transversion

A

Purine-pyrimidine substitution or vice versa

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22
Q

Define Missense Mutation

A

Causes one amino acid to replace another

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23
Q

Define Nonsense mutation

A

Creates a STOP codon at the site of the mutation

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24
Q

Define Neutral mutation

A

Changes the amino acid content of the protein, but has no functional consequences

25
Q

Define Silent, aka synonymous, mutation

A

Does not change the amino acid content of the protein

26
Q

What are the functional consequences of single-nucleotide substitutions IF the change protein activity?

A
  • Those that alter protein activity may increase or decrease it, by a small or large amount
  • If the amino acid substitution changes the protein’s 3D shape or ability to move as it works, it will disrupt the protein’s function
27
Q

How do amino acids differ in size, polarity, bendability, and electrical charge? (ON EXAM)

A

Arginine, histidine and
lysine are positively charged

Glutamic acid and aspartic acid are negatively charged
(Some of the neutral ones are polar, some are non polar) (SLIDE 14)

28
Q

A Protein’s 3D Shape Is Determined by

A

Interactions Among Amino Acids

29
Q

Alanine can replace glycine. Why?

A

They both are small and uncharged

30
Q

Arginine can’t replace glycine. Why?

A
  • Arginine is large and charged

- Glycine is small and uncharged

31
Q

What are synonymous mutations?

A
  • When base substitutions do not change the amino acid content of the protein
  • May change the splicing of the mRNA (intronic mutations may also)
32
Q

Explain the concept of trinucleotides

Hint: Long faced people. Caused by anticipation

A

-Whether it expands or contracts may depend on the parent of origin
- The larger it gets, the more it expands from one generation to the next
One indiv = 60 repeats
Child = 250 repeats
Grandchild = 5,000 repeats

33
Q

Fragile X Syndrome Is Due To

A

An Expanding CCG Repeat In The X Chromosome (Xq28)

34
Q

Explain COMMON Fragile Sites

A

They are all over the genome, in everyone’s chromosomes

35
Q

Explain RARE Fragile Sites

A

Associated with diseases—ex. Fragile X mental retardation syndrome—fragile site depicted here

36
Q

How do transposable elements affect gene activity? (ESSAY QUESTON)

A

Definition- Can move from one place to another within the same cell’s DNA
- They can “cut and paste,” (nonreplicative transposition) and leave their original place to insert elsewhere, or they can make a copy of themselves and “copy and paste” (replicative transposition) themselves into another location
(FUN FACT: 45% of the human genome has come from transposons)

37
Q

An Example WhereTransposable Elements Can Jump Back Out And Restore Gene Function

A

In corn, there is a pigment gene for which the C allele produces purple pigment, and is dominant over the c allele, which produces no pigment (and therefore yellow or white corn kernels)

38
Q

Explain the Ac element

A

The Ac element produces transposase, while the D element does not

By producing transposase, the Ac element can cause the Ds element to transpose into the pigment gene’s sequence

Also, the Ac element itself can transpose as well (SLIDE 34 and 35)

39
Q

Explain the D element

A

The Ds element can transpose back out again, thereby restoring the function of the pigment gene and allowing the cell to produce purple pigment again

40
Q

Transposable Elements Can…

A

Also Activate Genes By Acting as a Promoter

41
Q

Transposable Elements Can Cause

Chromosome Rearrangements That…

A

Disrupt The Activity Of Genes

42
Q

How DoThe Activity Of Transposons Regulate?

A
  • The transposable elements produces the enzyme transposase, which is what enables transposition
  • In many cases, the cell methylates the DNA in the region of the transposon, which inhibits production of transposase
43
Q

Reverse mutation, aka reversion, replaces

A

The original (forward) mutation and restores the wild-type genotype

44
Q

Suppressor Mutations

A

Can hide or suppress the effects of other mutations

The individual is a double mutant, but has a normal phenotype

45
Q

Some Suppressor Mutations are Intragenic Which Means…

A

Within the same gene’s coding sequence

46
Q

Intergenic Supressor Mutations

A

In a second gene’s coding sequence

Ex. C  G nonsense mutation creates a UAG STOP codon where there was a UAC tyrosine codon

47
Q

A Gene’s Mutation Rate Is Influenced

By…

A
  • Spontaneous DNA mutation rate (varies from gene to gene)
  • Exposure to dietary, environmental and lifestyle factors
  • Capacity to repair mutations
  • Some mutations convey advantages in some environments
  • Stressful environment may increase mutation rate
48
Q

Spontaneous Mutations

A

Errors during DNA replication
(Hydrolytic and other reactions can cause base changes in DNA after
replication)

49
Q

Induced Mutations

A

Environmental agents such as UV light or radon
Chemical exposures
Metabolic byproducts such as the superoxide ion O2-

50
Q

Shifting the proton changes the number and position of hydrogen bonds the base makes, causing it…

A

To pair with a different base than it usually pairs with

51
Q

What is “Wobble?”

A

The ability to pair with an atypical base because of shifts in the arrangement of hydrogen bonds

52
Q

Incorporation Errors Lead To…And…

A
  • Replication Errors
  • During the next cell cycle, the strands with the mismatched bases serve as templates for DNA replication
  • Replication proceeds properly, resulting in one of the two new chromatids having the wrong base on both strands of its DNA
53
Q

Depurination

A

Hydrolysis reactions remove purine (A and G) rings by cleaving the N-glycosidic bond that holds them to the sugar (leaves a blank space in the sequence of bases, but there’s still a sugar/phosphate in the strand

54
Q

Deamination

A

Pyrimidines (C, U and T) can be deaminated by hydrolysis of the NH2 group; the reaction doesn’t require an enzyme

Some C’s exist in methylated form; they get deaminated to yield T’s

Unmethylated C’s get deaminated to yield U’s

55
Q

An Example of Induced Mutations Resulting

From Chemical Agents

A
  • Heterocyclic base analogs, ex. 5-bromouracil, can cause base mispairings
  • The addition of the Br causes the U to want to form three hydrogen bonds, instead of the usual two
56
Q

Intercalating agents insert themselves between nucleotides increasing…

A

the distance between stacked bases, confusing the DNA polymerase and causing insertions and deletions in the DNA

57
Q

Ionizing radiation (from X rays or radon in homes) causes many molecules to…

A

Form ions and highly reactive free radicals that cause breaks in the DNA

58
Q

The Sun’s UV Rays Cause…

A

Pyrimidine Dimers
-Bonds form between neighboring Cs or Ts in the same DNA strand

This brings the two neighboring nucleotides closer together, leaving
the bases unable to bond with the bases from the other DNA strand and prevents DNA replication, which prevents the cell from going through the cell cycle, causing the cell to go into apoptosis

59
Q

Eukaryotes have a special DNA polymerase, eta, that…

A

Puts AA across from the pyrimidine dimer and restores the DNA

Genetics (6 decks)

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