BK Genetics Exam 3: DNA Mutation and Repair

Question 1

What do Loss-of-function mutations do?

Answer 1

Impair the function of a protein and is detrimental

Question 2

What do Gain-of-function mutations do?

Answer 2

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

Question 3

What are germline mutations?

Answer 3

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

Question 4

What are somatic mutations?

Answer 4

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

Question 5

How do cells become more specialized?

Answer 5

As your cells replicate

and divide, they also differentiate into different types of tissues

Question 6

What happens when a somatic mutation arises?

Answer 6

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

Question 7

Do somatic mutations occur in meiosis or mitoses?

Answer 7

Mitosis. Somatic=Diploid

Question 8

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

Answer 8

• 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)

Question 9

How can somatic mutations be passed down to offspring?

Answer 9

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

Question 10

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

Answer 10

(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

Question 11

What is a conditional mutation?

Answer 11

Some mutations only cause consequences under certain conditions

Question 12

Give an example of a conditional mutation

Answer 12

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

Question 13

Most mutations occur from…

Answer 13

Substitutions, Insertions And

Deletions

Question 14

The ribosome reads mRNA…

Answer 14

In 3 base codons

Question 15

What does not shift the ribosomes reading frame?

Answer 15

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

Question 16

Deletion of a codon results in…

Answer 16

a loss of one amino acid

Question 17

Insertions And Deletions May

Arise Through…

Answer 17

Strand Slippage

Question 18

How does strand slippage occur?

Answer 18

• 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

Question 19

Repeated sequences may cause…

Answer 19

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)

Question 20

Define Transition

Answer 20

Purine-purine substitution or pyrimidine-pyrimidine substitution

Question 21

Define Transversion

Answer 21

Purine-pyrimidine substitution or vice versa

Question 22

Define Missense Mutation

Answer 22

Causes one amino acid to replace another

Question 23

Define Nonsense mutation

Answer 23

Creates a STOP codon at the site of the mutation

Question 24

Define Neutral mutation

Answer 24

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

Question 25

Define Silent, aka synonymous, mutation

Answer 25

Does not change the amino acid content of the protein

Question 26

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

Answer 26

- 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

Question 27

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

Answer 27

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)

Question 28

A Protein’s 3D Shape Is Determined by

Answer 28

Interactions Among Amino Acids

Question 29

Alanine can replace glycine. Why?

Answer 29

They both are small and uncharged

Question 30

Arginine can't replace glycine. Why?

Answer 30

- Arginine is large and charged | - Glycine is small and uncharged

Question 31

What are synonymous mutations?

Answer 31

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

Question 32

Explain the concept of trinucleotides | Hint: Long faced people. Caused by anticipation

Answer 32

-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

Question 33

Fragile X Syndrome Is Due To

Answer 33

An Expanding CCG Repeat In The X Chromosome (Xq28)

Question 34

Explain COMMON Fragile Sites

Answer 34

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

Question 35

Explain RARE Fragile Sites

Answer 35

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

Question 36

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

Answer 36

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)

Question 37

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

Answer 37

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)

Question 38

Explain the Ac element

Answer 38

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)

Question 39

Explain the D element

Answer 39

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

Question 40

Transposable Elements Can...

Answer 40

Also Activate Genes By Acting as a Promoter

Question 41

Transposable Elements Can Cause | Chromosome Rearrangements That...

Answer 41

Disrupt The Activity Of Genes

Question 42

How DoThe Activity Of Transposons Regulate?

Answer 42

- 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

Question 43

Reverse mutation, aka reversion, replaces

Answer 43

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

Question 44

Suppressor Mutations

Answer 44

Can hide or suppress the effects of other mutations | The individual is a double mutant, but has a normal phenotype

Question 45

Some Suppressor Mutations are Intragenic Which Means...

Answer 45

Within the same gene’s coding sequence

Question 46

Intergenic Supressor Mutations

Answer 46

In a second gene’s coding sequence Ex. C  G nonsense mutation creates a UAG STOP codon where there was a UAC tyrosine codon

Question 47

A Gene’s Mutation Rate Is Influenced | By...

Answer 47

- 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

Question 48

Spontaneous Mutations

Answer 48

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

Question 49

Induced Mutations

Answer 49

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

Question 50

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

Answer 50

To pair with a different base than it usually pairs with

Question 51

What is "Wobble?"

Answer 51

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

Question 52

Incorporation Errors Lead To…And...

Answer 52

- 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

Question 53

Depurination

Answer 53

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

Question 54

Deamination

Answer 54

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

Question 55

An Example of Induced Mutations Resulting | From Chemical Agents

Answer 55

- 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

Question 56

Intercalating agents insert themselves between nucleotides increasing...

Answer 56

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

Question 57

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

Answer 57

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

Question 58

The Sun’s UV Rays Cause...

Answer 58

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

Question 59

Eukaryotes have a special DNA polymerase, eta, that...

Answer 59

Puts AA across from the pyrimidine dimer and restores the DNA