exam 2: gene function: dissection thru mutation

Question 1

definition of genes

Answer 1

specific region on a chromosome that may or may not code for protein

Question 2

how do genes affect phenotype? Why do some alleles produce 1 phenotype and other alleles produce another phenotype

Answer 2

mutations

Question 3

definition of mutation

Answer 3

heritable changes in base sequences that modify info content of DNA

Question 4

a forward mutation

Answer 4

`wild (common>1&%)—>mutant

Question 5

reverse mutation (reversion)

Answer 5

mutant —-> wild

Question 6

types of mutations

Answer 6

-substitution
-deletion
-insertion
-inversion
-reciprocal translocation

Question 7

mutation: substitution

Answer 7

change identity of specific base

types:
1. transition:
purine to purine (A/G)
pyrimidine to pyrimidine (C/T)

2. transversion:
   purine to pyrimidine
   pyrimidine to purine

which is more likely to happen?
transition bc substituting a chemiclaly similar structure to another is an easier process

Question 8

mutation: deletion/ insertion

Answer 8

deletion: one or more base lost in dna

insertion: one or more bases added to DNA

Question 9

mutation: inversion

Answer 9

one piece of DNA rotates 180 in chromosome
-if large enough piece, may involve >1 gene

GATGTGA
AGTGTAG

Question 10

mutation:reciprocal translocation

Answer 10

pieces of 2 nonhomologous chromosome change places

Question 11

mutation rate (how often)

Answer 11

approx. 1 in 10000- 1 in 1000000 gametes carry a mutated allele
-> 1 mutation in 30000 (0.03-3 gametes)

Question 12

rate: forward mutations usually occur more often than reversions. Why?

Answer 12

1. way more ways to do that (convert wild-> mutant)
2. more wild type alleles in a pop. than a mutant allele in a pop.

Question 13

what causes mutation

Answer 13

-spontaneous
-in response to smth

Question 14

spontaneous mutation

Answer 14

-some are completely random
-mutation occurs but does not become transparent until environment changes

ex. antibiotic resistance?

Question 15

question regarding antibiotic resistance

Answer 15

due to spontaneous: should expect only a few random individuals to have resistant genotype

due to exposure of antibiotic: should expect to see resistance develop in an equal # of individuals exposed to the same antibiotic

Question 16

Antibiotic resistance experiment (luria and Delbruck)

Answer 16

if spontaneous: only some plates would have resistance bacteria AND they would appeatin diff, random #

if result of exposure: all plates would have abt the same # of resistant bacteria

RESULT: spontaneous mutation

Question 17

why do resistant bacteria only become pervasive when in presence of antibiotic?

Answer 17

new selection pressure only resistant bacteria can survive

Question 18

spontaneous mutation: depurination

Answer 18

hydrolysis of A or G from sugar phosphate backbone ; no base (lose A/G)

Question 19

Spontaneous mutation: replication error

Answer 19

DNA polymerase incorporates wrong base during replication
-very rare: 1 base in 109 mutates bc of this error
why so rare: reciprocal translocation(nonhomolog)

Question 20

spontaneous mutation:deamination

Answer 20

loss of amino from base; particularly bad if lost from C changes to U

what controls protein repair enzyme?
genes

Question 21

spontaneous mutation: unequal exchange of homologous chromosomes

Answer 21

(recombination between homologous)

will duplicate some genes on 1 homologue and delete those genes from the other homologue

=-~
=-~
—->
=–~
=~

Question 22

spontaneous mutation: transposable elements

Answer 22

Transposable elements (TE): several hundred to several thousand nucleotides that move from 1 place to another in genome; may interupt gene (copy and move 1 genome to another)

Question 23

Info on Transposable elements (TE)

Answer 23

-can cause serious mutation if TE moves inside exon of a gene
-5% of human genome composed of TEs called Alu elements
-300 bp long Alu elements is able to copy and insert themselves anywhere in genome (random)

homozygous: no insert
heterozygous: insert

Question 24

spontaneous mutation: trinucleotide repeats

Answer 24

tandem repeats of specific amino acid codon can change in # ( 3 bases that get repeated over and over )

Question 25

why do trinucleotide repeat mutation matter

Answer 25

-tandem repeats of specific aa codon can mutate in # of repeats
-few can lead to thousands

how would change in repeat # affect polypeptide?
changes the folding-> r-groups–> change function

examples:
1. fragile X syndrome
2. huntington’s disease

Question 26

fragile X

Answer 26

gene involved in the formation of neural synapses (multiple CGG repeats )

5-54 repeats develop normal synapses
200-400: fragile X syndrome
50-200 may show signs but have high risk have producing gametes 200-400 repeats
==>premutation alleles: mutatuon occurs during gametogenesis

*the higher the repeats, the greater the risk of producing gamates w even more repeats (expressivity)

*severity of disease replated to repeat # (more repeats, more severe redardation) - intensity

much greater in women

Question 27

huntington

Answer 27

huntingtin-34 repeats

42 or more: have disease ( kill neuron)
35-41: premutation alleles (expansion mutation) -risk of mutation highest in man

Question 28

nonspontaneous mutation: mutagen

Answer 28

chemical/ physical agent that raise frquency of mutations above spontaneous rate

Question 29

ways mutagens occur

Answer 29

1. X-rays: break sugar phosphate backbone; when pieces ligated back tgt, they ligate the bases but the bases may in inverted/ deleted (DNA make extra copies of that)
2. UB radiation: form dimers between adjacent bases
   -during translation (T-T)
   -T attached to backbone should not be stuck tgt, should be space
   -when expose, cause the dimers to alter and fuse tgt

Question 30

DNA repair mechanism

Answer 30

many enzymes work to repair mutation

ex. photolyse breaks uv-induced dimers

some remove damage DNA and replace w undamaged DNA

Question 31

DNA repair: base excision

Answer 31

-single base
repair enzymes remove a damanged base and remove it

Question 32

dna repair: nucleotide excision

Answer 32

multiple bases
enzymes that remove several bases surrounding damaged DNA and replace the

Question 33

Dna repair: mismatch repair enzymes

Answer 33

rmoves and replace mismatch base (and some around it) incorrectly yout in by DNA polymerase

Question 34

if theres too much damage, and DNA repair ezymes cant fix, then what

Answer 34

cells go thru apotosis (kill themselves to stop further mutation)

if apotosis fail?
cancer

if mutation oocur in genes controlling dna repair,?
cancer

Question 35

CCR5 receptor mutation and HIV resistance

Answer 35

resistance ppl have deletion part of the CCR5 receptor makes a non fucntional receptor
(a piece of the receptor that virus use to enter cell is missing, therefore they cant enter)
-must be homo for mutation to be resistance
-heter have intermediate resistance (half fucntional half not)

=an good ex of a random mutation that doesnt become apparant until the envuronment changes and provides selective advantage for the mutant allele