gene mutations

Question 1

what are somatic mutations

Answer 1

occur in any cell of the body apart from germ cells (egg and sperm). cannot be inherited by offspring

Question 2

what are germ-line mutations

Answer 2

occur in gametes (egg/sperm). is inherited by offspring

Question 3

3 types of base-pair substitution mutation:
1. silent mutation

Answer 3

changes codon for an amino acid to another codon for that amino acid
no change in amino acid

Question 4

3 types of base-pair substitution mutation:
2. missense mutation

Answer 4

changes codon for an amino acid to codon for another amino acid
change in amino acid

Question 5

effect of missense mutations differ in severity -

Answer 5

neutral mutation - conservative amino acid substitution substitutes similar amino acid - less likely to alter function
eg. alanine for glycine

nonconservative amino acid substitution substitutes different amino acid - more likely to alter function
eg. glycine for glutamate

Question 6

3 types of base-pair substitution mutation:
3. nonsense mutation

Answer 6

change codon for amino acid into stop codon (translation termination)
-premature termination of translation

Question 7

mutation in 1st/2nd/3rd letter of codon is more likely to produce change in amino acid

Answer 7

1st

Question 8

frameshift mutation -

Answer 8

addition or deletion of 1/more bases changes the reading frame and changes all amino acids downstream of the mutation

Question 9

regulatory mutations alter
amount of protein produced by gene/amino acid sequence?

Answer 9

amount of protein product by gene NOT amino acid sequence

Question 10

regulatory mutations affect regions (2)

Answer 10

1. promoters and other regulatory protein binding sites
2. intron boundaries - affects intron splicing in eukaryotes

Question 11

what are promoter mutations

Answer 11

mutations that change consensus sequence nucleotides
-interfere with transcription initiation
-can reduce, enhance, or inhibit transcription

Question 12

how is pre-mRNA processed

Answer 12

splicing to remove introns

Question 13

what are splicing mutations

Answer 13

mutations that change nucleotides required for efficient splicing at intron-exon junctions
-can result in splicing errors and production of mutant proteins because introns are still there in mature mRNA

Question 14

what are cryptic splice sites

Answer 14

some base-pair substitution mutations produce new splice sites that replace original splice spite during mRNA processing
-leads to new possible forms of protein product

Question 15

origin of mutation - what is:
1. induced mutation

Answer 15

action of mutagen - environmental agent that changes nucleotide sequence
-mutagenesis - process of inducing mutations by mutagens

Question 16

origin of mutation - what is:
2. spontaneous mutation

Answer 16

when there’s no known mutagen
-can be caused by errors in DNA replication
-important for evolution

Question 17

types of spontaneous mutation
-DNA replication errors:

Answer 17

DNA pol can insert the wrong nucleotide
corrected by proof reading 3’ to 5’ exonuclease activity of DNA pol

Question 18

trinucleotide repeat disorders - caused by

Answer 18

DNA pol slipping during DNA replication, increasing no. of trinucleotide repeats causes longer stretches of the same amino acid in the protein
-EXAMPLE - huntington’s disease

Question 19

DNA nucleotide bases can spontaneously change to different structures called …. with slight differences in bonding and placement of hydrogen

Answer 19

tautomers
-amino (for adenine and cytosin) –> imino
-keto (for thymine and guanine) –> enol

Question 20

what are transposable elements

Answer 20

found in genomes of all prokaryotes and eukaryotes
-can modify genomes and cause mutations on insertion into genes (rare in eukaryotes)

Question 21

2 types of transposable elements

Answer 21

1. DNA transposons - in both eukaryote and prokaryote genomes
2. retrotransposons - in eukaryotes

both cause mutations by inserting into a gene and causing insertion mutation - BUT IS RARE IN EUKARYOTES

Question 22

insertion sequences in E.coli

Answer 22

has a transposase gene bracketed by short repeat sequences
-transposase - moves IS element from 1 DNA location to another
-if IS element moves into a gene - big insertion mutation and mutant allele created which produces no active protein product

Question 23

induced mutations are produced by

Answer 23

interactions between DNA and physical, chemical, or biological agents that generate mutations

Question 24

DNA repair mechanisms - using correct base on the damaged DNA strand
-photoreactivation repair:

Answer 24

DNA damage repaired by photoreactivation enzyme (PRE) which cleaves the thymine dimer bond
in E. coli - photolyase enzyme

Question 25

DNA repair mechanisms - using correct base on the damaged DNA strand
-base excision repair:

Answer 25

base specific DNA glycosylase
-uracil recognised as a noncomplementary base pair and replaced with complementary base (C)

Question 26

DNA repair mechanisms - using correct base on the damaged DNA strand
-nucleotide excision repair:

Answer 26

repairs lesions which distort DNA eg. thymine dimers

Question 27

human diseases can be caused by mutations in genes that encode proteins involved in …… …… mechanisms

Answer 27

DNA repair
-can cause hereditary cancer

Question 28

a base-pair change that results in premature termination of translation is called a

Answer 28

nonsense mutation

Question 29

what would result in a frameshift mutation

Answer 29

insertion of 2 bases

Question 30

trinucleotide repeat disorders can result from slippage of DNA polymerase during DNA replication that results in increased trinucleotide sequence length. How many CAG repeats are needed for disease symptoms of Huntington’s disease?

Answer 30

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