Chp 18

25 July 2022
4.7 (114 reviews)
40 test answers

Unlock all answers in this set

Unlock answers (36)
question
define mutations
answer
*inherited change in genetic info (dna) *ability to adapt to environmental change, y genetic variation(mutation) *causes diseases and disorders
question
What are 2 categories of mutations in EUK
answer
1. somatic mutations *in somatic tissue *does not produce gametes *divides by mitosis, mutation passed to daughter cells, results in genetically identical cells *earlier the somatic mutation occurs, the larger the clone of cells will contain that mutation *sm numerous bc large number of EUK cells *many sm have no effect on phenotype bc function of mutant cell is replaced by normal cell *cells w/ sm that stimulate cell division can increase and spread-these mutations can give rise to cells w/ selective advatange and is basis for cancer 2. germ-line mutations (main mutation in EUK) *in cells that produce gametes *can be passed to future generations producing organisms that carry mutation in somatic and germline cells
question
gene mutations
answer
affect a single gene *detected only by observing phenotypic effects *small dna lesion
question
chromosome mutations
answer
affect the number or structure of chromosomes *detected directly by looking at chromosomes under the mic
question
Types of gene mutations
answer
1. base substitutions 2. Insertions and deletions 3. Expanding nucleotide repeats
question
base substitutions
answer
* are the alteration of a single nucleotide in DNA *2 types 1.transition-purine is replaced with different purine (a-g , g-a ) or pyrimidine is replaced by different pyrimidine (t-c, c-t) 2. transversion- a purine is replaced by a pyrimidine (a-c, a-t, g-c, g-t) or pyrimidine replaced by purine (c-a, c-g, t-a, t-g) *2transitions=transversions
question
purines
answer
A G
question
PYRIMIDINES
answer
T C
question
insertions and deletions
answer
*mutation of addition or removal of one or more nucleotide pairs *appear more frequently *insertions and deletions w/in sequences that encode proteins may lead to frameshift mutation, changes in reading frame of the gene. *frame shift mutations alter amino acids encoded by nucleotides following the mutation, thus having drastic effects on phenotype *not all insertions and deletions lead to frameshift *any insert or delete consisting of any multiple of 3 nucleotides will leave reading frame intact, but may still affect phenotype *in frame insertions or deletion- mutations not affecting reading frame
question
expanding nucleotide repeats
answer
*mutation in which the number of copies of a set nucleotides increases in number *ex: FMR1- gene that causes fragile x-syndrome -cause of mental retardation -tip of each long arm of x-chromosome is attached by only a slender thread -normal fmr1 has 60 or less CGG -person with fragile x-syndrome has 100's or 1000's of copies of CGG *most diseases caused by EPR are caused by the expansion of a set of 3 nucleotides, most often CNG , n is any nucleotide *but can be caused expansion of more nucleotides *the # of copies of nucleotide repeat correlates w/ the severity or age of onset of the disease, also the instability of nucleotide repeats. *the more repeats present , probability of more repeat expansion. *the association of #'s , severity, and probabilty of expansion lead to anticipation, *anticipation- disease caused by NRE becomes more severe in each generation
question
expanding nucleotide repeats part 2
answer
*increasing in the # of nucleotides can produce diseases symptoms in different ways 1. nucleotide expands w/in the coding region, - producing a toxic protein that has xtra glutamine residues (aa encoded by CAG) -ex: huntington disease 2. repeat is outside the coding region and affects its expression. -ex: fragile x-syndrome - additional copies of nucleotide repeats cause dna to become methylated which turns of transcription
question
what is the mechanisms that lead to expansion of nucleotide repeats
answer
* expansion occurs in the course of dna replication *related to the formation of hairpins and other dna structures that form in single stranded dna *such structures may interfere with normal replication by causing strand slippage, misalignment of sequences, or stalling of replication
question
Phenotypic affects of mutations
answer
1. forward mutation 2.reverse mutations 3. missense mutation 4. nonsense mutation 5.silent mutation 6. neutral mutation 7. loss of functions mutation 8. gain of function mutation 9 . conditional mutations 10. lethal mutations
question
1. forward mutation 2.reverse mutations
answer
1. forward mutation-mutation that alters the wild-type phenotype 2.reverse mutations- changes a mutant phenotype back into wild type
question
3. missense mutation 4. nonsense mutation
answer
*both are effects of mutations on protein structure 3. missense mutation-base substitution that results in different amino acid in the protein 4. nonsense mutation-changes a sense codon (specifies an amino acid) into a nonsense codon (terminates translation) *if nonsense mutation occurs early in mrna sequence , protein will be shortentend and non functional
question
different codons specify the same amino acid
answer
...
question
5.silent mutation
answer
5.silent mutation-changes a codon to synonymous codon that specifies the amino acid *alters dna sequence w/out changing the amino acid sequence of the protein *some silent mutations have phenotypic effects *ex: isoaccepting trnas are used for different synomous codons, which synomous codon used may affect the rate of protein synthesis, affecting phenotype *other silent mutations alter sequences near the exon-intron junctions that affect splicing *other may influence the folding of mrna affecting its stability
question
6. neutral mutation
answer
* a missense mutation that alters the amino acid sequence of the protein but does not change its function *occur when 1amino acid is replaced by another that is chemically similar or when the affected amino acid has little influence on protein functions *ex: occur in genes that encode hemoglobin; mutation alters amino acid sequence but does not affect its ability to transport oxygen
question
7. loss of functions mutation
answer
*cause the complete or partial absence of normal protein functions *alters structure of protein so protein no longer works correctly *mutations can occur in regulatory regions that affect transcription, translation, or splicing of the proteins. *LOFM are recessive, individual must be homozygous for effect to show *ex: cystic fibrosis- mutations produce a non-functional form of cystic fibrosis transmembrane conductance regulator protein , which normally regulates the movement of chloride ions in and out the cell
question
8. gain of function mutation
answer
type of phenotypic mutation produces a new trait or causes a trait to appear in inappropriate tissues or at inappropriate times *dominant *ex: stimulate growth all the time even when growth factor is absent
question
9. conditional mutations
answer
expressed only under certain conditions
question
10.lethal mutations
answer
cause premature death
question
supressor mutations
answer
*a genetic change that hides or suppresses the effect of another mutation. *distinct from reverse mutation *produces an individual that has both the original mutation and the suppressor mutation but has the wild-type phenotype
question
What are the 2 classes of suppressor mutations
answer
1. intragenic suppressor-mutation in the same gene as that containing the mutation being suppressed *may change a 2nd nucleotide in mutated codon to produce codon that specifies the same aa of unmutated orignal codon *may suppress frameshift mutation by addition or deletion of nucleotide *may make compensatory changes in protein (missense alter folding of ppchain by changing the way aa interact in the proteins 2nd missense may recreate original folding pattern by restoring interactions between aa) 2. intergenic-*occurs in a gene other than the one bearing the original mutation. *Sometimes work by changin the way the mRNA is translated.
question
mutation rates
answer
*the frequency with which a wild-type allele at a locus changes into a mutant allele *expressed as number of mutations per biological unit
question
if repair systems are effective
answer
mutation rates will be low
question
if mutation rates are high
answer
repair systems of dysfunctional
question
adaptive mutation
answer
process by which a specific environment induces mutations that enable organisms to adapt to the environment
question
causes of spontaneous mutations
answer
*Spontaneous Replication Errors - tautomeric shifts, - wobble base-pairing, - strand slippage and - unequal crossing over. β€’ Spontaneous Chemical Changes - depurination - deamination
question
tautomeric shifts
answer
β€’ Tautomeric shifts (changes in the position of a proton) *Purines and pyrimidine bases exist in different chemical forms tautomers, *If bases are in rare tautomer form, other base pairing is possible β€’ Occur rarely in DNA bases and could lead to mismatched base pairing (incorporated error).
question
wobble base pairing
answer
*normal protonated and other forms of the bases are able to pair bc of flexibility in dna helical structure *Mismatching during replication can also occur due to flexibility in H-bonding (wobble). *Through wobble, T can pair with G and C with A. *Wobble base pairing then leads to a replicated error at the next round of replication which creates a permanent mutation
question
incorporated error
answer
when mismatched base has been incorporated into newly synthesized nucleotide chain
question
strand slippage
answer
*can occur when one nucleotide strand forms a small loop *if looped out nucleotides are on newly synthesized strand, insertion results *at next round the insertion will be replicated and both strands contain the insertion *if looped out nucleotides are on the template strand, the newly replicated strand has a deletion
question
strand slippage is most common in
answer
Strand slippage is most common in stretches of repeated sequence, such as trinucleotide repeats or homopolymeric runs.
question
unequal crossing over
answer
homologous chromosomes misalign *one with insertion, one with deletion *both strand slippage and unequal crossing over produce duplicated copies of sequences, and result in insertions and deletions
question
what are the 2 spontaneous chemical changes
answer
1. Depurination-loss of purine base from a nucleotide 2. Deamination-loss of amino acid group (NH2) from a base can be spontaneous or induced
question
depurination
answer
results from when covalent bond connecting the purine to the 1' carbon atom of deoxyribose sugar breaks producing an apurinic site *a site cannot act as a template from complementary bases in replication. *in absence of base pairing restraints incorrect nucleotide in new dna strand opp the apurinic site
question
deamination
answer
*(C-G, U-A, T-A) original C-G is replaced with T-A. Usually repaired by enzymes that remove Uracil from DNA
question
mutagen
answer
A mutagen is any environmental agent that significantly increases the rate of mutation above the spontaneous rate
question
6 types of chemically induced mutations
answer
1.Base Analogs-chemicals with structures similar to that of any of the four stranded bases of DNA 2.Alkylating Agents-chemicals that donate akyl groups such as methyl (CH3) and ethyl (CH3-CH2) groups to nucleotide bases 3.Chemically-induced Deamination 4.Hydroxylamine-specific base modifying mutagen that adds a hydroxyl group to cytosine converting it into hydroxylaminocytosine 5.Oxidative reactions-reactive forms of are produced in the course of normal aerobic metabolism, as well as radiation, ozone, peroxides, and certain drugs 6.Intercalating agents- proflavin acridine organe ethidium bromide and dioxin are agents that produce mutations squishing themselves btwn adjacent bases in dna, Distorted structure causes small insertions and deletions during replication.