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Human genetic disorders > week 1 reading > Flashcards

week 1 reading Flashcards

1
Q

define substitutions mutation

A

replacement of a single nucleotide by another (very common)

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2
Q

what is meant by the term transition?

A

Substitution mutation involving replacement by the same type of nucleotide - pyrimidine for a pyrimidine (C for T) or a purine for a purine (A for G)

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3
Q

what is meant by the term transversion?

A

substitution of a pyrimidine by a purine or vice versa

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4
Q

What is more frequent transitions of transverions?

A

transitions due to hotspots of CpG dinucleotides into a T

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5
Q

deletions

A

involves loss of one or more nucleotides

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6
Q

what can be the result of a deletion mutation?

A
  • if this occurs in a coding sequence and involves one, two or more nucleotides that are not a multiple of three, the reading frame ill be disrupted
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7
Q

what can be the cause of large deletions?

A

unequal crossover between repeat sequences

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8
Q

insertions

A

involves addition of one or more nucleotides to a gene

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9
Q

what can be the consequences of insertions?

A
  • if it occurs in a coding sequence and involves one, two, more nucleotides that are not a multiple of three, it will disrupt the reading frame
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10
Q

what can be the cause of a large insertion?

A

unequal crossover or insertions of transposable elements

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11
Q

define dynamic mutations

A
  • triple repeat expansion (insertion) that make the sequence more unstable as it expands in size
  • take place over number of generations within a family
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12
Q

what might be the reason for triplet repeat expansions?

A
  • unequal crossover or unequal sister chromatid exchange in non-replicating DNA
  • slipped-strand misfiring and polymerase slippage in replication DNA
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13
Q

eg. expansion (insertions) in relation to huntingtons

A
  • expansion of CAG repeat in doing region of HTT gene and some SCA genes result in a protein with an elongated polyglutamine tract that forms toxic aggregates within certain cells
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14
Q

What other subdivisions for mutations are there?

A

according to the effect on polypeptide sequence of the encoding protein - synonymous or non-synonymous

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15
Q

synonymous/ silent mutations

A
  • if it doesn’t alter polypeptide product of the gene
  • eg. single base pair substitution, particularly if it occurs in the third position of a codon will often result in other triplet coding for same amino acid with no alteration in properties of resulting protein
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16
Q

non-synonymous mutations

A
  • mutation leading to an alteration in encoded polypeptide
  • less frequent
  • likely to result in abnormal function, associated with disease or lethality
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17
Q

describe the three main ways in which non-synonymous mutations can occur

A
  • missense
  • nonsense
  • frameshift
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18
Q

missense mutation

A

single-base pair substitution resulting in coding for a different amino acid and synthesis of an altered protein

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19
Q

non-conservative substitution

A

altered porbtein

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20
Q

conservative substitution

A

no functional effect

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21
Q

nonsense

A

substitution leading to generation of one of the stop codons will result in premature termination of translation of a peptide chain - most times shortened chain unable to retain normal biological activity

22
Q

what happens to faulty mRNA transcripts containing premature termination codons due to a nonsense mutation?

A

degraded by the process of nonsense-mediated decay

23
Q

frameshift

A

mutation involving insertion or deletion of nucleotides that are not. multiple of three, it will disrupt the reading frame -> frameshift

24
Q

most common consequence of frameshift mutations

A
  • result in premature stop codon downstream to the mutation
    may lead to expression of truncated protein, unless the mRNA is degraded by nonsense-mediated decay
25
Q

What could be the effect of mutations in non-coding DNA ? eg. promoter sequence, enhancers

A

affects level of gene expression (mutations in miRNA or siRNA binding sites within UTRs can also result in disease)

26
Q

splicing mutations

A

mutations of highly conserve splice donor (GT) and splice acceptor (AG) sites result in aberrant splicing

27
Q

what is the result of splicing mutations?

A
  • loss of coding sequence (exon skipping) or retention of intronic sequence -> may lead to frameshift mutations
28
Q

What are the functional effects of mutations on the protein?

A
  • loss of function mutations
  • gain of function mutations
  • dominant negative mutations
29
Q

loss of function mutation

A
  • phenotypic effect
  • can result in either reduced activity (hypomorph) or complete loss of gene product (null allele/ amorph)
30
Q

loss of function mutations involving enzymes are inherited in what way?

A

autosomal/ X-linked recessive, because data;ytic activity of product of the normal allele is more than adequate to carry out the reactions of most metabolic pathways

31
Q

Haploinsufficiency

A
  • loss of function mutations in the heterozygous state
  • half-normal levels of gene product results in phenotypic effects
  • homozygous mutations result in more severe phenotypic effects
  • eg. familial hypercholesterolemia
32
Q

gain of function mutations

A
  • increased level of gene expression or development of a new function of the gene product
  • eg. point mutations or increased gene dosage - Charcot-marie-tooth disease
  • more severe in homozygous state
33
Q

dominant-negative mutations

A
  • mutant gene in heterozygous state results in loss of protein activity or function as a consequence of a mutant gene product interfering with the function of the normal gene product of the corresponding allele
34
Q

where are dominant-negative mutations most common in?

A
  • in proteins that are dimers or multimers
    eg. mutations in genes encoding structural proteins such as collagens can lead to osteogenesis imperfecta
35
Q

Define DNA

A

basic template that provides blueprint for the formation and maintenance of an organism
- DNA - chromosome - genes

36
Q

define chromosomes

A

factors that distinguish one species form another and enable transmission of genetic information form one generation to the next
- vehicle that facilitate reproduction and maintenance of a species

37
Q

cytogenetics

A

study of chromosomes and cell division

38
Q

How many chromosomes in humans?

A

46, abnormalities disrupts development and growth

39
Q

centromere

A
  • joins sister chromatids, consists of several hundred kilobases of repetitive DNA, responsible for movement of chromosomes at cell division
40
Q

p arm

A

short

41
Q

q arm

A

long

42
Q

telomere

A

tip of each chromosome arm
- shortening part of aging process

43
Q

role of telomeres

A
  • sealing ends of chromosomes and maintaining structural integrity
  • highly conserve through evolution
44
Q

telomerase

A
  • enzyme that replaces the 5’ end of the long strand during DNA replication which otherwise becomes progressively shorter until a critical length was reached when the cell could no longer divide and thus became senescent
45
Q

telomeres relation to cancer

A
  • increased activity leads to prolonged cell survival off tumour cells
46
Q

morphological classification of chromosomes

A
  • metacentric
  • Acrocentric
  • submetacentric
47
Q

metacentric

A

centromere located centrally

48
Q

acrocentric

A

centromere located terminally - formation of satellites instead of p arms

49
Q

submetacentric

A

centromere is an intermediate position

50
Q

satellites

A

in acrocentric chromosomes, stalk-like appendages, form nucleolus of resting interphase cell, contain multiple repeat copies of genes for ribosomal RNA

Human genetic disorders (5 decks)

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