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GIM > molecular genetics and pathology > Flashcards

molecular genetics and pathology Flashcards

1
Q

What is the major difference between DNA and RNA

A

DNA- deoxyribose
RNA- ribose
RNA also has an additional OH.

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2
Q

what significance does the extra OH in RNA have and why does it make the molecule unstable.

A

RNA can result in nucleophillic attack of the phosphodiesterase bond, which causes it to hydrolyse and split.

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3
Q

In what direction is the DNA synthesised

A

5 to 3 direction.

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4
Q

Is the sense strand the strand that gets copied or the other strand.

A

sense strand ends up in the mRNA

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5
Q

explain the process of DNA replication.

A

2 strands of DNA unravel
Each strand forms a template strand to which complementary nucleotides attach
This forms 2 new identical DNA strands.

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6
Q

How many Mbp is the human genome made up os

A

3000

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7
Q

what percentage of the human genome is non coding DNA

A

> 90%

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8
Q

how many protein coding genes are there

A

20,000

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9
Q

define single copy sequence

A

(non-repetitive)- sequence is not repeated anywhere else on another chromosome, .

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10
Q

Are most genes single copy sequences

A

Yes

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11
Q

2 types of repetitive sequences

A

Interspersed repeats- spread through the chromosome- Alu

Satellite- DNA large blocks of repeated DNA

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12
Q

define transcription

A

copying RNA

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13
Q

define translation

A

turning RNA into a protein

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14
Q

define gene

A

functional unit of DNA

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15
Q

main components of genes include.

A

exons, introns and regulatory sequences (promoter, enhancer, locus control regions)

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16
Q

where are problems arise in genes

in which processes

A 
transcription
cleavage and polyadenylation
Splicing
Translation 
Post translational modifications
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17
Q

where does transcription, cleavage and polyadenylation and splicing take place

A

Nucleus of the cell

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18
Q

where do translation and post translational modifications take place

A

cytoplasm

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19
Q

what is exon skipping

A

missing out exons when encoding protein sequences

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20
Q

why do we use exon skipping

A

helps create diversity and increase the number of potential sequences for proteins.

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21
Q

what is the first stage in gene evolution

A

duplication and divergence

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22
Q

what is a gene family

A

structurally related genes

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23
Q

what causes a duplication to take place in the ancestral gene.

A

Inaccuracy in the replication or crossing over of 2 genes next to each other.

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24
Q

what causes divergence (splitting of genes from there family/ origin)

A

mutations in these duplication genes

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25
Q

what is the name of a gene which becomes functionally inactive due to duplications and mutations in a previously active gene

A

Pseudogenes.

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26
Q

what are pseudogenes processed genes

A

intronless copies of other genes.

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27
Q

are processed genes function

A

mostly no.

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28
Q

How are processed genes formed

A

ancestral gene forms mRNA which then via reverse transcription reintegrates into a processed gene.

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29
Q

when a mutation occurs in a processed gene what is is called

A

a processed pseudogene

30
Q

which part of the chromosome are satellite DNA sequences found

A

centromeres and heterochromtic (lots of chromatin) chromosomal areas

31
Q

what time of repeats are in satellite DNA sequences

A

Simple tandemly repeats

32
Q

what are the main factors which are always present in satellite DNA sequences.

A

centromere repeat

chromosome specific.

33
Q

Is the repeat sequence sequence different maternally and paternally

A

Yes

34
Q

example of a satellite DNA which is found at the centromeme

A

alphoid

35
Q

how many bp repeat sequence is the alphoid

A

171

36
Q

does the alphoid sequence have chromosome specific variations

A

Yes

37
Q

why is alphoid DNA important in chromosome formation

A

is is required to assemble the centromere.

38
Q

where are interspersed DNA repeat sequences located

A

throughout genome

between and within genes.

39
Q

what is a example of a interspersed DNA repeat sequence.

A

Alu repeat.

40
Q

how many bp is Alu

A

300

41
Q

how many copies of Alu are these

A

500,000

42
Q

how are interspersed DNA sequences dispersed

A

retrotransposition.

43
Q

what is the name of the sequences which enable the maternal and paternal chromosomes to line up for meiosis 1

A

recongnition sequences.

44
Q

which chromosome has a lot of Alu repeats

A

chromosome 1

45
Q

what problems can result in lining up of chromosomes 1- due to excessive Alu repeats

A

the wrong sections can line up together

46
Q

what is the consequence of wrong sequences lining up in meiosis due to alu repeats.

A

imbalanced amount of exons with one strand being duplicated and the other having deletions.

47
Q

what are the different types of mutations

A

large deletion and insertions-
Duchennes muscular dystrophy
Charcot- marie tooth disease.

Gross rearrangements-
haemophilia A

Point mutations
Trinucelotide repeat expansions.

48
Q

F8 gene in on chromosome X has a repeat sequence on chromosome 1 but they are in the opposite direction what occurs in chromosome X in order for haemophilia to occur

A

Intrachromosomal recombination occurs.

This results in inversion as all the exons are till present but in a different orientation-

49
Q

define point mutation

A

single nucleotide changed

50
Q

define missense mutation

A

change in nucleotide could mean a different amino acid. this could be conservative where the amino acid is swapped for a similar amino acid

51
Q

define silent mutation

A

change in nucleotide but same amino acid is coded for.

52
Q

Why are CpG sites more prone to mutations.

A

they are the site of methylation.

53
Q

Methylated cytosine is similar to which base (and can therefore be substituted for it)

A

thymine

54
Q

define nonsense mutation

A

Truncated protein produced

55
Q

define frame shift

A
  • Deletion of a base results in a change in the frame of which the codons are read after the deletion.
  • Alters protein sequence beyond mutation
  • May truncate protein- if stop codon results.
56
Q

define change in splice junction mutation.

A
  • Change in the bases of a splice junction from GT (common splice site) to AT will result in the splice junction not being recognised.
  • Therefore the DNA sequence be spliced form the next GT and this will result in some intron being part of the mRNA and hence protein.
57
Q

what are the references used in mutation nomenclature

A

– Genomic DNA (g.)
– cDNA (c.)
– Protein (p.)

58
Q

how is the base number at which the mutation takes place numbered.

A

Splice junction mutation- number of the base before the splice junction (122), +1 because it is the next base,

C. = cDNA., 5C>T means the fifth base is changed from C to T.
P = protein, Val2 Ala means that alanine, the second amino acid, has been changed to valine.
59
Q

what type of inheritance are loss of function mutations typically

A

recessive

60
Q

what is the mutation which is commonly found in achondroplasia

A

FGFR3 G380R (glycine to arginine)

61
Q

when do you have dominant achondroplasia

A

often result as the protein, which is formed from the mutation, has a gain in function.

62
Q

when do you get recessive achondroplasia

A

often result as the protein, which is formed, has a loss of function.

63
Q

define trinucelotide repeat expansions

A

3 nucleotides alternatively repeated.

64
Q

what common disorders is the polyglutamine repeat (CAG) commonly found in

A

– Huntington’s disease

– Spinocerebellar ataxias

65
Q

conditions which are caused by large non-coding repeat expansions

A 
–	Fragile X syndrome – transcriptional silencing
–	Myotonic dystrophy
–	Mutational instability
–	Occasional (eg Huntington’s)
–	Frequent (eg fragile X)
66
Q

define polymorphism

A

where the number of repeats of a sequence is within the normal range

67
Q

what trinucleotide repeat cues fragile X syndorme

A

CGG repeat expansion

68
Q

how do you get from a permutation to a mutation to form a large non-coding repeat expansions to cause a disease

A

over generations of passing on the permutations and if enough permutations occur then a mutation will occur.

69
Q

Fragile X I heritance pattern is caused by anticipation. define anticipation

A

Over generations the number of CGG repeats increase

70
Q

what does the CCG mutation inffragile x syndrome cause

A

altered chromatin structure resulting in the shutdown of transcription of the gene.

GIM (14 decks)

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