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Flashcards in molecular genetics and pathology Deck (70):
1

What is the major difference between DNA and RNA

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

2

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

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

3

In what direction is the DNA synthesised

5 to 3 direction.

4

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

sense strand ends up in the mRNA

5

explain the process of DNA replication.

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

6

How many Mbp is the human genome made up os

3000

7

what percentage of the human genome is non coding DNA

>90%

8

how many protein coding genes are there

20,000

9

define single copy sequence

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

10

Are most genes single copy sequences

Yes

11

2 types of repetitive sequences

Interspersed repeats- spread through the chromosome- Alu
Satellite- DNA large blocks of repeated DNA

12

define transcription

copying RNA

13

define translation

turning RNA into a protein

14

define gene

functional unit of DNA

15

main components of genes include.

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

16

where are problems arise in genes
(in which processes)

transcription
cleavage and polyadenylation
Splicing
Translation
Post translational modifications

17

where does transcription, cleavage and polyadenylation and splicing take place

Nucleus of the cell

18

where do translation and post translational modifications take place

cytoplasm

19

what is exon skipping

missing out exons when encoding protein sequences

20

why do we use exon skipping

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

21

what is the first stage in gene evolution

duplication and divergence

22

what is a gene family

structurally related genes

23

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

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

24

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

mutations in these duplication genes

25

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

Pseudogenes.

26

what are pseudogenes processed genes

intronless copies of other genes.

27

are processed genes function

mostly no.

28

How are processed genes formed

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

29

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

a processed pseudogene

30

which part of the chromosome are satellite DNA sequences found

centromeres and heterochromtic (lots of chromatin) chromosomal areas

31

what time of repeats are in satellite DNA sequences

Simple tandemly repeats

32

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

centromere repeat
chromosome specific.

33

Is the repeat sequence sequence different maternally and paternally

Yes

34

example of a satellite DNA which is found at the centromeme

alphoid

35

how many bp repeat sequence is the alphoid

171

36

does the alphoid sequence have chromosome specific variations

Yes

37

why is alphoid DNA important in chromosome formation

is is required to assemble the centromere.

38

where are interspersed DNA repeat sequences located

throughout genome
between and within genes.

39

what is a example of a interspersed DNA repeat sequence.

Alu repeat.

40

how many bp is Alu

300

41

how many copies of Alu are these

500,000

42

how are interspersed DNA sequences dispersed

retrotransposition.

43

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

recongnition sequences.

44

which chromosome has a lot of Alu repeats

chromosome 1

45

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

the wrong sections can line up together

46

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

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

47

what are the different types of mutations

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

Gross rearrangements-
haemophilia A

Point mutations
Trinucelotide repeat expansions.

48

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

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

49

define point mutation

single nucleotide changed

50

define missense mutation

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

define silent mutation

change in nucleotide but same amino acid is coded for.

52

Why are CpG sites more prone to mutations.

they are the site of methylation.

53

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

thymine

54

define nonsense mutation

Truncated protein produced

55

define frame shift

• 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

define change in splice junction mutation.

• 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

what are the references used in mutation nomenclature

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

58

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

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

what type of inheritance are loss of function mutations typically

recessive

60

what is the mutation which is commonly found in achondroplasia

FGFR3 G380R (glycine to arginine)

61

when do you have dominant achondroplasia

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

62

when do you get recessive achondroplasia

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

63

define trinucelotide repeat expansions

3 nucleotides alternatively repeated.

64

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

– Huntington’s disease
– Spinocerebellar ataxias

65

conditions which are caused by large non-coding repeat expansions

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

66

define polymorphism

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

67

what trinucleotide repeat cues fragile X syndorme

CGG repeat expansion

68

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

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

69

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

Over generations the number of CGG repeats increase

70

what does the CCG mutation inffragile x syndrome cause

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