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Year 2 EMS GiM > Molecular Genetics and Pathology > Flashcards

Molecular Genetics and Pathology Flashcards

1
Q

What is less stable; RNA or DNA?

A

RNA is less stable.

-hydroxyl (OH) group on C2&raquo_space; neutrophilic attack&raquo_space; breaks chain

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2
Q

What direction are DNA and RNA synthesised in?

A

5’ to 3’ direction.

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3
Q

What strand is normally written in DNA shorthand?

A

The ‘sense’ strand.

-strand that ends up as mRNA

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4
Q

How many base pairs are present in a human haploid genome?

A

~3,000 Mbp.

chr 1 = 263, chr 22 = 39

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5
Q

What proportion of DNA is non-coding?

A

> 90%.

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6
Q

How many protein-coding genes are there?

A

~20,000.

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7
Q

What is the average size of a gene (kb)?

A

50-100 kb.

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8
Q

What are the classes of genome sequences? (2)

A
  • Single copy sequences (non-repetitive)

- Repetitive sequences

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9
Q

What is transcription?

A

DNA&raquo_space; mRNA.

  • by RNA polymerase
  • 1st step of gene expression
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10
Q

What is translation?

A

mRNA&raquo_space; proteins.

-at ribosomes

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11
Q

What are regulatory sequences?

A

Components of genes.

  • promoters
  • enhancers
  • locus control regions
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12
Q

What is the general process of gene production?

A 
(NUCLEUS)
>>transcription
>>cleavage and polyadenation
>>splicing
>>(CYTOPLASM)
>>translation
>>postranslational modifications
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13
Q

What is alternative splicing?

A

Exon skipping.

-large variation; single gene can code for multiple proteins

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14
Q

What are pseudogenes?

A

DNA sequences that resemble protein-coding genes, but are non-functional due to mutations.
-cannot be translated

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15
Q

What are processed genes?

A

Intronless copies of other genes.

-occasionally remain functional (e.g. PGK2)

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16
Q

What causes processed genes?

A

Spliced RNA copy genes being reverse transcribed&raquo_space; DNA and re-entering genome.
-e.g HIV

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17
Q

What are the main types of repetitive sequences?

A
  • ‘Satellite’ DNA

- Interspersed repeat

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18
Q

What is satellite DNA?

A

Large repetitive DNA sequences at centromeres and heterochromatic chromosomal regions.
-various sizes (polymorphic)

19
Q

What is alphoid DNA an example of?

A

Satellite DNA.

  • 171 bp unit
  • at centromeres, required for assembly
  • particularly repetitive
20
Q

How is alphoid DNA used to identify individual chromosomes?

A

It’s chromosome specific.

21
Q

What are interspersed repeats?

A

Repeats scattered around the genome.

-may form part of gene structure

22
Q

Give an example of an interspersed repeat (most widely distributed).

A

Alu repeat.

  • 500,000 copies
  • 5% of genome
  • dispersed by retrotransposition
23
Q

What problem can occur during meiosis 1 (crossing over)?

A

Misalignment of chromosomes due to interspersed repeats.
»unbalanced ‘hybrid’ chromosomes
-1 deletion, 1 duplication

24
Q

What size deletion is most likely to remain functional?

A

3bp deletion.

-doesn’t cause a frameshift mutation

25
Q

Why can large deletions / insertions be hard to detect?

A

Sequence either side remains the same.

26
Q

What type of mutation causes Duchenne muscular dystrophy?

A

Deletions.

27
Q

What type of mutation causes Charcot-Marie-Tooth disease?

A

Duplication.

28
Q

What mutation causes Haemophilia A?

A 
F8C mutation (x-linked).
>> FVIII deficiency
-recombination and inversion of F8C gene
29
Q

Why is the F8C mutation hard to detect in haemophilia A?

A

Exons are still present.

30
Q

What are the types of point mutation? (3)

A
  • Silent
  • Missense
  • Nonsense
31
Q

What is a silent point mutation?

A

Mutation codes for the same AA.

-if >1% of chromosomes = polymorphism

32
Q

What is a missense point mutation?

A

Codes for another AA.

-conservative if small functional change (e.g. Asp&raquo_space; Glu)

33
Q

What is a nonsense mutation?

A

Truncated protein formed.

-often&raquo_space; stop codon

34
Q

What DNA sequence is particularly susceptible to mutation (1/3 of mutations)?

A

CG&raquo_space; TG.

-position of methylation

35
Q

How can mutation outside the coding frame cause disease?

A

Due to splicing.

  • begins at wrong point
  • always GT&raquo_space; AT
36
Q

What us the nomenclature for mutation?

A

TYPE - genomic DNA = g.

  • cDNA =c.
  • protein = p.

POSITION from codon (e.g. 128)

MUTATION - e.g. A>G, del.T, dup.

37
Q

Examples of mutation nomenclature.

A

c. 658delG

c. 122+1G>A

38
Q

What type of inheritance do loss of function mutations normally have?

A

Recessive.

-50% gene function adequate

39
Q

What type of mutation does dominant inheritance normally result from?

A

Gain / alteration of function.

e.g. achondroplasia

40
Q

What mutation causes achondroplasia?

A

FGFR3 G380R.

-glycine&raquo_space; arginine

41
Q

What are trinucleotide repeat expansions?

A

3 nucleotides tandomly repeated.

-e.g. polyglutamine (CAG) repeats

42
Q

What disorder does polyglutamine (CAG) repeats have an association with?

A

Huntington’s disease.

43
Q

What trinucleotide repeat is associated with Fragile X syndrome?

A

CGG repeat expansion.

-in non-coding area&raquo_space; DNA alteration

Year 2 EMS GiM (12 decks)

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