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Past Paper Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

Explain how 3 classes of mutation, other than a nonsense mutation, can result in no protein expression

A
  1. INDEL causes a frameshift, premature termination codon, nonsense mediated decay
  2. Mutation that affects splicing, premature termination codon, nonsense mediated decay
  3. Large deletion, removal of element required for transcription or translation
  4. Point mutation affecting regulatory element or transcription start site
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2
Q

What is happening in G0 phase of the cell cycle?

A

Cells are quiescent

They are metabolically active but not dividing

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3
Q

What are the essential elements required for constitutive splicing?

A

5’ splice site: GU
Branch point: A
3’ Splice site AG
Polypyrimidine tract

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4
Q

What is the polypyrimidine tract?

A

Uracil/Cytosine rich region in an intron in the mRNA transcript, before the 3’ splice site
Binds U2AF

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5
Q

What are the essential elements required for alternative splicing?

A

ESE and ESSs in the exons
ISE and ISS in the introns
SR proteins
hnRNPs

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6
Q

At what are are pre symptomatic tests usually performed?

A

Usually at/after age 18

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7
Q

3 reasons why are pre symptomatic tests are not usually performed until age 18?

A
  1. Autonomy: The child has the right to decide for themselves, and is not generally considered to have the ability to until age 18
  2. Psychological damage of knowing that you are growing up with an incurable disease
  3. Stigmatisation - the child may then be treated differently by their family and friends
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8
Q

Reason why a pre-symptomatic test would be performed under age 18?

A

If there was a treatment they could be taking sooner that would cause them to suffer less in the future

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9
Q

Example 2 examples of presymptomatic tests that is given under age 18

A

Testing the RET gene for mutations that could lead to Multiple Endocrine Neoplasia type 2 (MEN2) - children can be given a thyroidectomy
Testing for familial hypercholesterolaemia means they can start taking statins and control their diet

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10
Q

What are the 4 main differences between apoptosis and necrosis?

A
  1. Programmed vs unprogrammed
  2. Physiological vs pathological
  3. Not associated with inflammatory response vs is associated
  4. Caused by lack of growth factors/activation of p53 vs external factors such as viruses, hypoxia
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11
Q

What percentage of the genome is made up of introns?

A

21-35%

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12
Q

What is an exon?

A

Region of the transcript that is included in the fully processed mRNA
May be coding and translated into protein, or non-coding

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13
Q

What is a promoter region?

A

Cis-acting
Regulatory element
Lies upstream of the gene
Recruits RNA Polymerase

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14
Q

What percentage of the genome is made up of promoters?

A

0-10%

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15
Q

What is the 3’ UTR?

A

The untranslated region of an mRNA transcript between the termination codon and the polyA tail

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16
Q

What percentage of the genome is made up of 3’ UTRs?

A

0-10%

17
Q

What is the difference between the coding region and exons?

A

Exons are included in the fully processed mRNA. Includes coding regions
The coding region is translated into a polypeptide

18
Q

Name 6 sources of missing heritability

A 
Rare variants
Structural variants
Epigenetics
Gene interactions
Overestimated heritability
Epistasis
19
Q

What is epistasis?

A

Interactions between two genes (that are not two alleles of the same gene)
Usually caused by one gene suppressing another

20
Q

How does rare variants lead to missing heritability?

A

Rare variants have not yet been captured on SNP chips

21
Q

How can studies be modified to find more rare variants?

A

Comprehensive genome sequencing of large sample sizes may identify the contribution of rare variants

22
Q

What 3 factors affect how much someone who has inherited an autosomal dominant condition will be affected by it?

A

Penetrance
Expressivity
Anticipation

23
Q

Example of an inherited autosomal dominant condition with variable penetrance, and what penetrance does it have?

A

Inherited breast cancer

Penetrance 50-80%

Medical Genetics (8 decks)

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