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1 - FunMed > Genetics > Flashcards

Genetics Flashcards

1
Q

What are the two types of bases?

A

Pyramidine - T and C - one ring

Purine - G and A - two rings

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2
Q

What is present at the 5’ end?

A

Free phosphate group

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3
Q

What is present at the 3’ end?

A

Free OH group

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4
Q

Which direction does replication occur in?

A

5’ to 3’ so nucleotides are added to the 3’ end and DNA Polymerase move towards 5’ ends

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5
Q

What are Okazaki fragments?

A

Fragments formed during DNA replication on the lagging strand due to replication having to occur in the 3’ to 5’ direction

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6
Q

What enzyme joins the Okazaki fragments?

A

DNA ligase

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7
Q

Why is there such a low level of mistakes in DNA replication?

A

A process performed by DNA polymerase known as editing where the incorrect nucleotide is removed and replaced with the correct one

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8
Q

What is base excision repair?

A

When a single incorrect base is removed followed by the backbone and replaced and rejoined by DNA ligase

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9
Q

What is nucleotide excision repair?

A

When a dimer (usually pyramidine) is excised by removing the surrounding 12 bases and replacing them using DNA polymerase and rejoining them by DNA ligase

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10
Q

What is DNA mismatch repair?

A

When an insertion or deletion causes the two strands to not match up MutS binds to the mismatched pair and MutL binds to the nearest nick. They then move together creating a loop which is excised and the nucleotides replaced by DNA polymerase and joined together by DNA ligase

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11
Q

What is homologous end joining?

A

Where the break in the double stranded DNA is simply joined together using ligase meaning some bases are lost

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12
Q

What is non-homologous end joining?

A

When the other homologous chromosome is used to identify the sequence lost in the DNA break and degradation. The sequence is replicated and inserted into the missing section and rejoined by DNA ligase

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13
Q

What is the G light band?

A

Rich in genes and mainly made up of G and C nucleotide

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14
Q

What is the G dark band?

A

Sparse in genes and mainly made up of A and T bases

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15
Q

What are control elements?

A

Sequences such as promoters and enhancers that regulate transcription

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16
Q

What is a pseudogene?

A

Non-functional copy of a gene that has acquired so many errors that it can no longer code for a protein

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17
Q

What is translocation?

A

The joining of part of one chromosome to a second chromosome

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18
Q

What is Downs syndrome?

A

Trisomy 21, abnormal facial appearance, hypotonia, learning difficulties and low IQ, congenital heart defects

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19
Q

What is Edwards syndrome?

A

Trisomy 19, heart and kidney malformation, clenched hands with overlapping fingers

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20
Q

What is Patau syndrome?

A

Trisomy 13, multiple malformations most notably along midline structures, e.g. incomplete lobation of the brain, cleft lip, congenital heart disease

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21
Q

What is Klinefelter syndrome?

A

47, XXY – infertility, lack of testosterone, poor development of sexual characteristics, tall

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22
Q

What is Turner syndrome?

A

45, X – short stature, primary amenorrhoea, ovaries involute before birth, congenital heart disease

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23
Q

What is the central dogma?

A

Explains that DNA codes for RNA which codes for proteins

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24
Q

Which DNA polymerase performs translation?

A

2

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25
Q

What are the 5 stages of translation?

A
  • Initiation-the polymerase binds to the gene
  • Elongation-the polymerase transcribes the gene
  • Termination-the polymerase stops transcribing the gene
  • Processing-the mature mRNA is formed
  • Export-the mRNA leaves the nucleus to be translated
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26
Q

Which DNA polymerase makes ribosomal RNA?

A

1

27
Q

Which DNA polymerase makes tRNA?

A

3

28
Q

What is the promoter region?

A

Sequence upstream of the coding region that acts as a template for the assembly of a multi component complex called the preinitiation complex, which brings pol II to the gene

29
Q

What is a transcription factor?

A

DNA binding proteins that enhance or repress the assembly of the pre initiation complex determining the transcription of the gene

30
Q

What is 5’ capping?

A

The addition of a 7-methylguanosine to the first nucleotide on the 5’ end of pre-mRNA

31
Q

What is the 3’ poly A tail?

A

repeated adenine nucleotides added to the 3’ end of the pre-mRNA

32
Q

What is the function of 5’ capping and the 3’ polyA tail?

A

They increase the stability of the mRNA ensuring it doesn’t get degraded as fast
They also aid the export from the nucleus and ensure that during translation the mRNA is fully intact

33
Q

What complex performs splicing?

A

Spliceosome

34
Q

What is alternative splicing?

A

Where there is selective inclusion or exclusion of specific exons so from one pre-mRNA many different mRNAs (and therefore proteins) can be made

35
Q

What is protein targeting?

A

the mechanism whereby proteins are transported to the appropriate destinations such as the inside of an organelle, the plasma membrane or the exterior of the cell

36
Q

What ribosomes are found in prokaryotes and eukaryotes ?

A

P - 30s and 50s

E - 40s and 60s

37
Q

What ribosomes do mitochondria contain?

A

Same as prokaryotes - 30s and 50s

38
Q

Which direction does translation occur?

A

5’ to 3’

39
Q

Where does translation begin?

A

At the start codon - AUG which attaches to the P site

40
Q

Describe the process of translation

A

• Translation always occurs from the 5’ end of the mRNA to the 3’ end
• Initiation – the reading frame begins from the first codon which is the start codon AUG which codes for methionine. The tRNA with the methionine attached occupies the P site (peptidyl-tRNA binding site)
Elongation – the tRNA molecule with the anticodon complimentary to the next codon on the mRNA now attaches and occupies the A site. The methionine will then detach from its tRNA and form a peptide bond with the amino acid on the tRNA in the A site. The first tRNA molecule, now with no tRNA attached, moves into the E site (exit site) and leaves the ribosome
• Translocation – the ribosome then moves to the next mRNA codon so that a new tRNA can attach to the codon in the A site and the tRNA, now with two amino acids attached, moves into the P site
• Termination – when the ribosome reaches a stop codon a release factor enters the A site and causes the peptide to be released from the final tRNA. Another release factor will then cause the final tRNA molecule to be released from the P site and cause the ribosome to be dismantled

41
Q

What is tRNA wobble?

A

Where the tRNA can bind to codons with the same first two bases but a different third base

42
Q

What is the wild-type allele?

A

The normal form

43
Q

Define polymorphic

A

When the frequency of a variant allele is >1%

44
Q

What is a silent mutation?

A

No change to the code – new codon codes for same amino acid due to degeneracy

45
Q

What is a missense mutation?

A

A point mutation where a single change change in a nucleotide changes one single amino acid to another

46
Q

What are the two different types id missense mutations?

A

♣ Conservative – subtle change – amino acids similar in structure – change in protein is small
♣ Non-conservative – large change in structure – large impact on the protein

47
Q

What is a nonsense mutation?

A

Where the amino acid changes to a stop codon

48
Q

What is a de novo mutation?

A

A newly arising mutation

49
Q

What is variable penetrance?

A

Where certain individuals who possess a mutation may be asymptomatic, it depends upon lifestyle, other genes and environment

50
Q

What is anticipation?

A

Where the disease manifests at a younger age in successive generations (e.g. Huntingdon’s)

51
Q

What is hemizygous?

A

Where only one copy of a gene is present - usually located on a sex chromosome

52
Q

How does Sanger sequencing work?

A

Uses dideoxynucelotides which terminate synthesis allowing the sequence to be read using gel electrophoresis as fragments of different lengths are separated

53
Q

What is epigenetics?

A

The study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself

54
Q

What is euchromatin?

A

loosely packed, transcribed, gene expression

55
Q

What is heterochromatin?

A

more tightly packed, not transcribed, gene silencing

56
Q

What are the three types of epigenetic modification?

A

DNA methylation, histone modification and non-coding RNAs

57
Q

What is DNA methylation?

A

The addition of methyl groups by DNA mehyltransferase to cytosines on the DNA strand causing the gene to be inactivated

58
Q

What is histone modification?

A

Changes to the histones resulting in the DNA becoming more/less tightly packed meaning is less/more likely to be transcribed

59
Q

What are non-coding RNAs

A

RNAs that target specific sequences and turn genes off

60
Q

What is bivalent chromatin?

A

Chromatin that is both active and inactive at the same time (it contains both activating and repressing epigenetic modifications) – poised for activation for inactivation

61
Q

How are epigenetic modifications involved in cancer?

A

In cancers there are often mutations in the epigenetic enzymes – genes are activated or inactivated when they shouldn’t be

62
Q

What is X inactivation?

A

The silencing of one of the X chromosomes by epigenetic modification in females so that the genes are not expressed twice

63
Q

What is imprinting?

A

Where only one allele is expressed depending on whether it was inherited by your mother or father

1 - FunMed (3 decks)

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