29. Processing and translation Flashcards

1
Q

What is the purpose of RNA processing in eukaryotes?

A

To generate mature mRNA from premRNA in the nucleus

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2
Q

What are the 3 key processing types that eukaryotes have between transcription and translation?

A
  1. 5’ capping
  2. 3’ polyadenylation
  3. RNA splicing
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3
Q

What does 5’ capping do?

A

Addition of 7-methyl guanosine cap protects RNA from degradation by nucleases and is recognised by translation machinery

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4
Q

What does 3’ polyadenylation do in processing?

A

A poly A tail of up to 200 is added by poly(A) polymerase which enhances RNA stability and regulates nucleus to cytoplasm transport

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5
Q

What does RNA splicing do?

A

It involves the removal of introns and joining of the exons

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6
Q

What is the process of introns to be removed?

A
  1. snRNP (small nuclear RNA and protein) finds and binds to the splice sites
  2. snRNP and other proteins associate to dorm the spliceosome
  3. The spliceosome cuts at the exon intron boundary and the intron forms a loop
  4. The two cut ends are joined and the intron is degraded
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7
Q

What is alternative splicing?

A

Alternative splicing can make different mRNA from the same gene
- Means not always cutting out the same parts

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8
Q

What are the four ways alternative splicing can occur?

A
  1. Exon skipping
  2. Mutually exclusive exon
  3. Alternative 5’ splicing donor sites
  4. Alternative 3’ splice donor sites
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9
Q

What does exon skipping involve?

A

Leaving out an exon

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10
Q

What does mutually exclusive exon mean?

A

Multiple slight different exon options

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11
Q

What does alternative 5’ donor sites mean?

A

Multiple options of a splice start

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12
Q

What does alternative 3’ acceptor sites mean?

A

Multiple options of a splice end

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13
Q

What does it mean for the genetic code to be degenerate?

A

There is more than one codon per amino acid

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14
Q

What are synonymous codons?

A

Codons that encode the same amino acids are synonymous codons

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15
Q

What does ‘wobble of the code’ describe?

A

Wobbles of the code describes codons where the last base is irrelevant

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16
Q

How many start and stop codons are there?

A

There is only 1 start codon AUG and 3 stop codons

17
Q

What are the 3 key processes of translation?

A
  1. Initiation - ribosome finds and binds to start codon on mRNA
  2. Elongation - Polypeptide chain grows by addition of individual amino acids carried to the ribosome by tRNA
  3. Termination - translation finds stop codons and dissociates
18
Q

In prokaryotes how is translation initiated?

A
  1. Recognition of the consensus ribosome binding site - Shine-Dalgarno sequence located in the 5’ UTR
  2. Binding of small ribosome unit and initiation factors
  3. A special initiator tRNA in prokaryotes: fMet-tRNA binds
  4. Initiation factors are released and the large ribosome unit binds forming the initiation complex
19
Q

What are the steps in the translation initiation of eukaryotes?

A
  1. Small ribosome unit binds to initiator tRNA and initiation factors, forming pre-initiation complex.
  2. This complex finds and binds to the 5’ cap.
  3. The pre-initiation complex moves along mRNA scanning for Kozak consensus sequence, indicating the start site
  4. Initiation factors dissociate and the large ribosome unit binds forming initiation complex
20
Q

During translation elongation what are the binding sites for tRNA in the ribosome?

A
  1. A site is for codon recognition between anticodon and codon (mRNA)
  2. P site is for peptide bond formation and amino acid translocation
  3. E for Exit of uncharged tRNA and translation machinery progresses
21
Q

When does translation terminate?

A

When a stop codon is encountered.

  1. A release factor recognised the stop codon and enters the A site
  2. Stop codons do not encode amino acids and the release factors do not carry AA
  3. Release factor separates the last tRNA from the last AA