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BIOL 113 > Lecture 6 > Flashcards

Lecture 6 Flashcards

1
Q

What ‘adapter’ links mRNA and amino acids?

A

tRNA.

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2
Q

How long is a tRNA molecule, and what shape is it?

A

80 nucleotides roughly.

Clover leaf.

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3
Q

Do base pairs form within tRNA structure?

A

Yes.

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4
Q

How does tRNA base pair with a codon?

A

Anticodon.

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5
Q

Where are amino acids attached on a tRNA?

A

3’ hydroxyl group on end of RNA chain.

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6
Q

How specific is tRNA?

A

Specific for single amino acid determined by anticodon.

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7
Q

What carries out specific attachment on tRNA?

A

amino-acyl tRNA synthetases.

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8
Q

How many amino-acyl tRNA synthetases are there?

A
  1. One for each amino acid.
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9
Q

What are the 3 binding sites on amino-acyl tRNA synthetase for?

A

Specific tRNA.
Corresponding amino acid.
ATP.

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10
Q

2 steps in attachment process of amino-acyl tRNA synthetase?

A

ATP hydrolysed and amino acid joined to AMP.

Correct tRNA binds, and amino acid transferred from AMP to tRNA.

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11
Q

How many amino acid codons in genetic code, and how many tRNAs?

A

61 amino acid codons.

40-40 tRNAs.

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12
Q

When G is in wobble position, what can the 3rd base in the codon be?

A

U or C.

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13
Q

When A is in wobble position, what can the 3rd base in the codon be?

A

U.

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14
Q

When C is in wobble position, what can the 3rd base in the codon be?

A

G.

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15
Q

When U is in wobble position, what can the 3rd base in the codon be?

A

A or G.

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16
Q

When I is in wobble position, what can the 3rd base in the codon be?

A

U, C or A.

17
Q

What is the ribosome composed of?

A

rRNA and proteins.

2 subunits.

18
Q

What are the 2 subunits in ribosomes called?

A

Large and small.

19
Q

What does the ribosome do?

A

Binds mRNA and amino-acyl tRNAs.

Catalyses stepwise formation of peptide bonds.

20
Q

In which direction do ribosomes move along the mRNA?

A

5’ to 3’.

21
Q

What does a ribosome ensure?

A

Correct reading frame used.

22
Q

What is the A site, P site and E site?

Which subunit are these found on?

A 
A = Aminoacyl tRNA binding site.
P = peptidyl-tRNA binding site.
E = Exit site.

Large subunit.

23
Q

What’s found on the small subunit of the ribosome?

A

mRNA binding site.

24
Q

3 stages of protein synthesis, and what happens in each?

A

Initiation - small subunit binds mRNA and initiator amino acyl tRNA then large subunit binds.
Elongation - peptide bonds formed as the ribosome moves along mRNA.
Termination - one of the three stop codons enters A site, releasing completed protein.

25
Q

What is the start codon?

A

AUG.

26
Q

Where does initiation of protein synthesis get its energy from?

A

GTP hydrolysis and proteins called invitation factors.

27
Q

3 steps in elongation of protein?

A

Codon recognition - conversion of GTP to GDP.
Peptide bond formation.
Translocation - converts another GTP to GDP.

28
Q

What catalyses peptide bond formation?

A

Peptidyl transferase - RNA enzyme (ribozyme).

29
Q

What is added to end of polypeptide chain on termination?

A

Water.

30
Q

When the ribosome dissociates after polypeptide released from tRNA in P-site, what is hydrolysed?

A

2XGTP.

31
Q

What are polyribosomes?

A

Several ribosomes that translate an mRNA at once.

32
Q

Where does transcription and translation happen in prokaryotes and eukaryotes?

A

No nuclear membrane in prokaryotes, so both coupled.

mRNA must be transported to cytoplasm before translation can occur in Eukaryotes.

33
Q

How do proteins travel in prokaryotes and eukaryotes? Why?

A

Protein diffuse through cytoplasm in prokaryotes.. no organelles.
Proteins must be trafficked to correct site as several different organelles in eukaryotes.

34
Q

How are proteins targeted to ER?

A

SRP binds to signal peptide momentarily halting protein synthesis. Then SRP binds to receptor protein in ER membrane.
SRP then leaves, and polypeptide resumes growing, translocating across membrane.
Signal cleaving enzyme cuts off signal peptide.
Rest of completed polypeptide leaves ribosome, folding into final conformation.

BIOL 113 (6 decks)

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