Protein Synthesis Flashcards

1
Q

What is the central dogma of molecular biology?

A

It describes the two-step process, involving transcription and translation, by which the information in genes flows into proteins.

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2
Q

What is synonymous alteration (in genes)?

A

It is when a nucleotide changes in the chain, but the coding remains the same.

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3
Q

What does the Svedberg unit (S/Sv) measure?

A

It is a unit for sedimentation rate ie. how quickly a particle ‘settles’.

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4
Q

What are the two subunits of a ribosome called, and what rRNA (and proteins) are they themselves made up of?

A

The ribosome is split into two subunits, a smaller 40S subunit, and a larger 60S subunit. The 40S is made up of 18S rRNA (and 33 proteins), while the 60S is made up of 5S, 5.8S and 28S rRNA (and 49 proteins).

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5
Q

What are the three sites in the ribosomal subunits called?

A

Aminoacyl tRNA binding site, Peptide binding site and Exit (APE).

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6
Q

Name and describe (in a few sentences) the three stages of protein synthesis.

A

INITIATION: assembly of the ribosome on mRNA together with the first initiator tRNA - aminoacyl tRNA (met-tRNAi)
ELONGATION: charged tRNAs are delivered to the ribosome, and the amino acids are added one at a time, building the polypeptide
TERMINATION: a stop codon is encountered, which signals the end of protein synthesis and the release of the polypeptide

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7
Q

What is the name of the eukaryotic initiation factor that binds to the 40S subunit at the beginning of initiation, and what is its purpose?

A

It’s called EIF3, and it’s there to prevent the association of the 40S subunit with the 60S subunit.

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8
Q

What two substances attach to the met-tRNAi before it settles into one of the sites?

A

EIF2 and GTP

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9
Q

In which site does the met-tRNAi settle?

A

The P site

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10
Q

What term do we use to refer to the complex consisting of the 40S ribosomal subunit, EIF3, met-tRNAi, EIF2 and GTP?

A

The 48S preinitiation complex

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11
Q

What happens when a start codon is found?

A

The EIF3 dissociates, and the GTP gets hydrolyzed along with it, releasing energy that allows the 60S subunit to join the complex.

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12
Q

Which site does a second tRNA occupy, and with the help of which factor?

A

It occupies the A site, with the help of EIF1.

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13
Q

What enzyme mediates the charging of tRNA?

A

Aminoacyl tRNA synthase

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14
Q

What does peptidyl transferase do?

A

It forms peptide bonds between adjacent amino acids.

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15
Q

What does translocase do?

A

It aids in the movement of met-tRNAis between sites in the ribosomal subunit.

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16
Q

What is a polysome?

A

An mRNA with multiple different ribosomes attached to it.

17
Q

What causes the release of the polypeptide chain?

A

The recognition of a stop codon, and the consequent hydrolysis of the terminal peptidyl-tRNA.

18
Q

What is the energy cost for charging of tRNAs with amino acids?

A

It is 1 ATP per amino acid.

19
Q

What is the energy cost for the initiation of polypeptide synthesis?

A

It is 1 GTP and nATP (the n being the number of nucleotides scanned along the mRNA).

20
Q

What is the energy cost of the elongation of the polypeptide?

A

It is 2 GTP per amino acid.

21
Q

What is the energy cost of the termination of polypeptide synthesis?

A

It is 1 GTP.

22
Q

List the properties of a prokaryotic ribosome (ribosome name, subunit names, large and small subunit components).

A
  • 70S ribosome
  • 50S and 30S subunits
  • 50S: 23S and 5S rRNA (31 proteins)
  • 30S: 16S (21 proteins)
23
Q

List the properties of a eukaryotic ribosome (ribosome name, subunit names, large and small subunit components).

A
  • 80S ribosome
  • 60S and 40S subunits
  • 60S: 5S, 5.8S and 28S (49 proteins)
  • 40S: 18S (33 proteins)
24
Q

For the antibiotic Streptomycin, list its target in bacteria and its effect on protein synthesis.

A

It affects the small ribosomal subunit, and inhibits the initiation misreading of the genetic code.

25
Q

For the antibiotics Tetracyclines, list their target in bacteria and their effect on protein synthesis.

A

They affect the small ribosomal subunit, and inhibit the met-tRNAis binding to the ribosome.

26
Q

For the antibiotic Chloramphenicol, list its target in bacteria and its effect on protein synthesis.

A

It affects the large ribosomal subunit, and inhibits peptidyl transferase activity.

27
Q

For the antibiotic Erythromycin, list its target in bacteria and its effect on protein synthesis.

A

It affects the large ribosomal subunit, and inhibits translocation.

28
Q

For the antibiotics Neomycins, list their target in bacteria and their effect on protein synthesis.

A

They affect multiple sites, and inhibit the several effects.