BioChem 7.3 Translation

Question 1

Outline the structure of a ribosome.

Answer 1

Ribosomes are made of rRNA and proteins.
It is composed of 2 sub-units: a large sub-unit and a small sub-unit.
It consists of 3 binding sites for tRNA.
It has one binding site for mRNA.

Question 2

What is the structure of a tRNA?

Answer 2

A tRNA molecule is a polynucleotide chain. It is folded back to form a region of double helix, according to RNA complementary base pairing rule.
It contains 3 loops.
It contains an anti-codon with 3 RNA bases.
It has a binding site for an amino acid.

Question 3

How are tRNA molecules charged?

Answer 3

tRNA molecule has to be linked to a specific amino acid through a tRNA - activating enzyme.

1. Specific amino acid binds to active side of a tRNA-activating enzyme.
2. ATP binds to active site of the enzyme to provide energy stored in the 3 phosphate groups.
3. 2 of the phosphate groups break away which releases energy captured by the amino acid.
4. A specific tRNA molecule binds to the active site of tRNA activating enzyme which active site has to be complementary to the anti codon of tRNA.
5. High energy bond between the amino acid and tRNA molecule is formed which activates the tRNA molecule. The energy carried by the tRNA molecule will be used for to form a peptide bond.
6. The tRNA molecules leaves the enzyme to find a ribosome

Question 4

What is the tRNA activating enzyme an example of?

Answer 4

tRNA activating enzyme is an example of enzyme-substrate specificity

Question 5

What is the first process of translation?

Answer 5

Initiation

1. The small ribosome sub-unit binds to the mRNA
2. The complementary anti-codon of the tRNA molecule binds to with the start codon at the P-Site
3. The large sub-unit of the ribosome binds to the mRNA.

Question 6

What is the second process of translation?

Answer 6

Elongation

1. A second tRNA molecule moves into the A-site
2. A peptide bond forms between the two amino acids held in A Site and P site.

Question 7

What is the third process of translation?

Answer 7

Translocation

1. The ribosome moves 3 nucleotides along the mRNA strand.
2. the first tRNA molecule moves into E-site and exits the ribosome
3. A-Site is available for a new tRNA molecule.

Question 8

What is the fourth process of translation?

Answer 8

Termination
1. Eventually the ribosome will reach the stop codon
2. The ribosome breaks apart into two sub-units
Polypeptide is complete.

Question 9

In which direction does translation occur?

Answer 9

5’ to 3’ direction

Question 10

What is the difference of the function of free ribosome and ribosome on the RER?

Answer 10

Free ribosome: make protein primarily for inside the cell.

Ribosome on RER: make protein for export out of the cell or for lysosome (i.e. hormones such as insulin)

Question 11

Is translation in eurkayrotic cells as quick as in prokaryotic cells?

Answer 11

No. Translation in prokaryotes can occur immediately after transcription due to the absence of the nuclear membrane.

Question 12

What is a polysome?

Answer 12

A polysome is formed when several free ribosome attach themselves to the same strand of mRNA.
The advantage of this is that it produces the same amount of polypeptides in a shorter amount of time.

Question 13

What kind of bonds maintain the tertiary and quaternary structure of protein?

Answer 13

Hydrogen Bonds
Disulfide bridges
Ionic Bonds
Hydrophobic Interactions (Inter molecular Forces)