2.1.2 Translation

Question 1

What is translation?

Answer 1

Translation is the assembly of polypeptides at ribosomes.

Question 2

Why is the sequence of amino acids in a protein critical?

Answer 2

As the sequence of amino acids forms the primary structure of the protein. The primary structure then determines the tertiary structure, as the protein folds up and is held in a 3D shape by hydrogen, ionic and hydrophobic interactions forming between R-groups on amino acids. The tertiary structure is what allows the protein to function, if it’s tertiary stuructre is disturbed then the protein may not be able to function (e.g. the active site on an enzyme may have changed shape and is no longer complementary to the substrate).

Question 3

Where is ribosomal RNA made?

Answer 3

The nucleolous.

Question 4

What is a ribisome made up of?

Answer 4

Ribosomal RNA (rRNA) and protein.

Question 5

Where is tRNA made?

Answer 5

Transfer RNA is made in the nucleus and passes into the cytoplasm.

Question 6

Outline the structure of a tRNA molecule?

Answer 6

Folded into hairpin shapes and at one end have three exposed bases where a particular amino acid can bind. At the other end they have three exposed nucleotide bases, which is known as a anticodon. Each anticodon can bind with its complementary codon temporarily.

Question 7

Outline the events that take place during translation?

Answer 7

1. A molecule of mRNA binds to a ribosome. Two codons are attatched to the small subunit of the ribosome and exposed to the large subunit. The first expressed mRNA codon is always AUG.
2. Using ATP energy and an enzyme, a tRNA with the anticodon UAC forms hydrogen bonds with this codon and the tRNA molecule has the specific amino acid attatched.
3. A secondary tRNA molecule, binds to the second exposed codon with it’s complementary anticodon, again the tRNA molecule carrying a amino acid.
4. A peptide bond is formed between the two adjacent amino acids. An enzyme catalyses this.
5. The ribosome now moves across the mRNA and the process is repeated. The first tRNA molecule now leaves and is able to collect more amino acids.
6. This process will repeat until a stop codon is reached.

Question 8

How does cyclic AMP activate proteins?

Answer 8

It changes their 3D strucutre so that their shape is a better fit to their complementary molecules.

Question 9

How does protein synthesis differ in prokaryotes?

Answer 9

The DNA is not inside a nucleus. Translation can begin as soon as mRNA has been made.

Question 10

S&C

Answer 10

1. cAMP will inhibt the glycogen synthase, it will do this by binding to an allosteric site and changing the enzymes shape so that the active site is less exposed.
2. Glucose 6-P activates glycogensynthase by binding to an allosteric site, changing its shape and exposing the active site.