Translation

Question 1

What is translation?

Answer 1

The process that produces a polypeptide using sequences of mRNA.

Question 2

When does translation occur?

Answer 2

When mRNA becomes attached to a ribosome.

Question 3

Describe a codon

Answer 3

Every 3 bases on an mRNA strand make up a codon.

Question 4

What is each codon complementary to?

Answer 4

A triplet of bases on the original DNA strand.

Question 5

What does a mature mRNA transcript do?

Answer 5

Carries a start codon which starts translation and a stop codon which causes translation to finish when the polypeptide chain is complete.

Question 6

Describe tRNA

Answer 6

1. One molecule of tRNA is made up of a single strand of nucleotides however it has a folded 3-dimensional shape.
2. It folds back on itself and hydrogen bonds form between many of its bases.
3. Each molecule of tRNA is folded in such way that only a particular set of triplet bases are exposed. This exposed triplet is called an anticodon.

Question 7

What does each anticodon correspond to?

Answer 7

A specific amino acid carried by the tRNA at its attachment site.

Question 8

What does the attachment site allow tRNA to do?

Answer 8

Transport a specific amino acid to mRNA on the ribosomes.

Question 9

What happens during translation?

Answer 9

Triplet codons on mRNA and anticodons on tRNA translate the genetic code into a sequence of amino acids. These amino acids become linked together by peptide bonds.

Question 10

What is the process of translation? (1st 3 stages)

Answer 10

1. Mature mRNA transcript leaves the nucleus and becomes attached to a ribosome.
2. tRNA molecules carry specific amino acids from the cytoplasm to the ribosome.
3. A start codon (AUG) is recognised.

Question 11

What is the process of translation? ( the stages 3-6)

Answer 11

4. tRNA molecule (carrying an amino acid) aligns itself next to its complementary codon on mRNA strand.
5. Next codon is ‘read’ and appropriate tRNA molecule (carrying amino acid) aligns itself next to complementary codon.
6. Peptide forms between adjacent amino acids.

Question 12

What is the process of translation? (Stages 7-9)

Answer 12

7. First tRNA releases the amino acid and goes to pick up another amino acid.
8. Steps 4-7 are repeated until a stop codon is reached.
9. Once the last tRNA molecule releases its amino acid the newly formed polypeptide chain leaves the ribosome.

After leaving the ribosome the polypeptide chain may undergo post translation modification.

Question 13

What does 1 gene equal to?

Answer 13

Many proteins

Question 14

What can different proteins be produced from?

Answer 14

The same gene.

alternative RNA splicing and Post translation modification makes this possible.

Question 15

Describe Alternative RNA splicing

Answer 15

Within a length of DNA some parts of the base sequence will code for a particular protein but be non- coding for another.

By selecting which parts of the sequence are treated as exons and which are treated as introns it is possible to produce more than one protein from the same gene.

This is called Alternative RNA splicing.

Question 16

What does Alternative RNA splicing allow?

Answer 16

It allows a primary transcript to form different mature mRNA molecules depending on which sequences are treated as introns and which as exons.

Question 17

Describe Post translation modification

Answer 17

After translation polypeptide chains can be modified by:

• cleavage (cutting and combing polypeptide chains)
• by adding a phosphate or a carbonate to the chain.

Once the polypeptide chains have been modified they are called proteins.

Question 18

What is a protein?

Answer 18

Completed molecule at the end of protein synthesis which is able to carry out a specific function within the body.