3.10 Protein Synthesis

Question 1

Where is DNA contained, in a eukaryotic cell (specifically)? (1 mark)

Answer 1

Within a double membrane called the nuclear envelope that encloses the nucleus.

Question 2

Where does protein synthesis occur? (1 mark)

Answer 2

In the ribosomes

Question 3

Why is transcription needed? (1 mark)

Answer 3

A DNA molecule is too large to leave the nucleus to supply the coding information needed to determine the protein’s amino acid sequence.

Question 4

How does transcription work? (1 mark)

Answer 4

The sequences of genes are copied and transported to the site of protein synthesis.

Question 5

What does transcription produce? (1 mark)

Answer 5

Shorter molecules of RNA.

Question 6

What is the strand that contains the code for the protein called? (1 mark)

Answer 6

The sense strand.

Question 7

Does the antisense strand code for the protein? (1 mark)

Answer 7

No.

Question 8

What is the function of the antisense strand? (2 marks)

Answer 8

It acts as a template strand during transcription, so that the complementary RNA strand formed carries the same sequence as the sense strand.

Question 9

Describe transcription. (5 marks)

Answer 9

1. The section that contains the gene unwinds and unzips (RNA helicase).
2. Free RNA nucleotides base pair with complementary bases on the antisense strand.
3. Phosphodiester bonds form between the RNA nucleotides (RNA polymerase).
4. The completed short strand of RNA is called messenger RNA (mRNA).
5. mRNA detaches from template and leaves nucleus through a nuclear pore.
6. The DNA helix reforms and the mRNA molecule travels to a ribosome.

Question 10

What does RNA polymerase do? (1 mark)

Answer 10

Catalyses the formation of phosphodiester bonds between RNA nucleotides.

Question 11

What is a short strand of RNA formed during transcription called? (1 mark)

Answer 11

mRNA

Question 12

How does mRNA leave the nucleus? (1 mark)

Answer 12

Through a nuclear pore.

Question 13

What are the two subunits in eukaryotic ribosomes composed of? (1 mark)

Answer 13

Protein and ribosomal RNA (rRNA).

Question 14

Where does mRNA go after leaving the nucleus? (1 mark)

Answer 14

Travels to a ribosome and binds to a specific site on the small subunit.

Question 15

What is translation? (1 mark)

Answer 15

The mRNA is decoded (translated) into a sequence of amino acids.

Question 16

What is the anticodon? (1 mark)

Answer 16

Three bases on the end of a tRNA molecule.

Question 17

What do tRNA molecules carry? (1 mark)

Answer 17

Carry an amino acid corresponding to the codon.

Question 18

What happens when the tRNA anticodons bind to the complementary codons along the mRNA? (2 marks)

Answer 18

The amino acids are brought together in the correct sequence to form the primary structure of the protein, a polypeptide.

Question 19

Describe the stages of translation. (5 marks)

Answer 19

1. The mRNA attaches to ribosome
2. A tRNA with the complementary anticodon binds to the mRNA start codon.
3. Another tRNA then binds to the next codon on the mRNA.
4. A peptide bond forms between the first and second amino acid (brought by the tRNA molecules)
5. The ribosome then moves along the mRNA, releasing the first tRNA.
6. This repeats, until the ribosome reaches the stop codon an the polypeptide chain is released.

Question 20

When do the secondary and tertiary structures of the protein form? (1 mark)

Answer 20

As the amino acids are joined together forming the primary structure of the protein, they fold into secondary and tertiary structures.

Question 21

Where may the protein undergo further modifications? (1 mark)

Answer 21

Golgi apparatus

Question 22

Can multiple polypeptide chains be formed from the same mRNA molecule at once, why not/can they? (2 marks)

Answer 22

Yes, because many ribosomes can follow on the mRNA behind the first.