3.10 Protein Synthesis

Question 1

Which 2 main processes does protein synthesis consist of?

Answer 1

transcription

translation

Question 2

What is transcription?

Answer 2

Process of copying sections of DNA base sequence

to produce mRNA

so that genetic information can be transported out of the nucleus via nuclear pores

to site of protein synthesis

Question 3

Where does transcription occur?

Answer 3

Nucleus

Question 4

Outline the steps of transcription of DNA during protein synthesis:

Answer 4

1. DNA helix unwinds
2. Helicase breaks hydrogen bonds between complementary DNA bases
3. Free nucleotides align with exposed bases by complementary base pairing
   
   1. (antisense strand used as template, 3’ to 5’ direction for continuous joining of bases)
4. Adjacent nucleotides joined using phosphodiester bonds using RNA polymerase, forming mRNA
5. mRNA moves out of nucleus via nuclear pore to ribosome

Question 5

Which strand is used as the template during transcription?

Answer 5

antisense strand

(runs in 3’ to 5’ direction)

Question 6

What is translation?

Answer 6

Process by which mRNA is decoded by tRNA

into sequence of amino acids.

Occurs at ribosome.

Question 7

Where does translation occur?

Answer 7

Ribosome

Question 8

Outline the steps by which mRNA is translated by a ribosome:

Answer 8

1. mRNA attaches to ribosome
2. Read in triplet codons, each corresponding to an amino acid.
3. Complementary tRNA anticodon attaches to mRNA, bringing corresponding amino acid.
4. Adjacent amino acids joined using peptide bonds by peptidyl transferase. tRNA released by ribosome.
5. Repeated until stop codon reached.
6. Polypeptide has formed.

Question 9

What is the structure of tRNA?

Answer 9

clover shaped

contains triplet anticodon, which is complementary to mRNA

Question 10

What are the 3 types of mRNA present in a cell?

Answer 10

mRNA (messenger) - copies gene from DNA so that genetic information can move out of nucleus. Translated by ribosome.

tRNA (transfer) - clover shaped. carries corresponding amino acids to ribosome by binding using triplet anticodon.

rRNA (ribosomal) - forms ribosome. (protein + rRNA ⟶ ribosomal subunit)

Question 11

Ribosomes act as the binding site for ___ & ___.

Answer 11

mRNA & tRNA

Question 12

What is the name of the enzymes used to join adjacent nucleotides in transcription?

Answer 12

RNA polymerase

Question 13

What is the name of the enzyme which catalyses the formation of peptide bonds?

Answer 13

peptidyl transferase