RNA & protein synthesis

Question 1

What is a codon?

Answer 1

The sequence of 3 bases on the mRNA that codes for a single amino acid.

Question 2

What is the genome?

Answer 2

The complete set of genes in a cell including those in the mitochondria and/or chloroplasts

Question 3

What is the proteome?

Answer 3

The full range of proteins produced by the genome.

Question 4

What is transcription?

Answer 4

The process of making pre-mRNA using the DNA template.

Question 5

What happens during transcription?

Answer 5

• An enzyme unwinds a section of DNA , exposing the nucleotide bases of the template strand
• Exposed bases pair with complementary RNA nucleotides present in the nucleus
• The enzyme RNA polymerase moves along the strand joining RNA nucleotides together.
• As the RNA polymerase adds the nucleotides, the DNA strand reforms so that only around 12 base pairs on the DNA are exposed at any time.
• When the RNA polymerase reaches a stop sequence of bases, it detaches & the pre-mRNA molecule is complete.

Question 6

Where do ribosomes function?

Answer 6

In the cytoplasm

Question 7

Where are ribosomes made?

Answer 7

In the nucleus

Question 8

What are ribosomes made from?

Answer 8

Protein & rRNA

Question 9

Where does tRNA function?

Answer 9

In the cytoplasm

Question 10

Where is tRNA made?

Answer 10

In the nucleus

Question 11

What are two important structural characteristics of tRNA?

Answer 11

The anticodon sequence & the amino acid binding site.

Question 12

What are the 3 main phases of translation?

Answer 12

• Initiation
• Elongation
• Termination

Question 13

What happens during the initiation phase?

Answer 13

• The ribosome becomes attached to the start codon AUG at one end of the mRNA molecule
• The tRNA molecule with the complementary anticodon moves to the ribosome & binds with the codon on the mRNA, the tRNA carries the amino acid methionine.

Question 14

What happens during the elongation phase?

Answer 14

• The next tRNA with the complementary anticodon will enter the ribosome and pairs with the next codon on the mRNA
• The two amino acids form a peptide bond (using ATP)
• The ribosome moves along the the mRNA, allowing a new tRNA to enter the ribosome
• The empty tRNA is released from the ribosome to be ‘recycled’

Question 15

How many amino acids per second can be added to the polypeptide chain during elongation?

Answer 15

15 per second

Question 16

How many ribosomes can pass immediately behind the first?

Answer 16

50 so that identical polypeptides can be assembled at the same time.

Question 17

What happens the termination phase?

Answer 17

• The synthesis of the polypeptide continues until a ribosome reaches a stop codon
• The ribosome, mRNA & last tRNA molecule all separate & the polypeptide chain is terminated