Protein Synthesis - Transcription

Question 1

What are the two stages of protein synthesis?

Answer 1

Transcription and Translation

Question 2

Why does protein synthesis occur?

Answer 2

The DNA is too big to leave the nucleus and cannot travel to a ribosome, so the DNA is coverted to mRNA.

Question 3

Which stage of protein synthesis occurs first?

Answer 3

Transcription

Question 4

Where does transcription occur?

Answer 4

Nucleus

Question 5

(Transcription) - stage 1 - what is the first stage of transcription which involves the enzyme DNA helicase?

Answer 5

• DNA helicase attaches to the DNA at the beginning of the gene.
• Causes the unwinding of the DNA helix and breaks the hydrogen bonds.

Question 6

(Transcription) - stage 2 - what happens after the unwinding of the DNA helix?

Answer 6

• The two strands separate
• one strand is the coding strand
• the other strand is the template strand

Question 7

(Transcription)- stage 3 - What does the template strand do?

Answer 7

It is used to make the a mRNA copy of DNA.
(U replaces T)

Question 8

(Transcription)- stage 4 - What do the free nucleotides do?

Answer 8

• The free nucleotides are present in the cell nucleus
• they line up by complementary bases pairing next to the exposed DNA bases on the template strand.

Question 9

(Transcription)- stage 5 - what does RNA polymerase do?

Answer 9

RNA polymerase joins the sugar phsophate back bones of the new mRNA molecules being made, until its complete.

Question 10

(Transcription)- stage 6 - What happens when the enzyme has passed a section?

Answer 10

The DNA molecule reforms
(2 strands re-join)

Question 11

(Transcription)- stage 7 - what is the final step of transcription?

Answer 11

the mRNA carries the same code as the DNA coding strand
- except U has replaced T)

Question 12

What are introns?

Answer 12

the non-coding part of the amino acids

Question 13

What happens to the introns/ how is pre-mRNA produced?

Answer 13

• introns are copied from the DNA to mRNA
  producing pre-mRNA

Question 14

What happens to the introns/ how is functional mRNA produced?

Answer 14

they cut out of the mRNA using enzyme before it leaves the nucleus
- produces functional mRNA
- mRNA is capped before it leaves the nucleus to prevent it from being damaged in the cytoplasm

Question 15

What happens when the functional mRNA leaves the nucleus?

Answer 15

• it travels to the ribosomes