S12 Gene Expression

Question 1

Which direction does transcription occur in?

Answer 1

5’ to 3’

Question 2

What initiates transcription?

Answer 2

Promoter recognition initiation factors e.g. TATA promotor sequence.

An activator can be elsewhere on the sequence though.

Question 3

What are the three post-transcription modifications (pre-mRNA to mRNA)?

Answer 3

1. Splicing
2. Polyadenylation
3. Capping

Question 4

What is splicing?

Answer 4

Removing introns (non-coding DNA)

Question 5

What is polyadenylation? How does it occur?

Answer 5

Adding many adenosine to the 3’ end.

To prevent degradation.

AAUAA sequence recognised, causes sequence cleavage from RNA polymerase. polyA polymerase adds many As.

Question 6

What is capping?

Answer 6

A 5’ cap (5’-5’ linkage)

Prevents degradation

Question 7

Which direction is upstream?

Which direction is downstream?

Answer 7

3’ to 5’

5’ to 3’

Question 8

Where does transcription occur?

Answer 8

In the nucleus

Question 9

Which strand of DNA is used to make complementary mRNA?

Answer 9

Template strand (not the coding strand)

Question 10

What is the initiation codon and which amino acid does it code for?

Answer 10

AUG

Methionine

Question 11

What are the termination codons?

Answer 11

UAA
UAG
UGA

Question 12

Describe the genetic code:

Answer 12

1. Degenerate
2. Non-overlapping (and no gaps)
3. Universal

Question 13

What is wobble base position?

Answer 13

Binding in the 3rd nucleotide of a mRNA codon to the tRNA anticodon is weaker allowing no-Watson-Crick base pairing to occur in the 3rd position.

Question 14

What are the 4 wobble base pairings?

Answer 14

1. Guanine - Uracil
2. Hypoxanthine (I) - Uracil
3. Hypoxanthine - Adenine
4. Hypoxanthine - Cytosine

Question 15

Which direction is the mRNA read in?

Answer 15

5’ to 3’

Question 16

Which direction is the protein formed in?

Answer 16

N-terminal to C-terminal

Question 17

What two subunits is the eukaryotic 70s ribosome made up of?

Answer 17

40s and 60s subunits

Question 18

What is the name given to a tRNA molecule with an amino acid attached?

Answer 18

Amino acyl tRNA

E.g. methionyl tRNA

Question 19

How do the amino acid and tRNA molecule bind?

Answer 19

1. The amino acid and an ATP molecule binds to the enzyme, aminoacyl-tRNA synthetase
2. The amino acid is phosphorylated (ATP hydrolysed)
3. tRNA molecule binds to the enzyme which then binds to the amino acid and AMP is released
4. The amino acyl tRNA molecule unbinds from the enzyme

Question 20

What are the two sites in translation called?

Answer 20

P and A sites

Question 21

Describe the structure of a tRNA molecule:

Answer 21

‘Clover’ shaped, one strand that folds back on itself (forming hydrogen bonds between complementary bases). Anticodon at the base of the molecule. Amino acids attaches to the top of the molecule (to -OH).

Question 22

What are the types of RNA?

Answer 22

1. rRNA
2. mRNA
3. tRNA
4. miRNA
5. Non-coding RNA

Question 23

From rRNA, mRNA and tRNA order based on the number of kinds of each and how many copies of each (high to low)…

Answer 23

Number of kinds of each - mRNA, tRNA, rRNA

Copies of each - rRNA, tRNA, mRNA