Gene expression

Question 1

What is the process of transfering information from RNA to DNA

Answer 1

Reverse transcription

Question 2

Can information be transfered from protein to DNA

Answer 2

No

Question 3

What is TATA box

Answer 3

A specific Promotor

Question 4

What binds onto the promotor

Answer 4

Enhancer (A TF)

Question 5

What binds onto the enhancer

What’s it’s function

Answer 5

Activator Protein.

It recruits more TF to form a complex

Question 6

What’ s the complex formed by activator protein for

Answer 6

Make it easier for RNA polymerase to attach on

Question 7

What is the nature of CTCF

Answer 7

A protein

Question 8

What sequence does it bind to

Answer 8

CCCTC (found in all insulator)

Question 9

What does CTCF prevents

Answer 9

The binding of enhancers onto promotor

Question 10

In Direct methylation, where is the methyl group added

Answer 10

Cytosine on CCCTC

Question 11

Does Direct Methylation raise or drop a gene’s expression level from

Answer 11

It depends on the underlying genetic sequence

Question 12

What is the function of mediator

Answer 12

• Mediator binds to RNA which controls transcription of gene
• May be an enhancer or silencer

Question 13

What are the steps in transcription

Answer 13

A. Initiation
1. TATA-box binding protein binds to the DNA at the TATA box sequence in DNA.
- Transcription factors assemble at a specific promoter region along the DNA

2. Other components of TFII (transcription factor 2) and RNA polymerase II bind.
   - A mediator complex protein arrives carrying the enzyme RNA polymerase
   - RNA polymerase is inserted into place between the strands of the double helix
3. Transcription factors at cis-acting enhancers thousands of bases away can trigger elongation.
   - Initiation process requires contact between the transcription initiation complex and activator proteins
   regions)

B. Elongation
1. Elongation of the RNA occurs 5’ to 3’ simply with the template strand. The coding strand goes around the ‘outside’ and is not actually directly involved.
- RNA polymerase unzips a small portion of the DNA helix, exposing the bases on each
strand
- Only one strand is copied, acting as the template for the synthesis of a protein
molecule
C. Termination
1. In some cases this occurs in response to a particular DNA sequence, in others randomly after the end of the gene to be transcribed.

Question 14

What molecules contribute the nucleotides of mRNA

Answer 14

Ribonucleotide triphosphate

Question 15

What is the product of the above transcription

Answer 15

pre-mRNA or primary transcript

Question 16

What mineral is required for the RNA polymerase

Why is energy input required

Answer 16

Mg 2+

To break the high-energy triphosphate bonds

Question 17

What are the 3 steps done to the aforementioned product

Answer 17

5’ capping, 3’ Polyadenylation, splicing

Question 18

What are the 4 purpose for 5’ capping

Answer 18

To stabilze the RNA

– Regulation of nuclear export (1 mark)
– Prevention of degradation by exonucleases (1 mark)
– Promotion of translation (1 mark)
– Promotion of 5’ proximal Splicing(1 mark)

Question 19

What is the enzyme used for 3’ PolyAdenylation

What are the 4 functions of 3’ Polyadenylation

Answer 19

Poly A polymerase

– Protect mRNAs from degradation by exonucleases (1 mark)
– Participate in transcriptional termination (1 mark)
– Facilitate export of the mRNA from the nucleus (1 mark)
– Participate in translation (1 mark)

Question 20

What is splicing

What is the protein required for splicing

Answer 20

Splicing is the process by which non-coding sequences (introns) in the pre-mRNA are removed and the remaining protein-coding sequences (exons) are ligated together. (2 marks)

spliceosome

Question 21

Different cells will splice the primary transcipt in different ways.

What the name of the process

Answer 21

Alternate Splicing

Question 22

In what organelle is translation done

Answer 22

Ribosome

Question 23

How many subunits are in the ribosome

Answer 23

2

Question 24

Name the nucleic acid component of ribosome

Answer 24

Ribosomal RNA (rRNA)

Question 25

What is the code on mRNA called

Answer 25

Codon

Question 26

Does codon always corresponds to an amino acid

Answer 26

No, it can be a stop codon

Question 27

If the codon is 5’ AAC’ 3’, what is the anticodon

Answer 27

3’UUG 5’, ie 5’GUU 3’

Question 28

What is the region in Ribosome that the tRNA is checked by matching the codon and anticodon

Answer 28

A

Question 29

What is the region where the amino acid is detached from the tRNA

Answer 29

P

Question 30

What is the region that the tRNA is ejected

Answer 30

E

Question 31

What are the procedures for Translation

Answer 31

A. Initiation
The first stage of translation involves the assembly of the three components that carry out the
process (mRNA, tRNA, ribosome)
1. The small ribosomal subunit binds to the 5’-end of the mRNA and moves along it until it reaches the start codon (AUG)

2. Next, the appropriate tRNA molecule bind to the codon via its anticodon (according to
   complementary base pairing)
3. Finally, the large ribosomal subunit aligns itself to the tRNA molecule at the P site and
   forms a complex with the small subunit

B. Elongation
1. A second tRNA molecule pairs with the next codon in the ribosomal A site

2. The amino acid in the P site is covalently attached via a peptide bond (condensation
   reaction) to the amino acid in the A site
3. The tRNA in the P site is now deacylated (no amino acid), while the tRNA in the A site
   carries the peptide chain

C. Translocation
1. The ribosome moves along the mRNA strand by one codon position (in a 5’ → 3’ direction)
2. The deacylated tRNA moves into the E site and is released, while the tRNA carrying the peptide chain moves to the P site
3. Another tRNA molecules attaches to the next codon in the now unoccupied A site and the process is repeated
D. Termination
The final stage of translation involves the disassembly of the components and the release of a
polypeptide chain
1. Elongation and translocation continue in a repeating cycle until the ribosome reaches a stop
codon
2.These codons do not recruit a tRNA molecule, but instead recruit a release factor that signals
for translation to stop
3. The polypeptide is released and the ribosome disassembles back into its two independent
subunits