Gene Expression

Question 1

What are the enzymes and substrates of:
DNA replication
RNA Production
Protein Production

Answer 1

DNA replication: DNA polymerase (dNTP’s)
RNA Production: RNA polymerase (NTP’s)
Protein Production: Ribosome (Amino Acids)

Question 2

What happens at the three stages of transcription?

Answer 2

Initiation:
Recognition of promoter (TATAA) by transcription factor which binds in the 5’ - 3’ and recruits the RNA polymerase
Elongation:
Polymerase joins the nucleotides via phosphodiester bonds forming the mRNA strand that is identical to the coding strand (complementary to the template strand)
Termination:
Polymerase recognises the stop codon and releases the completed mRNA strand

Question 3

What are the types of RNA processing?

Answer 3

Capping: (protection of the pre-mRNA)
A methylated Guanine triphosphate is added via a 5’ - 5’ cap to the start of the pre-mRNA
Tailing: (protection of the pre-mRNA)
PolyA-polymerase adds ~ 200 Adenine onto the end of the pre-mRNA
Splicing: (form mature mRNA)
Introns are removed to leave the mature mRNA

Question 4

What are the stages in protein translation?

Answer 4

Initiation:
Recognition of the AUG codon by methionyl-tRNA in ribosome (requires ATP) and positioning in the P-site
Elongation:
Amino-Acyl-tRNA with anti-codons complementary to the codons in the A-site enter the ribosome where peptidyl-transferase joins methionine to the new amino acid
Empty tRNA is ejected from the P-site as the ribosome moves 1 codon a long and the new peptidyl-tRNA enters the P-site
Termination:
Hydrolysis of the Ester bond between tRNA and the polypeptide chain occurs when the stop-codon is in the A-site (no tRNA molecule is complementary)

Question 5

How are amino-acyl-tRNA molecules formed?

Answer 5

Amino acid and ATP binds with amino-acyl tRNA synthetase
ATP is hydrolysed releasing PPi and AMP (which activates the amino acid - binds via covalent bonds)
Matching tRNA enters and swaps with AMP forming Ester bond
Releasing AMP and the charged amino-acyl tRNA molecule

Question 6

What are wobble bases?

Answer 6

tRNA molecules that recognise more than 1 base
Alanine (I) base bonds with: U, C, A
Guanine (G) base bonds with: U

Question 7

What are stem loops?

Answer 7

Stem loops are formed when antiparallel complementary sequences on the same strand form H-bonds
Found on all tRNA molecules and within DNA