Transcription And Translation

Question 1

RNA polymerase binding

Answer 1

Transcription factor 2 d binds to TATA box in promoter sequence (-25) by TBP ( TATA box binding protein )
- introduces kink to determine start and direction of replication
- acts as a platform for further transcription factors and RNA polymerase 2

Transcription begins at +1

Question 2

Initiation of transcription

Answer 2

Selection of first nucleotide of growing RNA by RNA polymerase

Question 3

Elongation of transcription

Answer 3

Addition of further nucleotides to the RNA chain in the 5’ to 3’ direction
Transcription bubble travels in one direction along DNA strand

Question 4

Termination of transcription

Answer 4

Release of finished RNA
Forms stem loop structure followed by a chain of U’s
RNA cleaved off by a specific enzyme

Question 5

Pre mature to mature mRNA

Answer 5

Introns are spliced out
Only exons remain
AAAAA poly adenosine tail added
5’ cap added

Question 6

Enhancers

Answer 6

Regulate transcription positively or negatively

DNA binding proteins
Steroid receptors

Question 7

Aminoacyl-tRNA synthetases

Answer 7

Bind amino acid to complementary tRNA molecule
ATP provides energy required to form covalent bond

Question 8

Ribosomes

Answer 8

Composed of two subunits
- 4 rRNA molecules
- protein component

Question 9

Initiation of translation

Answer 9

Formation of initiation complex
- Small ribosomal subunit binds to 5’ end of mRNA and moves along it until AUG start codon is found
- Energy provided by GTP hydrolysis
- requires initiation factor proteins
- AUG start codon detected attaches to UAC initiator anticodon
- Large protein subunit joins assembly line and tRNA is in Peptidyl site

Question 10

Elongation of translation

Answer 10

Codons on mRNA form base pairs with anticodons on tRNA molecules
Elongation factors bring complementary tRNA molecule to aminoacyl site
GTP is hydrolysed to release EF-1a from tRNA and it is regenerated by EF-By

Question 11

Peptide bond formation and translocation

Answer 11

Peptidyl transferase catalyses peptide bond formation between amino acids in P and A sites
EF-2 moves ribosome along one codon
Empty tRNA moves into exit site

Question 12

Termination of translation

Answer 12

Site encounters stop codon with pairs with no tRNA molecule so chain is stopped
Release factor protein attaches to end and ribosome disassociates
GTP hydrolysed allowing finished protein to be cleaved off

Question 13

Free ribosomes

Answer 13

proteins for cytosol, nucleus and mitochondria

Question 14

Ribosomes bound to RER

Answer 14

proteins for plasma membrane, ER, Golgi, secretion