Transcription & Translation

Question 1

What happens during initiation in transcription?

Answer 1

Code is recognised - transcription factors bind at TATA region (upstream of gene) and attract RNA polymerase (transcription initiation complex)

Question 2

What happens during elongation in transcription?

Answer 2

RNA polymerase travels along templates strand and carries out complementary base pairing to form mRNA. 5’ to 3’ growth

Question 3

What happens during termination in transcription?

Answer 3

Sequence-dependent termination of RNA chain growth. Methyl-guanine cap to the 5’ end which is then bonded with a 5’-5’ triphosphate link for stabilisation. 3’ end is polyadenylated (tailing)

Question 4

What is splicing?

Answer 4

When the introns and exons are removed from the pre-mRNA

Question 5

Describe mRNA

Answer 5

RNA polymerase II, 100,000s of kinds, a few copies of each present

Question 6

Describe rRNA

Answer 6

RNA polymerase I, few kinds, many copies of each

Question 7

Describe tRNA

Answer 7

RNA polymerase III, ~100 kinds, very many copies of each

Question 8

What is the role of rRNA?

Answer 8

Used to bind to the mRNA and provides location for tRNA. Eukaryotes - 80S - 60S & 40S sub-units, prokaryotes - 70S - 50S & 30S sub-units

Question 9

What is a charged tRNA molecule referred to as?

Answer 9

Aminoacyl-tRNA

Question 10

What is the wobble position?

Answer 10

Aspecific region in a tRNA molecule

Question 11

What is the function of transcription factors?

Answer 11

GIves transcription a direction

Question 12

What happens in donor site is mutate?

Answer 12

Splicing site is inhibited which can cause diseases

Question 13

What post-translational processes occur to transform pre-mRNA into mature mRNA?

Answer 13

Capping, tailing and splicing

Question 14

What happens during initiation in translation?

Answer 14

At 5’ cap end - 40S subunit binds to Met-tRNA (AUG recognition). 60S subunit then binds allowing elongation to occur

Question 15

What happens during elongation in translation?

Answer 15

N - C chain growth. Met-tRNA occupies P site, another aminoacyl-tRNA occupies A site (requires GTP). Methionine forms a peptide bond with next aa causing tRNA in P site to become uncharged. Translocation. Enzyme - peptidyl transferase

Question 16

What happens during termination in translation?

Answer 16

Stop codon (UAA, UAG or UGA - no corresponding tRNAs). Hydrolysis occurs to release the proteins into the cytoplasm

Question 17

Describe the structure of a tRNA molecule

Answer 17

Clover model, single stranded, uncharged. Amino acids activate them

Question 18

What is the function of the P site?

Answer 18

Holds the peptide chain

Question 19

What is the function of the A site?

Answer 19

Site accepting the tRNA

Question 20

Describe a bacterial cell’s components in regards to transcription and translation

Answer 20

Simpler promoters, different transcription factors, single RNA polymerase, coupled transcription-translation, no post-transcriptional processing, short-live mRNAs, simpler ribosomes (attack only 30S), distinctive translation initiation mechanism, different translation factors.

Question 21

How can mutations outside the coding region affect gene expression?

Answer 21

Promoter region mutations can affect gene expression - either activate or deactivate it.