transcription and translation

Question 1

basic principle of transcription

Answer 1

1) Numerous transcription activators bind to the TATA box in the promotor (upstream of the gene)
2) RNA polymerase binds to the template strand and synthesises an exact copy of the coding strand (except the thymines are replaced by uracil)
3) RNA is released, further processed and released from the nucleus

Question 2

when will RNA polymerase attach

Answer 2

when there are transcription factors attached to a promotor region e.g. TATA box

Question 3

thymines in MRNA are replaced by

Answer 3

uracil

Question 4

translation occurs

Answer 4

in the cytoplasm in ribozymes

Question 5

translation process 3 steps

Answer 5

initiation, elongation and termination

Question 6

initiation

Answer 6

o In eukaryotes, translation usually initiates at the first (most 5’ AUG codon)
o When the small subunit of the ribosome is in place, it has begun delineating where the two sites of translation will be.
o AUG codon is bound to the initiator tRNA- therefore the first (amino-terminal) amino acid in the polypeptide will always be methionine.
o This allows the large subunit to bind and the ribosome to assemble
o P site is filled with the initiator tRNA but the A-site is empty

Question 7

elongation

Answer 7

o The tRNA with an anticodon that corresponds to the codon in the A-site binds
o The amino acid on the tRNA in the A–site is transferred onto the amino acid on the tRNA in the P site
o the now empty tRNA moves to the exit site and is released
o the ribosome slides down the mRNA so that the tRNA with the growing peptide is in the P-site- leaving the A-site is free to bind to another aminoacyl-tRNA
o The growing peptide chain is transferred to the aminoacyl tRNA converting it to a peptidyl tRNA

Question 8

termination

Answer 8

o At the end of the coding region of the mRNA there is a special stop codon. There are no tRNAs with anticodons that bind to stop codons- stop codons are bound by termination factors.
o The release factors cause the cleavage of the complete protein chain from the tRNA in the P-site- protein then leave the ribosome.
o Translation ends with the mRNA and ribosomal subunits disassembling and the release of the newly synthesised protein

Question 9

transcription and translation in eukaryotes

Answer 9

occurs in the nucleus and cytoplasm and independently- one mRNA for one gene

Question 10

transcription and translation in prokaryotes

Answer 10

in prokaryotes transcription and translation occur in the same compartment and occur at the same time. Plus many genes are on one mRNA–> operon.