Gene Expression - Transcription in Pro- and Eukaryotes

Question 1

Rho-independent termination:

Answer 1

a terminating hairpin forms on the nascent mRNA interacting with the NusA protein to stimulate release of the transcript from the RNA polymerase complex

Question 2

Rho-dependant termination:

Answer 2

the Rho protein(RNA helicase) binds at the upstream rut site, translocates down the mRNA, and interacts with the RNA polymerase complex to stimulate release of the transcript

Question 3

Differences between pro- and eukaryotic gene expression: transcription and translation occurrence

Answer 3

prokaryotes: at the same time in the cytoplasm
eukaryotes: transcription in the nucleus then translation in the cytoplasm

Question 3

In prokaryotes is the coding sequences of genes continuous and what does this mean?

Answer 3

yes, meaning transcript is co-linear with gene

Question 4

Differences between pro- and eukaryotic gene expression: gene structure

Answer 4

prokaryotes: DNA sequence is read in the same order as the amino acid sequence
eukaryotes: noncoding introns within coding sequence

Question 5

Differences between pro- and eukaryotic gene expression: modification of mRNA after initial transcription but before translation

Answer 5

prokaryotes: none
eukaryotes: introns spliced out; 5’ cap and 3’ poly A added

Question 6

What 3 nuclear, RNA polymerases do eukaryotes principally have?

Answer 6

RNA polymerase I, II and III

Question 7

Core promoter:

Answer 7

recognized by general transcription factors that recruit RNA polymerase

Question 8

Promoter proximal and distal elements:

Answer 8

regulatory sequences and binding sites for transcriptional activators and repressors

Question 9

What are chromatin remodelling complexes recruited near gene promoters by?

Answer 9

transcription factors

Question 10

What does remodelling of chromatin increase?

Answer 10

accessibility for transcription

Question 11

What does adding a 5’ cap to the 5’ end do?

Answer 11

facilitates binding to a ribosome and protects mRNA from being digested by ribonucleases

Question 12

What happens when a poly A tail is added to the 3’ end?

Answer 12

sequence AAUAAA after the last codon signals an enzyme to cut the pre-mRNA; then another enzyme adds 100 to 300 adenines(the tail). the tail assists in export from the nucleus and is important for stability of the mRNA

Question 13

In eukaryotes, the coding sequences are interrupted by what?

Answer 13

non-coding sequences(introns) that are spliced out of the mature mRNA transcript

Question 14

The precursor mRNA transcript(pre-mRNA):

Answer 14

introns are removed by RNA splicing, leaving the protein coding sequences in the mature mRNA

Question 15

RNA splicing step 1:

Answer 15

small nuclear ribonucleoprotein particles bind to consensus sequences in RNA near the 5’ donor and 3’ acceptor splice sites

Question 16

RNA splicing step 2:

Answer 16

binding of snRNPs recruits other proteins

Question 17

RNA splicing step 3:

Answer 17

a cut is made between the 5’ exon and the intron

Question 18

RNA splicing step 4:

Answer 18

after the first cut at the 5’ end , the intron forms a closed loop

Question 19

RNA splicing step 5:

Answer 19

the free 3’ OH group at the end of the cut exon reacts with the 5’ phosphate of the other exon

Question 20

RNA splicing step 6:

Answer 20

the 3’ exon is cleaved and spliced to the 5’ exon and the mature mRNA is exported to the cytoplasm for translation

Question 21

RNA splicing step 7:

Answer 21

the excised intron is degraded in the nucleus

Question 22

can alternative splicing give more than one product for a single gene?

Answer 22

yes

Question 23

Can alternative splicing be regulated to give differential gene expression?

Answer 23

yes

Question 24

In prokaryotes, RNA transcripts are translated as they are also being what?

Answer 24

synthesised

Question 25

What must RNA transcripts be before being translated?

Answer 25

processed and transported to the cytoplasm