Lecture 28 - Transcription and RNA Processing

Question 1

what are 3 major cellular RNA functions?

Answer 1

1. messenger RNAs (mRNA)
2. transfer RNAs (tRNA)
3. ribosomal RNAs (rRNA)

Question 2

where are all RNAs transcribed from?

Answer 2

DNA templates by RNA polymerases (RNAP)

Question 3

where are RNAs synthesized in eukaryotes?

Answer 3

cell nucleus

Question 4

where are RNAs synthesized in prokaryotes?

Answer 4

cytosol

Question 5

what are the 3 stages of transcription?

Answer 5

1. initiation
2. termination
3. termination

Question 6

what is a barrier to transcription?

Answer 6

the packaging of eukaryotic DNA into chromatin

Question 7

where is transcription regulated?

Answer 7

in all cells

Question 8

what do sigma factors do?

Answer 8

direct bacterial RNA polymerase to promoters

Question 9

where do sigma factors bind?

Answer 9

to specific sequences that define bacterial promoters

Question 10

can sigma factor activity be regulated?

Answer 10

yes, in many ways

Question 11

what is the sigma unit of the RNA polymerase?

Answer 11

the specificity filter

Question 12

how does the sigma subunit work?

Answer 12

different sigma associate with the other subunits in the polymerase to search for the preferred promoter sequence

Question 13

in promoter binding what happens once the promoter region has been recognized?

Answer 13

sigma unbinds + core polymerase stays bound + processive

Question 14

what does eukaryotic RNA polymerases require?

Answer 14

general transcription factors for promoter recognition

Question 15

what are eukaryotic promoters often defined by?

Answer 15

TATA box + other core promoter elements

Question 16

how does transcription proceed?

Answer 16

highly processive manner

Question 17

what are elongation factors?

Answer 17

• they suppress the pausing of transcription

- rescue stalled polymerase enzymes

Question 18

what must happen to nucleosomes during elongation?

Answer 18

nucleosomes must be removed from the path of elongating polymerase for transcription to proceed

Question 19

what are 2 types of termination in prokaryotic transcription?

Answer 19

1. Rho-independent

2. Rho-dependent

Question 20

what happens in Rho-independent termination?

Answer 20

• G:C pairs form stable stem-loop structure

- terminator causes transcript to unbind from the bubble

Question 21

rho works like a _____

Answer 21

helicase

Question 22

how are prokaryotic genes organized?

Answer 22

into operons

Question 23

in bacteria cells, several ____ are often expressed ____

Answer 23

protein-coding genes

together

Question 24

what are operons?

Answer 24

protein-coding genes that are often expressed together

Question 25

what type of proteins do genes in the operon encode?

Answer 25

proteins that have related functions

Question 26

what is the expression of the operon regulated by?

Answer 26

repressor proteins

Question 27

where do repressor proteins bind?

Answer 27

to the operator region in the operon

Question 28

what is the difference between protein-coding genes in eukaryotes and prokaryotes?

Answer 28

-protein-coding genes in eukaryotes are always expressed individually

Question 29

what are transcribed mRNAs called?

Answer 29

pre-mRNAs because they undergo further processing before leaving the cell nucleus

Question 30

what are the 2 parts of transcribed mRNAs?

Answer 30

• 3’ poly (A) tail

- 5’ capping

Question 31

what does splicing do?

Answer 31

remove introns