Week 6_Transcription in prokaryotes and eukaryotes

Question 1

prokaryotes have ___ type of RNA polymerase

Answer 1

1

Question 2

RNA polymerase enzyme has ___ distinct sections

Answer 2

2

Question 3

what are the 2 distinct sections of RNA polymerase?

Answer 3

sigma factor

core enzyme

Question 4

what is sigma factor?

Answer 4

the part of RNA polymerase that promotes transcriptional initiation

Question 5

what is the core enzyme?

what is it made up of?

Answer 5

the part of RNA polymerase that synthesizes the RNA

made up of 2 alpha and 2 beta subunits

Question 6

what is the holoenzyme?

Answer 6

core enzyme + sigma factor

Question 7

how does the sigma factor (SF) initiate transcription in prokaryotes?

Answer 7

(1) SF binds to the promoter regions of genes (DNA sequence recognition)

(2) SF separates the coding and template strands

(3) enables the core enzyme to begin transcription

Question 8

describe elongation and termination for prokaryote transcription

Answer 8

(1) once transcription begins, the SF dissociates from the core enzyme

(2) the core enzyme completes transcription without the SF

(3) the SF will then associate with another core enzyme and initiate transcription of another gene

Question 9

in prokaryotes, transcription and translation are ___, meaning they happen…

Answer 9

coupled

they happen at the same time and in the same place within the cell

Question 10

why are transcription and translation coupled in prokaryotes?

Answer 10

no nucleus to separate genes and ribosomes –> the mRNA is translated as soon as it’s made

Question 11

in prokaryotes, many mRNAs are ___

Answer 11

polycistronic

Question 12

what is a polycistronic mRNA?

Answer 12

contains the coding region of more than 1 gene

Question 13

where do polycistronic mRNAs come from?

Answer 13

gene clusters called operons

Question 14

what do operons contain?

Answer 14

sets of genes that work together in a biological function

(genes that need to be expressed at the same time)

Question 15

genes in an operon are transcribed ___ and share…

Answer 15

transcribed together

share a single promoter region and termination region

Question 16

what is an example of an operon in prokaryotes?

Answer 16

lac operon

Question 17

what is a lac operon?

Answer 17

cluster of 3 genes involved in the transport and metabolism of lactose (a carbohydrate used for energy)

Question 18

what is the result of RNA polymerase transcribing a polycistronic mRNA containing the lac operon?

Answer 18

translated into 3 different proteins

lacZ, lacY, lacA

Question 19

what does the lac operon polycistronic mRNA contain?

Answer 19

1 promoter region

3 coding regions (lacZ, lacY, lacA)

1 termination region

Question 21

is transcription/translation coupled in eukaryotes?

Answer 21

no

Question 22

where does transcription occur in eukaryotes?

Answer 22

nucleus

Question 23

where does translation occur in eukaryotes?

Answer 23

cytoplasm

Question 24

there are ___ RNA polymerases with different roles in eukaryotes

they are:

Answer 24

3

RNA Pol I
RNA Pol II
RNA Pol III

Question 25

what does RNA Pol I do?

Answer 25

transcribes ribosomal RNA genes (rRNAs)

Question 26

what does RNA Pol II do?

Answer 26

transcribes mRNA genes

Question 27

what does RNA Pol III do?

Answer 27

transcribes transfer RNA genes (tRNA) and rRNA genes

Question 28

do eukaryotic RNA polymerases have sigma factor?

Answer 28

no;

they have transcription factors instead

Question 29

how is transcription initiated in eukaryotes?

Answer 29

proteins called transcription factors attach to the promoter region and attract RNA polymerase

Question 30

in eukaryotes an mRNA is called a ___ until it is modified in ___ important ways

Answer 30

pre-mRNA

3

Question 31

what are the 3 important ways eukaryotic pre-mRNAs are modified to become mRNAs?

Answer 31

(1) 7-methy-guanosine is added to the 5’ end of the mRNA (5’-cap)
- protects the mRNA from degradation on the 5’ end

(2) addition of a poly-A-tail (~200 adenines added to the 3’ end of the mRNA) (added by the enzyme poly-A polymerase).
- protects the mRNA from degradation on the 3’ end

(3) mRNA is spliced

Question 32

the ___ of a eukaryotic protein coding gene contains…

Answer 32

coding region

contains both coding and non-coding sequences

Question 33

what are exons?

Answer 33

DNA sequences that code for part of the protein

Question 34

what are introns?

Answer 34

“intervening” DNA sequences that do not code for part of the protein

Question 35

___ and ___ are both included in the pre-mRNA

Answer 35

introns and exons

Question 36

what is splicing?

Answer 36

introns are cut out of the mRNA and exons are spliced together

Question 37

what are the requirements for a mature mRNA?

Answer 37

(1) 5’ cap

(2) 3’ PolyA tail

(3) has been spliced

Question 38

all 3 mRNA modifications occur in the ___

Answer 38

nucleus

Question 39

splicing is done by an enzyme called the ___

Answer 39

spliceosome