Transcription

Question 1

What is transcription?

Answer 1

The process by which RNA is synthesized from a DNA template.

Question 2

Which enzyme catalyzes transcription?

Answer 2

RNA polymerase.

Question 3

What are the three main types of RNA produced by transcription?

Answer 3

mRNA, tRNA, and rRNA.

Question 4

In which direction is RNA synthesized?

Answer 4

5′ to 3′ direction.

Question 5

Is a primer needed for transcription?

Answer 5

No, RNA polymerase can initiate RNA synthesis de novo.

Question 6

Does RNA polymerase have proofreading activity?

Answer 6

No 3′→5′ exonuclease activity; thus, higher error rate than DNA replication.

Question 7

What is the template strand?

Answer 7

The DNA strand used by RNA polymerase to synthesize RNA.

Question 8

What is the coding strand?

Answer 8

The DNA strand with the same sequence as the RNA transcript, except T is replaced with U.

Question 9

What are promoter sequences?

Answer 9

DNA sequences that direct RNA polymerase where to begin transcription.

Question 10

What are the key promoter elements in prokaryotes?

Answer 10

The –35 (TTGACA) and –10 (TATAAT) boxes.

Question 11

What is the function of σ factor in prokaryotes?

Answer 11

To recognize and bind promoter sequences for RNA polymerase initiation.

Question 12

What constitutes the RNA polymerase holoenzyme in prokaryotes?

Answer 12

The core enzyme (α2ββ′ω) plus σ factor.

Question 13

What happens to the σ factor after initiation?

Answer 13

It is released once transcription elongation begins.

Question 14

What is a transcription bubble?

Answer 14

The region of unwound DNA where transcription occurs.

Question 15

What is the average speed of RNA polymerase in elongation?

Answer 15

50–90 nucleotides per second.

Question 16

Which enzymes relieve supercoiling during transcription?

Answer 16

Topoisomerases.

Question 17

What is Rho-independent termination?

Answer 17

Termination via a GC-rich stem-loop followed by a poly-U tract that destabilizes the RNA-DNA hybrid.

Question 18

What is Rho-dependent termination?

Answer 18

Involves Rho factor binding to the Rut site and disrupting the transcription complex using ATP.

Question 19

What is an operon?

Answer 19

A group of genes transcribed together under a single promoter.

Question 20

What is a polycistronic mRNA?

Answer 20

An mRNA molecule that encodes multiple proteins.

Question 21

What is the lac operon?

Answer 21

A bacterial operon induced in the presence of lactose.

Question 22

What is the trp operon?

Answer 22

A repressible operon inhibited by excess tryptophan.

Question 23

Where does transcription occur in prokaryotes?

Answer 23

In the cytoplasm.

Question 24

Is transcription coupled with translation in prokaryotes?

Answer 24

Yes, it occurs simultaneously.

Question 25

What are the three RNA polymerases in eukaryotes?

Answer 25

RNA Pol I (rRNA), RNA Pol II (mRNA), RNA Pol III (tRNA and 5S rRNA).

Question 26

Which polymerase transcribes mRNA in eukaryotes?

Answer 26

RNA polymerase II.

Question 27

What is the TATA box?

Answer 27

A conserved DNA sequence in eukaryotic promoters involved in transcription initiation.

Question 28

What are general transcription factors (GTFs)?

Answer 28

Proteins required for RNA polymerase II to initiate transcription.

Question 29

What is the role of TFIID?

Answer 29

It binds to the TATA box and recruits other GTFs to form the pre-initiation complex.

Question 30

What is the role of TFIIH?

Answer 30

Unwinds DNA and phosphorylates RNA Pol II to initiate elongation.

Question 31

What is the 5′ cap in eukaryotic mRNA?

Answer 31

A 7-methylguanosine cap added for stability and ribosome recognition.

Question 32

What is polyadenylation?

Answer 32

Addition of a poly-A tail (~250 nucleotides) to the 3′ end of eukaryotic mRNA.

Question 33

What is RNA splicing?

Answer 33

Removal of introns and joining of exons in pre-mRNA.

Question 34

What catalyzes splicing?

Answer 34

The spliceosome, composed of snRNPs.

Question 35

What is an intron?

Answer 35

A non-coding sequence removed during RNA splicing.

Question 36

What is an exon?

Answer 36

A coding sequence retained in mature mRNA.

Question 37

What is a spliceosome?

Answer 37

A large ribonucleoprotein complex that catalyzes intron removal.

Question 38

What are snRNPs?

Answer 38

Small nuclear ribonucleoproteins involved in splicing.

Question 39

What are enhancers?

Answer 39

DNA elements that increase transcription levels, often located far from the promoter.

Question 40

What are silencers?

Answer 40

DNA elements that repress transcription.

Question 41

What are transcription factors?

Answer 41

Proteins that bind DNA to regulate transcription.

Question 42

What is chromatin remodeling?

Answer 42

Structural modification of chromatin to allow transcription factor access.

Question 43

What is the function of histone acetylation?

Answer 43

Loosens chromatin structure, promoting transcription.

Question 44

What is the function of DNA methylation?

Answer 44

Usually represses transcription.

Question 45

What distinguishes eukaryotic from prokaryotic transcription?

Answer 45

Eukaryotes have more complex machinery, compartmentalization, and RNA processing.

Question 46

What is monocistronic mRNA?

Answer 46

An mRNA that encodes a single protein (typical in eukaryotes).

Question 47

What is the nuclear envelope's role in transcription?

Answer 47

Separates transcription (nucleus) from translation (cytoplasm) in eukaryotes.

Question 48

What modification marks the completion of transcription in eukaryotes?

Answer 48

Addition of a poly-A tail after cleavage at the polyadenylation site.

Question 49

What are cis-acting elements?

Answer 49

DNA sequences that regulate nearby genes (e.g., promoters, enhancers).

Question 50

What are trans-acting factors?

Answer 50

Proteins or RNAs that regulate gene expression from different locations (e.g., transcription factors).

Question 51

What is the CTD of RNA polymerase II?

Answer 51

The C-terminal domain involved in mRNA processing and polymerase regulation.

Question 52

What process begins once the CTD of Pol II is phosphorylated?

Answer 52

Elongation and RNA processing.

Question 53

What causes Rho to terminate transcription?

Answer 53

It catches up to paused RNA polymerase and disrupts the complex.

Question 54

What is a Rut site?

Answer 54

An RNA sequence recognized by Rho for termination.

Question 55

How are prokaryotic mRNAs typically processed?

Answer 55

Minimal processing; often translated while being transcribed.

Question 56

What role do topoisomerases play in transcription?

Answer 56

They prevent supercoiling during elongation.

Question 57

Why is the –10 box important?

Answer 57

It helps unwind DNA for transcription initiation.

Question 58

What determines which σ factor is used?

Answer 58

Environmental conditions or stress responses.

Question 59

Which σ factor is used for heat shock genes?

Answer 59

σ³².

Question 60

How does the lac repressor regulate the lac operon?

Answer 60

It blocks RNA polymerase from accessing the promoter unless lactose is present.

Question 61

How does cAMP-CRP complex affect the lac operon?

Answer 61

It activates transcription when glucose is low.

Question 62

What is attenuation in transcription?

Answer 62

Premature termination of transcription as a regulatory mechanism.

Question 63

Why is the coupling of transcription and translation efficient in prokaryotes?

Answer 63

Because both processes occur in the cytoplasm without a nuclear membrane.

Question 64

What type of RNA is synthesized by RNA Pol I?

Answer 64

rRNA (28S, 18S, 5.8S).

Question 65

What type of RNA is synthesized by RNA Pol III?

Answer 65

tRNA and 5S rRNA.

Question 66

What signals the end of a eukaryotic transcription unit?

Answer 66

The polyadenylation signal (AAUAAA).

Question 67

What is a pre-initiation complex?

Answer 67

The assembly of GTFs and RNA polymerase at the promoter before transcription begins.