Bio Lecture 16 Transcription

Question 1

What are the 4 types of RNA?

Answer 1

tRNA: transfers amino acids to ribosomes for protein synthesis
snRNA: involved in RNA processing and splicing
mRNA: is code used to make proteins
rRNA: makes up part of ribosomes, helps catalyze amino acids bonding together to make the protein

Question 2

What are the template strand and not template strand and how do they relate to the RNA strand being produced?

Answer 2

The template strand is used to make the RNA, so it will be an exact match to the non-template strand which is also called the coding strand.

Question 3

Where is the +1 position for transcription?

Answer 3

It is after the promoter and before the untranslated region which is before the part that is actually translated into the protein.

Question 4

What are the characteristics of a prokaryote RNA polymerase?

Answer 4

Has 6 subunits: 2 alpha, 1 beta, 1 beta’, 1 omega, and 1 sigma.
The sigma subunit enables binding to the DNA, but must release before the other subunits can carry out transcription.

Question 5

In prokaryotes, what are the two parts of the promoter that direct RNA polymerase where to bind and start?

Answer 5

-10 and -35 elements are in the promoter sequence upstream from the start of transcription. They are 6 nucleotides each. These are consensus sequences and are fairly conserved across various genes so RNA polymerase always know where to bind. -10 sequence is called the pribnow box and is A-T rich.

Question 6

Summarize the steps of prokaryote transcription.

Answer 6

1. RNA polymerase binds to DNA with help of sigma subunit
2. DNA is melted open without help of helicase
3. Sigma subunit dissociates
4. Elongation begins, DNA is only separated around the polymerase and is reattached behind it
5. Termination sequence signals stop of transcription

Question 7

What are the two ways that prokaryote transcription can be terminated?

Answer 7

1. Rho-Independent: palindrome sequence causes a hair pin loop in the RNA which disrupts the polymerase and disconnects it.
2. Rho-Dependent: rho protein is ATP dependent, it binds to the RNA and travels along it, when RNApol pauses at the termination site, rho will knock it off.

Question 8

How does rifampicin work?

Answer 8

It is used to treat tuberculosis.

Works by inhibiting initiation of transcription by binding to the beta subunit of RNApol.

Question 9

What are types of RNA polymerases in eukaryotes?

Answer 9

RNApol I: transcribes three major rRNAs
RNApol II: transcripbes mRNA
RNApol III: transcribes tRNA and small rRNA

Question 10

What are GTFs?

Answer 10

General Transcription Factors used to initiate transcription.
There are several in eukaryotes, but none in prokaryotes.
When associated with an RNApol, they are named TFII for example for transcription factor RNApol II.

Question 11

What are the general functions of TFIIs?

Answer 11

• required by RNApol II
• identify core promoter
• recruit polymerase
• orient polymerase in right direction
• regulate timing of transcription

Question 12

What are the characteristics of TFIID?

Answer 12

Contains a TATA binding protein (TBP) which is like the sigma subunit in prokaryotes. It allows the protein to find and bind the TATA Box sequence in the promoter.

Question 13

What does TFIIA do?

Answer 13

Assists TFIID in binding.

Question 14

What does TFIIB do?

Answer 14

Orients Polymerase.

Question 15

How does RNA polII interact with the GTFs during initiation?

Answer 15

It is bound to the GTFs at the promoter. Carboxy-terminal domain of RNApolII is held in place by the GTFs. All together this is called the pre-initiation complex.

Question 16

What are the functions of TFIIH?

Answer 16

• Helicase activity to unwind the DNA at the initiation site
• Kinase activity to phosphorylate the C-terminal domain of RNApolII. Once phosphorylated, the RNApolII breaks free of TFs and begins transcription on its own.

Question 17

What are post-transcriptional modifications and when do they happen and in what order?

Answer 17

As the new RNA comes off the polymerase, first a cap is added to the 5’ end.
As introns are encountered, they are removed.
As soon as transcription terminates, a poly A tail is added to the 3’ end.

Question 18

What is the 5’ cap?

Answer 18

It is 7-methylguanosine which is a guanosine base that has been methylated at carbon 7 in the base ring. This process protects the new RNA from degradation and helps locate it in the ribosome for translation.

Question 19

What is the poly-A tail?

Answer 19

The primary transcript is cleaved 10-35 nucleotides down from a given sequence. Poly A polymerase then adds ~200 A nucleotides.
This stabilizes the mRNA, is a signal for export out of the nucleus, helps re-initiate translation.

Question 20

What are spliceosomes?

Answer 20

They are made of snRNA and proteins. It is the complex that splices out introns during the post processing of RNA.

Question 21

What is alternate splicing?

Answer 21

Different combinations of introns and exons from the same gene can produce different proteins.

Question 22

In which direction does RNApol always transcribe?

Answer 22

5’ to 3’ because there has to be the phosphate group on the 5’ end in order to attach the nucleotide to the 3’ OH group.

Question 23

How is transcription different from replication?

Answer 23

Uses ribonucleotides and Uracil
Only occurs in specific areas of the genome and only copies a small portion at a time
RNA product is not connected to template
RNApol doesn’t need a primer
Only one DNA strand is used for a template
Many copies are made

Question 24

What is the TATA box?

Answer 24

The binding site for the transcription complex for eukaryotes. It is located at -10.