Transcription

Question 1

What is transcription?

Answer 1

The process of expressing DNA where DNA is transcribed into RNA

Question 2

Why is RNA being unstable so important?

Answer 2

Prevents expression of genes that are no longer needed since RNA can exist for short amount of time

Question 3

What happens during the initiation stage in transcription?

Answer 3

DNA is unwound by initiator proteins

Question 4

What happens during the initiation stage in transcription? (3)

Answer 4

• DNA unwinds
• RNAP binds to promoter
• Other transcription factors bind

Question 5

How many sides of DNA is transcribed and what are they called

Answer 5

• 1 strand

- Antisense strand or template strand (3’ - 5’)

Question 6

What is the DNA strand that is not transcribed called?

Answer 6

-Sense strand or coding strand (5’ - 3’)

Question 7

What happens during the elongation stage? (2)

Answer 7

• RNA polymerase matches the complementary ribonucleotides (NTPs)
• RNA is elongated

Question 8

Whats the difference between elongation in transcription and DNA replication? (2)

Answer 8

• dNTPs are used for DNA rep, and NTPs are used for transcription
• U/A instead of T/A

Question 9

What are the types of NTPs? (4)

Answer 9

1) ATP
2) UTP
3) CTP
4) GTP

Question 10

When happens during termination?

Answer 10

RNAP falls off at termination sequence

Question 11

What are the types of RNA that can be transcribed and what are their purposes? (3)

Answer 11

1) tRNA - carry amino acids to the ribosome
2) mRNA - encode proteins for translation
3) rRNA - make up the ribosomes used to translate proteins

Question 12

What are the coding regions in genes for eukaryotes? (2)

Answer 12

1) Extrons - coding regions

2) Introns - non-coding regions

Question 13

Why are mRNAs processed differently after transcription in eukaryotes and bacteria?

Answer 13

mRNA in eukaryotes needs to be stable for longer since it is transported out of the nucleus

Question 14

What is the post-transcriptional modifications to the 5’ end to make the RNA last longer? Why?

Answer 14

• An enzyme adds a 5’ cap (called 7-methylguanosine molecule)
• Delays ribonuclease from degrading the RNA

Question 15

What are the post-transcriptional modifications to the 3’ end to make the RNA last longer?

Answer 15

• Polyadenylation: a poly(A) tail is added to the 3’ end

- The tail binds a protein called the poly(A)-binding protein

Question 16

What is the purpose of the poly-A-tail? (2)

Answer 16

• To protect the RNA 3’ end from ribonuclease

- To mark it for transport out of the nucleus

Question 17

How are introns removed?

Answer 17

Splicing

Question 18

What is mRNA splicing?

Answer 18

introns being cut out

Question 19

What performs splicing?

Answer 19

A complex called spliceosome

Question 20

What is alternative splicing? What is its purpose?

Answer 20

• When exons are spliced together in a different order

- Allows a variety of proteins to be made from a single gene

Question 21

What is a mRNA that can encodes one or more proteins?

Answer 21

Poly-cistronic mRNA

Question 22

What is the difference between mRNA processing in eukaryotic and prokaryotic cells? (2)

Answer 22

• Prokaryotes: can encode multiple proteins on a single transcript
• Prokaryotes: Translation and transcription can occur at the same time

Question 23

What are trypotophan operon (Trp) and how do they work?

Answer 23

trp binds to repressor, which binds to operator at high conc, which blocks RNAP

Question 24

What are lac operators and how do they work?

Answer 24

repressor detaches from lac operator when lactose is present

Question 25

What is reverse transcription?

Answer 25

The process of making DNA from RNA

Question 26

Which species has reverse transcription?

Answer 26

in a class of viruses called retroviruses (HIV, Herpes, etc.)

Question 27

What is the enzyme that performs reverse transcription?

Answer 27

Reverse transcriptase