MBG Chapter 11

Question 1

What is the central dogma of Molecular Biology?

Answer 1

DNA being replicated –> Transcription—> RNA transcript –> Translation—> Polypeptide (amino acids)

Question 2

Where does transcription and translation take place in an eukaryotic cell?

Answer 2

Transcription takes place in the nucleus

Translation happens in the cytoplasm

Question 3

Where does transcription and translation take place in a prokaryotic cell?

Answer 3

It happens inside the cell

Question 4

Do prokaryotes have introns and exons?

Answer 4

Just exons because they are very tightly packaged with genes

Question 5

What is an intron?

Answer 5

Non coding

Question 6

What is an exon?

Answer 6

Coding

Question 7

Does pre mRNA or mRNA contain introns and exons?

Answer 7

Just pre mRNA contains exons.

Question 8

Where does the G-cap and poly A tail are added?

Answer 8

After transport of the mRNA to the cytoplasm but before translation

Question 9

What is the first amino acid that is translated in eukaryotes and prokaryotes?

Answer 9

Eukaryotes- MET

Prokaryotes - fMET

Question 10

Give 3 general features of RNA synthesis

Answer 10

Ribonucleotides rather than deoxyribonucleotides
Only 1 strands is used as template
No primer required
Catalyzed by RNA polymerases in the 5’ to 3’ direction

Question 11

Steps in transcription in prokaryotes

Answer 11

1) RNA polymerase binds, unwinds and joins first 2 nucleotides
2) Complementary nucleotides continue to be added
3) Transcription stops

Question 12

What is a tetrameric core and Holoenzyme?

Answer 12

Tetrameric core: α2 β β’
- transcribes any DNA
Holoenzyme: α2 β β’ σ
- transcribes specific genes

Question 13

What are function of α2 subunits of RNA polymerase such as tetrameric core and holoenzyme?

Answer 13

α- assembly of the tetrameric core

Question 14

What are function of β subunits of RNA polymerase such as tetrameric core and holoenzyme?

Answer 14

β - ribonucleoside triphosphate binding site

Question 15

What are function of β’ subunits of RNA polymerase such as tetrameric core and holoenzyme?

Answer 15

β’ - DNA template binding region

Question 16

What are function of σ subunits of RNA polymerase such as tetrameric core and holoenzyme?

Answer 16

σ - initiation of transcription specifically at a promoter

-helps RNA polymerase find the start of a particular gene

Question 17

What sites are the initiation of transcription?

Answer 17

35 Sequence 5’TTGACA 3’

10 sequence 5’TATAAT 3’

Question 18

How are the 35 and 10 sites read?

Answer 18

Identification of the 35 and 10 sequences are read on the non template strand ( 5’ to 3’) but transcribes the 3’ to 5’ (template strand)

Question 19

How is transcription and translation in prokaryotes?

Answer 19

Translation and transcription is tightly coupled in prokaryotes!
DNA can be transcribed and translated in one single continuous line!

Question 20

What are Balbiani rings in eukaryotes?

Answer 20

Puffs in eukaryotic chromosomes that are sites of localized unwinding due to gene transcription

Question 21

RNA polymerase I

Answer 21

Location - Nucleolus

Ribosomal RNA’s, excluding 5S rRNA

Question 22

RNA polymerase II

Answer 22

In Nucleus

Nuclear pre-mRNA’s

Question 23

RNA polymerase III

Answer 23

In Nucleus

tRNAs, 5S RNA and other small nuclear RNA’s

Question 24

RNA polymerase IV

Answer 24

in Plant nucleus

Small interfering RNAs (siRNAs)

Question 25

RNA polymerase V

Answer 25

In Plant nucleus

Some siRNAs plus non coding (antisense) transcripts of siRNA target genes

Question 26

How many RNA polymerases do Eukaryotes have?

Answer 26

3

RNA polymerase I, II, III

Question 27

What are the eukaryotic promoters?

Answer 27

5 different boxes including the TATA box at the end and a +1 position

Question 28

What place does transcription occur in eukaryotes?

Answer 28

The TATA box positions transcription start point and also the +1

Question 29

What are spliceosomes?

Answer 29

RNA/ protein structure

5 snRNA associate with proteins to form protein (snRNP) complexes that splice out introns

Question 30

Explain transcription and RNA processing in Eukaryotes?

Answer 30

Transcription factors (TFII D, A, B, F) form a pre-initiation complex

1) TFIID binds to the TATA box
2) TFIIA joins the initiation complex
3) TFIIB binds to the initiation complex
4) TFIIF has unwinding activity joins the complex and polymerase II also binds here
5) TFIIE binds to the initiation complex

Question 31

What are Facilitated Chromatin Transcription (FACT) proteins?

Answer 31

Modifies histones to allow polymerase II to transcribe by removing part of the nucleosome structure

Question 32

How many steps does RNA processing have?

Answer 32

3 steps

Question 33

What is RNA processing?

Answer 33

Adding of the G-cap, polyA tail and removing introns

Question 34

What are the 3 major steps of RNA processing?

Answer 34

G-Cap, PolyA tail after AAUAAA sequence and removal of introns

Question 35

What is the benefit of introns?

Answer 35

Presence of introns allows for alternate splicing to occur which generates diversity in gene expression

Question 36

How are introns spliced out?

Answer 36

1) snRNP is assembled
2) 5’ splice site cleaved
3) 3’ site cleaved
4) Exons joined and introns are removed

Question 37

How many snRNAs are there?

Answer 37

5

U1, U2, U4, U5 AND U6

Question 38

What ways can introns be removed from the pre m-RNA?

Answer 38

2 ways
Splicesomes
Ribozyme

Question 39

What is a ribozyme?

Answer 39

Introns can be ribozymees (an RNA enzyme)

Question 40

How does a ribozyme work?

Answer 40

Reaction requires a Guanine 3’ OH group

• Involves sequential phosphodiester bond transfers
• 3’ OH attacks