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Flashcards in Control Of Gene Expression Deck (245)
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1

Do all cells contain the same genes?

Yes but different genes are expressed in each cell type

2

What is a gene from the perspective of a molecular biologist

A sequence of genomic DNA that encoded a single functional RNA

3

Give the 4 key steps in protein synthesis from DNA

Which steps are regulatory

Transcription-> splicing -> editing and export-> protein synthesis and degradation

All of them

4

Is protein synthesis from DNA compartmentalised

Yes
Transcription is in the nucleus and translation is in the cytoplasm

5

What are Exon’s and introns

What are promoters

Exon: expressed DNA segments
Introns: intervening sequences

Promoter: sequences which ensure that the gene is transcribed at the appropriate time and in the correct cell type

6

In mRNA what are coding regions flanked by

Untranslated regions (UTRs) at both 5’ and 3’ ends

7

Which RNAs are most abundant

tRNA and rRNA

8

How often do prokaryotic cells divide

Every 20 mins

9

How is prokaryotic DNA adapted for speed and rapid response to altered environment

No nucleus
No introns
mRNA is translated while still being transcribed

10

What is antitermination

The prokaryotic cell’s aid to fix premature termination of RNA synthesis during RNA transcription and often occurs when RNA polymerase ignores the termination signal and continues until a second signal is reached

11

What is transcription
What is it catalysed by
In what direction does it occur

The synthesis of single stranded RNA from a double stranded DNA template
Catalysed by RNA polymerase
Occurs in 5’ to 3’ direction

12

For any region of dsDNA what is copied by RNA in prokaryotes

Only one strand (the coding strand)

13

Is transcription continuous?

No it occurs in discrete units

14

Compare the length of the completed RNA chains to the whole bacterial DNA

What does this suggest?

RNA: 100 - 10,000 nucleotides
DNA: 4.7x10^6 nucleotides

RBA is copies in discrete units in the continuous DNA molecule with well defined starting and stopping points

15

Which strand on dsDNA may act as the coding strand

Either can

16

In bacterial, how many RNA polymerases are required

Only one RNA polymerase synthesises all mRNA, rRNA, and tRNA

17

How long do rRNA and tRNA molecules in bacterial cells last

They are very stable and persist for many generations

18

Compare the stability of rRNA, tRNA, and mRNA

rRNA and tRNA persist for many cell divisions due to their high stability

mRNA is rapidly degraded and replaced
The average half-life of E. coli mRNA is 2 minutes

19

What is required for prokaryotic RNA synthesis

DNA template to copy
riboNTPs (eg ATP, GTP)
No primer needed

20

What riboNTPs are required for prokaryotic RNA synthesis

APT
GTP
CTP
UTP

21

How does the precursor NTP interact with a growing RNA chain

What is the NTP usually

The phosphate attached to the 5’-OH terminus of the precursor NTP forms an Ester bond with the 3’-OH at the end of the growing chain with concomitant release of phosphate

ATP or GTP

22

What is on the very 5’end of an RNA chain

A triphosphate

23

How does the newly created RNA strand relate to the 2 strands of DNA

It is complementary and anti parallel to the template strand

It has the same sequence (replacing U with T) as the coding strand

24

What is the error frequency in prokaryotic RNA production

1 error per 10^4 nucleotides

25

How does error frequency compare between RNA and DNA synthesis in prokaryotes

Much higher in RNA as RNA polymerase has no proof reading 3’-5’ exonuclease activity and there are no other correction mechanisms

26

What must happen to DNA before RNA can be synthesised

DNA melting

27

Discuss the structure of an RNA polymerase

Core is made of β subunit, β’ subunit, and 2 α subunits which are identical
β subunits are claw-like clamps

The holoenzyme also consists of a σ subunit as well

28

What is the difference between the core and holoenzyme in prokaryotic RNA Polymerase

Core binds DNA randomly

The σ in the holo is limiting, ensuring the specific binding to transcription start sites (it is a promoter)
This reduces non specific binding

29

Is RNA polymerase asymmetric

Yes
While there are 2 α subunits, the other subunits are all different

30

What is the first and principal stage in gene expression

Is this for eukaryotes or prokaryotic cells?

Transcription

Both