MOLECULAR BIOLOGY OF THE GENE

Question 1

what processes occur in the nucleus?

Answer 1

transcriptional control

processing control

Question 2

what processes can gene expression be regulated?

Answer 2

transport control, translational control, mRNA degradation control, protein degradation control

Question 3

what is transcriptional control?

Answer 3

t

Question 4

what are interim regions?

Answer 4

i

Question 5

what is ‘junk’ DNA needed for?

Answer 5

needed for organism plasticity, control of gene expression

Question 6

describe the gene structure

Answer 6

Promoter
Transcriptional ‘start’ and ‘stop’ signal
Exons and introns
Upstream regulatory regions

Question 7

what does the promoter do?

Answer 7

stitches a gene on

Question 8

why aren’t genes all expressed infall cells at the same time?

Answer 8

some genes may be expressed in response to an external stimulus, others during a particular point in the cell cycle, development etc. (timing is important)

Question 9

How does a cell keep control over which genes are expressed or not?

Answer 9

the promoter

Question 10

what are transcriptional activators?

Answer 10

t

Question 11

what is gene expression driven by?

Answer 11

RNA polymerase II

Question 12

why are transcription factors needed?

Answer 12

In order for a gene to be expressed (switched on) a number of DNA-binding proteins TF bind in and around promoter region

Question 13

how is gene expression fine-tuned?

Answer 13

via the binding of other DNA-binding proteins to distal regions termed upstream enhancer sequences

Question 14

what is open chromatin?

Answer 14

o

Question 15

what do activators do?

Answer 15

Activators bind

to enhancer sequence and increase expression significantly than without them (basal/low expression)

Question 16

what does transcription create?

Answer 16

mRNAs, tRNAs and rRNA

Question 17

what produces mRNAs, tRNAs and rRNA?

Answer 17

enzyme RNA polymerase

Question 18

what is RNA polymerase I?

Answer 18

responsible for the production of the large ribosomal RNA

Question 19

what is RNA polymerase II?

Answer 19

responsible for the production of mRNA

Question 20

what is RNA polymerase III?

Answer 20

responsible for the production of tRNA and the small ribosomal RNA molecules

Question 21

how does RNA polymerase bind to promoter?

Answer 21

RNA p molecules collide randomly with the DNA in the nucleus and bind with specific DNA sequences called promoters, the TATA sequence/box

Question 22

what does RNA polymerase open?

Answer 22

opens up a short length of the DNA double helix exposing a specific section of DNA on each strand.

Question 23

what are the 2 types of transcriptional repressors?

Answer 23

Interacts with activator - binding site next to activator - blocks function
Overlapping binding sites (activator, repressor) - stops activator from binding

Question 24

what is the 5’ end of the mRNA molecule capped by?

Answer 24

addition of methylated G nucleotide

3’ end is cleaved at a specific site and a poly – A tail added

Question 25

how is methylated G nucleotide added to 5' end?

Answer 25

by removal of a phosphate by a phosphatase | addition of a GMP via a guananyl transferase addition of a mythyl group via a methyl transferease

Question 26

what are introns?

Answer 26

non coding regions

Question 27

what are exons?

Answer 27

coding regions

Question 28

how are introns removed?

Answer 28

by RNA splicing

Question 29

what is RNA splicing ?

Answer 29

s

Question 30

what is alternative splicing?

Answer 30

a

Question 31

what is the 1st AA in a polypeptide?

Answer 31

AUG (methionine) -start codon

Question 32

what is translational control?

Answer 32

t

Question 33

how does translational control occur?

Answer 33

mRNA associates with ribosomes which translate the RNA sequence into a polypeptide chain (protein) Many ribosomes attach to each mRNA (multiple bubbles)

Question 34

what is the purpose of the half-life of mRNA?

Answer 34

another way in which the cell can regulate gene expression levels

Question 35

how does translational initiation occur?

Answer 35

an initiator tRNA carrying a methionine associates with a small ribosomal unit in association with eukaryotic initiation factor 2 ( eIF2).

Question 36

what occurs after tRNA binds to eIF2?

Answer 36

The small ribosomal unit recognises the a 5’ end of a mRNA capped with two additional initiation factors eIF4G and eIF4E, and scans along the mRNA for a start codon (AUG), which then allows the large subunit bind.

Question 37

what is stage 1 of translational elongation?

Answer 37

An aminoacyl – tRNA binds to the A site and the tRNA molecule at the E site is released

Question 38

what is stage 2 of translational elongation?

Answer 38

Carboxyl end of the polypeptide chain is uncoupled from the tRNA in the P site and joined by a peptide bond to the AA attached to the new tRNA molecule in the A site via a peptide transferase enzyme.

Question 39

what is stage 3 of translational elongation?

Answer 39

Large ribosomal sub unit steps one codon along the mRNA

Question 40

what is stage 4 of translational elongation?

Answer 40

Small ribosomal subunit steps one codon along so that the new peptidyl –tRNA in the A site moves to the P site as and the tRNA that occupied the P site of the ribosome moves 1 codon along the mRNA molecule and becomes the new E –site. This generates a new A site.

Question 41

what is translational elongation driven by?

Answer 41

Elongation factors EF1 and EF2

Question 42

what is translational termination?

Answer 42

t

Question 43

what occurs in translational termination?

Answer 43

Protein synthesis stops when the ribosome encounters a stop codon (UAA, UAG, UGA). Cytoplasmic release factors bind to the stop codon and free the carboxyl end of the growing polypeptide chain.

Question 44

what is the one gene-one protein hypothesis?

Answer 44

o

Question 45

what are isoforms?

Answer 45

Alternative mRNAs of a single gene (e.g. Casp8)