control of gene expression 2

Question 1

control of eukaryotic transcriptional initiation

Answer 1

• activator proteins bind upstream the enhancer sequence and active the basal transcription complex
• multiple epigenetic mechanisms control gene expression via local chromatin condensation: histone modification and in vertebras’ direct DNA methylation on cytosine helps maintain patterns of gene repression in some somatic cells

Question 2

multiple epigenetic mechanisms control gene expression via local chromatin condensation:

Answer 2

histone modification and in vertebras’ direct DNA methylation on cytosine helps maintain patterns of gene repression in some somatic cells

Question 3

around 95% of human genes show..

Answer 3

alternative splicing -introns ar removed from pre-mRNA

Question 4

RNA editing

-post transcriptional editing increases e.g. alternative splicing

Answer 4

increases the number of distinct proteins that can be encoded in a genome

Question 5

in vivo modification of mRNA

Answer 5

-splitting of mRNA -addition of uridine to mRNA -deletion of uridine from mRNA

Question 6

in different tissues..

Answer 6

diff alternative splicing will occur

Question 7

what regulated alternative splicing

Answer 7

repressors and activators e.g. if activator is present then the intron will be spliced

Question 8

miRNA

Answer 8

microRNA -small-non coding RNA molecules -22 nucleotides -function in RNA silencing and post transcriptional regulation of gene expression

Question 9

microRNA role is to

Answer 9

specifically regulate gene expression -key in biological processes such as development, cell birth and death and cancer

Question 10

how to miRNA regulate gene expression

Answer 10

by blocking translation of specific mRNAs and cause their degradation

Question 11

RNAi

Answer 11

RNA interference -double stranded -a biological process in which RNA molecules inhibit gene expression or translation, by neutralizing targeted mRNA molecules

Question 12

where are RNAi found in nature

Answer 12

yeast, bacteria, the mouse and fruit fly

Question 13

model organisms

Answer 13

great for experiments because: share with humans many genes and key biochemical and physiological functions that have been conserved by evolution

Question 14

andrew fire and craig mellow and their discovery on RNAi

Answer 14

-injecting double stranded RNA reduced expression of specific genes -it does this by reducing levels of mRNA -this RNA interference is sequence specific

Question 15

siRNA

Answer 15

small interfering RNA

Question 16

siRNA and gene control

Answer 16

regulates gene expression by blocking translation of specific mRNAs and cause their degradation

Question 17

what can RNAi act as

Answer 17

a defence mechanism against dsRNA viruses and transposable elements

Question 18

RNAi and worm

Answer 18

1.e.coli, expressing double stranded RNA, eaten by worm 2.double stranded RNA injected into gut

Question 19

fate of target RNA silenced by RNAi

Answer 19

1. cleavage of target RNA 2.translation repression and eventual destruction 3. formation of heterochromatin on DNA fro which target RNA is being transcribed

Question 20

UTRs (untranslated regions) can control…

Answer 20

mRNA stability

Question 21

control stability- cytosolic aconitase and transferrin receptors

Answer 21

Without Iron

• cytosolic acontase is complimentary to the transferrin receptor mRNA
• this means the mRNA is stable and can be translate
• iron uptake into cell

with excess iron

• iron is complementary to part of the cytosolic aconitase
• this changes the shape of the cytosolic acontaise so it can no longer fit onto the transferrin mRNA
• thereofore mRNA is not stable and no transferrin receptors will be translated for and no iron will be uptake

Question 22

control of translation- ferritin translation

Answer 22

-Ferritin is a blood cell protein that contains iron

No iron present

• cytosolic aconitase can fit onto the transferrin mRNA
• translation is blocked
• no ferritin made

Excess iron

• iron is complementary to cytosolic aconitase and changes its configuration
• will no longer fit onto the ferritin mRNA
• therefore ferritin mRNA will be translated
• iron bound within cell

Question 23

types of RNAi

-all double stranded and cause the translation of mRNA to be reduced without damaging actual DNA

Answer 23

dsRNA cleavage.

MicroRNA.

Three prime untranslated regions and microRNAs.

RISC activation and catalysis.

siRNA

Question 24

miRNA processing and mechanism of action

Answer 24

1. pri-miRNA is cleaved
2. leaves the nucleus via special pores
3. pre-miRNA is diced by a dicer making it single stranded
4. associates with argonaute and othe rrpoteins and forms a RISC molecules (RNA induced silencing complex)
5. causes rapid degradation by slciing mRNA
6. unable to be translated and therefore degraded