Introduction to the Control of Gene Expression

Question 1

how many genes does the genome contain and how many are expressed?

Answer 1

-contains 50,000 genes but only 10,000 expressed

Question 2

what is differential gene expression?

Answer 2

the different interpretation of the genome in each cell

Question 3

explain how gene expression is regulated in terms of time and space

Answer 3

• time: embryos express different genes to adults

- space: different tissues or cells express different genes (eg brain vs heart)

Question 4

where are totipotent cells found and what is their differential ability?

Answer 4

• found in early embryos

- have the ability to differentiation into any type of cell

Question 5

what type of cells can pluripotent cells differentiate into?

Answer 5

most cell types but not placental tissue

Question 6

what do certain transcription factors do when added to specialised cells?

Answer 6

-de-programme them and make them pluripotent

Question 7

what is β thalassaemia caused by?

Answer 7

by the insufficient expression of β-globin

Question 8

why don’t zygotes need to transcribe genes?

Answer 8

they have maternal pre-formed mRNA

Question 9

explain how the ribosome finds the start sequence?

Answer 9

it binds to and recognizes the cap and will keep going until it recognizes the start sequence which is the first AUG near the kozak sequence.

Question 10

what two proteins recognize the cap?

Answer 10

EFI3 and EFI4

Question 11

how does ferritin work?

Answer 11

• a protein that acts as a sponge for ions
• binds Fe2+ and retains in cytoplasm as store for excess
• when [Fe2+] , Fe binds to Fe starvation inhibitor and translation occurs as the ribosomal subunit access to the mRNA

Question 12

what is the function of the UTRs?

Answer 12

they stabilise the mRNA and regulate the life span

Question 13

what does the 3’ UTR sequence do?

Answer 13

causes proteins to bind which protects the RNA from degradation

Question 14

what is the promoter region in eukaryotes and prokaryotes

Answer 14

TATA box and pribnow box

Question 15

What is β-thalassaemia and what kind of mutations cause this disease?

Answer 15

• blood disorder that reduces the production of haemoglobin.
• the β-globin protein is structurally normal (unlike sickle cell disease).
• Mutations that cause this disease are usually single base changes

Question 16

Give examples of post translational control

Answer 16

EARLY EMBRYOGENESIS:

• During the first 4-8 weeks of cell division, there is no gene expression.
• At the end of blastocyst formation, genes are expressed due to the up-regulation of translation from maternally-derived preformed mRNAs.

ENVIRONMENTAL STRESS:
-exposure to heat shock or pathogens can cause global changes in translation.
There are many specific examples, such as ferritin.

Question 17

what is the function of the 5’ UTR?

Answer 17

determining how efficiently the ribosome initiates translation.

Question 18

what are miRNAs, and what is their function and how many are encoded in the human genome?

Answer 18

• 500 small non-coding RNAs that are transcribed by RNA Pol II
• they act to control post-transcriptional regulation of up to 1/2 of human genome

Question 19

describe the synthesis of miRNAs and explain how they work

Answer 19

• each precursor miRNA transcript is processed to form a double-stranded intermediate
• further processed to form a mature, single-stranded miRNA.
• this miRNA assembles with a set of proteins into a complex called RISC, which then searches for mRNAs that have a nucleotide sequence complementary to its bound miRNA.
• depending on how extensive the region of complementarity is, the target mRNA is either rapidly degraded by a nuclease within the RISC (this happens when there is an extensive match)
• or transferred to an area of the cytoplasm where other cellular nucleases destroy it (this happens when there is a less extensive match).