control of gene expression

Question 1

how many genes does the human genome contain and how many of these are actually expressed?

Answer 1

50,000 and only 10,000 are 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 with respect to time and space?

Answer 3

time - embryos express different genes to adults

space - brain expresses different genes to muscle cells

Question 4

what is an example of a congenital disorder?

Answer 4

bithorax gene mutation in drosophila

Question 5

where are totipotent cells found?

Answer 5

in zygotes

Question 6

what tissue can pluripotent stem cells not differentiate into?

Answer 6

placental tissue

Question 7

how are iPS formed?

Answer 7

introducing new genes and transcription factors to turn on genes that were off

Question 8

what does the primary transcript consist of?

Answer 8

both exons and introns

Question 9

what is beta thalassemia caused by?

Answer 9

insufficient expression of beta globin

Question 10

why don’t zygotes need to transcribe genes?

Answer 10

they have pre existing maternal RNAs

Question 11

how do cells respond to viral infections?

Answer 11

they transcribe genes that code for antiviral proteins

Question 12

explain how the ribosome finds the start sequence?

Answer 12

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 13

what two proteins recognize the cap?

Answer 13

EFI3 and EFI4

Question 14

how does ferritin work?

Answer 14

→Ferritin binds to iron and retains it in the cytoplasm as a store for excess.

→ferritin is needed when there is excess iron.

→When there are low levels of iron, an inhibitor blocks the ribosomal subunit from interacting with the ferritin mRNA.

→ no translation of the ferritin mRNA takes place.

→in an excess of iron, the iron binds to the inhibitor, taking it away from the ferritin mRNA.

→This allows the ribosomal subunit access to the mRNA, so translation occurs.

Question 15

what is the function of the UTRs?

Answer 15

they stabilize the mRNA and regulate their life span.

Question 16

what does the 3’ UTR sequence do?

Answer 16

causes proteins to bind which protects the RNA from degradation

Question 17

what is the promoter region in eukaryotes and prokaryotes

Answer 17

TATA box and pribnow box

Question 18

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

Answer 18

→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 19

Give examples of translational control

Answer 19

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 20

What is the function of the 5’ UTR?

Answer 20

→determining how efficiently the ribosome initiates translation.

Question 21

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

Answer 21

→The human genome encodes over 500 small, noncoding RNAs that are transcribed by RNA Polymerase II.

→These RNAs are referred to as microRNAs or miRNAs.

→miRNAs act to control the post-transcriptional regulation of as many as one-third of all human genes.

Question 22

Describe the synthesis of miRNAs and explain how they work

Answer 22

→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).