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Flashcards in Control of Gene Expression Deck (34)
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1
Q

Out of the human genome,how many genes are actually expressed ?

A

In any given cell, only 10,000 genes are expressed

2
Q

Where are totipotent cells found?

A

In zygotes

3
Q

What is β thalassaemia?

A

Group of genetic blood diseases caused by insufficient expression of β-globin reducing haemoglobin production

4
Q

What is the genotype?

A

The genetic makeup of cells and organisms determining characteristics

5
Q

What are the different translational control mechanisms in the body?

A
  • Early embryogenesis
  • Environmental stress
  • 5’ UTR
  • Fe starvation
  • 3’ UTR
  • Small non coding RNAs
6
Q

What is differential gene expression?

A

The expression of different genes in different cells at different times giving the cell its functions

7
Q

What is the role of miRNAs?

A

Control part of the post-transcriptional regulations of 1/3 of all human genes by regulating several target genes

8
Q

How does β thalasaemia differ from sickle cell disease?

A

In β thalasaemia, the β globin protein is structurally normal

9
Q

How are intracellular iron levels controlled?

A

Via translation of Ferritin

10
Q

How does the genome differ from cell to cell?

A

It doesn’t, the genome is identical in every cell

11
Q

How is the miRNA able to target genes?

A

Single stranded miRNA searches for complementary mRNA on target proteins

  • If an extensive match is found: mRNA is rapidly
    degraded and RISC released
  • If a less extensive match is found: mRNA translation is
    reduced; mRNA sequestered and eventually degraded
12
Q

How is gene expression controlled in early embryogenesis?

A

During the first 4-8 cell divisions no genes are expressed
After blastocyst formation the 1st genes are expressed
- due to up regulation of maternally derived preformed mRNA translation

13
Q

What is a pluripotent cell?

A

A cell that can give rise to all cell types except placental cells

14
Q

What role does the 5’ UTR play in translation control?

A

Determines how efficiently the ribosome initiates translation e.g.

  • Globin: very efficient
  • Ferritin: very inefficient
15
Q

How many small non coding RNAs are present in the human genome?

A

Human genome encodes 500+ small non coding RNAs transcribed by RNA Pol II

16
Q

How is differential expression regulated in time?

A
  • During development (i.e in an embryo vs. adult)

- In response to hormones, infections and other signals

17
Q

How many forms of β thalasaemia are there?

A

There are multiple independently arising forms of the disease

18
Q

How is differential expression regulated tightly in space?

A

Different tissues and cell types express different genes (i.e. brain vs. muscle cells)

19
Q

How does environmental stress control gene expression in humans?

A

Exposure to heat shock or pathogens can cause global translation changes

20
Q

How does Ferritin help maintain the bodies cellular iron levels?

A

Ferritin binds iron and retains it in the cytoplasm as an excess store
Ferritin is only required when iron levels are in excess

21
Q

What is the result of β thalassaemia caused by the single base change at the intro-exon junction?

A

CACAGCTCCT -> CACGGCTCCT
Deletion causes intron to not be spliced
Gene not exported to cytoplasm

22
Q

What is the translational control of gene expression?

A

The regulatory mechanisms of the rate at which proteins are formed

23
Q

What are small non coding RNAs?

A

RNA molecules that aren’t translated into proteins e.g. miRNA

24
Q

What is meant by a totipotent cell?

A

A cell that can differentiate into every cell type

25
Q

What are the 2 major types of β thalasaemia?

A
  1. single base change

2. single base change at intron-exon junction

26
Q

Why is differential gene expression regulation so important?

A
Dependent on the protein encoded for, the cell function and outcome differs 
If not regulated properly can cause:
- Metabolic disease
- Metastasis 
- Congenital disorders
- Cancer
27
Q

What is the role of the 3’ UTR?

A

Determines the stability of mRNA e.g.

  • Globin confers stability
  • Immune stress hormones are very unstable
28
Q

How does an excess of Iron result in the translation of Ferritin?

A
  1. Inhibitor bound to Ferritin mRNA loop
  2. Iron binds to inhibitor
  3. Inhibitor no longer able to bind to Ferritin mRNA loop
  4. Ribosome can now move along mRNA and translate
    Ferritin protein
  5. Ferritin goes on to bind to excess iron molecules
29
Q

What is the consequence of the single base change β thalasaemia?

A

ATAAA -> ACAAA
Mutation occurs in TATA box so RNA Pol II can’t bind
Results in the gene not being transcribed

30
Q

What is the effect of the Drosophila Homeotic mutants?

A

Bithorax Gene Mutation
- Fruit-fly has an extra pair of wings

Antennapedia Gene mutation
- Flies express an extra pair of legs as gene over
expressed

31
Q

Where are miRNAs derived from?

A

Obtained by processing larger precursors

32
Q

How many genes does the human genome contain?

A

Approximately 50,000 genes present in human genome

33
Q

Outline how miRNA is formed

A
  1. Precursor miRNA molecule with 5’ cap and
    polyAdenylated tail exported into cytoplasm
  2. Enzymes cleave off the loop, the single stranded RNA
    on 5’ and 3’ ends
    => producing a short double stranded RNA molecule
    (30 bp long)
  3. RISC proteins bind to the double stranded RNA
  4. Proteins unwind double strands forming single
    stranded miRNA
34
Q

How are stem cells formed?

A

We can reprogramme cells using TFs