16. Introduction to control of gene expression

Question 1

Describe the genotype? (6pts)

Answer 1

1. Genotype= The genetic makeup of an organism.
2. Human cells all contain the same genetic blueprint.
3. Human genome contains 50,000 genes.
4. In any given cell type only 10,000 genes are expressed.
5. Genome is identical in every cell
6. Genome must be differentially interpreted in different cells at different times leading to differential gene expression.

Question 2

Describe gene expression (1pts)

Answer 2

Gene expression is both regulated in time during development and in response to hormones, infection or other signals and in space as different cell types require different genes to be expressed.

Question 3

Describe how genetic information flows?

Answer 3

Genetic information flows from DNA to RNA and then to proteins which have a number of broad functions. They can be involved in cellular metabolism, cell shape/motility, cell differentiation and cell proliferation.

Question 4

Describe what failure to regulate gene expression tightly may lead to? (4pts)

Answer 4

Failure to regulate gene expression tightly may lead to:

1. Metabolic diseases= affects proteins involved in metabolism
2. Metastasis= the spreading of cancer cells throughout the body.
3. Congenital disorders= Issues with differentiation of specific organs
4. Cancer= as cells are not controlled in the body.

Question 5

Describe the Bithrorax gene

Answer 5

Gene that controls the number of segments in an organism. Duplication of wings in the fly due to a mutation in the bithorax gene.

Question 6

Describe Antenapedia?

Answer 6

Gene involved in the formation of legs in flys. When expressed incorrectly the fly will develop two legs instead of an antenna.

Question 7

Describe totipotent cells

Answer 7

Cell that can give rise to all tissues in the organism. They have the ability to develop into a total individual.

Question 8

Describe Pluripotent cells?

Answer 8

Cells that can give rise to all tissues except placental tissue

Question 9

Describe Blood stem cells

Answer 9

Pluripotent stem cells then develop into blood stem cells which can self renew and give rise to other cells.

Question 10

Describe Reprogramming? (3pts)

Answer 10

1. Take a committed cell e.g skin cell
2. Reprogram in a lab to pluripotent stem cells by forcing them to change the expression of the gene.
3. These pluripotent stem cells are then forced to differentiate.

Question 11

What is the big goal?

Answer 11

The big goal is the ability to isolate adult stem cells from all development compartments.

Question 12

Describe B-thalassemia? (2pts)

Answer 12

1. A group of genetic diseases caused by insufficient expression of B-globin which is the protein that transports hydrogen in red blood cells across the organism.
2. In most types of B-thalassamia the B-globin protein is structurally normal.

Question 13

Describe base change mutations in B-thalassemia?

Answer 13

There is no expression of the protein due to the base change mutation. The mutation destroys the tata box therefore is is no longer recognised by RNA polymerase.

Question 14

Describe a single base mutation in B-thalassaemia?

Answer 14

Unable to remove the intron therefore RNA is not processed correctly so the gene will not be expressed

Question 15

Name post-transcriptional gene regulation?

Answer 15

1. Translation

2. RNA stability

Question 16

Describe translational control (3pts)

Answer 16

1. Early embroygensis- during first 4-8 cell divisions there is virtually no gene expression. At the end of blastocyt fromation first genes to be expressd are due to up-regulation of translation from maternally derived pre-formed mRNAs.
2. Environmental stress- exposure to heat shock or pathogens can cause global changes in translation
3. Ferritin

Question 17

Describe ELF3 and ELF4 proteins ? (2pts)

Answer 17

1. ELF3 and ELF4 promote the binding of the ribosome and the recognition of the capsid and initiation of translation.
2. Some viruses are able to repress protein synthesis in cells as they inactivate the proteins eLF3 and eLF4.

Question 18

Describe the 5UTR?

Answer 18

The 5UTR is not the bit that determines whether a ribosome binds but it plays a major role in determining how efficiently the ribosome initiates translation. Globin is very efficiently translated and Ferritin is very ineffectively translated.

Question 19

Describe Ferritin?

Answer 19

Ferritin binds iron and retains it in the cytoplasm as a store for excess. Ferritin is only needed in times of iron excess.

Question 20

Describe what happens in the absence of iron? (3pts)

Answer 20

1. Fe starvation inhibitor recognises the ferritin mRNA molecule which causes the cap protein to bind to the ribosomal unit.
2. The ferritin starvation inhibitor prevents the molecules movement across mRNA.
3. This RNA is then expressed in cells.

Question 21

Describe what happens in excess iron? (3pts)

Answer 21

1. Iron binds to the inhibitor
2. The binding makes the inhibitor incompatible for binding to the 5 prime UTR.
3. As a result the inhibitor is released and the ribosome will be able to move along and translate the ferritin MRNA into proteins.

Question 22

Describe how 3 UTR’s play a role in stabilising the stability of the mRNA?

Answer 22

3 UTR’s play a role in stabilising the MRNA molecule and determine its lifespan. Some 3 UTR’s give their MRNA great stability like globin while other UTR’s such as immune stress hormones give their mRNA’s very short life spans.

Question 23

Describe microRNAs? (4pts)

Answer 23

1. The human genome encodes over 500 microRNA’s that are transcribed by RNA Polymeraise II.
2. microRNA’s are small non-coding RNA’s.
3. These miRNA’s act to control the post-transcriptional regulation of human genes.
4. Any given miRNA can regulate several target genes.