L18- Gene to cell

Question 1

What are examples of gene expression compartmentalisation?

Answer 1

• Transcription: X chromosome inactivation
• Splicing: apoptosis changes
• Translation: mTOR

Question 2

How does X chromosome inactivation occur?

Answer 2

• Used to compensate dosage in both sexes
• With a IncRNA- the X-inactive specific transcript (XIST)
• Xic (X inactivation centre) is a locus on all mammalian X chromosomes which contains XIST

Question 3

What does XIST do?

Answer 3

• Codes for a non-coding RNA which binds its chromosome in cis
• Chromosome ends up as heterochromatin aka a Barr body which cannot be transcribed
• Inactivation is randomly in one X or the other

Question 4

What is the intrinsic pathway of apoptosis?

Answer 4

• Internal stimuli such as DNA damage, oxidatives stress and hypoxia
• Cause loss of outer Mt membrane and release cytochrome C into cytoplasm
• Cytochrome C forms complex with Apaf-1 and caspase 9 to form apoptosome
• Apoptosome activates caspase 3 which activates cytoplasmic endonuclease and proteases that degrade the cell and its contents

Question 5

What are the BCL genes?

Answer 5

• Bcl-xL is antiapoptotic

* Bcl-XS promotes cell death

Question 6

What is mTOR?

Answer 6

• Master of translation regulation- gene

* Target of rapamycin

Question 7

What is rapamycin?

Answer 7

• It forms a gain of function complex with FKBP12 and mammals have only one mTOR gene which forms two complexes

Question 8

What are the two mTOR complexes?

Answer 8

mTORC1- characterised by presence of raptor (regulatory associated protein of mTOR), inhibited by rapamycin

mTORC2- characterised by presence of rictor (raptor independent companion of mtor), insensitive to rapamycin

Question 9

What does mTORC1 do?

Answer 9

• Acts as a central hub for sensing nutrients and allowing translation to occur.