Part 3

Question 1

Oxygen is essential in … synthesis through its role as an …….. …….. in the ETC

This accounts for ..% of the total oxygen uptake in most cells.

Low oxygen levels are therefore ….. to cells, leading them to die through ……..

Answer 1

Oxygen is essential id ATP synthesis through its role as an electron acceptor in the electron transport chain.

This accounts for 90% of the total oxygen uptake in most cells

Low oxygen levels are therefore extremely toxic to cells, leading them to die through necrosis

Question 2

How do low oxygen conditions occur in the body?

Answer 2

Oxygen (and nutrient) concentration decreases quickly at the distance form blood vessels increases

Question 3

Cells are usually within 0.05mm? of a blood vessel

At what distance does hypoxia set in?

Answer 3

Hypoxia sets in at 150um from a blood vessel.

Question 4

When can general hypoxia occur?

Answer 4

When environmental oxygen levels are low
in premature babies
following poisoning
because of anaemia

Question 5

Local hypoxia can occur because of what?

Answer 5

Ischaemia following heart attack and stroke

Cancer ( tumour growth collapses blood vessel)

Question 6

What is the cellular response to hypoxia?

Answer 6

Specialised oxygen sensing enzymes detect hypoxia
They activate a range of transcription factors (hypoxia inducible factors) that move to the nucleus and alter gene expression.

Question 7

What do hypoxia inducible factors do?

Answer 7

They turn on genes in response to a loss of oxygen

HIF are made constantly and another enzyme breaks it down constantly

This enzyme requires oxygen so when oxygen levels are low it cant break down Hypoxia inducible factors so they accumulate .

Question 8

What happens when Hypoxia inducible factors move to the nucleus and alter genes?

Answer 8

• The cell cycle stops at the G1 phase
• The cell switches to glycolysis and anaerobi metabolism to produce ATP
• There is a rapid down-regulation of protein synthesis

Question 9

What is angiogenesis?

Why and how does it occur?

Answer 9

The making of new blood vessels, it occurs in response to hypoxia as many genes are growth factors that stimulate cells in nearby blood vessels to branch off, proliferate and move towards the hypoxic cell

Question 10

How do cells survive nutrients deprivation?

Answer 10

Through quiescence - it helps save resources and energy and reduces the amount of proteins it makes

Also helps cells at low temperatures, low oxygen

Question 11

Cellular quiescence is often associated with a low ……… state, characterised by a decrease in ……. uptake and ………., reduced protein ………. rates and activation of ……….. as a means to provide nutrients for survival.

Answer 11

Cellular quiescence is often associated with low metabolic state. Characterised by a decrease in glucose uptake and glycolysis, reduced protein synthesis rates and activation od autophagy as a means to provide nutrients for survival.

Question 12

What is autophagy?

Answer 12

Autophagy (self eating) is a major mechanism that allows the cells to survive in response to multiple stresses including nutrient deprivation and starvation.

Question 13

How does autophagy work?

Answer 13

Lysosomes fuse with autophagosomes to degrade its content allowing cells to eliminate damages or harmful components and recycle their constituents to maintain nutrient and energy homeostasis

Question 14

Autophagy is a response to what?

and what can it do?

Answer 14

The assumption that nutrient depletion is temporary and can restore normal functions

It can form a membrane around a whole bit of the cell (isolation membrane)

Question 15

What is an isolation membrane?

Answer 15

An isolation membrane is the formation of a membrane around a whole bit of the cell meaning the cell doesnt need anything in that region.
It is an autophagosome and degradative enzymes can be pumped in to break down components

Question 16

What can proteosomes do during nutrient deprivation?

Answer 16

Proteosomes can degrade unwanted or damaged proteins recycling them into amino acids to allow for more protein synthesis

Question 17

What are proteosomes and what are their function?

Answer 17

Proteosomes are multi-protein complexes. They play an important role in the general stress response including heat shock, infection and oxidative stress by degrading damaged or misfolded proteins.

Question 18

What are some damaging toxic environments for cells?

Answer 18

Radiation (UV light)
Free radicals an oxidative stress
Toxins and poisons (from bacteri, food etc.)

Question 19

What is reactive oxygen species?

Answer 19

The process of producing ATP through the electron transport chain relies on oxygen as the ultimate electron acceptor

Oxygen accepts four electrons
sometimes this doesn’t work properly and a highly reactive species is created

Question 20

What is the anti-oxidant defence?

Answer 20

Glutathione is an anti-oxidant found in cells.
In its reduced form it readily donates electrons to reative oxygen species, forming more stable molecules and protecting more sensitive molecules from damage

Question 21

What is superoxide dismutase?

Answer 21

enzyme that converts highly reactive superoxide free radicals (O2-) to less reactive hydrogen peroxide

Question 22

What is catalase?

Answer 22

Catalase is an enzyme that converts hydrogen peroxide to water and oxygen

Question 23

What happens in the DNA damage response?

Answer 23

1) DNA damage is detected
2) Cells stop going through the cell cycle (quiescence)
3) DNA repair is initiated
4) If DNA damage is too extensive the cell undergoes apoptosis