S2: Energy II: Acetyl CoA, Mitochondria and Oxygen Flashcards
What is aerobic respiration?
Aerobic respiration occurs only in the presence of O2 and yields more energy in the form of ATP and requires the citric acid cycle and oxidative phosphorylation. It take place in the mitochondria.
Explain the structure of mitochondria and where different aspects of respiration occur on them
There is an outer mitochondrial membrane and an inner mitochondrial membrane with the intermitochondrial space in between. On the inside there is the matrix.
Matrix - TCA cycle occurs
Inner mitochondrial membrane - Oxidative phosphorylation occurs
Describe the citric acid cycle (kreb cycle)
Pyruvate undergoes the links reaction to become acetyl CoA. CO2 and NADH is generated in this process.
ACoA enters TCA cycle which and reacts with 4C acid (oxaloacetate) to become a 6C acid (citrate).
Amount of oxaloacetate remains the same it is continually recycled.
Citrate then goes under a series of reaction resulting in loss of 2CO2 becoming a 4C molecule.
Net production in TCA cycle
Forr each glucose (2 pyruvate):
• 6 NADH (within)+ 2
NADH (In producing ACoA)
• 2 FADH2
• 2 GTP
• 4 CO2 + 2CO2 (in
producing ACoA)What is the purpose of TCA cycle?
The purpose is to generate the NADH and FADH2 to be used in the ETC thus providing most electrons for oxidative phosphorylation.
TCA also integrates carbohydrate, lipid and protein metabolism as these can enter as ACoA.
What regulates entry into the citric acid cycle?
The formation of ACoA from pyruvate which uses the enzyme pyruvate dehydrogenase.
What regulates pyruvate dehydrogenase?
This enzyme is inhibited by NADH and ACoA (products of the link reaction).
The enzyme is also regulated by phosphorylation ATP (covalent modification) which inhibits its activity
This is because build up informs the enzyme that the energy needs of the cell are being met or that fatty acids are being broken down to produce NADH and acetyl CoA - inhibiting pyruvate dehydrogenase spares glucose.
It is stimulated by ADP and pyruvate
What happens to excess glucose?
Excess glucose –> increased pyruvate –> increased fatty acid synthesis (instead of TCA)
Explain ways pyruvate dehydrogenase is activated
In muscle –> it is activated via action of phosphatase (which removes phosphorylation). This phosphatase in muscle is stimulated by Ca2+. This allows the muscle to link contraction to a process that will generate ATP.
Explain in ways phosphatase is activated
Muscle = via Ca2 which activates pyruvate dehydrogenase involved in producing ATP
Liver and adipose tissue= Insulin stimulates the phosphatase which funnels glucose to fatty acid synthesis. This process is for storage rather than producing ATP.
State 3 more regulation points within the citric acid cycle
- The convertion of ACoA –> Citrate under the action of the enzyme citrate synthase.
- Isocitrate –> a-ketogluterate by enzyme isocitrate dehydrogenase.
- a-ketogluterate –> Succinyl CoA by enzyme a-ketodehydrogenase.
What enzyme converts ACoA to Citrate and what regulates it?
Citrate synthase
It is inhibited by citrate. This means in cases where there is enough ATP the ACoA will be directed to other routes e.g. fatty acid synthesis
What enzyme converts Isocitrate to a-ketogluterate and what regulates it?
Isocitrate dehydrogenase
It is inhibited by NADH, ATP, Succinyl CoA
What enzyme converts a-ketogluterate to Succinyl CoA and what regulates it?
a-ketodehydrogenase
It is inhibited by NADH, ATP and Succinyl CoA
What is Beriberi?
It is a deficiency in thiamine (vitamin B1).
It is common in far-east where rice is a staple diet.
Thiamine is a prosthetic group for enzymes pyruvate dehydrogenase and a-ketogluterate dehydrogenase. These enzymes are important in regulating the TCA cycle so someone with Beriberi has an inability to generate sufficient ATP.
This disease is therefore characterised by cardiac and neurological symptoms.
