The TCA cycle is a central pathway in the catabolism of what compounds?
Sugars, fatty acids, ketone bodies, alcohol and amino acids
The TCA cycle occurs where?
Is the TCA cycle oxidative or reductive?
What does the TCA pathway require to function?
AcetylCoA, NAD+, FAD and oxaloacetate
What is the main function of the TCA cycle?
Break the C-C bond in acetate (as acetylCoA) and oxidise the C atoms to CO2
In the TCA cycle what is the involvement of H+ and e-?
Removed from acetate and transferred to NAD+ and FAD+
Can the TCA cycle function in anaerobic conditions?
Per molecule of glucose, what does the TCA cycle produce?
Describe the chemical 'strategy' of the TCA cycle.
Produce intermediates (C5 tricarboxylic acids and keto acids) that readily lose CO2 producing C4 acids that are interconvertible.
What are the anabolic functions of the TCA cycle?
C5 and C4 intermediates used in non-essential amino acid synthesis
C4 intermediates used for the synthesis of haem and glucose
C6 intermediates used for synthesis of fatty acids
What is the main method of TCA cycle regulation?
One Irreversible step is catalysed by isocitrate dehydrogenase
This enzyme allosterically controlled by ADP/ATP and NAD+/NADH ratios
ADP activates (low energy signal)
NADH inhibits (high energy signal)
Give an equation for the complete oxidation of glucose and the overall release of energy
C6H12O6 + 6 O2 ---> 6 CO2 + 6 H2O
by the end of the TCA cycle what has happened to glucose's bonds and bond energy?
All C-C bonds broken
All C atoms oxidised to CO2
All C-H bonds broken and H+/e- transferred to NAD+ and FAD
All energy has gone into ATP/GTP formation
Chemical bond energy of the e- is in NADH or FAD2H form.
How much energy is released from the oxidation of NADH and FAD2H?
NADH = 220kJ/mol
FAD2H = 152kJmol
What is the energy from the oxidation of NADH and FAD2H used for?
Give a brief description of electron transport
Electrons from NADH and FAD2H transferred through a series of carrier molecules in the inner mitochondrial membrane to molecular oxygen, releasing free energy
The free energy released from electron transport drives what process?
how many electron transfer complexes are their?
A series of 4
3 of the electron transport complexes have another function, what is this?
They act as proton translocation complexes (proton pumps)
how is an electrochemical gradient set up across the inner mitochondrial membrane?
Protons moved into the inter membrane space across the impermeable inner mitochondrial membrane of the mitochondrion using electrochemical energy generated from electron trnasport
how and why do NADH and FAD2H utilise the protons pump differently
NADH releases more energy, so uses all three proton pumps while FAD2H only uses 2
What is the role of oxygen in the electron transport chains?
final electron acceptor
How much energy is required to produce one ATP molecule via oxidative phosphorylation
How is the proton gradient across the inner mitochondrial membrane used in ATP synthesis?
Protons can only flow through ATP synthase complexes, this produces ATP from ADP and Pi.
How many moles of ATP produced per mole of NADH and FAD2H
NADH = 2.5
FAD2H = 1.5
electron transport and ATP synthesis are highly coupled, when ATP concentration is high, what happens to these processes?
ATP synthesis stops due to lack of substrate
This prevents H+ transport back into matrix
H+ concentration continues to increase in intermembrane space until reaching a level that prevents further buildup of H+
In the absence of proton pumping, electron transport stops.
What substances can increase permeability of the inner mitochondrial membrane to protons and what is this effect called?
what is proton leak?
protons crossing inner mitochondrial membrane into the matrix without passing through the ATP synthase complex
how is pmf dissipated when proton leak occurs?
What proportion of energy is leaked and under what curcumstances might this proportion increase?
Normally 20-25% of Basal metabolic rate dissipated as heat, increases when uncoupling occurs
What is the purpose of uncoupling proteins?
Uncouple electron transport and ATP synthesis to produce heat
What are the three uncoupling proteins?
What is the function of Thermogenin and where is it found?
Non-shivering thermogensis enabling mammals to survive the cold
Expressed in brown adipose tissue
Where is UCP2 found and what diseases is it linked to?
Heart failure, diabetes, obesity, metabolic syndrome
Where is UCP3 found and what are its functions?
Found in skeletal muscle, brown adipose tissue and the heart.
Uncoupling of electron transport
Appears to be involved in fatty acid metabolism and protecting against reactive oxygen species damage.
what are noradrenaline's effects on metabolism?
Stimulates lipolysis and hence more NADH and FAD2H are produced
Hence higher levels of pmf dissipated as heat
What are the differences between substrate level and oxidative phosphorylation
Oxidative requires membrane associated proteins, substrate level requires soluble enzymes
In oxidative couple occurs indirectly through creation and utilisation of pmf, in substrate level energy coupling occurs directly through phosphoryl group transfer
Oxidative cannot occur without oxygen, substrate level can occur to limited extent anaerobically
Oxidative is a major process in high energy cells, substrate level is a minor process in high energy cells
What are the general features of a lipid?
Most contain CHO (phospholipids contain P and N)
More reduced than carbohydrates
What are the three major classes of lipid?
Fatty acid derivatives
Hydroxy-methyl-glutaric acid derivatives
Fat soluble vitamins
What types of fatty acid derivatives are found in the body and what are their functions?
Fatty acids - Fuel molecules
Triacylglycerols - Fuel storage and insulation
Phospholipids - Components of plasma membranes and plasma lipoproteins
Eicosanoids - Local mediators/signalling molecules
What types of Hydroxy-methyl-glutaric acid derivatives are found in the body and what are their functions?
Ketone bodies - Water soluble fuel molecules
Cholesterol - Membranes and steroid hormone synthesis
Cholesterol esters - Cholesterol storage
Bile acids and salts - Lipid digestion
How are triacylglycerols broken down in the small intestine and what are the products of breakdown?
Pancreatic lipase in a complex process requiring colipase and bile salts
Releases glycerol and fatty acids
Where is glycerol metabolised?
Why are some polyunsaturated fatty acids required in the diet? Give an example of a required polyunsaturate and it's use
Cannot be synthesised by the body
Arachidonic acid - Starting point of eicosanoid synthesis
What are the three ketone bodies produced by the body?
Acetone - formed from spontaneous decarboxylation of above, not intentionally formed
Where are ketone bodies synthesised and what from?
What is the normal level of ketone bodies in the blood and what could be responsible for this rising?
<1mM is normal
This can increase during starvation to 2-10mM = Physiological ketosis
10mM = Pathological Ketosis, caused by type 1 diabetes
What are the basic properties of ketone bodies and what are clinical consequences of these properties?
Water soluble - allows excretion in urine (ketonuria) and high plasma concentration
Strong organic acids - In high concentration can cause ketoacidosis
How is acetone useful in diagnosis of type 1 diabetes
Acetone is volatile so can be excreted through the lungs. There is a strong smell of acetone on the breath of untreated type 1 diabetes patients
During ketone body synthesis what ratio controls what key enzyme?
Controls Hydroxy-methyl-glutaryl CoA (HMG-CoA) Lyase/reductase enzymes
How do changes in the Insulin/glucagon ratio affect ketone synthesis?
Reduction in insulin and increase in glucagon stimulates HMG-CoA lyase and hence increased levels of ketone bodies produced
What does the synthesis of ketone bodies require? (substrate and conditions)
Fatty acids available for oxidation (excess lipolysis)
Plasma insulin/glucagon ration to be low, normally due to fall in plasma insulin
How and where are ketone bodies used and how does plasma concentration affect their use?
As fuel molecules in all mitochondria containing cells including the nervous system
Converted to AcetylCoA and used in TCA cycle
Rate of use proportional to plasma concentration
What is Acetyl CoA produced by?
Certain Amino acids
How and where is AcetylCoA utilised?
Oxidised in TCA cycle (mitochondria)
Important intermediate in lipid biosynthesis (the major site of which is the liver, some in adipose tissue)