Session 3 Flashcards
(26 cards)
What is the major function of the Pentose Phosphate pathway?
Produce NADPH
Produce C5 ribosomes that are used in Nucleotide synthesis
What happens in Phase I of the Pentose Phosphate pathway?
Glucose 6-phosphate is oxidized and decarboxylated by glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in a reaction requiring NADP+.
What happens in Phase II of the Pentose Phosphate pathway?
Converts any unused C5-sugar phosphates to glycolysis intermediates
Why is the Pentose Phosphate pathway important?
Produces NADPH used in lipid synthesis.- Liver & Adipose tissue
RBCs require NADPH to prevent disulphide bridges
Explain Glucose 6-phoshate dehydrogenase deficiency
Rate-limiting enzyme in the pentose phosphate pathway
Point mutation, X-linked
Reduced activity of the enzyme- low levels of NADPH.
Can’t prevent the formation of these disulphide bridges in RBCs - form insoluble aggregates called Heinz bodies
Why is Pyruvate Dehydrogenase important in Glycolysis?
Pyruvate dehydrogenase (PDH) converts Pyruvate to Acetyl CoA in an irreversible reaction
What mechanisms control Pyruvate Dehydrogenase?
Reaction is energy sensitive. ATP/NADH inhibit and ADP promotes allosterically.
Activated when there is plenty of glucose to be catabolised.
Acetyl~CoA allosterically inhibits PDH
Outline the Krebs cycle
Oxidative pathway in Mitochondria Requires NAD+, FAD and Oxaloacetate Breaks the C-C bond in Acetate Needs O2 Defects in it would be lethal Makes intermediates that can be used to make AA etc.
What regulates the Krebs cycle?
ATP/ADP ratio
NADH/NAD+ ratio
One of the irreversible steps allosterically inhibited by high-energy signal and activated by the low-energy signal
Outline Oxidative Phosphorylation
NADH and FAD2H contain high energy electrons transferred to oxygen releasing large amounts of energy to drive ATP synthesis.
How does Uncoupling produce heat?
Increased permeability of the inner mitochondrial membrane to protons so P.M.F lost as heat
What are the 3 uncoupling proteins?
UCP1 - Expressed in Brown adipose tissue, non shivering thermogenesis
UCP2 - Widely distributed- links to diabetes?
UCP3 - skeletal muscle, brown adipose tissue & heart. Involved in modifying fatty acid metabolism & protecting against ROS damage.
Noradrenaline activates UCP1 and increases P.M.F
Contrast oxidative & substrate level phosphorylation.
O - Energy coupling occurs indirectly S - Occurs directly
O - Needs Oxygen S - Doesn’t
O - Needs membrane proteins S - Needs soluble proteins
What are the 3 classes of lipids?
Fatty acid derivatives eg TAGs
Hydroxy-methyl-glutaric acid derivatives eg Ketone bodies, Cholesterol
Fat soluble vitamins eg A, D, E & K
How are dietary lipids (mainly Triacylglycerol) broken down?
Hydrolysed by pancreatic lipase in the small intestine to release glycerol and fatty acids
How is Glycerol metabolised?
Enters blood stream from small intestine, travels to Liver where it is broken down.
What properties of Fatty acids make them ideal for storage?
Hydrophobic
Highly reduced molecules
What properties of Fatty acids make them ideal for storage?
Hydrophobic
Highly reduced molecules
When are Ketone bodies synthesised?
Extra point - What does it require?
When glucose concentration is low.
Extra point - Low insulin/glucagon ratio
Fatty acids to be available
What can produce Acetyl CoA?
Fatty Acids Sugars Alcohol Certain amino acids Oxidised via Krebs cycle Important intermediate of lipid biosynthesis
How are Ketone bodies used?
Can be converted to Acetyl CoA and enter Krebs cycle
How is Ketoacidosis caused?
Acetoacetate and Beta-hydroxybutyrate are relatively strong organic acids
Acetone is volatile and may be excreted via the lungs
Why is Ketonuria possible?
Because Ketones are water soluble. When concentration gets too high they reach the urinary threshold
What are the 3 Ketones produced in the body?
Acetone
Acetoacetate (Synthesised in Liver from AcA)
Beta Hydroxybutyrate (Synthesised in Liver from AcA)
