Topic 7 Flashcards
Describe lipids
structurally diverse
generally insoluble in water
phospholipids contain P and N as well as the usual C H O
more reduced than carbs
- release more energy when oxidised
- complete oxidation requires more oxygen
What are the three classes of lipids?
fatty acid derivatives - fatty acids, fuel molecules - triacylglycerols hydroxy-methyl-glutaric acid derivatives - ketone bodies, water soluble fuel molecules vitamins
Describe triacylglycerols
hydrophobic
stored in anhydrous form
stored in adipose
utilised in prolonged exercise, starvation, pregnancy
storage/ mobilisation under hormonal control
What tissues are involved in TAG metabolism?
gi tract
blood
liver, adipose, muscle
Describe the metabolism of TAGs
tryglycerides hydrolysed in GI tract by pancreatic lipases to fatty acids and glycerol
fatty acids converted back to triacylglycerides in the SI
packaged into lipoprotein particle, chylomicrons
released into circulation via lymphatics
carried to adipose tissue
stored as triglyceride
or, carried to consumer tissues- not cells w/o mitochondria and not brain as the FA canβt pass through blood brain barrier
released as fatty acids when needed, increase in glucagon or adrenaline and decrease in insulin
carried to tissues as albumin fatty acid complex
no ATP synthesis
stops in absence of oxygen
Describe the fatty acid cycle in adipose tissue
glucose transport glycolysis esterification lysis re esterification
How are fatty acids activated?
outside mitochondria, in cytoplasm
FA activated by linking to coenzyme A (via a high energy bond) by the action of fatty acyl CoA synthase
activated FA fo not readily cross the inner mitochondrial membrane
How is fatty acyl-CoA transported across the mitochondrial membrane?
by carnitine shuttle
regulated, so controls rate of FA oxidation
inhibited by malonyl CoA
defects can occur in this transport system (Exercise intolerance)
look at picture
What is beta oxidation?
more energy derived from FA oxidation than glucose oxidation
this is the pathway for FA metabolism
Describe glycerol metabolism
transported in the blood to the liver where is it metabolised by glycerol kinase into glycerol phosphate
this forms DHAP and triacyglycerol synthesis
What is acetyl-CoA?
the main convergence point for catabolic pathways
acetyl (CH3CO) linked via sulphur atom, high energy of hydrolysis
so you get an activated acetyl group
CoA contains vit B5 panthenoic acid
What are the functions of acetyl-CoA?
the most important intermediate in both catabolic and anabolic pathways
What are the ketone bodies produced in the body?
acetoacetate acetone π«-hydroxybutyrate normal plasma <1mM starvation 2-10mM untreated type 1 diabetes >10mM
How are ketone bodies synthesised?
by liver mitochondria
Acetyl CoA is converted by synthase to produce HMG-CoA which converts to mevalonate and then cholesterol by HMG- CoA reductase (statin drugs block this)
HMG- CoA is also converted by lyase into the three ketone bodies in humans
How is ketone body production controlled?
acetyl co a diverted out from Krebs cycle
low NAD+ substrate availability and NADH product inhibition lead to isocitrate dehydrogenase and πͺ- ketoglutarate dehydrogenase in the TCA cycle being inhibited
as these enzymes regulate the TCA cycle, the intermediates before that build up leadings to acetyl co a being diverted as it is building up from the TCA cycle
