Energy Production In Lipids Flashcards
What elements make up lipids?
Mostly C, H, O some with P and N
Compare the reduction of lipids to carbohydrates
Lipids are more reduced than carbohydrates
Lipids release more energy when oxidised
Complete oxidation which requires more O2
What are the 3 classes of lipids?
Fatty acid derivatives
Hydroxy-methyl-glutaric acid derivatives
Vitamins
What are fatty acid derivatives?
Fatty acids - fuel molecules
Triacylglycerols (triglycerides) - fuel storage and insulation
Phospholipids
What are hydroxy-methyl-glutaric acid derivatives?
Ketone bodies - water soluble fuel molecules
Cholesterols - membranes and steroid hormone synthesis
Which vitamins are fat soluble?
A, D, E, K
What are the features of triglycerols?
Hydrophobic
Stored in anhydrous form
Stored in specialised tissue - adipose tissue
Utilised in prolonged exercise, starvation and pregnancy
Storage/mobilisation under hormonal control
Formed in esterification reaction
Describe how triglycerides move to the liver
Broken up into glycerol and fatty acids
Glycerol travels from GI tract through the blood into the liver
Describe how triglycerides move to adipose tissue and muscles
Broken up into glycerol and fatty acids
Fatty acids converted to chylomicrons and transported in blood
Moves into adipose tissue
From adipose tissue, converted to fatty acids to travel in the blood
This is then transported to muscles
Describe the first stage of metabolism of triacylglycerol (TAG) in GI tract
Hydrolysis of lipids in small intestine by pancreatic lipase
Split into fatty acids and glycerol
Recombined in small intestine and transported as TAG by lipoproteins (chylomicrons)
Stored in adipose tissue as triglycerides
Released as fatty acids when needed
Carried to tissues as albumin-fatty acid complex
Where is metabolism of TAG stage 1 in GI tract not used?
Not used in cells without mitochondria
Not used in brain, fatty acids do not easily pass blood-brain barrier
What does low extracellular glucose result in (in terms of lipids)?
Results in fatty acid release as alternative fuel
Describe the features of fatty acids
Can be saturated or unsaturated (kink)
Amphipathic (hydrophilic and hydrophobic groups)
Certain polyunsaturated FA are essential
Describe stage 2 of fatty acid metabolism (mitochondrial)
Occurs in mitochondria
FA activated by linking to coenzyme A outside mitochondrion
Transported across inner mitochondrial membrane using cartinine shuttle
FA cycles through sequence of oxidative reactions, with acetyl CoA removed each cycle
What is fatty acid activation?
Occurs outside mitochondria in cytoplasm
Fatty acids activated by linking to coenzyme A by action of fatty acrylic CoA synthase
Uses ATP, produces AMP and 2Pi
Activated FA do not readily cross inner mitochondrial membrane
Describe the cartinine shuttle
Transports fatty acrylic-CoA across mitochondrial membrane
Transport protein in middle
Regulated so controls rate of FA oxidation
Inhibited by malonyl-CoA
Defects can occur in transport system
Describe the features of fatty acid catabolism
Beta-oxidation
Activated by ATP
Transported through carnitine shuttle
Cleaved to give acetyl CoA and shorter fatty acid, with reduction of FAD and NAD+
Beta-oxidation occurs in most tissues and WBC (not brain or RBC)
Stops in absence of O2
No ATP synthesis
Describe glycerol metabolism
Glycerol -> glycerol phosphate using glycerol kinase, converting ATP to ADP
Glycerol phosphate can go to triacylglycerol synthesis or into glycolysis via dihydroxyacetone phosphate, reducing NAD+
What are the 3 ketone bodies produced in the body?
Acetoacetate
Acetone
Beta-hydrocybutyrate
What is the normal plasma ketone body concentration?
,1mM
What is the plasma concentration of ketone bodies in starvation?
2-10mM (physiological ketosis)
What is the plasma concentration of ketone bodies in someone with untreated type 1 diabetes?
> 10mM (pathological ketosis)
Breath smells fruity
Where are ketone bodies synthesised?
Liver mitochondria
What are the features of ketone bodies?
Water soluble molecules
Permits relatively high plasma concentrations
Alternative substrate if glucose absent
What happens if ketone bodies are above renal threshold?
Excreted in urine
Ketonuria
