Lipid metabolism Flashcards
lipids
- solubility in water
- how does the length of the chain and number of double bonds impact solubility in water
- 4 examples
- what 2 lipids are important energy sources
- low solubility
- longer chain, fewer double bonds, lower solubility
- Fatty acids
- Triacylglycerols
- Steroid
- Phospholipids
- FFAs and TAG
difference between a saturated and unsaturated fat
- unsaturated has at least 1 double bond
phospholipids
- what do they do
- what makes them up and the bonds
- part of cell memebrane
- hydrophilic phosphate head attached to a glycerol unit which is attached to 2 hydrophobic fatty acids, all connected via ester bonds
triacylglycerols
- where are they usually found
- what do they do in the body
- what are they made of
- dietary lipids
- energy store in adipose tissue and muscle
- 1 glycerol unit and 3 fatty acids connected by ester bonds
digestion and absorption of triacylglycerols
- Ingestion- Large lipid droplets reduced in size to fine lipid droplets by bile acids (made in liver & released by gallbladder)
- Intestinal lumen- pancreatic lipase hydrolyses the ester bonds forming 2 fatty acids and 2-monoacylglycerol (1 FA to glycerol)
- Enterocytes- these products freely enter the intestinal cells where TAG is reformed
- Bloodstream- lipids packaged into chylomicrons and exported into lymph nodes, then the blood and are distributed for energy metabolism or storage
chylomicrons
- structure
- function
- Single layer of phospholipids with a hydrophobic core
- transport triglycerides and deliver them to body cells
fat content of the human body
- where are lipids stored in the body
- what is visceral fat and subcutaneous fat
- impact of lipolysis during exercise
- adipose tissue, and muscle
- sub is fat under skin, vis is fat around our internal organs
- breakdown triacylglycerol for energy to field muscles during exercise
breakdown and synthesis of triacylglycerols
- where do they both occur
- 3 key enzymes that allow lipolysis
- what happens to glycerol after breakdown
- what happens to glycerol during synthesis
- the cytosol of adipose tissue and muscle
1. Adipose TAG Lipase (AGTL)
2. Hormone-sensitive lipase (HSL)
3. Monoacylglycerol acyltransferase (MGL) - to the liver to form glucose or can be used to re-synthesise triacylglycerol
- Three fatty acids are added to glycerol in 2 steps via the enzyme glycerol phosphate acyltransferase
exercise and lypolysis
- 3 influencers of the rate of lipolysis
- low-moderate intensity exercise
- high intensity exercise
1.Epinephrine: increases lipolysis (β-adrenergic pathway)
2.Epinephrine also decreases lipolysis (α-adrenergic pathway)
3.Insulin reduces lipolysis
↑ [epinephrine] and ↓ [insulin] drive the cAMP pathway favourably to activate AGTL, HSL & MGL
↑ [epinephrine] and stable or ↑ [insulin] suppress the cAMP pathway to inhibit AGTL, HSL & MGL, carb fuel source used more due to this
what happens to lipolytic products during exercise of muscle and liver
- Muscle – FFA are primarily used for β-oxidation and ATP provision
- Liver – glycerol is used for gluconeogenesis and some FFA may enter for Triacylglycerol synthesis
fatty acid degradation in the muscle
- what is the process called
- where does it happen
- one challenge for fatty acids
- how does it overcome this challenge
- what does a single cycle of beta-oxidation produce
- what happens after 1 cycle and when does it finish
- β-oxidation in the mitochondria where it must cross 2 membranes
1. FFA’s react with Coenzyme A forming Acyl-CoA which can pass to the inter-membrane space
2. the AA Carnitine binds to and takes the Acyl group (forming Acylcarnitine), allowing transport into the mitochondrial matrix
3. Acyl-CoA is then reformed inside the mitochondrial matrix
4. Acyl-coA enters the β-oxidation pathway (cleavage of the 3rd carbon = beta) in the mitochondrial matrix - A single cycle of β-oxidation (4 reactions that degrade acyl-coA) produces: x1 acetyl-coA, x1 FADH2, x1 NADH, and Acyl-coA (Minus 2 carbons)
- Acyl-coA then begins another cycle until you are left with 2 carbon acetyl coA which enters the TCA cycle (fully oxidised)
what does acyl mean
Acyl denotes any fatty acid chain and therefore some fatty acids undergo more cycles of β-oxidation, e.g. palmitate (16 carbons) undergoes 7 cycles (last cycle yields 2 acetyl coA)
energy yield of beta oxidation
- produces no ATP
- but produces acetyl co a, NADH and FADH2 that enter the TCA cycle and ETC to the produce huge amounts of ATP
beta-oxidation removes 2 carbons at a time, what happens when there’s an odd number of carbons in fatty acids
- once a 5 carbon acylCoA molecule is reached we get 2C AcetylCoA as normal and a 3-carbon Propionyl CoA molecule
- This then undergoes 3 reactions, forming SuccinylCoA which enters at reaction 5 of the TCA cycle
- then oxidised but misses reactions 4 and 5 producing NADH so less energy efficient
4 ways exercise speeds up fatty acid oxidation
- Stimulating lipolysis in adipose tissue and muscle
- Increasing blood flow to the working muscle, increasing FFA delivery
- fatty acid binding protein (FABP-PM) moved to a better place on plasma membrane for greater FFA uptake into muscle
- Increasing activity of AMP-activated protein kinase (AMPK), which deactivates acetyl coA carboxylase, reducing synthesis of longer fatty acid and triacylglycerols
