lipid metabolism Flashcards
what are lipids? what are the three main types?
- diverse biological compounds> low solubility in water
- steroids, triglycerides and phospholipids
what are the roles of steroids?
- cell signalling
- membrane function
what are the roles of fatty acids and triglycerides?
- high ATP yield
what do phospholipids form?
- form membranes
- present at interface between lipids and water
how do lipids differ to carbohydrates?
- lipids= hydrophobic
- longer the chain and fewer double bonds= lower solubility
- diff structural properties alters digestion, absorption and metabolism
what makes up phospholipids? what do they affect?
- consists of a glycerol unit connected by 2 FA’s and a phosphoric bond via ester bonds
- affect cell signalling
what are membrane lipids referred to as?
- amphipathic
- because one end is hydrophobic while other is hydrophilic
describe triacylglycerol
- 90-95% of dietary fat
- energy store in adipose tissue & muscle
- one glycerol unit and 3 FFA’s connected by ester bonds
what do lipid hydrolases involve?
- lipoprotein lipase, hormone- sensitive lipase and adipose TAG lipase
what fibres are TAG stores greater in?
- greater in type 1 muscle fibres compared to type 2
what needs to happen before TADs goes through the membrane?
- must be broken down in order to pass through
describe the first step of digestion and absorption regarding the lipid droplets
- lipid droplets are reduced in size via bile acids made in the liver and released in the gallbladder
what happens in the intestinal lumen during step 2 of digestion and absorption
- pancreatic lipid hydrolyses the ester bonds to yield 2FA’s and 2 monoglycerol
what do the fatty acids and monoglycerols do in step 3?
- enter the intestinal cells and reform triacylglycerols
describe step 4 in relation to chylomicrons
- lipids are packaged into chylomicrons
- exported into lymph nodes and into the bloodstream
what are chylomicrons?
- class of lipoprotein that transports insoluble triacyclglycerol
- single layer of phospholipids w a hydrophobic core
what happens once chylomicrons are formed?
- pass into extracellular space
- then lymphatic vessels and into the bloodstream
where is fat stored in the human body?
- mainly stored in adipose tissue & muscle (0.2-0.8%)
where is adipose tissue found? what percentage is in males/ females?
- subcutaneous fat (under skin)
- visceral fat (around organs)
- 15% in man, 23% in women
what is the cytoplasm of an adipocyte dominated by?
- large lipid droplet filled with triacylglycerol (80%)
- serves as huge energy reserve
where are triacylglycerol stores? why are they here?
- contained in lipid droplets w/ in adipocytes/ muscle fibres near mitochondria
- reduce distance for ATP production
what does exercise speed up?
- Fatty acids degradation in adipose tissue and muscle via beta- oxidation
what does beta oxidation produce? what does this enter?
- produces acetyl- coA
- enters the krebs cycle
what enzymes catalyse the breakdown of triacylglycerol?
- adipose TAG
- Lipase Hormone
- Sensitive Lipase
- monoacylglycerol
- acyltransferase
where does synthesis of triacylglycerol occur? what forms the TAG glycerol breakdown?
- occurs in cytosol
- glycerol generated from dietary glucose forms the TAG glycerol backbone
how are the three fatty acids added during the synthesis of triacylglycerols?
- added in 2 steps via enzyme Glycerol Phosphate Acetyltransferase
is synthesis or breakdown more predominant in fed state?
- synthesis of TAG> breakdown
is synthesis or breakdown more dominant during exercise?
- breakdown> synthesis of TAG
how do fatty acids circulate in the blood?
- attached to albumin
when does the lipolysis rate increase during exercise?
- within 5-10 minutes of exercise
what is the rate of lipolysis influenced by?
- epinephrine increases lipolysis via B- adrenergic pathway
- decreases lipolysis via a- adrenergic pathway
- insulin decreases pathway
what hormones are involved in low intensity exercise? what pathway does this drive?
- ^ epinephrine and decreases insulin
- drives the cAMP pathway activating AGTL, HSL + MGL
what hormones are involved in high intensity exercise? what does this suppress?
- ^ epinephrine and insulin
- supresses cAMP pathway
describe the fate of lipolysis products during exercise
- FFA’s in muscle remain& FFA’s from adipose tissue are imported into the muscle via FABP-PM
- boost available energy
what are fatty acids primarily used for?
- beta oxidation and ATP provision
what are fatty acids primarily used for in the liver?
- gluconeogenesis and some FFA may enter for triacylglycerol synthesis
how does fatty acid degradation in the muscle occur?
- occurs through beta oxidation in the mitochondria
how many steps does fatty acid degradation include? What do the steps do?
- 3 step process of activating FFA’s & transporting across the membrane
how are fatty acids activated in step 1?
- activated by a reaction with CoA forming Acyl- coA
- passes to the inter-membrane space
what happens in step2 of FFA degradation regarding the acyl group?
- carnitine takes the Acyl group allowing transport into the mitochondrial matrix
what happens to the acyl chain in the last step of degradation?
- acyl chain is then taken from carnitine to reform Acyl-coA in the matrix
what does beta- oxidation involve?
- oxidation of the B- carbon in the acyl chain
how does acyl- coA enter the beta oxidation pathway?
- in the mitochondrial matrix
how many reactions does 1 cycle of beta oxidation involve?
- 1 cycle involves 4 reactions that degrade acyl- coA
what are the products of beta oxidation? what do they enter?
- produces 8 acetyl-coA, 7FADH2 and 7NADH
- enter krebs cycle and ETC
- krebs cycle and ETC pull B- oxidation and yield a large amount of energy
what happens if there is an odd number of carbons in FFA’s?
- occurs when beta oxidation removes 2 carbons at a time
- once a 5 carbon acyl- coA molecule is reached it is broken down into acetyl- coA & a 3 carbon propionyl CoA molecule
what does 3 carbon propionyl CoA undergo to form?
- undergoes 3 reactions forming succincylCoA
- enters at reaction 5 of the KC
- then fully oxidised to generate ATP
how does exercise speed up fatty acid oxidation in muscles?
- stimulates lipolysis
^ blood flow= ^ FFA delivery - enhance translocation of FA binding protein at the plasma membrane
^ muscle uptake of FFA’s
what does exercise increase? what does this enzyme do?
- increased AMP- activated protein kinase
- deactivates acetyl-CoA carboxylase
- reduces FFA synthesis & favours lipolysis
what is the blood plasma fatty acid profile during low intensity exercise?
- slight initial increase which is maintained throughout
- post exercise small increase before returning to baseline
what is the blood plasma fatty acid profile during moderate intensity exercise?
- initial decrease before a gradual increase throughout
- large increase post exercise before baseline return
what is the blood plasma fatty acid profile during high intensity exercise?
- large initial decrease (reliant on anaerobic sources)
- sustained low throughout due to release of insulin
- post exercise large ^
what does ingesting carbohydrates during a prolonged exercise bout maintain?
- maintains plasma glucose
what would someone with a high fat and low carbohydrate diet have ?
- high plasma triacylglycerol use
what is FatMAX?
- max % of V02 where fat can be oxidised
what is max fat oxidation?
- rate of fat oxidation at a given intensity
what happens as exercise intensity increases?
- there is an increase of fat oxidation up to 60%
what are the points where carb and lipid connect?
- glycerol
- fatty acids
- oxaloacetate
describe how glycerol connect carbohydrate and lipid metabolism
- can be converted to glucose in the liver
- forms a minor part of triacylglycerol
describe how fatty acids connect carb and lipid metabolism
- meet at acetyl- coA but can’t be converted back to pyruvate
- can not replenish carbs
describe how oxaloacetate connects carb & lipid metabolism
- can be used to reform glucose through beta oxidation into acetyl- coA through the KC
- no conversion of acetyl- coA so it is lost as C02
can fatty acids be converted into glucose?
- no but glucose can be converted into FFA’s through acetyl-coA and through L-glycerol- 3-phosphate
what are plasma lipoproteins?
- carriers of TAG and cholesterol esters coated by phospholipids
what are apolipoproteins?
- signal sites on the outside> ratio of lipid to apolipoprotein mass determines property and function
what is rate of LDL: HDL a measure of?
- a measure of cardiovascular health
what are the measurements of the different lipoproteins?
chylomicrons= 0.92-0.94 g/mL
VLDL= 0.96-1.00g/mL
LDL= 1.02- 1.06g/mL
HDL= 1.06- 1.21g/mL
which lipoprotein contains the most cholesterol?
- low density lipoproteins
what do chylomicrons and VLDL carry?
- carry TAG
what do LDL and HDL carry?
- carry cholesterol but HDL carries it towards the liver
what is a healthy lipidemic profile?
- low triacylglycerols, total cholesterol and LDL with high HDL
where do chylomicrons enter from?
- enter the blood from the small intestine
how are chylomicrons broken down?
- broken down by lipases into TAGs for energy provision
where are chylomicron fragments transported to? what are they converted to?
- chylomicron fragments are transported to the liver & converted to VLDL
what happens to the VLDL?
- recirculated into the blood to then form LDL offloading more TAD
how many apolipoprotein isomers are there?
- 3 APOE
- w each persons carrying 2 alleles
describe Alzheimer’s disease risk factors
- risk is either ^ or decreased depending on how apolipoprotein E signals in the body
what is pathogenesis of obesity?
^ in energy uptake& decrease in EE
- adipose tissue dysfunction
- decreased adiponectin
- altered blood lipid profile
- increased inflammatory
- decreased risk
how is the effect of acute exercise on plasma lipids tested?
- by a fat tolerance test> pts ingest a high fat meal
- measure the response of plasma lipids to the meal
what can an acute bought of exercise lead to?
- can suppress TAG appearance in the blood plasma & improve lipid profile
what are the benefits of chronic exercise on lipids?
- shown to improve lipid profile
- increases adiponectin levels
what does adiponectin increase? what other benefits are there?
- increases lipid oxidation, improves insulin sensitivity and is linked to lower inflammation
is adiponectin higher or lower in obese people?
- lower
what does exercise lower in obese people?
- lowers inflammation
- however, unclear if it directly related to weight loss
what have lab studies demonstrated?
- exercise can match diet- induced weight loss however it is very complicated
what is the respiratory exchange ratio?
- volume of exhaled C02 divided by the volume of 02 consumed
