introduction to lipids Flashcards
what are the functions of lipids? 3
- phospholipids and cholesterol: cell membranes
- triglyceride is a key energy store
- steroids and fatty acids play regulatory roles as hormones, vitamins and bile acids
explain how cellular energy is stored short term? 4
- ATP (and other phosphate bonds)
- redox agents (NADH, FADH2)
- ionic transmembrane gradients (H+ across the mitochondrial membrane can drive the formation of ATP)
- all of the above are labile
how is some energy stored inside the cell when you can’t have anymore ATP?
creatine phosphate
how can energy be stored long term? 2
- large, stable efficient energy precursors
- carbohydrates and fats
what is acetyl-CoA used as? 4
- an energy mediator
- converts glucose into cholesterol, citric acid+ amp and fatty acids
- cannot be transported in plasma
- instead organisms use Co-enzymeA
what can the production of cholesterol be blocked by?
statins
explain carbohydrates as energy? 4
- starch is digested into sugars in the gut
- sugars are absorbed from gut into the bloodstream
- sugars are absorbed by the liver and stored as glycogen (via the hepatic portal vein)
- sugars are stored through the body as glycogen
where is there no glycogen?
in the brain as it needs glucose or ketone bodies from plasma constantly
what is the citric acid cycle? 6
- acetyl-CoA gets turned into energy by burning O2 and CO2
- start with a 4 carbon chain
- acetyl-CoA gets added to make citric acid ( a 6 chain carbon)
- oxygen is then added
- this releases carbon dioxide and ATP
- the 4 carbon chain is then reformed and the cycle continues
what does fatty acid synthesis leads to? 2
- fatty acids with an even number of carbons
- this consumes ATP
what is beta-oxidation? 2
- breaking down fatty acids
- fat mobilisation which shortens fatty acid by 2 carbons at a time, this produces ATP and acetyl-CoA
what are fatty acids? 4
- simple straight carbon chains +COOH
- in humans they are mostly 16-20 carbons long
- 50% have double bonds
- acyl group
explain double bonds in fatty acids and what they mean? 3
- 0 double bonds= saturated
- 1 double bond=monounsaturated
- 2 or more double bonds= polyunsaturated
what is cholesterol? 5
- essential component of cell membranes
- precursor of bile acids, steroid hormones and vitamin D
- ring system makes it very rigid
- from the diet or made in the liver
- major emphasis on recycling- a lot is used in bile salts- endogenous pathway needs cholesterol
what are cholesterol esters? 3
- a large portion of plasma cholesterol is esterified (75%)
- broken down by lipases to free cholesterol and fatty acids
- cholesterol is amphipathic (both hydrophilic and hydrophobic parts) as the alcohol group is hydrophobic when esterified
what are steroids? 4
- cholesterol
- vitamin D - produced by skin by the action of light on a cholesterol derivative
- cortisol- hormone secreted by the adrenal cortex
- testosterone- male sex hormone
what are ketone bodies? 6
- soluble chemicals
- made from acetyl-coA during fasting, by the liver
- lasts for 5 hours
- ‘use it or lose it’
- during fasting they are the main energy source especially by the brain and the heart
- acetone is a waste product made spontaneously by decarboxylation and is eliminated by the kidney
- Acetoacetic acid and beta-hydroxybutyric acid
what is special about the melting point of unsaturated fatty acids? 2
- lower
- more liquid at room temperature which increases the fluidity of cell membranes
why do manufacturers use saturated fats?
- they are less vulnerable to rancidity and are, in general, more solid at room temperature than unsaturated fats
explain cis and trans carbon chains? 4
- cis carbon-carbon double bonds (cis unsaturated fats) create a kink
- the kink lowers the melting temperature
- saturated fats and trans unsaturated fats lack this kink
- the kink interferes with stacking and solidification, making it liquid
what do fatty acids in diet affect? 6
- cholesterol levels
- triglyceride levels
- trans unsaturated fats are bad
- saturated fats are bad and increase LDL
- cis unsaturated fats are either monounsaturated or polyunsaturated, and are probably good for you
- high melting temperature= soluble and non mobilisable
what are the 4 pathways for lipid transport?
- exogenous pathway (from gut to liver and periphery (muscle and adipose tissue))
- endogenous pathway (from liver to periphery)
- reverse cholesterol transport (from periphery to liver)
- bile production (from lover into gut)
explain the exogenous pathway? 3
- lipids from diet
- packaged by small intestine into chylomicrons (increased lipids in plasma after fatty meal)
- chylomicrons taken up by the liver or periphery
explain the endogenous pathway? 2
- made in the body
- lipid from liver packaged into the VLDL
explain the reverse cholesterol transport? 2
- occurs when lipid supplies in liver are being exhausted- thus a sign of reduced body lipid
- HDL in blood indicates reverse path activity
explain bile production? 4
- bile released into the cystic duct
- cholesterol is converted into bile ducts
- bile is necessary to digest fats in diet as it emulsifies fat
- most bile acids are reabsorbed by the gut and returned to the liver and recycled
what is needed for pathway to move fats in and out of blood vessels? 6
- receptors and enzymes
- lipoprotein lipase
- metabolises triglycerides into fatty acids and glycerol
- this is because TG cannot go through the cell membrane
- cells surface-linked enzyme s in capillary walls
- in order to remove TG from VLDL and to move the TG across the capillary membrane, the TG must be metabolised by lipoprotein lipase
what are lipoprotein particles? 4
- lipids are not soluble in plasma
- they must be packaged to be transported
- lipoprotein particles in plasma are soluble and carry lipids
- apolipoproteins: proteins in LP particles that can hold lipids and they are amphipathic (detergent like)- apolipoprotein E (apoE)
how are lipids identified? 4
- lipid is much less dense than protein
- triglycerides are very low density
- cholesterol is mid-way between Tgs and proteins
- bigger lipoprotein particles usually are carrying a lot of lipids thus are lower in density
what are LDLs? 6
- low density lipoprotein
- most dangerous lipoprotein
- LDL contents get incorporated in atheroma
- LDL in blood may be storage for cholesterol that cannot be stored elsewhere
- excess LDL accumulates in atheroma
- LDL is eventually left over after periphery absorbs endogenous TG from VLDL from liver
what are HDLs? 4
- the good lipoprotein
- increased HDL means lower cardiovascular risk
- lipid reverse cholesterol transport
- appears when cholesterol is being used up
what are VLDLs? 4
- very low density lipoprotein
- signifies risk of atheroma
- transport endogenous cholesterol and TG from liver to adipose and muscle
- after TG is removed by periphery from VLVL, IDL is left
what is IDL? 3
- intermediate density lipoproteins
- IDL will become LDL
- is a sign of CV risk
what is chylomicron? 3
- not usually associated with CV risk
- normally high after fat containing meals
- carries lipids from gut to periphery for exogenous lipids
what happens in the islet of langerhans in the pancreas? 2
- beta cells release insulin when there is too much blood glucose
- alpha cells release glucagon to convert glycogen into glucose
what is type II diabetes mellitus? 6
- adult onset diabetes
- high blood glucose
- poor plasma glucose control
- insulin resistance
- relative insulin deficiency
- obesity/genetic predisposition
what is hypercholesterolaemia? 5
- high fasting levels of plasma cholesterol
- hyperchol is a subclass
- increased risk of ateriosclerosis
- HDL reduces risk
- due to combination of environmental and genetic factors
what are statins? 4
- drugs used to treat hypercholesterolaemia
- block endogenous cholesterol synthesis by blocking HMG-CoA reductase
- the entry step to cholesterol synthesis
- simvastatin is one of the most commonly prescribed drugs especially in men over 50
what is metabolic syndrome? 2
- a group of risk factors that occur leading to increased risk for CAD, stroke and type 2 diabetes
- main causes: insulin resistance, central obesity, waist circumference and high blood pressure
