introduction to lipids Flashcards
1
Q
what are the functions of lipids? 3
A
- phospholipids and cholesterol: cell membranes
- triglyceride is a key energy store
- steroids and fatty acids play regulatory roles as hormones, vitamins and bile acids
2
Q
explain how cellular energy is stored short term? 4
A
- 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
3
Q
how is some energy stored inside the cell when you can’t have anymore ATP?
A
creatine phosphate
4
Q
how can energy be stored long term? 2
A
- large, stable efficient energy precursors
- carbohydrates and fats
5
Q
what is acetyl-CoA used as? 4
A
- an energy mediator
- converts glucose into cholesterol, citric acid+ amp and fatty acids
- cannot be transported in plasma
- instead organisms use Co-enzymeA
6
Q
what can the production of cholesterol be blocked by?
A
statins
7
Q
explain carbohydrates as energy? 4
A
- 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
8
Q
where is there no glycogen?
A
in the brain as it needs glucose or ketone bodies from plasma constantly
9
Q
what is the citric acid cycle? 6
A
- 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
10
Q
what does fatty acid synthesis leads to? 2
A
- fatty acids with an even number of carbons
- this consumes ATP
11
Q
what is beta-oxidation? 2
A
- breaking down fatty acids
- fat mobilisation which shortens fatty acid by 2 carbons at a time, this produces ATP and acetyl-CoA
12
Q
what are fatty acids? 4
A
- simple straight carbon chains +COOH
- in humans they are mostly 16-20 carbons long
- 50% have double bonds
- acyl group
13
Q
explain double bonds in fatty acids and what they mean? 3
A
- 0 double bonds= saturated
- 1 double bond=monounsaturated
- 2 or more double bonds= polyunsaturated
14
Q
what is cholesterol? 5
A
- 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
15
Q
what are cholesterol esters? 3
A
- 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
16
Q
what are steroids? 4
A
- 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
17
Q
what are ketone bodies? 6
A
- 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
18
Q
what is special about the melting point of unsaturated fatty acids? 2
A
- lower
- more liquid at room temperature which increases the fluidity of cell membranes
19
Q
why do manufacturers use saturated fats?
A
- they are less vulnerable to rancidity and are, in general, more solid at room temperature than unsaturated fats
20
Q
explain cis and trans carbon chains? 4
A
- 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
21
Q
what do fatty acids in diet affect? 6
A
- 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
22
Q
what are the 4 pathways for lipid transport?
A
- 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)
23
Q
explain the exogenous pathway? 3
A
- lipids from diet
- packaged by small intestine into chylomicrons (increased lipids in plasma after fatty meal)
- chylomicrons taken up by the liver or periphery
24
Q
explain the endogenous pathway? 2
A
- made in the body
- lipid from liver packaged into the VLDL
25
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
26
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
27
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
28
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)
29
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
30
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
31
what are HDLs? 4
- the good lipoprotein
- increased HDL means lower cardiovascular risk
- lipid reverse cholesterol transport
- appears when cholesterol is being used up
32
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
33
what is IDL? 3
- intermediate density lipoproteins
- IDL will become LDL
- is a sign of CV risk
34
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
35
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
36
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
37
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
38
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
39
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
