lipid metabolism Flashcards
(39 cards)
types of lipids and functions
triglycerides (fuel)
glycerophospholipids (membranes)
cholestserols (steroid hormones for communication, bile salts for digestion)
vitamins
triglycerdies
glycerol
3 fatty acids
joined by ester bonds
unsaturated or saturated
sources of triglycerides
diet
carbohydrates (in liver)
how can we absorb dietary liqpids
need to be converted to a more absorbable form
1) Bile salts (from gull bladder) and molecules from the pancreas ( lipases, co-lipases, bicarbonate ions) emulsify into small droplets of the fat
2) These have larger SA
3) therefore can be broken down by lipases into fatty acids from triacylglycerols
4) form micelles (fatty acids and 2 monoaclglycerol), absorbed by epithelial cells lining the small intestine (via the action of bile salts)
5) fatty acids and 2 mono..) are put together with some other fats, cholesterol and apolypoproteins which then bind with nascent chylomicrons
6) leave the cell into the lymphatics, packaged as chylomicrons to move around the bloodstream
chylomicrons
fat bundled in micelles
how are chylomicrons formed
- micelles enter via diffusion (fat soluble) through membrane
- processed through small ER which reforms the triaglycerols from the fatty acids
- apolypoprotiens are added from vesicles from RER
- proteins added to the bundles of fat
- golgi then processes further to modify them ect
chylomicron strucures
phospholids on outside inside - non polar fats - tryglycerols, cholesterol ext apopprotin can sit or embed in phospholiuds
where are chylomicrons exocytosed to
into lymphatics
mature in blood stream
Chylomicron fate
- Chylomicrons formed by cells of gut and enter lymphatics into blood stream
- recognised by lipoproteins of target cells
- lipoprotein lipase recognise due to the apoproteins in the surface (recognition signals)
- allows fatty acids to enter the tissues
- glycerol and other remnants go back to the liver
- can then be repackage into chylomicrons or other
fate of fatty acids and tissues
muscle use for energy
repacked into triglycerol to store fat
what happens to chylokmiron remnants
- recognised by receptors on liver
- taken up in endocytic vesicles
- components left over from the chylomicrons (cholesterol, cholesterol ester, amino acids- from the apoproteins, glycerol) can be used in the liver
chylomicrons entering fatty tissue
- Triacylglycerols digested by lipoprotein lipase (LPL), sits on surface of cells that want to use fat
- LPL produced by adipose (Fat storage), muscle (for burning energy) and lactating mammary gland cells (production of milk)
- Regulated by insulin, can be released and absorbed
- Fatty acids (from the triacylglycerols) absorbed by cells; other remnants (glycerol) are absorbed by liver
generating fat from carbs
e. if you eat too much food, stored as fat
- fatty acids and glycerol synthesized in the liver
- glucose is the source of carbons
- reactions occur in the cytosol/cytoplasm
fatty acids can be stored as triacylglycerols, oxidised as fuel or used to make components of membranes
wha are fatty acids packaged with once synthesised in liver
with proteins to form VLDL(lipoprotein)
what happens if fats are required for tissues outside the liver
need to be package
then can circulate rest of body
where are endogenous lipids formed and how
in liver
- Glycolysis pathway from glucose
- DHAP (dihydroxyacetone phosphate) precursor for glycerol 3 phosphate then into glycerol
- other components of the pathway can be used to make fatty acids(citrate to acetyl co a to malonyl co a to palmitate), this can combine with the glycerol 3 phosphate made to form triacylcerate
(glycolysis can use intermediates)
- once triglycerols made packaged with apoldprotein, phosphloids, cholesterol, cholesterol estesrs
- released as low density lipoprotein into the blood
how are the endogenous lipids (triglycerides) packages to form lipoprotins
with proteins from RER processes through golgi into exocytic vesicles - into lipoproteins termed VLDL (very low density lipoproteins) FROM ENDOGENOUS LIPIDS NOT DIETARY
VLDL fate
Triacylglycerols digested by lipoprotein lipase (LPL) (just as chlymicrons
- LPL is produced by adipose, muscle and lactating mammary gland cells
- Regulated by insulin
- Fatty acids absorbed by cells, by the cells that need access to this fat
- VLDL remnant remains
what happens to the VLDL remnants
- Glycerol recycled to the liver, can then be packaged with fatty acids (produced from citric acid cycle) packaged together to form CLDL
- recognised by lipoprotein lipase on target cells
- fatty acids taken up by cell
- glycerol released, remnant components remain
what is an energy source during fasting
fatty acids
fatty acid oxidation
- long chain fatty acids released from adipose tissue, stimulated by reduced insulin and increased glucagon (when we need to release fuel for the tissues)
- taken up by other tissues and used as a fuel eg muscle, either come from the chylomicrons, VLDL or from acids released from adipose tissue (3 different sources)
- several different pathways but main one is Beta oxidation
Beta oxidation steps
Fatty acids enter tissues by diffusion
activated to fatty acyl CoA (via fatty acyl AMP) using ATP
- fatty acyl-CoA transported into mitochondria
- converted to acetyl CoA, producing NADH, FADH2
repeated until all carbons have been converted to acetyl CoA (2C)
- acetyl CoA enters TCA cycle (to produce electron carriers to donate e-) to produce ATP
Fatty acids can be very long i.e. contain lots of carbon, this produces lots of energy
Acetyl Co A only 2 carbons
- 1 ATP used in the TCA cycle, but can still produce much more ATP overall as many carbons are found in the fatty acid tails (net gain)
- Fatty acyl Co A processed to produce acetyl co A to enter TCA cycle
- process repeats again due to the long chain
what can fatty acyl Co A be used for
- remake triacylglycerols for energy storage
- used to make membrane lipids (eg phospholipids)
- used to make energy
types of cholesterol
bile salts
steroid hormones
