Lipid Metabolism Flashcards
What are lipids?
- a diverse class of molecules
- lipids are soluble in organic solvents
What is included as steroids?
hormones, vitamins, structural components of cell membranes
what are eicosanoids?
- carboxylic acids that act as second messengers in inflammatory responses
- they are synthesized from highly unsaturated FAs
What are triacylglycerols?
- esters of 3 carboxylic acids w/ glycerol
- the carboxylic acids are usually called FAs
- when we think of fat this is usually what we mean
What does C18:3 n-3 mean in fatty acid nomenclature?
- C18 means there are 18 carbon atoms in the fatty acid
- 3 means there are 3 double bonds in the fatty acid
- n-3 = the position of the first double bond from the methyl end of the molecule
(linolenic acid = omega 3)
What are saturated vs unsaturated FAs?
- saturated = no double bonds
- unsaturated = 1 or more double bonds
- polyunsaturated = 2 or more double bonds
- double bonds in the cis conformation are what is naturally produced by animals
- hydrogenation of FAs results in trans FAs
why do we hydrogenate fats?
b/c the more double bonds you have, the more likely that fat will remain liquid at lower temps
What are the 3 major roles of FAs?
- source of fuel
- building blocks of phospholipids & glycolipids (brain & retina)
- precursors for hormones & intracellular messengers & signaling
How are fatty acids stored?
as triacylglycerols
What do bile salts do?
emulsify big fat globules into smaller micelles so lipases can get easier access and break the triacylglycerols down into free FAs & monoglycerides to be transported across the gut epithelium
What do pancreatic lipases do to TAGs?
they hydrolyze them into 1 mc of glycerol & 3 FA mcs
How are FA absorbed?
- free FA are emulsified w/ bile salts into micelles (small droplets)
- micelles diffuse into the epithelial cell
- no energy required
What happens to fats in the epithelial cells of the gut?
- FA link to reform TAGs
- TAGs combine w/ proteins inside the golgi body to form chylomicrons
- chylomicrons diffuse into lacteals in the lamina propria of the villus
What is the internal structure of a villus?
How are chylomicrons transported in the bloodstream?
- chylomicrons may be joined by some other lipids (VLDLs -> more fat than protein) synthesized by the liver
- needs to be a release of lipase into the bloodstream to break down the TAGs in the chylomicrons & the VLDLs into free FAs to be taken up by cells
- cells use the free FAs for ATP or resynthesized TAGs for storage
- density of the chylomicrons get smaller as lipid is taken up by the cells & you end up w/ an LDL (bad cholesterol)
- LDL can be taken up by the liver for further processing but LDL in excess will remain in the blood & deliver cholesterol to the cells instead (stiffens mbs & causes atherosclerotic like changes)
- only really in humans & swine
- HDLs (good cholesterol) are synthesized by the liver (high in most other spp)
- these are cholesterol scavengers & pull excess from your tissues, removing stiffness
What is the source of lipase in the blood (not the gut -> that is the pancreas)?
- hormone sensitive lipase in the blood released in response to stress or glucagon, etc. in anticipation of a meal or due to a need for energy
Where is the main energy storage in the body?
- fat reservoir in adipocytes
Why are TAGs more concentrated stores of metabolic energy than proteins or carbs?
b/c they are anhydrous (no water so can pack more into a given volume) & highly reduced
How much energy does complete oxidation of a FA yield compared to that of carbs or protein?
FA = ~9 kcal/g
CHO & Prot = ~4 kcal/g
Where are TAGs stored?
in the cytoplasm of adipose cells
How do you get ATP from FAs?
FAs can be broken down through B-oxidation into acetyl-CoA, fed into the TCA cycle to get ATP
What are medium-chain triglycerides (MCTs)?
- triacylglycerols w/ FAs that have 6-12 Cs
- these FAs are too short to be easily used for storage (in fat) or synthesis of essential FAs
- they are catabolized for energy instead
- theoretically less likely to cause weight gain
what are the essential FA and how do we use them?
C18:2 n-6 linoleic acid & C18:3 n-3 linolenic acid are nutritionally essential in vertebrates
- plants can usually only produce FAs up to 18 carbons
- animals need FAs w/ greater than 18 Cs for metabolites
- they can usually elongate linolenic & linoleic acids
- these are low in Western Diets
What is meant by “you are what you eat”?
- the FA composition of the animal mirrors the FA composition of their diet
- they can do a small amt of bioconversion of FA
