Lipid Metabolism Flashcards
what are the 4 biological roles of lipids?
- energy source
- structural components of all membranes
- lubricants (oils in the body)
- signaling molecules (cholesterol is precursor to all steroids)
where (3) and when does fatty acid synthesis occur?
in liver and adipose tissue, and lactating mammary glands during the fed state
what happens to the fatty acids synthesized in the liver?
they become VLDLs
what happens to the fatty acids synthesized in adipose tissue?
they are stored
what happens to the fatty acids produced in lactating mammary glands?
they are incorporated into milk fat
give the steps of the citrate shuttle to get citrate out of the mitochondria and into the cytosol
- pyruvate is converted to acteyl CoA by pyruvate dehydrogenase and input conversion of NAD+ to NADH + H+ and of CoAsh to CO2
- acetyl CoA combines with oxaloacetate and is converted to citrate by citrate synthase and input of H2O and release of CoAsh
- that citrate is then either shuttled to the cytosol to be converted back to acetyl CoA and oxaloacetate by ATP-citrate synthase and input of H2O and CoASH and input conversion of ATP to ADP + Pi in exchange for one molecule of malate, then the acetyl CoA enters the first committed step of fatty acid synthesis or
- is converted to isocitrate by aconitase
give the formula for fatty acid synthesis
7 malonyl CoA + Acetyl CoA + 14 NADPH + H+ yields plamitate + 8 CoASH + 7 CO2 + 14 NADP+ + 6 H2O
how is acetyl CoA carboxylase (which converts acetyl coA to malonyl coA) regulated?
- activate by citrate
- activated by insulin and glucose
- inhibited by glucagon
what is palmitate?
a completely saturated 16 carbon fatty acids chain with no double bonds
in the endoplasmic reticulum, what two things can happen to plamitate?
- elongation
2. desaturation
what is elongation?
2 carbons can be added one at a time from a malonyl coA
what is desaturation?
formation of unsaturated FAs, add one double bond at a time
what are the only 3 positions that double bond can be added to on palmitate?
- delta 9
- delta 5
- delta 6
what does delta mean for number of the palmitate chain?
number beginning from the carboxyl end
what does omega mean for numbering of the palmitate chain?
number beginning from the methyl end
describe how elongation and desaturation and essential omega fatty acids work together to add double bonds to palmitate
desaturation can only add double bonds at delta 9, delta 5, and delta 6 carbons, but as the chain is elongated, there are now new delta positions so more double bonds can be added there. omega fatty acids can add double bonds to the methyl end of the chain, so by working together and great number of double bonds can be added to our chain
describe how the citrate shuttle is regulated via the citric acid cycle
isocitrate dehydrogenase, which converts isocitrate to alpha-ketogluterate, is inhibited by a high NADH + H+ to NAD+ ratio. when this ration is high, it leads to a buildup of isocitrate which is then converted to citrate by aconitase (a reversible reaction) and enters the cytosol for fatty acid synthesis instead since ration indicated we have enough energy to store it as fatty acid
what is TAG?
glycerol + 3 FAs
where does TAG synthesis occur?
in the endoplasmic reticulum
what is TAG synthesis a vital prerequisite for?
TAG synthesis must occur for liver transport and storage of fatty acids and adipose storage of fatty acids
describe TAG transport or storage in the liver (3)
- TAG is packaged into VLDLs and enter the bloodstream
- then taken up by extrahepatic tissues (FAs can go anywhere)
- this is facilitated by lipoprotein lipase
in the fed state, where does a lot of TAG packaged into VLDLs go?
to adipose tissue
when does mobilization of stored TAG occur?
in the fasted state
describe how mobilization of fat (stored TAG) occurs (3)
- hormone sensitive lipase in adipose will break down TAGS into glycerol and free FAs
- glycerol goes to the lvier for gluconeogenesis
- fatty acids enter the bloodstream and are used for energy by other tissues
how are free fatty acids transported through the blood following fat mobilization?
by albumin
describe regulation of hormone sensitive lipase
- inactivated by insulin
2. not activated by glucagon, just activated by the absence of insulin
what is the rate of fatty acid oxidation proportional to?
proportional to free fatty acid concentration in plasma
where does fatty acid oxidation occur? what does this mean?
occurs in the mitochondria, so fatty acids have tog et to the mitochondria
how do free fatty acids get to the mitochondria for fatty acid oxidation?
the carnitine cycle
describe the carnitine cycle, which is how fatty acids get to the mitochondria for oxidation
- fatty acids enter the cell and are converted to fatty acyl CoAs (FACoA)
- CPT-I replaces CoA with a carnitine to create fatty acyl carnitine (FA carnitine) and release of CoA
- carnitine-palmitoylcarnitine translocase transports FA carnitine into mitochondria in exchange for a carnitine
- CPT-II replaces carnitine with CoA to create FaCoA
what is B (beta) oxidation?
the break down of FACoA to acetyl CoA
where does B oxidation occur?
in the mitochondria
what is the function of B oxidation?
to supply energy
when does B oxidation occur?
some in the fed state but mostly occurs in the fasted state
give the equation for B oxidation
palmitoyl CoA + 7 CoASH + 7 FAD + 7 NADH+ + 7 H2O yields 8 acetyl CoA + 7 FAOH2 + 7 NADH + 7 H+
how much ATP is rpdocued from B oxidation of one palmitoyl CoA to acetyl CoA? give breakdown
FADH2 gives 7 x 1.5 ATP = 10.5 ATP
NADH+H+ give 7 x 2.5 ATP = 17.5 ATP
equals 28 ATP
what happens to the 8 acetyl CoA’s produced from B oxidation? how much ATP total from the 8 acetyl CoA’s?
they enter the citric acid cycle to yield even more ATP
1 acetyl CoA from citric acid cycle yields 10 ATP x 8 = 80 ATP from the acetyl CoA’s from B oxidation
from B oxidation plus citric acid cycle of the acetyl CoA’s produced in B oxidation, how much total ATP is yielded per one molecule of palmitate?
108 ATP
