lipids Flashcards
what are the main classes of lipids
fatty acids phospholipids triacylglycerol TAG steroids glycolipids
what is a lipid?
an organic, hydrophobic molecule
fat
Where are lipids found?
in cell membranes
in the blood
in droplets in adipose tissue
function of lipids?
structural component of membranes energy stores enzyme co-factors (g-proteins) signalling molecules hormones
How are FA’s released from TAGs
so when the ephinephrine adrenaline levels increase (sympathetic) energy is required so need to release FA’s from stores in adipose tissue
this increase causes kinases to activate lipases which hyrdolyse TAGs and release FAs into the circulation
in the blood unesterified FA’s are carried by albumin proteins and esterified FA’s are carried by lipoprotein like chylomicrons to other organs or tissues
starvation and ketosis
when in periods of starvation or energy deprivation ketosis occurs
low glucose and energy levels
Fatty acids produce acetyl CoA- so if the levels of CoA are too high then it inhibits pyruvate dehydrogenase and activates pyruvate carboxylase which causes oxaloacetate to be diverted for gluconeogenesis
if acetyl CoA can no longer feed into C.A.C and bind with oxaloacetate then ketosis occurs and it’s turned into ketone bodies
what can ketone bodies be used for in the body?
skeletal and cardiac muscle can use them for fuel/energy
also the brain
the liver cannot use them
how can excess ketone bodies be harmful?
they can cause the body to become very acidic
how is it identified in a patient that they may be producing ketone bodies? and which patients are likely to have this problem?
a fruity odour on their breath
diabetic patients as they don’t produce enough insulin so without this they break down fat for energy… so increase in acetyl CoA etc
breakdown of TAG process
starts in the mouth with amylase
then broken down in the small intestine by the action of bile salts and pancreatic lipases creating monoglycerol and 2 fatty acid chains
After digestion, monoglycerides and fatty acids associate with bile salts and phopholipids to form micelles. Micelles transport these molecules to the enterocyte (cells) to be absorbed (only the monoglycerides and fatty acids can pass through the membrane)
in the enterocyte- they are re-synthesised into TAG and then they get taken up by protein to move into the circulation.
Fatty acid synthesis key points:-
where?
start and end product?
what energy does it use up?
occurs in the cytosol in the liver, lactating mammary gland or adipose tissue
starts with acetyl CoA and ends with palmitic acid (fatty acid)
uses ATP and 14 NADPH
Citrate shuttle
acetyl CoA is split to form citrate which then moves through the mitochondrial membrane
once through CoA is added back on producing oxaloacetate
oxaloacetate is then turned into malate (NADH used)
malate is turned into pyruvate (which can shuttle back across the membrane) NADPH used
now we have acetyl CoA in the cytosol.
what shuttle is needed to move from mitochondria to cytosol?
citrate shuttle
what shuttle is needed to move from cytosol to mitochondria?
carnitine
Process of fatty acid synthesis after citrate shuttle?
acetylCoA carboxylase (activated in high levels of citrate) is needed to turn acetyl CoA into malonyl CoA lots of steps but overall 8 acetyl CoA make 1 palmitate
then multi-functional fatty acid synthase (a massive 7 enzyme structure) is used
has an ACP arm that moves substrate from one active site to the next along chain
it synthesises fatty acid 2 carbons at a time
makes palmitic acid (a common fatty acid)
