case 5 - teach me physiology lipid metabolism Flashcards
what are cholesterol and phospholipids used for
functions such as the synthesis of the cell membrane and the synthesis of steroid hormones
what happens when energy is needed from the fat stored in adipose tossue
triglycerides are hydrolysed into fatty acids and glycerol by triglyceride lipase
what is this stimulated by
adrenaline and glucagon
where do these fatty acids then go and what do they do
they enter the circulation where they bind immediately to albumin. when conjugated to albumin, the fatty acids are soluble in blood and so can be transported to tissues including the liver
what happens when glycerol enters the hepatocytes
glycerol is immediately converted into glycerol-3-phosphate, which then enters the glycolysis pathway.
what happens in the mitochondria
fatty acids need to be oxidised and degraded, this occurs in the mitochondria by a series of reactions known as beta-oxiidation
what happens in beta oxidation
two carbon segments are progressively released from the fatty acid chain until acetyl-CoA is generated.
NADH and FADH2 are generated as byproducts
what then happens to this acetyl-CoA
it binds immediately with oxaloacetate to form citrate and then enters the TCA cycle to release energy in the form of ATP
what is excess acetyl-CoA converted into
acetoacetic acid using HMG-CoA as an intermediate and then transported to other tissues
what is the acetoacetic acid converted into
beta-hydroxybutyric acid, and small amounts of acetone.
what is acetoacetic acid
a keto acid
what are acetoacetic acid, beta-hydroxybutyric acid and acetone known as
ketone bodies
what can ketone bodies do
can travel in the blood to other tossies where they are then used for energy. however, they can also play a significant role in disease states.
what is lipogenesis
is an essential mechanism that provides an energy store which can be used at times when the body’s energy requirement cannot be met by glucose alone
when and how are fatty acids synthesised
synthesised within the cytoplasm of the hepatocytes, following maximal conversion of glucose to glycogen.
what happens to the remaining glucose
is converted to pyruvate via the glycolysis pathway, and transported into the mitochondria where it is converted to acetyl-CoA
what is the citrate shuttle
If not entering the TCA cycle, acetyl-CoA needs to leave the mitochondria and enter the cytosol. However, the inner mitochondrial membrane is impermeable to acetyl-coA, and therefore it must traverse the membrane in an altered form; as citrate
explain the steps of the citrate shuttle
Acetyl-CoA joins with oxaloacetate to form citrate
Citrate is able to cross the mitochondria membrane
Citrate is then converted back into acetyl-CoA and oxaloacetate within the cytosol
what happens once the acetyl-CoA is in the cytosol
it can be converted to malonyl-CoA by acetyl-CoA carboxylase. this step is important in the regulation of lipogenesis as it is allosterically activated by citrate and inhibited by AMP
what does fatty acid synthase then do
creates an elongated fatty acid chain from the malonyl-CoA molecules, adding two carbon atoms for each molecule of malonyl-CoA.
what happens as the malonyl-CoA molecules are added
they lose a carbon atoms creating CO2
what are triglycerides made from
three fatty acid molecules and a molecule of glycerol
what transports triglycerides from the liver to their destination in adipose tissue
very low density lipoprotein (VLDL)
what are the hormones that regulate lipogenesis
glucagon and adrenaline are the hormones that inhibit lipogenesis. alongside negative feedback from the presence of lipoproteins in the blood.
what is the main hormone to stimulate lipogenesis
insulin
