ENERGY STORES - LIPIDS

what are some features of triacylglycerol's

Primary storage form of lipids (predominantly in adipose tissue, but also in small amounts in liver & muscle - too much in these impairs cellular function)

what are two types of adipose tissue

white and brown adipose tissue

what are features of adipose white tissue

must of the cell is filled with a fat droplet

few mitochondria

storage of triacylglycerol's

what are features of adipose brown tissue

multiple small fat droplets

many mitochondria

highly oxidative

non shivering thermogenesis

how are lipids transported in the circulation

fatty acids

lipoproteins

which organ plays a central role in lipid and lipoprotein metabolism

the liver

How are TAGs transported?

Chylomicrons transport TAGs absorbed form the gut through the lymphatic system into blood for use in metabolism in peripheral tissues or storage in adipose tissue

what enzyme breaks down the chylomicrons

lipoprotein lipase

how does lipoprotein lipase break down the chylomicrons

the lipoprotein lipase interacts with the chylomicron core and brings about glycolysis by releasing the glycerol and free fatty acids, these free fatty acids then pass into the tissues where they can be stored or used

what are chylomicron remnants

TAG's depleted compounds which are processed in the liver

what do very low density lipoproteins do

transport newly fat rich particles from the liver to adipose tissues

what do low density lipoproteins do

carry a mixture of lipids around the body

what do high density lipoproteins do

return lipids to the liver from other tissues

what does lipase enzymes do

hydrolyze TAG to release the fatty acids

what does the lipoprotein lipase do

degrades the TAGs into fatty acids so they can be taken in by tissues

what does adipose tissues build up and what do they use to release them

they build up TAG's and use lipase to release them as FA's

what does adipose hormone sensitive lipase do

resides in adipose tissue and is sensitive to hormones and is turned on and does glycolysis in the adipose tissue releasing fatty acids into free fatty acids into the circulation which is distributed to other parts of the body to be used. (hormones = adrenaline, glucagon, growth hormone) -used in times of stress, fasting, starvation`

how is fatty acids broken down in the cell to produce ATP

FA's move into the mitochondria matrix via acyl carnitine and are Beta oxidized into acetyl CoA which is then introduced into the Krebs cycle to make more energy. removal of 2 carbon units each time as acetyl CoA

how are Fatty acids synthesized

when energy is abundant the FA's are synthesized from acetyl CoA in the liver and adipose tissues, leads to the repeated addition of 2 carbon units to build up the long chain of FA, this occurs in the cytosol

which enzyme complex controls all the enzymes involved in fatty acid synthesis

fatty acid synthase

define lipogenesis

filling up adipocytes with fatty acids

define adipogenesis

making more adipocytes

what does insulin and glucagon do to acetyl CoA carboxylase the enzyme involved in FA synthesis

insulin increases its activity and glucagon and adrenaline decreases its activity

why does insulin increase Fatty acid synthesis

there is plenty of energy present so acetyl CoA is added to a chain of carbon molecules, which forms Fatty acid chain's which can be store in the liver and adipose tissue as fats in times of plenty (e.g. Insulin)

why does glucagon and adrenaline decrease fatty acid synthesis

energy is required (ATP) so fatty acid break down (Beta oxidation) is increased to make more Acetyl CoA so that the Krebs cycle can carry on producing ATP and NADH's and FADH2's which are used in the ETC to produce ATP

describe the full process of TAG's when they first enter the duodenum to when FA's in the blood can be used up or stored as fat

TAG's are digested in the stomach and released into the duodenum. The gall bladder secretes Bile into the duodenum. The bile salts and phospholipid's bind to the fat droplets and form micelles. These micelles are smaller and increase the SA so rate of absorption increases. They also contain inside the glycerol and FA's. once they reach the jejunum/ ileum they reach enterocytes (villi), where they diffuse across the cell membrane due to their small size. Once inside the enterocyte cells the FA's and glycerol join together to form TAG's. TAG's are enclosed into a lipoprotein called a Chylomicron, this molecule travels along the lymphatic system until it reaches the blood. Where it comes into contact with capillary lipoprotein lipase and causes the release of FA's and glycerol into the blood stream where they can be used up or stored. The chylomicron remnants (TAG depleted compound) are process in the liver.