glycogen and fat

glycogen storage sites

LIVER

• 10 percent of liver is glycogen

• broken down into glucose during exercise and overnight fast for use by other tissues

• liver glycogen used to buffer blood glucose

SKELETAL MUSKE

• 2 percent of mass of skeletal muscle is glycogen

• is an energy store only for muscle

• msiing key enzyme is g6p

• used to provide energy during strenuous exercise

short term energy storage

• large polymer of glucose molecules

• linear backbones of ⍺-1,4 linkages with branchpoints at every 12 – 15 glucose molecules formed by secondary ⍺-1,6 linkages

• has a central protein core- glycogenin

• is branched so easy access for glycogen degrading enzymes

glycogen symthesis

white adipose tissue

• energy storage

• cushioning/mechanical fucntions

• large uniocular lipid droplet

• low mithcondrial content

• undetectable ucp1 expression

• no theromogenic capacity

beige adipose tissue

• adaptive thermogenesis

• endocrine functions

• small multiocular lipid roplets

• medium mitochondrial content

• inducible UCP1 expression

• medium thermogenic capacity

brown adipose tissue

• thermogenesis and energy expenditure

• endocrine functions

• small multiocular lipid droplets

• high mitochndrial content

• high UCP1 expression

• high thermogenic capacity

fatty acid structure

carbon backbone terminated by a COOH at one and and a CH3 at the other

triacylglycerols

• main constiutent of body fat

• energy storage

• esters of glycerol, a 3 carbon alochol backbone and 3 fatty acids

• can be saturated or unsaturated

lipolysis

• TAG to fatty acids and glycerol

• fatty acids undergo beta oxidation to generate acetyl coA for TCA cycle for ATP production

• glycerol component can be utilised in gluconeogenesis

albumin

bind fatty acids in hydrophobic pockets enabling transport in the blood

solubilised fatty acids and prevemts formation of harmful aggregates

enhances transcytossi across capillary endothelia enabling tissue delivery

binding is transient enabling exchange at tissue sites

lipoprotein

• transport lipids in blood

• core of hydrophobic lipids surrounded by an outer shell of aphiphatic proteins, hosphoipids and cholesterol

• 4types

• Chylomicrons: carry dietary triglycerides from the intestine to other tissues • Very-low density lipoproteins (VLDL): transport triglycerides synthesised in the liver to the adipose tissue for storage • Low-density lipoproteins (LDL): transport cholesterol from the liver to peripheral tissues • High-density lipoproteins (HDL): transport cholesterol from the peripheral tissues to the liver

pancreatic lipase

secreted into small intestine

digestion of lipids in food

lipoprotein lipase

endothelial cells

hydroysis of TAG in lipoproteins toaid uptake into tissues

apidose triglyceride lipase

apidocytes and other lipid storage cells

hydrolysis of stored TAG to yield diaceylglyerol and fatty acid. first and rate limiting step of lipolysis

Adipose hormonesensitive lipase (HSL

Adipocytes and other lipid-storing cells

Hydrolysis of DAG to yield monoacylglycerol (MAG) + FA. Activated by: glucagon, adrenaline, ACTH. Inhibited by: Insulin

Adipose monoacylglycerol lipase (MAGL/MGL)

Adipocytes and other lipid-storing cells

Hydrolysis of MAG to yield FA and glycerol

lipogenesis

• process of synthesin and storing lipids as TAGs from diestar fags and de novo fatty acid synthesis

• occurs especially in liver, adipose, muscl

• TAG synthesised from fatty acyl CoA and a glyerol precursosr glycerol 3 phospate

• adipose specialised tissies for synthesis stprage and relase of TAGs

• muscle TAG turnover for local use

• liver uses TAGs primarily to generate lipoproteins

• metabolic derangement leads to excess TAG accumulation in muscle and liver—> ectopic fat

release of fatty acids from stored TAGs

• hormone sensitive lipase catalyses the main rate controlling step

• this is activated by glucagon signalling and inhibited by insulin signalling

• glycerol is transported to liver where it can be used in gluconeogenesis to form glucpse

• fatty acids are transported in circulation bound to albumin and transported inot cells where they undergo beta oxidation in mitochondria

chylomicrons

carry dietary triglycerides from the intestine to other tissues

very low density lipoproteins

transport triglycerides synthesised in the liver to the apidose tissues for stoage

low density lipoproteins

transport cholesterol from the liver to peripheral tissues

high density lipoprotein

transport cholesterol from the peripheral tissues to the liver

mitochondrial beta oxidation of fatty acids

1. activation: fatty acids activated to fatty acyl coa by coA and ATP in the cytoplasm

2. oxidation: acyl coa dehydrogenase removed 2x H forming a double bond and FADH

3. hydration

4. oxidation: hydroxyl group is oxidised and NADH formed too

5. thiolysis: beta ketothiolase cleaves the molecule forming one molecule acetyl CoA and a shorter fatty acyl coA which re enters the cycle

6. each cycle produces 1 FADH2, 1 NADH, and 1 Acetyl-CoA

7. cycle continues, shortening the fatty acids by 2 carbons until it is completely broken down