3.6 energy stores: glycogen and lipids Flashcards
where is glycogen stored
liver and muscles
what is the glycogen stored in liver used for
buffering blood glucose level
what is the glycogen stored in muscles used for
To provide glucose to generate energy during exercise
how does glucose form glycogen (simple details) (inclu. enzyme)
Moving the phosphate around, then adding the glucose to an existing glycogen chain using glycogen synthase
how does glycogen form glucose (simple details) (inc. enzyme)
To breakdown a glucose from glycogen, we use phosphorylase
why is glycogen metabolism controlled reciprocally
- It is controlled reciprocally to prevent futile cycle
So only one side of the cycle is on at each time for energy efficient
2 methods of glycogen metabolism
allosterically and by hormones
3 molecules of allosteric control in glycogen metabolism
a. AMP (signals low enrgy levels)
b. Calcium (signals increased activity in muscles)
c. Glucose (signals enough energy)
2 hormones in glycogen metabolsim
insulin
glucagon
how does insulin work in glycogen metabolism
- Released after a meal when blood glucose is high.
- Activates phosphatases, promoting:
○ Glycogenesis (glycogen synthesis).
○ Inhibition of glycogenolysis (glycogen breakdown)
how does glucagon work in glycogen metabolism
- Released during fasting or low blood glucose.
- Activates kinases, promoting:
○ Glycogenolysis (glycogen breakdown).
○ Inhibition of glycogenesis (glycogen synthesis).
how does glucagon function
- Glucagon act on a cell surface receptor of liver cells for:
- Intracellular signal
- Activation of a protein kinase which activates phosphorylase to breakdown glycogen into glucose
how does insulin function
- Insulin opposes this effect by acting on its own cell surface receptors for:
- A different intracellular signal that ultimately activates a protein that opposes kinases - phosphatase which activates glycogen synthase
diseases involved in aberrant fat handling/metabolism (and what species are affected)
obesity - all animals
pregnancy toxaemia - cows, sheep
hepatic lipidosis - cats, horses
diabetes - dogs, cats
what is the primary form of lipid storage
triacylglycerols (TAGS)
where is lipids stored (3)
- adipose tissues
- small amount in liver and muscles
properties of TAGS
non-polar
non toxic
highly energy dense
2 types of adipose tissue
white adipose tissue (WAT)
brown adipose tissue (BAT)
properties of WAT (5)
- Single fat droplet
- Few mitochondria
- Specialized to store triacylglycerol
- Secretes multiple adipokines
- Multiple anatomical depots
properties of BAT
- Multiple small fat droplets
- Many mitochondria
- Highly oxidative
- Non-shivering thermogenesis for heat production (regulated by uncoupling proteins)
- Smaller quantities of depots (e.g. periscapular depot)
- Mostly observed in neonates (new born), smaller animals
which 2 forms are lipids transported in blood as
- fatty acids (mostly bound to albumin)
- lipoproteins
which organ is used for lipid metabolism
liver
what happens to the chylomicrons after transporting lipids to the liver
they become chylomicron remnants
what happens to chylomicron remnants
they are processed in the liver to form VLDL, LDL, HDL
what are VLDL used for
Transport newly synthesized TAG from the liver to adipose tissue
what are LDL used for
carry a mixture of lipids around the body
what are HDL used for
Return lipid to liver from other tissues
what are the 5 types of lipase involved in hydrolyses of TAGS
- pancreatic lipase
- lipoprotein lipase
- adipose triglyceride lipase
- adipose hormone sensitive lipase
- adipose monoacyglycerol lipase
what are the uses of the 5 types of lipase
process of lipolysis
- Fatty acids are oxidized in the mitochondria of active tissues to produce ATP (requires oxygen)
- Important in active tissues
○ e.g. skeletal muscle - Oxidation occurs in the mitochondrial matrix
- Requires transport of activated fatty acids molecules across the mitochondrial membrane, which is a controlled process (acyl carnitine via CPT1 transporter)
○ It is inhibited by malonyl-CoA which is intermediate in fatty acid synthesis - the use reciprocal regulation - Activated fatty acids = fatty acyl CoA
- Once in the mitochondrial matrix, fatty acyl CoA is broken down by the repeated removal of 2-carbon fragments as acetyl CoA
○ This process is beta-oxidation
- Important in active tissues
Palmitate (a fatty acid with 16 carbons), it undergoes 7 cycles, each cycle removing 2 carbons as acetyl CoA, this results in 8 acetyl CoA
where does fatty acid synthesis occurs mostly
liver and adipose tissues
process of fatty acid synthesis
- Fatty acids are synthesized from acetyl CoA when energy is abundant
- Synthesis occurs by repeated condensation of 2 carbon units to build up an even numbered long chain of fatty acids
- Synthesis cannot occur by reversing the B-oxidation breakdown pathway○ It uses unique path with some unique enzymes and occurs in cytosol
Thus reciprocal regulation
what enzyme is involved in fatty acid synthesis
acetyl CoA carboxylase (ACC)
how is ACC inhibited and activated
inhibit: glucagon and adrenaline
activate: insulin
what does malonyl CoA do
inhibit CPT 1 and thus transport of acyl CoA into mitochondria for breakdown
what is the 16 C lipid called
palamitate
why would ACC release the lipid when it gets to 16C
When the chain is 16 C long (palmitic acid), it becomes too big for the enzymes and is released
what is lipogenesis
Lipogenesis = building fats
what is adipogenesis
Adipogenesis = expansion of adipose tissue
