Chapter 27 Flashcards
where are fatty acids stored?
adipose tissue
what are fatty acids stored as?
triacyclglycerols (TAG)
what are triacylglycerols?
fatty acids that are linked to glycerol with ester linkages
where is adipose tissue most prominent?
subcutaneous (below the skin) and visceral (around internal organs)
why do muscles store fatty acids?
for use in producing energy
what are the three ways in which fatty acid triacyclglycerols are accessible from adipose tissue?
- degradation of TAG to release fatty acids and glycerol into the blood for transport to energy-requiring tissues
- activation of the fatty acids and transport into the mitochondria for oxidation
- degradation of the fatty acids to acetyl CoA for processing by the citric acid cycle
where does fatty acid degradation occur?
the mitochondria
what’s the difference between the use of glucose and lipids in producing ATP?
glucose can produce energy without oxygen
fatty acids require oxygen to produce energy
how are triacylglycerols stored in adipocytes?
as a lipid droplet
what stimulates the breakdown of lipids (lipolysis)?
epinephrine and glucagon acting through 7TM receptors
what is lipolysis?
the breakdown of lipids
what role does Protein Kinase A play in the breakdown of lipids?
it phosphorylates perilipin
what is perilipin associated with in lipolysis?
the lipid droplet and hormone-sensitive lipase
what is fatty acid breakdown dependent on?
glucagon and epinephrine
what happens in lipolysis after PKA phosphorylates perilipin?
Perilipin is activated and activates ATGL
where are most stores of TAGs found?
fat cells
when TAG’s are broken down, where does Glycerol go?
glycerol is transported to the liver for glycolysis and gluconeogenesis
when TAG’s are broken down what happens to the fatty acids?
they are transported to tissues for fatty acid oxidation
what must happen to fatty acids before they are oxidized?
they must be linked to Coenzyme A
how is CoA attached to fatty acids?
by a sulfhydryl bond
what is the rate determining step of fatty acid oxidation?
the attachment of CoA to the fatty acid by a sulfhydryl bond (forming Acyl CoA)
how is the reaction of fatty acid to Acyl CoA made irreversible?
by the hydrolysis of PPi
what happens after the fatty acid is linked to CoA and activated?
it is transferred to carnitine
what does carnitine do to fatty acids?
it transports them into the mitochondria
what catalyzes the transfer of a fatty acid to carnitine?
carnitine acyltransferase I
what transports the acyl carnitine into the mitochondria?
a translocase
what does carnitine acyltransferase II do?
it transfers the fatty acid to CoA in the mitochondria
What are the four steps of fatty acid degradation (β-oxidation)?
- Oxidation (FAD)
- Hydration (H2O)
- Oxidation (NAD+)
- Thiolysis (CoA)
what are the products after one round of fatty acid degradation?
Acyl CoA (-2 Carbons) + Acetyl CoA
what is reduced in the first oxidation step of fatty acid degredation?
FAD is reduced to FADH2
what is reduced in the second oxidation of fatty acid degradation?
NAD is reduced to NADH
how many cycles does it take to completely degrade a fatty acid?
7 cycles
how many ATP does the overall β - oxidation reaction yield?
106 molecules of ATP
what does it mean if a fatty acid is saturated?
it contains only single bonds on the carbon chain
what does it mean if a fatty acid is unsaturated?
it contains single and double bonds on the carbon chain
when are isomerase and reductase needed?
when a fatty acid contains an even number amount of double bonds
when is just isomerase needed?
when a fatty acid contains one or an odd number of double bonds
Can β - oxidation proceed in unsaturated fatty acids?
No. Isomerase (or isomerase and reductase) are needed to saturate it
what does isomerase do to an unsaturated fatty acid?
it transfers the double bond from the cis to the trans position, to allow β-oxidation
what do isomerase and reductase do to an unsaturated fatty acid?
isomerase converts the first double bond from cis to trans
reductase gets rid of the second double bond
what do fatty acids with an odd number of carbons produce during the thiolysis reaction?
Propionyl CoA
where does the newly generated Succinyl CoA go after Thiolysis of a fatty acid with an odd number of carbons ?
The Citric Acid Cycle
what are the 3 types of ketone bodies?
acetoacetate
3-hydroxybutyrate
acetone
where are ketone bodies synthesized?
in liver mitochondria
where are ketone bodies secreted?
into the blood
what happens when there is a build up of Acetyl CoA?
Acetyl CoA can be converted to ketone bodies
what causes a build up of Acetyl CoA?
the slow down of the citric acid cycle
what does acetoacetate in the blood indicate?
abundance of acetyl CoA subunits
what does an abundance of acetyl CoA lead to?
decrease in lipolysis
what might use acetoacetate over glucose?
normal fuels for respiration, heart muscle, and renal cortex
what is a ketogenic diet?
a diet rich in fats and low in carbohydrates but with adequate proteins
what can ketogenic diets lead to?
formation of substantial amounts of ketone bodies
what do ketogenic diets do in children with epilepsy?
it helps reduce seizures in children suffering from drug-resistant epilepsy
can fatty acids be converted into glucose?
no
what happens when there is a decrease in oxaloacetate?
it slows down the Citric Acid Cycle
why can acetyl CoA derived from fats not lead to the net synthesis of oxaloacetate or glucose?
because although two carbons enter the cycle when acetyl CoA condenses with oxaloacetate, two carbons are lost as CO2 before oxaloacetate is regenerated
Pyruvate to Acetyl-CoA is a(n) ___ reaction
irreversible
what can excess production of ketone bodies cause?
acidosis
what is diabetic ketosis?
an overproduction of ketone bodies that occurs in patients with diabetes due to lack of insulin function
what happens if insulin is absent or not working?
glucose cannot enter cells
energy must be derived from fats
fatty acid release from adipose tissue is enhanced
why does acetyl CoA build up?
because the oxaloacetate, which can be generated from glucose, is not available to replenish the citric acid cycle
what happens when all energy must be derived from fats?
it leads to the production of acetyl CoA
why isn’t glucose utilized much when insulin is absent?
insulin isn’t there to turn on glucose pathways
what is the predominant fuel for the brain?
Glucose
what happens at the beginning of starvation?
protein degradation is initially the source of carbons for gluconeogenesis in the liver
the glucose is released into the blood for the brain to use
what happens after several days of fasting?
the brain starts to use ketone bodies as a fuel
why are ketone bodies a better energy source than protein degradation during starvation?
ketone body use stops protein degradation and prevents tissue failure
ketone bodies are synthesized from fats, the largest energy store in the body
what are ketone bodies synthesized from?
fats, the largest energy store in the body
why aren’t amino acids a good source of energy?
using amino acids as an energy source causes the degradation of proteins which can cause organ failure
what happens during starvation when ketone bodies begin to run out?
protein degradation starts
why does protein degradation happen at the beginning of starvation?
the body needs time to build ketone body levels
what is GLUT4?
glucose transporter for adipose tissue and muscle
insulin dependent
what regulates GLUT4?
insulin
what happens to GLUT4 when glucose is low?
GLUT4 doesn’t get induced
what is GLUT2?
glucose transporter in liver
low affinity, high capacity
where does acetyl CoA go to get oxidized?
how many grams of glucose are needed per day for brain survival during starvation?
40 grams
how many grams of glucose are needed normally for brain survival?
120 grams
what is survival dependent on?
survival is time dependent on triacylglycerol amount
what happens after lipid stores are gone and proteins are used for energy again?
death imminent
what is the sparing effect?
ketone levels increase as days of starvation increase
glucose levels decrease as days of starvation increases
