Chapter 10 Lipid Metabolism Flashcards
Average man has how many kgs of triacylglycerols?
Average women?
10 kgs
14 kgs
The majority of the mass of an adipocyte is its:
Fat droplet….
How much of adipose mass is made up of triacylglycerols?
82%
82% of adipose tissue mass is:
TAGs
Proteins that regulate access to the triacylglycerols in the lipid droplet are known as:
Perilipins
What are perilipins?
Proteins that regulate access to TAGs inside lipid droplets
The “wall” of the fat droplet is a:
Phospholipid mono layer
What is the activated form of glycerol?
Glycerol 3-phosphate
Glycerol 3-phosphate is crucial for the synthesis of triacylglycerols.
What enzyme is abbreviated as GPDH?
Glycerol-3-phosphate dehydrogenase
GPDH plays a role in converting dihydroxyacetone phosphate to glycerol 3-phosphate.
What is the activated form of fatty acid?
Acyl CoA
Acyl CoA is essential for the synthesis of triacylglycerols.
What enzyme is responsible for activating fatty acids?
Acyl CoA Synthetase (ACS)
ACS catalyzes the formation of acyl CoA from fatty acids.
Where does triacylglycerol synthesis primarily occur?
Cytosol
The cytosol is the site for various metabolic processes, including triacylglycerol synthesis.
What enzyme is abbreviated as GPAT?
Glycerol Phosphate Acyltransferase
GPAT catalyzes the first step in the synthesis of triacylglycerols by transferring acyl groups to glycerol 3-phosphate.
Fill in the blank: The activated form of glycerol is _______.
Glycerol 3-phosphate
Fill in the blank: The enzyme that activates fatty acids is called _______.
Acyl CoA Synthetase (ACS)
In triacylglycerol synthesis, what adds the final acyl group to the glycerol backbone?
Triacylglycerol Synthase Complex
What is lipolysis?
Triacylglycerol breakdown
Lipolysis is the metabolic process of breaking down triacylglycerols into free fatty acids and glycerol.
Where does lipolysis occur?
In the cytosol
This process takes place in the cytosol of tissues.
What enzyme is primarily responsible for lipolysis?
Triacylglycerol Lipase (HSL)
HSL is crucial for initiating the breakdown of triacylglycerols.
What positions does Triacylglycerol Lipase (HSL) hydrolyze?
Positions 1 and 3
HSL hydrolyzes the ester bonds at these specific positions of triacylglycerols.
What is the role of monoacylglycerol lipase in lipolysis?
Hydrolyzes the ester bond at position 2
This enzyme further breaks down monoacylglycerols into free fatty acids.
Insulin inhibits:
Catecholamine action
What hormones increase during exercise that promote lipolysis?
Epinephrine and norepinephrine
These hormones are released from the adrenal medulla and sympathetic neurons respectively.
What type of receptors are involved in lipolysis on adipocytes?
B-adrenergic receptors
These receptors respond to catecholamines like epinephrine.
What signaling pathway is activated during lipolysis?
CAMP pathway
This pathway is crucial for the activation of lipolysis.
What enzyme is activated by PKA in the lipolysis process?
Triacylglycerol lipase (HSL)
HSL is responsible for breaking down triacylglycerols into free fatty acids.
What role does perilipin play in lipolysis?
Regulates HSL access to lipid droplets
Perilipin is a protein that controls the access of HSL to triacylglycerols.
What process attracts triacylglycerol lipase to lipid droplets?
Phosphorylation
Phosphorylation of specific proteins facilitates the recruitment of HSL.
When does the rate of lipolysis peak after exercise commences?
5 minutes
The rate of lipolysis reaches its maximum shortly after exercise begins.
Catecholamine action is inhibited by:
Insulin
What does insulin do in lipolysis?
Activate phosphodiesterase, which deactivates cAMP, hydrolyzing cAMP to AMP
Lipolysis has occurred. What happens with the products?
Adipose derived FFAs and glycerol will generally enter circulation
Is glycerol hydrophobic or hydrophilic?
Hydrophilic
How are FFAs transported through the blood?
They must be carried
What carries FFAs through the blood?
Albumin
Albumin carries _____ through blood.
FFAs or NEFAa
What is the most abundant plasma protein?
Albumin
Albumin is the:
Most abundant plasma protein
Fatty acids are absorbed through:
FABP and FAT (CD 36)
Glycerol generally heads to the liver and becomes:
Glycerol 3-Phosphate
In a reversible action, Glycerol 3-Phosphate can become:
DHAP
(Dihydroxyacetone Phosphate)
Where does β-oxidation occur?
In the mitochondria
In fatty acid degradation, what process is happening in the mitochondria?
β-oxidation
What restricts Acyl groups from crossing the inner mitochondrial membrane?
It’s size
Longer than 14 Carbons can’t cross
Acyl groups longer than _____ can’t cross the inner mitochondrial membrane.
14 carbons
What carries Acyl groups across the inner mitochondrial membrane?
Carnitine
What replaces CoA with carnitine?
CAT 1
(Carnitine Acyltransferase 1)
CAT 1 replaces _____ with carnitine.
CoA
CAT 1 replaces CoA with:
Carnitine
What moves Acyl-carnitines into the mitochondrial matrix?
Translocase
Translocase moves Acyl-carnitine into the:
Mitochondrial matrix
Translocase moves _____ into the mitochondrial matrix.
Acyl-carnitine
What replaces carnitine with CoA?
CAT 2
What are the four reactions of β-oxidation?
Dehydrogenation (FADH2 produced)
Hydration
Dehydrogenation (NADH produced)
Spitting
One round of products from β-oxidation include:
1 FADH2
1 NADH
1 Acetyl-CoA
1 FA-CoA
Round of β-oxidation are repeated _____ until the Acyl group is fully:
As necessary
Degraded
Most Fatty Acids have an even or odd number of Carbons?
Even
How much ATP do we get from palmitate?
106 ATP
Where does fatty acid synthesis primarily occur?
Cytosol
This is in contrast to fatty acid oxidation, which takes place in the mitochondrial matrix.
What is the role of citrate lyase in fatty acid synthesis?
It converts citrate to acetyl-CoA in the cytosol
This process costs 1 ATP.
What is the equation for the reaction catalyzed by citrate lyase?
citrate + CoA + ATP → acetyl CoA + oxaloacetate + ADP + P
This reaction highlights the conversion of citrate to acetyl-CoA.
What enzyme produces malonyl-CoA during fatty acid synthesis?
Acetyl-CoA Carboxylase (ACC)
Malonyl-CoA is a key intermediate in the fatty acid synthesis pathway.
What is the price of producing malonyl-CoA through ACC (Acetyl-CoA Carboxylase)?
1 ATP
The ATP is used in a way that is not for phosphorylation.
True or False: Acetyl-CoA is produced in the cytosol.
False
Acetyl-CoA is produced in the mitochondrial matrix.
What is Fatty Acid Synthase (FAS)?
Multienzyme complex
What does FAS catalyze?
All synthesis reactions
What is the role of NADPH in the palmitate synthesis process?
Reducing agent for FAS, 2/cycle
What is the result of each round of fatty acid synthesis?
A longer (by 2 carbons) nascent fatty acid
How are the two carbons added in each cycle of fatty acid synthesis?
By the three-carbon malonyl-CoA
What is the default fatty acid product of the synthesis process?
Palmitate
What results when acyl groups are removed from FAs before palmitate is produced?
Shorter fatty acids
This occurs when there are less than 7 rounds of FA Synthase activity.
What is the role of elongases in fatty acid synthesis?
Add carbons to palmitate after FAS
What do desaturases do in the context of fatty acids?
Remove electrons from saturated FAS
Where do desaturases primarily act on fatty acids?
Only within the first 10 carbons of the FA
Fill in the blank: _______ are fatty acids that cannot be synthesized by the body and must be obtained from the diet.
[Essential fatty acids]
What are essential fatty acids?
Fatty acids that must be consumed because the body cannot synthesize them.
Which fatty acids must be consumed as essential fatty acids?
Linoleate and α-linolenate
How many carbons do linoleate and a-linolenate have?
18 carbons each
What types of foods are sources of essential fatty acids?
Fish and plants
What are the two categories of essential fatty acids mentioned?
Omega-6 and Omega-3 fatty acids
At what positions do the double bonds occur in omega-6 and omega-3 fatty acids?
6 and 3 carbons from the end of the fatty acid
Fill in the blank: We have no enzymes that can desaturate fatty acids beyond _______.
C10
What effect does exercise have on FAO in muscle?
Exercise increases FAO in muscle mainly by increasing FFA concentration
What is the primary substrate for B-oxidation during exercise?
FFA concentration
What is one mechanism by which exercise stimulates FAO in muscle?
Stimulation of lipolysis in adipose tissue
How does blood flow to muscle change during exercise?
Augmented blood flow to muscle (autoregulation)
What is the rate of B-oxidation during exercise?
B-oxidation rates are high as products are rapidly consumed
What is the full name of AMPK?
AMP-dependent protein kinase
What does AMPK do?
Inhibits ACC (Acetyl-CoA Carboxylase)
What speeds FAO in muscle?
Exercise
What is the effect of AMPK inhibiting ACC?
Decreased malonyl-CoA for FAS
How does malonyl-CoA affect CPT/CAT I?
Inhibits CPT/CAT I
Fill in the blank: AMPK inhibits _______.
ACC
(Acetyl-CoA Carboxylase)
True or False: Malonyl-CoA activates CPT/CAT I.
False
What is the rate of conduction of FFAs through the plasma membrane?
Slow
Can FFAs support intense exercise?
No
What is the main purpose of carnitine supplementation in athletes?
To investigate potential benefits
What was the result regarding muscle carnitine levels after supplementation?
No increase in muscle carnitine
What was the result regarding body fat after carnitine supplementation?
No decrease in body fat
Where does ketone body formation occur?
Liver
The liver is the primary site for ketogenesis.
What happens to oxaloacetate levels when glucose is abundant?
Sufficient oxaloacetate is available to bind to acetyl-CoA to make citrate
High glucose levels promote the conversion of acetyl-CoA into citrate for the Krebs cycle.
What occurs to oxaloacetate levels when glucose is scarce?
Oxaloacetate levels decrease as it is used in gluconeogenesis
Gluconeogenesis is the process of forming glucose from non-carbohydrate sources.
What accumulates when oxaloacetate is depleted?
Acetyl-CoA accumulates
Accumulation of acetyl-CoA is a key trigger for ketone body formation.
What is produced as a result of acetyl-CoA accumulation?
Ketone bodies are produced
Ketone bodies serve as an alternative energy source during periods of low glucose availability.
Extra-hepatic tissues oxidize_____ after their conversion to Acetyl-CoA
Ketones
How much ATP is used in muscle to oxidize ketones during prolonged exercise?
7%
The two main ketones produced are:
Acetoacetate
Hydroxybutyrate
After β-oxidation, a fatty acid turns into Acetyl-CoA. What are the next steps to become glucose?
Enter Citric Acid Cycle
Loses 2 CO2
Becomes Oxaloacetate which can be used for gluconeogenesis to make glucose
FFAs cannot support intense exercise.
True or False?
True
Is conduction of FFAs through the plasma membrane slow or fast?
Slow
What primarily influences the concentration of plasma fatty acids during exercise?
The balance of lipolysis in adipose tissue, blood flow, and FA uptake in the muscle
Lipolysis refers to the breakdown of fats and other lipids by hydrolysis to release fatty acids.
What happens if acyl-CoA demand isn’t met by lipolysis in muscle?
Cytoplasmic concentration decreases, stimulating uptake from plasma
Acyl-CoA is a key molecule in fatty acid metabolism.
What effect does a bigger gradient have on plasma fatty acid concentration?
Leads to a decrease in plasma fatty acid concentration
A bigger gradient typically facilitates a faster rate of diffusion.
What physiological process increases plasma free fatty acid concentration?
Lipolysis in adipose tissue
Free fatty acids (FFA) are released into the bloodstream during lipolysis.
