Metabolic: lecture 26

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which statement about fat storage is correct?

Fats carry more energy per carbon than polysaccharides. (correct)

Fatty acids complex more water compared to glucose.

Fats provide short-term energy storage.

Fats are less efficient than carbohydrates in energy storage.

What is the primary role of chylomicrons in lipid metabolism?

To break down triglycerides into fatty acids.

To transport dietary fatty acids into the blood. (correct)

To deliver energy for immediate use in muscles.

To store glucose as glycogen.

What happens to fatty acids released from chylomicrons during transport?

They undergo oxidation in the liver first.

They are directly used for energy without regulation.

They are converted to glucose for energy.

They bind to serum albumin for distribution in blood. (correct)

Which process describes the conversion of diacylglycerol (DAG) to monoacylglycerol (MAG)?

Hydrolysis Signup and view all the answers

What is the advantage of using fats as an energy source in mammals?

Fats provide sustainable energy for extended periods. Signup and view all the answers

What do medium chain triglycerides (MCT) primarily help with in lipid metabolism?

Avoiding excess liver metabolism during drug delivery. Signup and view all the answers

Which is NOT a significant pathway for fatty acid mobilization?

Imported fatty acids from food industry. Signup and view all the answers

How do fatty acids enter the myocyte for oxidation?

Via specific transporters. Signup and view all the answers

What is the effect of PKA on glycogen synthase?

Inhibits glycogen synthase Signup and view all the answers

What happens to glycolysis when PKA is activated?

Glycolysis is inhibited Signup and view all the answers

In the process of converting fatty acids for mitochondrial oxidation, what is formed from fatty acid, CoASH, and ATP?

Fatty acyl-CoA and AMP Signup and view all the answers

What is required for the transport of large fatty acids into mitochondria?

Acyl-carnitine/carnitine transporter Signup and view all the answers

How does glycerol enter glycolysis?

Through phosphorylation by glycerol kinase Signup and view all the answers

What is the primary function of PFK-2 in relation to glucose metabolism?

Inhibits glycolysis Signup and view all the answers

Which statement correctly describes the fate of small fatty acids in relation to their mitochondrial entry?

They diffuse freely across mitochondrial membranes Signup and view all the answers

What is the main product of the first stage of fatty acid oxidation?

Acetyl-CoA Signup and view all the answers

During the hydration step of β-oxidation, what compound is formed on the β carbon?

Alcohol Signup and view all the answers

What is the role of NAD in the β-oxidation pathway?

Hydride acceptor Signup and view all the answers

After the oxidation of unsaturated fatty acids, what happens to FADH2 production?

It decreases by one Signup and view all the answers

Which isoform of acyl-CoA dehydrogenase works with fatty acids containing 12-18 carbons?

Very-long-chain AD Signup and view all the answers

What is the final step in β-oxidation that releases acetyl-CoA?

Thiolysis Signup and view all the answers

What is the net reaction of the β-oxidation pathway?

Thiolysis of the carbon-carbon bond Signup and view all the answers

How many ATP are produced from one molecule of NADH during the oxidation process?

2.5 ATP Signup and view all the answers

What is the total ATP yield from the oxidation of one molecule of Palmitoyl-CoA?

108 ATP Signup and view all the answers

Which enzyme is responsible for the formation of FADH2 during β oxidation?

Acyl-CoA dehydrogenase Signup and view all the answers

Which of the following enzymes produces NADH in the citric acid cycle?

Malate dehydrogenase Signup and view all the answers

How many FADH2 molecules are produced from the oxidation of Palmitoyl-CoA?

7 FADH2 Signup and view all the answers

What is the role of adenylyl cyclase in the activation of PKA?

It converts ATP into cAMP. Signup and view all the answers

Which enzyme directly converts diacylglycerol (DAG) to monoacylglycerol (MAG)?

Hormone-sensitive lipase (HSL) Signup and view all the answers

Which enzyme is analogous to succinate dehydrogenase in the TCA cycle during fatty acid oxidation?

β-hydroxyacyl-CoA dehydrogenase Signup and view all the answers

What is the end product of the reaction performed by acyl-CoA acetyltransferase (thiolase)?

Acetyl-CoA Signup and view all the answers

Study Notes

Lipid Metabolism

One-third of energy needs come from dietary triacylglycerols (TAGs).
Fatty acid oxidation is a major energy source.
About 80% of mammalian heart and liver energy needs are met by fatty acid oxidation.

Hibernating Animals and Polar Bears

These animals obtain most energy from stored fatty acids.

Fats Provide Efficient Fuel Storage

Fatty acids carry more energy per carbon because they are more reduced.
Fatty acids can be packed more efficiently because they are nonpolar.
Glucose and glycogen provide short-term, fast-delivery energy needs.
Fats provide long-term (months) energy storage and slow delivery.

Mobilization of Fats

Dietary fats provide quick delivery.
Storage fats provide slower delivery.
Dietary fatty acids are packaged into chylomicrons.
Fatty acids are released and absorbed in the small intestine.
Emulsification of fats occurs in the small intestine, breaking down TAGs to monoglycerides and free fatty acids.
These smaller molecules are taken up by the intestinal mucosa, converted to triacylglycerols, and packaged into chylomicrons.
Chylomicrons facilitate transport through lymphatic and bloodstream.
Within the intestinal mucosa, broken-down lipids reassemble into TAGs. Bile salts emulsify dietary fats.
Fatty acids are hydrophilic/lipophilic, requiring emulsification to avoid flushing out of the body.

Lipids Are Transported in the Blood

Lipids are hydrophobic and need packaging with apolipoproteins for transport.

Application: Avoiding Hepatic Metabolism During Drug Delivery

Small lipophilic drugs associated with long-chain triglycerides can be incorporated into chylomicrons and taken from the intestines to the lymph to the bloodstream, thus avoiding the liver.
MCT = medium chain triglycerides
GML = glyceryl monolinoleate, a long-chain triglyceride
SEDDS = a self-emulsifying formula made with GML

Types of Lipoproteins

Chylomicrons: largest
VLDL: very low-density lipoprotein
IDL: intermediate-density lipoprotein
LDL: low-density lipoprotein
HDL: high-density lipoprotein

Lipases Cleave Fatty Acids from Glycerol Backbone of TAGs

Lipases cleave fatty acids from glycerol backbones of triacylglycerides (TAGs) to give glycerol + 3 fatty acids.

Hormones Trigger Mobilization of Stored Triacylglycerols

Glucagon and epinephrine bind to receptors in adipocyte membranes.
Adenylyl cyclase is stimulated, producing cAMP.
cAMP activates protein kinase A (PKA).
PKA phosphorylates hormone-sensitive lipase (HSL).
Perilipin molecules on lipid droplets dissociate from CGI, activating adipose triacylglycerol lipase (ATGL).
Released fatty acids enter the bloodstream.

Glycerol from Fat Enters Glycolysis

Glycerol kinase phosphorylates glycerol, using ATP.
Subsequent oxidation of glycerol 3-phosphate recovers more ATP—cost-covered.
This allows for limited anaerobic catabolism of fats.

Fatty Acids Must Be Transported into Mitochondria for Oxidation

Fats are degraded to fatty acids and glycerol in adipocytes.
Fatty acids are transported to tissues via blood.
Small (<12 carbons) fatty acids diffuse freely across mitochondrial membranes.
Larger fatty acids use acyl-carnitine/carnitine transporter for transport into mitochondria.

Intracellular Transport Requires Conversion to Fatty Acyl-CoA

Fatty acids are converted to fatty acyl-CoA using CoA synthetase, ATP, and CoASH.
This reaction is very favorable.

Acyl-Carnitine/Carnitine Transporter

Acyl-carnitine/carnitine transporter facilitates transport of fatty acyl carnitine into the mitochondrial matrix.
A counter-exchange with carnitine occurs.

Fatty Acid Oxidation Occurs in the Mitochondria in Three Stages

Stage 1: oxidative conversion of 2-carbon units from fatty acids to acetyl-CoA via β-oxidation, generating NADH and FADH₂.
Stage 2: oxidation of acetyl-CoA into CO₂ via the citric acid cycle, generating NADH and FADH₂.
Stage 3: ATP production from NADH and FADH₂ via oxidative phosphorylation.

The β-Oxidation Pathway

Each pass of β-oxidation removes one acetyl-CoA molecule.
Oxidation (FAD), hydration, oxidation (NAD), and thiolation reactions yield acetyl-CoA, regenerating FAD and NAD.

Oxidation of Unsaturated Fatty Acids

Oxidation yields one fewer FADH₂ molecule during isomerization but generates 1 FADH₂ during the first step of the next cycle.
NADPH reduces the remaining unsaturated bond.

NADH and FADH₂ Yield of ATP

NADH and FADH₂ generated during fatty acid oxidation serve as sources for ATP production.
These values assume 2.5 ATP per NADH and 1.5 ATP per FADH₂ during oxidative phosphorylation.

Hydration Step 2: Enoyl-CoA Hydratase

Two isoforms: soluble short-chain (crotonase) and membrane-bound long-chain hydratase.
Water adds across the double bond, producing alcohol on β-carbon.
Analogous to a fumarase reaction in the citric acid cycle.

Oxidation Step 3: β-hydroxyacyl-CoA dehydrogenase

Uses NAD as the hydride acceptor.
Analogous to malate dehydrogenase in the citric acid cycle.

Oxidation Step 4: Acyl-CoA acetyltransferase (thiolase)

CoA-SH picks up the fatty acid chain.
Net reaction = thiolysis of carbon-carbon bond, producing acetyl-CoA.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz delves into the critical aspects of lipid metabolism, focusing on how fats serve as an energy source for various animals, particularly hibernating species like polar bears. It covers the mobilization of dietary fats, energy efficiency of fatty acids, and the comparison between short-term and long-term energy storage mechanisms.