Biochemistry of Fat Metabolism

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Questions and Answers

What is the primary role of adipose tissue lipase in fat metabolism?

Synthesizing triglycerides from carbohydrates

Stimulating the release of insulin

Breaking down triglycerides into fatty acids and glycerol (correct)

Transporting fatty acids into the blood

Which process describes the conversion of fatty acids to their CoA esters?

Lipogenesis

Fatty acid activation (correct)

Fatty acid synthesis

Beta-oxidation

What is the end product of the β-oxidation pathway?

Fatty acids

Acetyl-CoA, NADH, and FADH2 (correct)

Glycerol

Glucose

What role do ketone bodies play during starvation?

They provide an alternative energy source for tissues Signup and view all the answers

Which lipid is a precursor for steroid hormones?

Cholesterol Signup and view all the answers

What is the primary advantage of triglycerides as an energy source compared to glycogen?

Triglycerides yield more energy per gram. Signup and view all the answers

Which fatty acid is characterized as palmitic acid and has the molecular formula C16:0?

A saturated fatty acid. Signup and view all the answers

What happens to glycerol during prolonged fasting or starvation?

It enters glycolysis and is converted to pyruvate. Signup and view all the answers

Which type of enzyme is responsible for breaking down triglycerides into free fatty acids and glycerol?

Lipase. Signup and view all the answers

Where does the process of fatty acid β-oxidation primarily occur?

In the mitochondrial matrix. Signup and view all the answers

What is the role of coenzyme A in fatty acid metabolism?

To form thioester bonds with fatty acids. Signup and view all the answers

How does fatty acyl-CoA enter the mitochondria for β-oxidation?

Via the carnitine shuttle. Signup and view all the answers

What biochemical pathway does glycerol enter once it is metabolized?

Gluconeogenesis. Signup and view all the answers

During the process of fatty acid β-oxidation, what is conserved as biological energy?

NADH and FADH2 from electron carriers. Signup and view all the answers

What is the role of monoacylglycerol lipase in adipose tissue?

To hydrolyze diacylglycerol to free fatty acids. Signup and view all the answers

What are ketone bodies converted from in the liver?

Excess Acetyl CoA Signup and view all the answers

Which tissues can utilize ketone bodies for energy?

Most tissues, excluding liver Signup and view all the answers

Why can't the liver utilize ketone bodies?

It lacks the necessary enzymes Signup and view all the answers

What is the primary fuel source for the brain?

Glucose Signup and view all the answers

Which of the following describes the transport of free fatty acids in the blood?

They are carried by albumin Signup and view all the answers

What is the three-carbon unit produced from the β-oxidation of fatty acids with an odd number of carbons?

Propionyl-CoA Signup and view all the answers

In the breakdown of fatty acids for energy in mitochondria, which sequence describes the reactions involved?

Oxidation, oxidation, decarboxylation Signup and view all the answers

What could be a consequence of a deficiency in synthesizing carnitine?

Accumulation of lipid droplets in the mitochondrial matrix of liver cells Signup and view all the answers

What role does carnitine play in the transport of fatty acids into mitochondria?

Facilitates the transport of fatty acyl-carnitine Signup and view all the answers

Which step in the β-oxidation pathway results in the production of a carbonyl group?

Removal of 2 hydrogen atoms Signup and view all the answers

What is the main outcome of each round of β-oxidation?

Produces a carbon chain that is 2 carbons shorter Signup and view all the answers

What is the role of the enzyme carnitine acyltransferase II in fatty acid transport?

Converts fatty acyl-carnitine back into fatty acyl-CoA Signup and view all the answers

In the last steps of β-oxidation, what is produced from the oxidation of the β-carbon?

Acetyl-CoA Signup and view all the answers

What physiological conditions can lead to ketogenesis?

Starvation and Type I diabetes Signup and view all the answers

Which cofactor is reduced during the steps of β-oxidation to generate NADH?

NAD+ Signup and view all the answers

How many NADH and FADH2 are produced from one cycle of β-oxidation?

One NADH and one FADH2 Signup and view all the answers

Which statement about the complete oxidation of a 16-carbon fatty acid is true?

It generates ATP equivalent to yielding Acetyl-CoA Signup and view all the answers

What happens to a fatty acid once it is converted into propionyl-CoA?

It is converted into succinyl-CoA for the TCA cycle Signup and view all the answers

Which enzyme facilitates the addition of water in the β-oxidation pathway?

Enoyl-CoA hydratase Signup and view all the answers

Which factor regulates the entry of fatty acids into mitochondria?

Carnitine shuttle activity Signup and view all the answers

What is the initial step in the utilization of fatty acids for β-oxidation?

Activation to fatty acyl-CoA Signup and view all the answers

At the end of a β-oxidation cycle, what happens to the length of the fatty acyl-CoA?

It becomes shorter by 2 carbons Signup and view all the answers

Study Notes

Fat as Fuel

Fat, stored as triglycerides, is a crucial long-term energy source.
Adipose tissue lipase breaks down triglycerides into fatty acids and glycerol.
Fatty acids are activated to CoA esters and transported into mitochondria via the carnitine shuttle system.
The β-oxidation pathway yields acetyl-CoA, NADH, and FADH₂.
Factors regulating fatty acid oxidation influence the breakdown process.
Ketogenesis creates ketone bodies, significant during starvation, when fats are the primary fuel source.

Biological Functions of Lipids

Lipids, including phospholipids and cholesterol, make up cell membranes.
Lipids are precursors for hormones, including steroid hormones and prostaglandins.
Triglycerides serve as long-term energy storage.
Cholesterol is crucial for hormone synthesis and cellular function.

Efficiency of Triglycerides as Fuel

Triglycerides are stored in adipose tissue as compact droplets.
70 kg adults typically store 11 kg of fat.
Triglycerides yield more energy per gram, compared to carbohydrates or proteins. (38 kJ per gram)

Structure of Triglyceride Fat

Triglycerides consist of glycerol and three fatty acid chains.
Common fatty acids include palmitic (16:0), stearic (18:0), oleic (18:1), and linoleic acid.

Breakdown of Stored Triglycerides

Lipases, activated by adrenaline and glucagon, break down triglycerides.
This process results in the release of fatty acids into the bloodstream, bound to albumin.
Fatty acids are essential fuels for various tissues and organs, particularly the muscles and heart.

Metabolism of Glycerol

Glycerol is water-soluble and absorbed by all tissues.
It enters the glycolysis pathway and converts into pyruvate, then into the TCA cycle for oxidation to CO₂ .

Fatty Acid Metabolism

Reactions of fatty acid oxidation occur in the mitochondrial matrix.
Fatty acids are transported across mitochondrial membranes as CoA thioesters.
This metabolic process conserves energy by transferring hydrogen atoms to NAD+ and FAD, producing NADH and FADH₂.
A series of four enzyme reactions breaks down fatty acids to acetyl-CoA.

Activation of Long Chain Fatty Acids

ATP is required to activate long-chain fatty acids.
The enzyme fatty acyl-CoA synthetase is crucial at this step.

Coenzyme A

Coenzyme A is integral in forming thioester bonds with carboxylic acids.
In this process CoA is part of the acyl-CoA molecule.

Transport of Fatty Acyl-CoA into Mitochondria

The carnitine shuttle facilitates fatty acid transport across mitochondrial membranes.
Acyl-CoA reacts with carnitine (in stage one) and enters via an inner mitochondrial membrane transporter (translocase) into the matrix. (stage two)
Carnitine acyltransferase I transfers the fatty acid group to carnitine; carnitine acyltransferase II releases the fatty acid back into CoA.

Overview of β-Oxidation Pathway

The β-oxidation pathway involves reactions that remove two-carbon units from fatty acids.
This process produces NADH, FADH₂, and acetyl-CoA, that enters the TCA cycle.
Each cycle removes two carbon atoms.

Reactions of β-Oxidation (individual steps described in the presentation)

Individual reactions in the β-oxidation are numbered for clarity and proper labeling.

Summary of β-oxidation pathway

Fatty acids are broken down to 2 carbon units, yielding acetyl-CoA
Acetyl CoA enters the TCA cycle.

Energy Yield from Fatty Acid Oxidation

Complete oxidation of a 16-carbon fatty acid yields 106 ATP molecules.
This is more than glucose oxidation because fat is a more compact fuel source.

Regulation of Fat Metabolism

Factors such as adrenaline and glucagon regulate the release of fatty acids from adipose tissue.
The rate of entry into mitochondria via the carnitine shuttle has controlling mechanisms.
The electron transport chain reoxidizes NADH and FADH₂, regulating the rate of fatty acid oxidation.

Metabolism of Odd-Numbered Fatty Acids

Odd-numbered fatty acids undergo β-oxidation until three carbons remain (propionyl-CoA).
Conversion of propionyl-CoA to succinyl-CoA allows for entry into the TCA cycle.

Ketone Body Formation

During starvation or type I diabetes, the liver produces ketone bodies from acetyl-CoA due to excess acetyl-CoA.
This creates acetoacetate and β-hydroxybutyrate.
These are important alternative fuels for the brain and other tissues when glucose supply is low.

Ketone Bodies Utilization

Ketone bodies (acetoacetate and β-hydroxybutyrate) can be used for energy by most tissues.

Summary of Mitochondrial Events

Events in the mitochondrial matrix, such as pyruvate processing, fatty acid oxidation, and the citric acid cycle (Krebs cycle), are summarized for better understanding and retention of related processes.

Multiple Choice Questions (MCQs)

The presentation includes a series of MCQs related to the concepts covered.
Their answers are included in the slides. These are not covered in detail in these notes.

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Description

This quiz explores essential concepts in fat metabolism, focusing on the role of adipose tissue lipase, the conversion of fatty acids to CoA esters, and the significance of ketone bodies during starvation. It also discusses the precursors for steroid hormones. Test your knowledge on these critical biochemical processes.