Biochem Unit 13 - Fatty Acid Oxidation

What are the major physiological functions of fatty acids?

Building blocks of phospholipids and glycolipids, modification of proteins, serving as hormones and intracellular messengers, and as a source of energy.

What is the difference between saturated and unsaturated fatty acids?

Saturated fatty acids have no double bonds, while unsaturated fatty acids have one or more double bonds.

What is the role of lipase enzymes?

Lipase enzymes cleave fatty acids from triglycerides, producing free fatty acids.

Why must fatty acids and other lipids be transported by lipoproteins?

Lipids are insoluble in aqueous systems, so they need to be solubilized for transport in the blood.

What roles do coenzyme A and carnitine play in fatty acid oxidation?

Coenzyme A is involved in the activation of fatty acids, while carnitine facilitates the transport of fatty acids into the mitochondria for oxidation.

What are the four steps in the oxidation of a saturated fatty acid?

1. Activation by acyl-CoA synthetase; 2. Transport into mitochondria; 3. Beta-oxidation; 4. Formation of acetyl-CoA.

When are isomerase and reductase enzymes required in fatty acid oxidation?

They are required for the oxidation of unsaturated fatty acids to rearrange or reduce double bonds.

How is the total amount of ATP from a fatty acid calculated?

By considering the number of acetyl-CoA molecules produced and the energy yield from each, along with the ATP generated during beta-oxidation.

What are the regulatory mechanisms controlling fatty acid oxidation and synthesis?

Hormonal regulation (insulin and glucagon), substrate availability, and feedback inhibition by products.

What are ketone bodies and when are they overproduced?

Ketone bodies are produced during fatty acid oxidation, particularly in fasting or uncontrolled diabetes when carbohydrate availability is low.

What is the energy yield of fatty acids compared to carbohydrates?

Fatty acids generate more ATP per molecule than carbohydrates, providing about 9 kcal/gram compared to 4 kcal/gram for carbohydrates.

What is the significance of triglycerides as an energy source?

Triglycerides are a highly concentrated energy store and provide more than half the energy requirements for the liver, heart, and resting skeletal muscle.

How do dietary triglycerides contribute to energy requirements?

They supply over 40% of the daily energy requirement for humans.

What is the structure of phosphatidylcholine?

Phosphatidylcholine consists of a glycerol backbone, two fatty acid tails, and a phosphate group attached to a choline molecule.

What is the typical configuration of naturally occurring fatty acids?

Most naturally occurring fatty acids have a cis-configuration for their double bonds.

What is the significance of the omega (w) nomenclature in fatty acids?

The omega nomenclature indicates the position of the first double bond from the methyl end of the fatty acid chain.

What is the difference between exogenous and endogenous pathways in lipid transport?

Exogenous pathways involve dietary lipids, while endogenous pathways involve lipids synthesized in one organ for export to another.

What triggers the mobilization of stored triglycerides?

Low levels of glucose trigger the release of glucagon, which promotes the mobilization of triglycerides.

What is the role of protein kinase A (PKA) in triglyceride mobilization?

PKA phosphorylates hormone-sensitive lipase, activating it to break down triglycerides into free fatty acids.

What is the relationship between glucagon and insulin in energy mobilization?

Glucagon promotes the mobilization of energy sources, while insulin promotes energy storage.

What are the common types of lipoproteins involved in lipid transport?

Chylomicrons, VLDL (Very Low-Density Lipoproteins), LDL (Low-Density Lipoproteins), and HDL (High-Density Lipoproteins).

What is the primary storage form of fatty acids in the body?

Fatty acids are primarily stored as triglycerides (triacylglycerols).

What is the energy density of triglycerides compared to carbohydrates and proteins?

Triglycerides provide more energy per gram than carbohydrates and proteins due to their reduced and anhydrous structure.

What is the importance of double bonds in fatty acids?

Double bonds affect the stability and packing of fatty acids, influencing their physical properties and biological functions.

What role do perilipins play in lipid metabolism?

Perilipins coat lipid droplets and restrict access, but phosphorylation alters their conformation to allow access for hormone-sensitive lipase.

What is the process by which triglycerides are hydrolyzed?

Triglycerides are hydrolyzed to free fatty acids, making them available for transport from adipose tissue.

How do free fatty acids leave adipocytes?

Free fatty acids leave adipocytes and bind to serum albumin for transport.

What is the fate of fatty acids once they reach myocytes?

Fatty acids enter myocytes via a specific transporter and undergo β-oxidation to produce ATP.

How can glycerol enter glycolysis?

Glycerol can be converted to dihydroxyacetone phosphate to enter glycolysis.

What is required for fatty acid activation?

Fatty acid activation requires Coenzyme A and occurs in a two-step process.

What is the role of carnitine in fatty acid metabolism?

Carnitine facilitates the transport of acyl groups across the inner mitochondrial membrane.

What are the four steps of β-oxidation?

1. Oxidation by acyl-CoA dehydrogenase, 2. Hydration by enoyl-CoA hydratase, 3. Oxidation by β-hydroxyacyl-CoA dehydrogenase, 4. Thiolysis by acyl-CoA transferase.

What is produced during the β-oxidation of fatty acids?

Each round of β-oxidation produces FADH2, NADH, and Acetyl-CoA.

How is the number of β-oxidation rounds calculated?

The number of rounds is calculated as (number of carbon atoms in fatty acid / 2) - 1.

What is the total ATP yield from the complete oxidation of palmitate?

The complete oxidation of palmitate yields 106 ATP after accounting for activation costs.

How do unsaturated fatty acids differ in metabolism?

Unsaturated fatty acids require additional enzymes such as isomerase and reductase during β-oxidation.

What happens to monounsaturated fatty acids during β-oxidation?

Monounsaturated fatty acids require isomerase to convert the double bond before completing β-oxidation.

What is the significance of the acyl adenylate intermediate in fatty acid activation?

The acyl adenylate intermediate provides a good leaving group (AMP) and allows CoA-SH to attach to the fatty acid.

What is the energy cost for fatty acid activation?

The energy cost for fatty acid activation is 2 ATP equivalents.

What is the function of acyl-CoA dehydrogenase?

Acyl-CoA dehydrogenase catalyzes the first step of β-oxidation, producing FADH2.

What type of reaction does a hydrolase enzyme perform?

A hydrolase enzyme performs hydrolysis, breaking bonds with water.

What is the outcome of the final round of β-oxidation for a 4-carbon fatty acid?

The final round of β-oxidation produces two molecules of Acetyl-CoA.

What is the importance of NADH and FADH2 in fatty acid oxidation?

NADH and FADH2 are