Chem Ch. 23

What is a triglyceride?

A molecule made of glycerol esterified to three fatty acids.

What tissue is the major storage depot for lipids?

Adipose tissue.

Why are triglycerides more efficient energy-storage molecules than glycogen?

They are more energy-dense and are stored without large amounts of associated water.

What is the function of bile salts in lipid digestion?

They emulsify lipids, increasing their surface area and making them easier for pancreatic lipases to digest.

What are ketone bodies?

Acetone, acetoacetate, and beta-hydroxybutyrate; they are produced from fatty acids in the liver through acetyl-CoA.

What is ketosis?

An abnormal increase in the level of ketone bodies in the blood.

What is ketoacidosis?

A serious condition in which high levels of acidic ketone bodies lower blood pH, making the blood too acidic.

Why do uncontrolled diabetics produce large amounts of ketone bodies?

Glucose cannot enter cells effectively, so cells break down fatty acids. Beta oxidation produces excess acetyl-CoA, which is used to make ketone bodies.

How do ketone bodies cause ketoacidosis?

Some ketone bodies, especially acetoacetate and beta-hydroxybutyrate, are acidic and directly lower blood pH.

When does the heart use ketone bodies?

Ketone bodies are a preferred energy source for the heart.

When does the brain use ketone bodies?

When glucose becomes scarce, such as during prolonged fasting or starvation.

Where does fatty acid biosynthesis occur?

In the cytoplasm.

What is the acyl group carrier in fatty acid biosynthesis?

Acyl carrier protein (ACP).

What is the function of NADPH in fatty acid biosynthesis?

It acts as a reducing agent.

How is fatty acid synthase structured?

It is a large multienzyme complex containing seven enzymes involved in fatty acid synthesis.

How do the enzymes of beta oxidation differ from fatty acid synthase?

The beta-oxidation enzymes are separate enzymes rather than one large multienzyme complex.

Where does fatty acid synthesis occur?

In the cytoplasm.

Where does beta oxidation occur?

In the mitochondrion.

Under what conditions does the liver synthesize ketone bodies?

During starvation or fasting, when glucose is scarce.

Under what conditions does the brain use ketone bodies for energy?

When glucose becomes scarce.

What pathway provides most ATP for working muscle?

Degradation of its stored glycogen.

How are fatty acids synthesized in the liver transported to adipose tissue?

They are transported in VLDLs.

What pathway provides most ATP for resting muscle?

Beta oxidation of fatty acids.

What are the major fuels for the heart, brain, and liver?

The heart primarily uses ketone bodies, the brain primarily uses glucose, and the liver obtains much of its energy from oxidation of amino acid carbon skeletons.

What is the general effect of insulin on metabolism?

Insulin stimulates anabolic/biosynthetic processes and inhibits catabolic processes.

What triggers insulin secretion?

Elevated blood glucose levels.

What are the primary target cells/tissues of insulin?

Liver, muscle, and adipose tissue.

What triggers glucagon secretion?

Decreased blood glucose levels.

What are the primary target tissues of glucagon?

Liver, muscle, and adipose tissue.

Where is insulin produced?

In the beta cells of the islets of Langerhans in the pancreas.

Where is glucagon produced?

In the pancreas, specifically the alpha cells of the islets of Langerhans.

How does insulin affect carbohydrate metabolism?

It increases glucose uptake, stimulates glycogen formation, and inhibits glycogen breakdown and gluconeogenesis.

How does glucagon affect carbohydrate metabolism?

It stimulates glycogen breakdown, releasing glucose and increasing blood glucose levels.

How does insulin affect lipid metabolism?

It stimulates the synthesis and storage of triglycerides.

How does glucagon affect lipid metabolism?

It stimulates lipid hydrolysis and beta oxidation.