CH 12: Lipid metabolism

What are fatty acids and triacylglycerols an important source of?

They are an important source of energy for many living cells.

How are fatty acids digested in the small intestine?

They are digested by pancreatic lipase to form fatty acids and monoacylglycerol.

What is monoacylglycerol converted to in intestinal wall cells?

It is converted to triacylglycerols.

What happens to fatty acids depending on an animal's current needs?

They may be converted to triacylglycerol or degraded to generate energy.

What stimulates triacylglycerol formation in adipose tissue during high serum glucose levels?

Insulin

What happens to triacylglycerol during low serum glucose levels?

Many hormones stimulate triacylglycerol degradation to form glycerol and fatty acids.

What is lipogenesis?

It is the synthesis of triacylglycerol.

What are the reactants in the pathway of lipogenesis?

Glycerol-3-phosphate or dihydroxy acetone phosphate reacts with acyl-CoA.

What is the function of phosphatidic acid?

It is converted to diacylglycerol by phosphatidic acid phosphatase and further acylated to form triacylglycerol.

What is lipolysis?

It is the process of metabolizing stored fat under low energy conditions.

When does lipolysis occur?

During fasting, vigorous exercise, and in response to stress.

How is lipolysis activated in the body?

Hormones like glucagon and epinephrine activate lipase enzymes by activating cAMP synthesis.

What are the products of lipolysis?

Fatty acids and glycerol are released into the blood.

Where is glycerol transported, and what can it be converted to?

Glycerol is transported to the liver where it can form either glucose or a lipid.

How are fatty acids transported in the bloodstream?

They bind to serum albumin and are transported to various tissues.

What is the function of fatty acids in energy generation?

They are degraded to form acetyl-CoA within mitochondria in a process known as beta-oxidation.

What is beta-oxidation?

It is the process of breaking down fatty acids to generate energy.

Where does alpha-oxidation primarily occur?

It primarily occurs in mitochondria.

What is the first step of beta oxidation?

Acyl Co-A ligase activates fatty acid in a reaction with ATP and CoASH.

Why must Acyl-CoA be attached to Carnitine?

Because mitochondrial inner membranes are impermeable to Acyl-CoA.

What is formed in the first oxidation step of beta oxidation?

Enoyl-CoA is formed, and FADH2 is the byproduct.

What are the products of the hydration of Enoyl-CoA?

L-beta-Hydroxyacyl-CoA is formed.

What is produced from the oxidation of L-beta-Hydroxyacyl-CoA?

Beta-Ketoacyl-CoA and NADH are produced.

What happens during the thiolytic cleavage step of beta oxidation?

An acetyl-CoA molecule is released along with Acyl-CoA.

What happens to most Acetyl-CoA produced during fatty acid oxidation?

It is used by the citric cycle or in isoprenoid synthesis.

What is ketogenesis?

The process where Acetyl-CoA is converted to ketone bodies such as acetoacetate and beta-hydroxybutyrate.

What is the first step of ketogenesis?

Condensation of two acetyl-CoA to form acetoacetyl-CoA.

What does HMG-CoA get cleaved into during ketogenesis?

cleaved to form acetyl-CoA and acetoacetate.

In which process is acetoacetate reduced to form beta-hydroxybutyrate?

It occurs during ketogenesis.

What forms acetone during ketogenesis?

is formed from acetoacetate by spontaneous decarboxylation.

What are the dietary sources of cholesterol?

Cholesterol is derived from diet or synthesized de novo.

Which cells in the body produce the most cholesterol?

Liver cells

What occurs in the first stage of cholesterol synthesis?

Formation of HMG-CoA from acetyl-CoA.

What is formed in the second stage of cholesterol synthesis?

HMG-CoA is converted to squalene.

What is the outcome of the third stage of cholesterol synthesis?

Squalene is converted to cholesterol.

What is the similarity between the first phase of cholesterol biosynthesis and ketosis?

Both processes are similar until the formation of HMG-CoA.

What follows the reduction of HMG-CoA in cholesterol synthesis?

Mevalonate is formed and further converted to farnesylpyrophosphate.

What requires NADPH during cholesterol synthesis?

The condensation of two farnesylpyrophosphates to form squalene

What are some enzymes involved in converting squalene to lanosterol?

Squalene monooxygenase and 2,3-oxidosqualene lanosterol cyclase are involved.

What final transformations occur to lanosterol to form cholesterol?

is transformed to 7-Dehydrocholesterol and then reduced to form cholesterol.

What is a precursor for all steroid hormones and bile salts?

Cholesterol

How is cholesterol degraded?

Cholesterol is derivatized to bile acids rather than degraded into smaller molecules.

What is the role of bile in fat absorption?

Bile enhances the absorption of dietary fat by emulsifying it.

What vitamins are fat-soluble and absorbed with bile salts?

Vitamins A, D, E, and K