Chapter 11 Lipid and Amino Acid Metabolism

Where does mechanical digestion of lipids occur?

mouth and stomach

Where does chemical digestion of lipids occur?

SI

What facilitates chemical digestion?

bile, pancreatic lipase, colipase, cholesterol esterase

What do digested lipids form and why?

micelles for absorption

Where are short-chain fatty acids absorbed?

across intestine into blood

Long-Chain Fatty Acids

absorbed as micelles and assembled into chylomicrons for release into lymphatic system

What mobilizes lipids to adipocytes?

hormone-sensitive lipase

What mobilizes lipids to lipoproteins?

lipoprotein tissue

Chylomicrons Function

transport mechanism for dietary triacylglycerol molecules via lymphatic system

VLDL Function

transports newly synthesized triacylglycerol molecules from liver to peripheral tissues in bloodstream

IDL

VLDL remnant in transition between triacylglycerol and cholesterol transport

IDL Function

picks up cholesteryl esters from HDL

LDL

primarily transports cholesterol for use by tissues

HDL

involved in reverse transport of cholesterol

Apoproteins

 control interactions between lipoproteins

How can cholesterol be obtained?

dietary sources or de novo synthesis in liver

What is the key enzyme in cholesterol biosynthesis?

HMG-CoA reductase

LCAT Function

catalyzes formation of cholesteryl esters for transport with HDL

CETP Function

catalyzes transition of IDL to LDL by transferring cholesteryl esters from HDL

Fatty Acids

carboxylic acids, usually single long chain but can be branched

Saturated Fatty Acids

double bonds between carbons

Unsaturated Fatty Acids

one or more double bonds

Where are fatty acids synthesized?

cytoplasm from acetyl-CoA transported out of mitochondria

Fatty Acid Synthesis Steps

activation, bond formation, reduction, dehydration, second reduction

Why is fatty acid synthesis repeated 8 times?

to form palmitic acid

Where does fatty acid oxidation occur?

mitochondria

Beta-Oxidation

uses cycles of oxidation, hydration, oxidation, cleavage

What do unsaturated fatty acids use for cleavage?

isomerase and additional reductase

When do ketone bodies forma and why?

in ketogenesis during prolonged starvation state due to excess acetyl-CoA in liver

Ketolysis

regenerates acetyl-CoA for use as energy sources and peripheral tissues

Protein Catabolism Location

occurs primarily in SI

When does catabolism of cellular proteins occur?

starvation

In protein catabolism, what is used for energy?

carbon skeleton of AA through gluconeogenesis or ketone body formation

Where are amino groups fed?

urea cycle for excretion

What does the fate of a side chain depend on?

its chemistry