Biochemistry Chapter 11: Lipid and Amino Acid Metabolism Flashcards
Where does mechanical digestion of lipids primarily happen?
stomach
Where does chemical digestion of lipids occur?
the small intestine and is facilitated by bile, pancreatic lipase, colipase and cholesterol esterase
Digested lipids can be:
form micelles for absorption or be absorbed directly
Short-chain fatty acids are absorbed
across the intestine into the blood.
Long-chain fatty acids are absorbed
as micelles and assembled into chylomicrons for release into the lymphatic system
Lipids are mobilized from adipocytes by
hormone-sensitive lipase
Lipids are mobilized from lipoproteins by
lipoprotein lipase
Chylomicrons
the transport mechanism for dietary triacylglycerol molecules and are transported via the lymphatic system.
VLDL
transports newly synthesized traacylglycerol molecules from the liver to peripheral tissues in the bloodstream.
IDL
A VLDL remnant in transition between triacylglycerol and cholesterol transport; it picks up cholesteryl esters from HDL.
LDL
primarily transports cholesterol for use by tissues.
HDL
involved in the reverse transport of cholesterol.
Apoproteins
control interactions between lipoproteins
Cholesterol can be formed from:
dietary sources or through de novo synthesis in the liver
The key enzyme in cholesterol biosynthesis
HMG-CoA reductase
LCAT
catalyzes the formation of cholesteryl esters for transport with HDL
CETP
catalyzes the transition of IDL to LDL by transferring cholesteryl esters from HDL
Fatty acids
carboxylic acids with a (usually) single long chain, although they can be branched.
Saturated fatty acids
have no double bonds between carbons
Unsaturated fatty acids
have one or more double bonds
Fatty acids are synthesized in___
the cytoplasm from acetyl-CoA transported out of the mitochondria
What are the five steps of fatty acid synthesis?
activation bond formation reduction dehydration 2nd reduction
(Repeated, ex. 8 times to get palmitic acid)
What is the only fatty acid that humans can synthesize?
palmitic acid
Where does fatty acid oxidation occur?
in the mitochondria following transport by the carnitine shuttle
Beta oxidation uses cycles of:
oxidation, hydration, oxidation & cleavage
What types of fatty acids require special enzymes?
branched and unsaturated
Unsaturated fatty acid enzymes
isomerase and an additional reductase
When do ketone bodies form?
during a prolonged starvation due to excess acetyl-CoA in the liver
Ketolysis
regenerates acetyl-CoA for use as an energy source in peripheral tissues
Where does the brain get its energy during starvation?
from ketone bodies (up to 2/3 of energy)
Where does protein digestion generally occur?
small intestine
When does catabolism of cellular proteins occur?
conditions of starvation.
How can amino acids be used for energy?
through either gluconeogenesis or ketone body formation.
