Lipid digestion & Metabolism Flashcards
What is esterification?
fatty acids joined with glycerol to form an ester.
What types of fatty acids are they? what makes them distinct?
- Saturated –> have NO double bonds
- Monounsaturated–> have 1 double bond
- Polyunsaturated–> have 2 or more double bonds
give an example of saturated, monounsaturated and polyunsaturated fatty acids.
- Stearic acid = saturated fatty a
- oleic acid = monosaturated
- Linoleic acid =polyunsaturated
what types of polyunsaturated fatty acids are there?
Cis (same side + folding of the molecule into a U shape) or Trans (opposite sides + linear shape)
What are the classes of lipids?
- sterols & steroids
- phospholipids
- glycolipids
What are sterols made of? give an example of one.
sterols are monohydroxy alcohol of steroidal structures ex: cholesterol
what are sterols & steroids precursors for?
- bile acids
- sex hormones
- cholecaliferol
what are the qualities of cholesteryl esters?
they have a lower solubility in water than cholesterol and are more hydrophobic
What is the main lipid constituent of the cell membrane?
Phospholipids
what are two types of phospholipids?
- glycerophosphatides
- sphingophosphatides
what do glycerophosphatides contain?
glycerophosphatides contain phosphoric acid and they form derivatives with other compounds in the form of phosphatidyl alcohols (ex: lecithin)
what is the most common sphingolipid?
sphingomyelins
How are sphingomyelins important in the nervous system?
they form the myelin sheath which protects neurons
what do glycolipids contain?
they contain carbohydrate component & spingosine moiety
what are the main glycolipids?
cerebrosides & gangliosides
what is the function of glycolipids? where are they found?
the main function of glycolipids is structural.
- Cerebrosides: found in white matter of brain
- Gangliosides: provide the carbohydrate determinants of the human blood group
what are the biological roles for lipids?
- source of energy
- structural components of membranes (both cellular and subcellular)
- lubricants for body surfaces (sebaceous glands)
- signaling molecules (extra and intra cellular)
digestion of lipids starts in the ________ by the action of _________.
MOUTH by the action of Lingual lipase
**STOMACH **by the action of Gastric lipase
which one is gastric lipase more effective at hydrolyzing triglycerides? medium chain fatty acids or long chain fatty acids?
Medium chain fatty acids
Do gastric lipase hydrolyze cholesteryl esters or phospholipids?
NO
Gastric motility is ______ by the presence of fat.
gastric motility is INHIBITED by the presence of fat (high satiety value).
what does the pancreas secrete to neutralize chyme entering the small intestine?
Bicarbonates (HCO3)
where does emulsification with bile salts occur?
Small intestine
most of triglyceride digestion is done by _________ in the _________
Pancreatic lipase in the duodenum
what is the end products of triglyceride break down by pancreatic lipase?
Monoglycerides and free fatty acids
Pancreatic lipase is ____ effective with a bile salt-lipid mixture
MORE
what is required for the activation of pancreatic lipase?
a cofactor called colipase
what enzyme is found in the mouth that digests lipids? what lipids does it digest? what are the end products?
Lingual lipase digests triacylglycerols into di-acylglycerol and fatty acids
what is the end product of digestion of phospholipids?
free fatty acids & lysophosphatidylcholine
what enzyme(s) digest phospholipids?
Phospholipase A2 and phospholipase B
what enzyme hydrolyzes cholesterol ester? what is it hydrolyzed to ?
cholesterol esterase.
Hydrolyzed to free cholesterol and fatty acids (in the small intestine)
what are the end products of lipid digestion?
- free fatty acids -monoacylglycerol - lysophosphatidylcholine -cholesterol
what is the main purpose of bile salt micelles?
to make lipids more soluble in water phase overlying enterocytes (more lipid molecules can be delivered to the brush border membrane by bile salt micelles)
how do monoglycerides and fatty acids enter the enterocyte?
by diffusion
what are the two mechanisms for uptake of lipid digestion products?
- Passive diffusion 2. Carrier-mediated transport (Ex: FATP4)
when are carrier mediated transport needed to uptake lipids?
when fatty acid concentrations are low
water soluble digested lipids (ex: glycerol) are effectively taken up by what method?
diffusion
how does degree of unsaturation affect absorption of lipids?
As unsaturation increases, absorption efficiency increases.
where in the enterocytes is triacylglycerol resynthesized?
in the endoplasmic reticulum
triacylglycerols are packaged into _____ in the _______.
triacylglycerols are packaged into lipoproteins in the golgi.
where does re-esterification of digested lipids occur?
at the cytosolic surface of the ER inside the intestinal mucosal cells
what are the two pathways for re-esterification of digested lipids?
- monoacylglycerol pathway (normal conditions most use this pathway) 2. glycerol-3-phosphate pathway
Chylomicrons are a type of ______?
Lipoprotein
What are apoproteins?
Triacylglycerol lipid droplets and cholesteryl esters surrounded by the polar phospholipids and proteins
what are the three types of lipoproteins in the small intestine?
- chylomicrons 2. VLDL 3. HDL
which lipoproteins are secreted after a fat rich meal?
Chylomicrons
which lipoproteins are secreted during fasting?
VLDL
what are some major apoproteins associated with chylomicrons?
- A-I -Apo A-IV -Apo B-48
what is needed for the addition of triglyceride to chylomicron?
it requires microsomal triglycerol transfer protein (MTP)
where does the final step of chylomicron formation occur? (addition of CHO)
in the golgi
why are lipids re-esterified?
to maintain low intercellular concentrations of digested lipids
what is the function of Apoproteins?
signaling & attracts digestive enzyme
what enzyme is involved in esterification of cholesterol ?
acyl CoA cholesterol acyltransferase
where do chylomicrons move to after leaving the intestinal cells?
into the lymphatic capillaries (vessels) by exocytosis and then enter the venous plasma via the left thoracic lymph duct
what enzyme is involved in the hydrolysis of triglycerides from chylomicrons? where does this occur?
lipoprotein lipases in the muscles & adipose tissues
in the liver (hepatocytes) triglycerides are assembled in the form of _______.
VLDL
LPL (lipoprotein lipase) in cardiac muscles has ______ affinity than that in adipose tissue.
Higher
during fasting what concentrations are there of VLDL and chylomicrons?
during fasting, chylomicrons are almost absent, and VLDL concentration (hepatic) is low
during fasting, lipoprotein lipase concentration in the ______ tissue is down regulated while that of _______ is maintained.
adipose= down regulated
cardiac muscles = maintained
what is used by the muscles for energy during fasting?
triglycerides (VLDL)
After a meal, (fed state) where are triglycerides (as chylomicrons) stored?
they are stored in the adipose tissue
