Lipid Metabolism Flashcards
How are Lipids digested?
TAGs are mixed with bile and pancreatic secretions
* Emulsification
* Digestion
What are the five different phases of lipid digestion/absorption?
- Hydrolysis of TAGs to free fatty acids
- Solubilization of FFA and monoacylglycerols by detergents–>transport from intestinal lumen toward cell surface
- Uptake of FFA and monoacylglycerols into the cell and resynthesis into TAGs
- Packaging of TAGs into chylomicrons
- Exocytosis of chlyomicrons into lymph
Lipid digestion in the mouth
chewing & release of lingual lipase
Lipid digestion in the stomach
Begins in the stomach
* Gastric/lingual lipase breakdown TAGs to short medium chain fatty acids (<12 carbons)
Lipid digestion in the small intestine
Definition of emulsification
- Emulsifies fats to allow absorption
- Emulsification: increases surface area of the hydrophobic liquid droplets
- Increases effectivity of the digestive enzymes
What are the 3 lipid digesting enzymes?
- Pancreatic lipase
- Cholesterol esterase
- Phospholipase A2
What does pancreatic lipase breakdown?
TAGs into mixture of 2-monoacylglycerol and FFAs
What does cholesterol esterase breakdown?
Cholesteryl esters to cholesterol and FFAs
What does Phospholipase A2 break down?
Removes one FA from carbon 2 of a phospholipid–>lysophospholipid
Where does biosynthesis of complex lipids take place?
Endoplasmic Reticulum
Can TAGs, Phospholipids and Cholesterol ester be transported in the blood/lymph?
NO because of their insolubility in water
Where are chlyomicrons made?
Intestine-released into the lymphatic vessels for transportion to the blood
Free fatty acids are transported in blood bound to what?
Albumin
Triacylglycerols and cholesterylester are transported in blood in what?
Lipoproteins
Chlyomicrons (CM)-where are they released, major components
- Released by the intestinal mucosal cells into lymph-transport fats from the intestines to liver
- TAGs (90%)
- CE and lipid-soluble vitamins
VLDLs important things to know
- Released by the liver into the blood (transfer TAGs from the liver to other tissues)
- VLDLs: contain 60% TAGS
- 20% cholesterol ester and free cholesterol
What lipoproteins lead to high TAGs in blood?
Chylomicrons and VLDL
LDLs important things to know
- LDLs are formed in the blood from VLDLs-not released from cells
- Highest percentage of cholesterol ester and free cholesterol
- Can lead to high cholesterol in blood
HDLs important things to know
- Highest percentage of proteins
- Deliver cholesterol ester to the liver in reverse cholesterol transport
What are the major tissues involved in lipids from our diet?
- Skeletal and adipose tissues
- Others include: heart, lung, kidney, and liver
Glycerol we eat is used where in the body mostly?
Nearly exclusively in the LIVER to produce glycerol 3-phosphate
De Novo Synthesis of Fatty Acids
WHY?
- Enables the liver to buffer high blood glucose levels
- Allows excess calories from the diet to be stored as TAGs
De Novo Synthesis of Fatty Acid takes place where?
CYTOSOL
* Primarily in liver/mammary glands in humans
De Novo Synthesis of Fatty Acids occurs how?
- 2 carbon units from Acetyl CoA repeatedly into the growing FA chain using ATP and reduced NADPH
What are the two enzymes used in the translocation of citrate?
Citrate synthase and ATP-Citrate Lyase
What is the Rate Limiting Step of De Novo Synthesis?
- Once inside the cytosol-Acetyl CoA is carboxylated to form malonyl CoA
- Catalyzed by Acetyl CoA carboxylase
Production of cytoslic acetyl CoA
Beta Oxidation of fatty acids-Important things to know
- Major pathway for the catabolism of saturated FAs & occurs in the mitochondria
- 2 carbon fragments are successively removed from the carboxyl end of the fatty acyl CoA-produces Acetyl CoA, NADH, FADH2
What are the 4 steps to produce acetyl CoA from fatty acyl CoA?
- Oxidation that produces FADH2
- Hydration step
- Second Oxidation that produces NADH
- Thiolytic Cleavage that releases a molecule of Acetyl Coa
Where does Beta Oxidation occur?
Mitochondrial Matrix
Inner mitochondrial membrane is impermeable to CoA to the matrix so they use a specialized carrier called -carnithine shuttle
Where do obtain carnithine from?
- Meat products (diet)
- Amino Acids Lys & Meth
Cholesterol is a precursor to what?
(3)
- Bile Acids
- Steroid hormones
- Vitamin D
Cholesterol is synthesized in the body where?
By nearly ALL HUMAN TISSUE
What regulates the body’s cholesterol levels?
The liver
How many carbons does cholesterol have?
27
What is the rate limiting step for cholesterol synthesis?
HMG CoA Reductase
Carnithine deficiences result ina decreased ability of tissues to use Long Chain Fatty Acids. Why is this?
Short/medium chains can pass through on their own but long chains cannot
If a 18 Carbon chain undergos beta oxidation-how many cycles till it can’t undergo anymore
7 cycles
What is the net effect of the cartithine shuttle?
Long chain fatty acyl CoA is transported from the outside to the inside of the mitochondria
What lipoprotein transports cholesterol to the cell and what lipoprotein reverses this action?
LDL, HDL
