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Questions and Answers
What is the primary function of Lipoprotein Lipase (LPL)?
What is the primary function of Lipoprotein Lipase (LPL)?
- To transport cholesterol to peripheral tissues
- To release fatty acids and glycerol from triglycerides (correct)
- To store excess glucose as glycogen
- To synthesize new fatty acids from glucose
What can cause steatorrhea?
What can cause steatorrhea?
- Blockages in pancreatic or bile ducts (correct)
- High-protein diet
- Increased absorption of carbohydrates
- Excessive fat intake without digestive enzymes
Which fatty acid is known as the precursor to all other fatty acids?
Which fatty acid is known as the precursor to all other fatty acids?
- Stearic acid
- Palmitic acid (correct)
- Linoleic acid
- Oleic acid
Which condition is associated with a decrease in fat-soluble vitamin absorption?
Which condition is associated with a decrease in fat-soluble vitamin absorption?
Where does the synthesis of fatty acids primarily take place?
Where does the synthesis of fatty acids primarily take place?
What is required for the activation of Lipoprotein Lipase (LPL)?
What is required for the activation of Lipoprotein Lipase (LPL)?
What occurs to the turbidity of blood after consuming a high-fat meal?
What occurs to the turbidity of blood after consuming a high-fat meal?
What type of fatty acids are more common in biological systems, cis or trans double bonds?
What type of fatty acids are more common in biological systems, cis or trans double bonds?
What is the primary function of bile salts in the emulsification process?
What is the primary function of bile salts in the emulsification process?
Which lipases primarily hydrolyze triacylglycerols with short and medium chain fatty acids?
Which lipases primarily hydrolyze triacylglycerols with short and medium chain fatty acids?
What role does colipase play in the digestive process?
What role does colipase play in the digestive process?
Which hormonal substance is responsible for inducing the secretion of bicarbonate in the pancreas?
Which hormonal substance is responsible for inducing the secretion of bicarbonate in the pancreas?
What are the primary products of dietary lipid degradation found in the jejunum?
What are the primary products of dietary lipid degradation found in the jejunum?
How does pancreatic lipase contribute to lipid digestion?
How does pancreatic lipase contribute to lipid digestion?
What is the role of peristalsis in the emulsification process of lipids?
What is the role of peristalsis in the emulsification process of lipids?
Which of the following statements regarding short- and medium-chain fatty acids is correct?
Which of the following statements regarding short- and medium-chain fatty acids is correct?
What is the primary function of the citrate-malate shuttle?
What is the primary function of the citrate-malate shuttle?
Which of the following compounds inhibits the activity of the fatty acid synthase enzyme?
Which of the following compounds inhibits the activity of the fatty acid synthase enzyme?
How does malonyl CoA play a role in fatty acid metabolism?
How does malonyl CoA play a role in fatty acid metabolism?
What is the end product of the fatty acid synthase reaction?
What is the end product of the fatty acid synthase reaction?
What effect does high insulin and low glucagon have on lipogenesis?
What effect does high insulin and low glucagon have on lipogenesis?
Which molecule is NOT involved in the synthesis of triacylglycerols?
Which molecule is NOT involved in the synthesis of triacylglycerols?
In which cellular compartment can fatty acids be elongated in humans?
In which cellular compartment can fatty acids be elongated in humans?
What prevents humans from synthesizing double bonds between the w carbon and the seventh carbon from the w end?
What prevents humans from synthesizing double bonds between the w carbon and the seventh carbon from the w end?
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Study Notes
Dietary Lipids: Digestion, Absorption, and Transport
- Triacylglycerols, phospholipids, and cholesteryl esters are primary dietary lipids.
- Digestion: Lipases play a crucial role in breaking down these lipids.
- Lingual and Gastric Lipases: Begin digestion with short and medium chain fatty acids (12 carbons or fewer).
- Pancreatic Lipase: Key enzyme for triacylglycerol breakdown in the small intestine (duodenum).
- Emulsification: Bile salts from the liver and gallbladder increase the surface area of lipid droplets, promoting digestion.
- Micelles: These structures, formed by bile salts, contain triacylglycerols, free fatty acids, cholesterol, and monoglycerides, facilitating absorption.
- Absorption in Jejunum: The primary products of lipid degradation (free fatty acids, cholesterol, monoglycerides) are absorbed into mucosal cells.
- Packaging: Short and medium chain fatty acids enter the portal circulation, while long chain fatty acids are re-esterified into triacylglycerols and packaged into chylomicrons.
- Chylomicron Function: Chylomicrons transport dietary lipids from the intestines to tissues.
- Lipoprotein Lipase (LPL): Located on capillary walls, LPL hydrolyzes triacylglycerols in chylomicrons, releasing free fatty acids for tissue use.
Fatty Acid Synthesis
- Palmitate (16:0): Key precursor for most fatty acids.
- Synthesis Process: Occurs primarily in the cytoplasm of liver and mammary glands, and to a lesser extent, adipose tissue.
- Citrate-Malate Shuttle: Translocates acetyl CoA from the mitochondria to the cytoplasm for fatty acid synthesis.
- Rate-Limiting Step: Acetyl-CoA carboxylase converts acetyl CoA to malonyl CoA, regulated by insulin, glucagon, citrate, and palmitoyl CoA.
- Malonyl CoA Inhibition: Prevents fatty acid degradation while simultaneously promoting synthesis.
- Elongation: Palmitate can be elongated in the ER or mitochondria, producing longer chain fatty acids.
- Desaturases: These enzymes introduce double bonds into fatty acid chains. Humans cannot introduce double bonds beyond the 9th carbon from the methyl end, requiring dietary essential fatty acids.
Triacylglycerol Synthesis
- Glycerol Phosphate: Obtained from dihydroxyacetone phosphate (DHAP) in liver and adipose tissue, or glycerol in the liver.
- Integration of Lipid and Carbohydrate Metabolism: High insulin levels promote lipogenesis by stimulating pyruvate dehydrogenase and inducing enzymes involved in fatty acid synthesis.
Steatorrhea
- Frothy, Foul-Smelling Stools: Resulting from undigested fat.
- Causes: Pancreatic lipase deficiency, bile duct obstruction, or cystic fibrosis.
- Consequences: Impaired absorption of fat-soluble vitamins (A, D, E, and K) and essential fatty acids.
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