Questions and Answers
What is the primary function of red blood cells?
To deliver oxygen to cells and remove carbon dioxide from body tissues.
What are the two parts of hemoglobin?
Globin and heme.
Where are red blood cells formed?
What happens to old red blood cells?
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How long is the lifespan of a red blood cell?
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What are the degradation products of heme?
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Match the bile pigments with their colors:
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The iron atom in heme interacts with carbon dioxide.
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What condition results from higher than normal bilirubin levels in the blood?
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What are chylomicrons formed from?
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What transports TAGs from intestinal cells to the bloodstream?
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The liver changes some fats into triglycerides only.
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What do fatty acids and glycerol get converted to in the cells?
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What is the primary function of adipose tissue?
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What is the main site of glycerol metabolism?
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What are the final products of the beta-oxidation of fatty acids?
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What is the first product formed during the oxidation of fatty acids?
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What happens to excess acetyl CoA when carbohydrates are insufficient?
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What needs to be present for acetyl CoA to react with oxaloacetate in the Krebs cycle?
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Ketogenic amino acids can be converted to ___ and/or ___ body synthesis.
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What is a function of the urea cycle?
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What are the final products of the urea cycle?
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Study Notes
Digestion and Absorption of Lipids
- Monoacylglycerols and free fatty acids are repackaged into TAGs (triacylglycerols) in intestinal cells.
- TAGs combine with phospholipids, cholesterol, and lipoproteins to form chylomicrons.
- Chylomicrons transport TAGs from intestinal cells to the bloodstream via the lymphatic system.
- Fats flow from lymphatics through the thoracic duct into the bloodstream and eventually reach the liver.
- In the liver, some fats are transformed into phospholipids, contributing to both fat and phospholipid composition in blood.
- Phospholipids like sphingomyelin and lecithin are essential for nerve and brain tissue formation, while lecithins assist in fat transport.
- Cephalin, another phospholipid, plays a role in normal blood clotting.
- Excess fatty acids and glycerol are either used for energy or repacked for storage in adipocytes within adipose tissue.
- Adipose tissue, located mainly beneath the skin and around vital organs, provides insulation and protects against mechanical shocks.
- Triacylglycerol reserves are the primary source of stored energy, significantly surpassing protein and glycogen.
Glycerol Metabolism
- Glycerol is transported to the liver or kidneys via blood and converted to dihydroxyacetone phosphate (DHAP), part of the glycolysis pathway.
- DHAP can further convert to lactic acid, glycogen, or pyruvic acid for entry into the TCA cycle.
Oxidation of Fatty Acids
- Fatty acid breakdown for energy occurs in three steps: activation by coenzyme A to form acyl CoA, transport into the mitochondrial matrix, and repeated oxidation.
- Acyl CoA refers to any fatty acid chain length, while acetyl CoA specifically denotes a two-carbon unit.
- The β-oxidation pathway involves a series of four reactions that repeatedly remove two carbon atoms from saturated fatty acids.
- The four steps of β-oxidation:
- Oxidation with FAD to produce FADH.
- Hydration to convert to a secondary alcohol.
- Oxidation to a keto group with NAD+.
- Chain cleavage to produce acetyl CoA and a shorter acyl CoA.
- Acetyl CoA enters the citric acid cycle for energy production.
- Fatty acids with odd-numbered carbon chains result in propionyl CoA, which is converted to succinyl CoA for entry into the citric acid cycle.
- Unsaturated fatty acids require initial reduction before undergoing β-oxidation.
Ketone Bodies
- When carbohydrate and lipid metabolism are imbalanced, excess acetyl CoA is converted to ketone bodies (acetoacetic acid, β-hydroxybutyric acid, acetone).
- Ketone bodies provide an alternative energy source, particularly during high-fat, low-carbohydrate diets or in diabetes.
- Ketosis can lead to acidosis and requires increased water intake to manage metabolites.
- In severe conditions, like diabetes, excess ketone bodies can cause dehydration and potentially fatal metabolic states.
Biosynthesis of Fatty Acids: Lipogenesis
- Acetyl CoA, produced in mitochondria, is transported to the cytosol via the citrate-malate shuttle system.
- In cytoplasm, acetyl CoA is converted to malonyl CoA in a reaction requiring ATP and CO2, catalyzed by acetyl CoA carboxylase.
- Fatty acid synthesis involves intermediates linked to acyl carrier protein (ACP).
Unsaturated Fatty Acid Biosynthesis
- Specific enzyme systems are needed for elongation and double bond introduction.
- Humans cannot synthesize linoleic and linolenic acids; they must come from dietary sources.
Amino Acid Utilization
- Amino acids enter the amino acid pool from dietary proteins, turnover, and liver synthesis (only non-essential).
- Utilization includes protein synthesis, non-protein nitrogen compound synthesis, energy production, and synthesis of non-essential amino acids.
- Degradation takes place in two stages: removal of the amino group and degradation of the carbon skeleton.
The Urea Cycle
- The urea cycle processes nitrogenous wastes, transferring carbamoyl groups to form urea, which is excreted.
- Intermediates from protein degradation can enter various pathways, including the citric acid cycle.
Hemoglobin Catabolism
- RBCs, primarily formed in bone marrow, have a lifespan of about four months before being broken down in the spleen or liver.
- Hemoglobin degradation yields amino acids, iron (stored as ferritin), and bile pigments.
- Bile pigments (biliverdin, bilirubin, stercobilin, urobilin) are excreted in urine and feces, with excess bilirubin causing jaundice.
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Description
Explore the complex processes involved in the digestion and absorption of lipids, including the transformation of monoacylglycerols and fatty acids into triacylglycerols. Understand the role of chylomicrons and phospholipids in fat transport and metabolism, as well as the significance of adipose tissue in energy storage.
