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Questions and Answers
Which enzyme breaks down dietary starch in the mouth?
Which metabolic process uses glucose to produce ATP without oxygen?
What is the primary purpose of glucose in the body?
What determines how rapidly a food can increase blood sugar levels?
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Which enzyme is inactivated in the stomach due to high acidity?
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Which part of the body does carbohydrate digestion primarily begin?
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What is the main purpose of glycogen synthesis in the body?
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'Remember that enzymes have an optimum pH for them to function' relates to which enzyme's inactivation in the stomach?
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'Foods are ranked based on how they compare to a reference food (white bread or glucose)' relates to which concept?
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What is the primary function of acetyl-CoA in cellular metabolism?
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Which step in the metabolism of glucose results in the production of NADH?
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What is the main role of NAD+ in cellular respiration?
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Inborn errors of metabolism often result from genetic mutations affecting which of the following pathways?
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What is the end product of the Pentose Phosphate Pathway?
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Which of the following processes directly produces ATP in cellular respiration?
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Which molecule transfers high-energy electrons to the electron transport chain during cellular respiration?
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Which process results in the production of most of the ATP in cellular respiration?
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Study Notes
Carbohydrate Digestion and Metabolism
- Carbohydrate digestion begins in the mouth, where dietary starch is broken down by α-amylase (ptyalin), causing the breakage of some (α 1→4) bonds during mastication.
- Chewing food increases the surface area for the enzyme, but metabolism is temporarily halted in the stomach due to high acidity, as α-amylase is inactivated.
- In the small intestine, pancreatic α-amylase breaks down starch into tri- and oligosaccharides, such as maltose and isomaltose.
- Brush border enzymes in the jejunum, including carbohydrases, lead to the full digestion of CHOs yielding monosaccharides, which can be absorbed by the small intestine.
Final Digestion of Carbohydrates
- carbohydrases, such as maltase, sucrase, and lactase, cleave disaccharides into monosaccharides, allowing for absorption by the small intestine.
- Lactase deficiency (lactose intolerance) leads to undigested lactose in the intestine, causing gas, bloating, and stomach pain due to fermentation by gut bacteria.
Absorption and Transport
- Monosaccharides are absorbed by intestinal mucosal cells and transported to the liver via the hepatic portal vein.
- Cellulose cannot be digested and forms bulk stool, binding cholesterol in the process.
Glycemic Index
- The glycemic index measures the impact of CHO-containing foods on blood glucose levels, with foods ranked based on how they compare to a reference food (white bread or glucose).
- Digestibility determines whether food can rapidly increase blood sugar.
Metabolic Pathways
- Glycolysis: a universal metabolic pathway that breaks down glucose into pyruvate, producing some ATP and NADH.
- Tricarboxylic Acid Cycle (Krebs Cycle): a series of chemical reactions that release stored energy through the oxidation of acetyl-CoA, producing CO2, ATP, NADH, and FADH2.
- Pentose Phosphate Pathway: a metabolic pathway parallel to glycolysis, generating NADPH and pentoses for nucleotide synthesis.
Inborn Errors of Metabolism
- Inborn errors of metabolism (IEM) are inherited biochemical disorders that interfere with normal metabolism of protein, fat, or carbohydrate.
- Medical foods and dietary supplements are used to treat IEM.
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Description
Test your knowledge on the further digestion of carbohydrates by pancreatic enzymes in the small intestine, particularly focusing on the breakdown of α-dextrins to tri- and oligosaccharides, maltose, and isomaltose. Explore the role of pancreatic enzymes and bicarbonate in starch digestion.
