Questions and Answers
What is the primary source of carbohydrates in the diet for most humans?
starch
What enzyme begins the digestion of starch in the mouth?
salivary α-amylase
Which enzymes continue the breakdown of starch in the small intestine?
pancreatic α-amylase
What are the major fates of glucose in animals and vascular plants? (Select all that apply)
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What is the series of reactions called that degrades glucose to pyruvate?
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Who established that fermentation is caused by microorganisms?
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Which pathway is glycolysis alternatively known as?
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What is produced from one molecule of glucose during glycolysis?
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The reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase produces ____ per mole of glucose.
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Pyruvate serves only as a product in glycolysis.
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What are the methods of ATP formation in glycolysis? (Select all that apply)
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How many ATP are consumed for reactions of hexokinase and phosphofructokinase?
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What is the net ATP gain per mole of glucose during glycolysis?
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Study Notes
Carbohydrate Digestion
- Dietary polysaccharides and disaccharides hydrolyze into monosaccharides.
- Starch is the primary carbohydrate source in most human diets.
- Digestion starts in the mouth with salivary α-amylase breaking down starch into oligosaccharides.
- Inactivation of salivary α-amylase occurs in the stomach due to low pH levels.
- Pancreatic α-amylase in the small intestine continues starch breakdown, producing maltose, maltotriose, and limit dextrins.
- Glycogen digestion follows a similar pathway to starch digestion, due to its analogous structure.
- Disaccharides and oligosaccharides require hydrolysis to monosaccharides for cellular uptake.
Fate of Glucose
- Glucose is a central metabolic molecule for plants, animals, and many microorganisms.
- Major fates of glucose include storage, oxidation through glycolysis to pyruvate, or oxidation via the pentose phosphate pathway.
- Glycolysis yields ATP and metabolic intermediates, while the pentose phosphate pathway generates ribose 5-phosphate and NADPH.
Glycolysis
- Glycolysis is a universal pathway for glucose catabolism, converting glucose into two pyruvate molecules.
- The process involves a series of enzyme-catalyzed reactions that conserve free energy as ATP and NADH.
Historical Perspective
- Fermentation of glucose to ethanol and CO2 by yeast has a long history, used in winemaking and baking.
- Louis Pasteur (1850s-1860s) discovered microorganisms cause fermentation.
- Eduard Buchner (1897) showed that cell-free yeast extracts can ferment glucose, which marked a major shift in biological understanding.
- The complete glycolysis pathway was elucidated in the 1930s, with key contributors including Gustav Embden, Otto Meyerhof, and Jacob Parnas.
- Glycolysis is often referred to as the Embden–Meyerhof–Parnas (EMP) pathway.
ATP Formation in Glycolysis
- ATP is generated via respiratory chain oxidation of NADH and substrate-level phosphorylation.
- Key reactions in glycolysis yield:
- Glyceraldehyde 3-phosphate dehydrogenase: 2 NADH (5 ATP)
- Phosphoglycerate kinase: 2 ATP
- Pyruvate kinase: 2 ATP
- Total ATP yield per mole of glucose is a net of 7 after accounting for consumption during glycolysis.
Catabolic Fates of Pyruvate
- Pyruvate serves as a precursor in various anabolic reactions, extending its metabolic roles beyond mere ATP production.
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Description
This quiz covers the carbohydrate metabolism processes as outlined in the BT 2013 Biochemistry curriculum. Focus on the digestion and hydrolysis of dietary polysaccharides and disaccharides, and their conversion into monosaccharides. Test your understanding of starch digestion and related biochemical pathways.
