Questions and Answers
What is generated during the citric acid cycle in mitochondria?
Where does the digestion of carbohydrates first begin?
What type of enzyme is salivary amylase?
Which part of the digestive system has no carbohydrate-splitting enzyme at work?
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What is the role of GluT 2?
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Which enzyme hydrolyzes terminal α-1→4 glycosidic linkages in the Small Intestine?
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What is one of the key products of carbohydrate hydrolysis by lactase?
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Which transporter has a high affinity for glucose and is found in neurons and the brain?
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Which glucose transporter is primarily responsible for insulin-mediated glucose uptake?
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What is the primary mechanism through which glucose and galactose are absorbed in the intestine?
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Which monosaccharide has the highest absorption rate in the intestine?
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Which glucose transporter is found in the liver endoplasmic reticulum?
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What role does sodium play in the absorption of glucose?
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Which glucose transporter is not under the control of insulin?
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How does glucose exit intestinal cells into the bloodstream?
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What impact does reduced GluT4 have on type 2 diabetes mellitus (DM)?
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What is the net yield of ATP produced from one molecule of glucose during glycolysis?
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Which of the following enzymes is involved in the conversion of glucose to glucose 6-phosphate?
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During glycolysis, which compound is produced along with NADH?
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What factors increase the rate of glycolysis?
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In the absence of oxygen, how many ATP molecules are produced from glycolysis?
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Which of the following statement about glycolysis is incorrect?
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Which of the following mechanisms is involved in the regulation of glycolysis?
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What is the primary role of phosphofructokinase in glycolysis?
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What is the final product of glycolysis?
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Which of the following statements about pyruvate kinase is true?
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What inhibits the activity of phosphofructokinase?
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What effect does insulin have on glycolysis?
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Which of the following enzymes is specifically inhibited by its product, glucose 6-phosphate?
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How do red blood cells primarily generate energy?
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What is the major function of fructose 2,6-bisphosphate in metabolic regulation?
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What unique structural characteristic do mature erythrocytes possess?
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What is the outcome of glucose oxidation regardless of oxygen availability?
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What is the biochemical significance of the Rapoport-Luebering shunt in red blood cells?
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How does the ATP/ADP ratio behave in mature red blood cells?
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What effect does hexokinase deficiency have on BPG concentration in red blood cells?
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What is true regarding the effect of 2,3-BPG on adult hemoglobin (Hb-A1)?
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What happens to the oxygen affinity of hemoglobin in pyruvate kinase deficiency?
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How does competitive inhibition affect glycolysis in mature red blood cells?
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Which of the following statements accurately describes 2,3-BPG's role in fetal hemoglobin (Hb-F)?
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Study Notes
Metabolism of Carbohydrates
- The citric acid cycle (CAC) generates reducing equivalents, NADH and FADH2, as part of tertiary metabolism within mitochondria.
- These reducing equivalents enter the electron transport chain (ETC) to release energy, contributing to cellular respiration.
Digestion of Carbohydrates
- Carbohydrates in the diet primarily consist of polysaccharides (starch, glycogen) and some disaccharides (sucrose, lactose).
- They are hydrolyzed into monosaccharides (glucose, galactose, fructose) in the gastrointestinal tract (GIT).
Digestion Process
- Mouth: Saliva contains salivary amylase which begins carbohydrate digestion by hydrolyzing α-1→4 glycosidic bonds.
- Stomach: No significant carbohydrate digestion occurs due to the absence of carbohydrate-splitting enzymes.
- Duodenum: Mixing with pancreatic juice introduces pancreatic amylase, which continues the hydrolysis of polysaccharides.
- Small Intestine: Intestinal juice contains multiple enzymes (amylase, lactase, maltase) that hydrolyze disaccharides and oligosaccharides to glucose.
Transporters for Glucose
- GluT 1: Found in RBCs, brain, and other tissues; responsible for glucose uptake.
- GluT 2: Located in intestinal cells, liver, and pancreatic beta cells; acts as a glucose sensor with low affinity.
- GluT 3: Present in neurons, with high affinity for glucose.
- GluT 4: Found in skeletal muscle and adipose tissue; insulin-mediated uptake.
- GluT 5: Serves as a fructose transporter in the small intestine.
- GluT 7: Located in liver endoplasmic reticulum, involved in glucose transport.
Absorption of Carbohydrates
- Only monosaccharides are absorbed by the intestine, with varying absorption rates.
- Simple/Passive Diffusion: Monosaccharides absorbed based on concentration gradients.
- Facilitated Diffusion: Glucose and galactose absorption is active and energy-dependent, mediated by specific carrier molecules.
Mechanism of Glucose Absorption
- Co-transport: Glucose co-transported with sodium into intestinal cells via sodium-dependent glucose transporter-1 (S GluT-1).
- Uniport: Glucose is transported into the bloodstream by GluT 2 without sodium dependency.
- GluT4: Insulin-regulated glucose transporter in muscle and fat cells; impairment leads to insulin resistance.
Glycolysis Overview
- Converts one glucose molecule into two pyruvate molecules, producing two NADH and two ATP molecules.
- Key pathway for energy generation and metabolic intermediates.
Energy Yield
- Aerobic Glycolysis: Produces a higher ATP yield in the presence of oxygen.
- Anaerobic Glycolysis: Limited ATP yield (2 ATP) when oxygen is absent.
Regulation of Glycolysis
- Three primary regulatory mechanisms: enzyme synthesis changes, covalent modification, and allosteric regulation.
- Hormonal influences: insulin boosts glycolysis by upregulating enzymes, while glucagon and catecholamines inhibit it.
Key Enzymes in Glycolysis
- Hexokinase: Phosphorylates glucose; inhibited by glucose-6-phosphate.
- Phosphofructokinase: Rate-limiting step; allosterically regulated by ATP and fructose 2,6-bisphosphate.
- Pyruvate Kinase: Converts phosphoenolpyruvate to pyruvate; regulated by fructose 1,6-bisphosphate and energy charge.
Fermentation Pathways
- Lactic acid and alcohol fermentation pathways follow glycolysis based on oxygen availability.
Unique Features of Glycolysis in Red Blood Cells
- Mature red blood cells rely exclusively on glycolysis for energy, lacking organelles that would utilize other metabolic pathways.
- Pyruvate is continuously converted to lactic acid without the use of mitochondrial processes.
Rapoport-Luebering Cycle
- Glycolytic diversion produces 2,3-bisphosphoglycerate (2,3-BPG) in red blood cells, influencing hemoglobin’s oxygen affinity.
Inherited Enzyme Deficiencies
- Deficiencies in hexokinase and pyruvate kinase impact 2,3-BPG levels, affecting hemoglobin's oxygen binding.
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Description
Test your knowledge on key concepts in Chapter 5 of biology, focusing on the digestive system and metabolic pathways. This quiz covers the citric acid cycle, carbohydrate digestion, and the role of various enzymes such as salivary amylase. Perfect for students looking to reinforce their understanding of these essential processes.
