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Questions and Answers
What is the structure of human insulin composed of?
What is the structure of human insulin composed of?
Why are fasting concentrations of C-peptide higher than those of insulin?
Why are fasting concentrations of C-peptide higher than those of insulin?
In which cellular structure is proinsulin converted to insulin?
In which cellular structure is proinsulin converted to insulin?
What role does insulin play in glucose metabolism?
What role does insulin play in glucose metabolism?
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What is a characteristic feature of insulin release after a meal?
What is a characteristic feature of insulin release after a meal?
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Where does the digestion of carbohydrates initially begin?
Where does the digestion of carbohydrates initially begin?
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Which enzyme is responsible for further digestion of starch in the small intestine?
Which enzyme is responsible for further digestion of starch in the small intestine?
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Which bond does isomaltase cleave during carbohydrate digestion?
Which bond does isomaltase cleave during carbohydrate digestion?
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What is the primary site for the absorption of dietary sugars in the digestive system?
What is the primary site for the absorption of dietary sugars in the digestive system?
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What is the role of the sodium-dependent glucose cotransporter 1 (SGLT-1)?
What is the role of the sodium-dependent glucose cotransporter 1 (SGLT-1)?
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Which metabolic pathway can glucose enter after being converted to G-6-P?
Which metabolic pathway can glucose enter after being converted to G-6-P?
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What is the primary effect of insulin on hepatic glycogen metabolism?
What is the primary effect of insulin on hepatic glycogen metabolism?
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What is the name of the process that converts glucose to glycogen?
What is the name of the process that converts glucose to glycogen?
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What enzyme catalyzes the conversion of glucose to G-6-P?
What enzyme catalyzes the conversion of glucose to G-6-P?
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How does insulin affect gluconeogenesis in liver cells?
How does insulin affect gluconeogenesis in liver cells?
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Which enzyme activity is increased by insulin to promote glycolysis?
Which enzyme activity is increased by insulin to promote glycolysis?
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What is the effect of insulin on fatty acid metabolism?
What is the effect of insulin on fatty acid metabolism?
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Which cells are responsible for obtaining glucose without endocrine control?
Which cells are responsible for obtaining glucose without endocrine control?
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What role do carbohydrates play in the body?
What role do carbohydrates play in the body?
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How is glucose formed when energy expenditure exceeds caloric intake?
How is glucose formed when energy expenditure exceeds caloric intake?
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Which of the following correctly describes polysaccharides?
Which of the following correctly describes polysaccharides?
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What classification do ribose and glucose fall under?
What classification do ribose and glucose fall under?
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What is the primary function of insulin in relation to glucose?
What is the primary function of insulin in relation to glucose?
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Which statement accurately describes oligosaccharides?
Which statement accurately describes oligosaccharides?
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What is a distinguishing feature of aldo sugars compared to keto sugars?
What is a distinguishing feature of aldo sugars compared to keto sugars?
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Which of the following best describes the relationship between carbohydrates and lipids?
Which of the following best describes the relationship between carbohydrates and lipids?
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What term describes the formation of glucose from noncarbohydrate sources such as amino acids and glycerol?
What term describes the formation of glucose from noncarbohydrate sources such as amino acids and glycerol?
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Which organ is primarily responsible for glycogen storage and glucose production during fasting?
Which organ is primarily responsible for glycogen storage and glucose production during fasting?
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What role does insulin play in glucose metabolism?
What role does insulin play in glucose metabolism?
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In prolonged fasting, what process accounts for essentially all glucose production?
In prolonged fasting, what process accounts for essentially all glucose production?
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Which hormone primarily regulates the suppression of hepatic glucose production?
Which hormone primarily regulates the suppression of hepatic glucose production?
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What condition is most likely to cause an increase in gluconeogenesis activity?
What condition is most likely to cause an increase in gluconeogenesis activity?
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What requirement is NOT necessary for the endocrine system in controlling blood glucose?
What requirement is NOT necessary for the endocrine system in controlling blood glucose?
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What is the primary function of glucose-6-phosphatase in the kidneys and liver?
What is the primary function of glucose-6-phosphatase in the kidneys and liver?
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Study Notes
Introduction
- Carbohydrates are vital for structural components like RNA and DNA, and provide energy as glucose.
- Glucose is derived from dietary carbohydrates, body stores, or synthesized from protein and triglycerides.
- Excess energy is stored as fat and glycogen.
- Energy expenditure triggers glucose formation from stores and non-carbohydrate sources.
- Insulin, glucagon, and epinephrine regulate blood glucose levels.
Classification and Structure
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Monosaccharides:
- Classified by the number of carbon atoms: trioses, tetroses, pentoses, hexoses, heptoses, octoses.
- Classified by the carbonyl group: aldoses (aldehyde group) and ketoses (ketone group).
- Examples: glucose (aldose), ribose (aldose), fructose (ketose), ribulose (ketose).
- Disaccharides: Two monosaccharide units.
- Oligosaccharides: Three to ten monosaccharide units.
- Polysaccharides: More than ten monosaccharide units, can be hundreds of units long.
Complex Carbohydrates
- Carbohydrates can be attached to non-carbohydrate structures through glycosidic bonds.
- Examples: purines, pyrimidines (found in nucleic acids), aromatic rings (steroids, bilirubin), proteins (glycoproteins, glycosaminoglycans), lipids (glycolipids).
Digestion of Carbohydrates
- Mouth: Salivary α-amylase breaks down α(1-4) bonds in dietary starch.
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Small Intestine:
- Pancreatic α-amylase continues starch digestion.
- Intestinal enzymes (isomaltase, maltase, sucrase, lactase, trehalase) further digest disaccharides.
Absorption of Monosaccharides
- Primarily absorbed in the duodenum and upper jejunum.
- Glucose and galactose: Transported via an active, energy-requiring process that requires sodium ions, using SGLT-1 transporter.
Fate of Glucose
- Glucose is either utilized for energy or stored as glycogen.
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Three pathways:
- Embden-Meyerhof pathway: Generation of energy from glucose.
- Hexose monophosphate shunt: Generation of energy from glucose.
- Glycogen synthesis: Storage of glucose as glycogen.
- Glycogenolysis: Breakdown of glycogen to glucose.
- Gluconeogenesis: Formation of glucose from non-carbohydrate sources (amino acids, glycerol, lactate).
Regulation of Glucose Metabolism
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Hormonal Regulation:
- Hormones influence glucose entry into cells and its fate.
- Key hormones: insulin and glucagon.
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Endocrine System Requirements:
- Steady glucose supply.
- Safe glucose storage.
- Stored glucose utilization when dietary absorption is limited.
Insulin
- Peptide hormone synthesized in pancreatic β cells.
- Primary hormone for glucose entry into cells.
- Anabolic hormone:
- Stimulates glucose uptake in muscle and fat.
- Promotes glucose conversion to glycogen or fat.
- Inhibits hepatic glucose production.
- Stimulates protein synthesis, inhibits protein breakdown.
- Structure: 51 amino acids in two chains, A and B, linked by disulfide bridges.
Insulin Action
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Effects on hepatocytes:
- Promotes glycogen synthesis.
- Inhibits glycogen breakdown.
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Effects on carbohydrate oxidation:
- Promotes glycolysis and carbohydrate oxidation.
- Promotes glucose metabolism via the hexose monophosphate shunt.
- Promotes pyruvate oxidation by stimulating pyruvate dehydrogenase.
- Inhibits gluconeogenesis.
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Effects on fat metabolism:
- Promotes fat synthesis and storage.
- Indirectly inhibits fat oxidation.
Insulin Release and Action
- Biphasic release in response to increased ECF glucose.
- Binds to receptors on most cells (except neurons, RBCs, retinal epithelium).
- Initiates a chain of events that increase glucose transporters on the cell surface and enhances glycogenesis.
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Description
This quiz explores the essential role of carbohydrates in biological systems, focusing on their classification and structure. You'll learn about monosaccharides, disaccharides, oligosaccharides, and polysaccharides, as well as the critical functions of glucose in energy metabolism. Test your knowledge and understanding of these important macromolecules.
