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Questions and Answers
What primarily triggers the release of insulin in response to blood glucose levels?
What primarily triggers the release of insulin in response to blood glucose levels?
What is the process by which glycogen is synthesized from glucose?
What is the process by which glycogen is synthesized from glucose?
How does glucagon affect liver glycogen?
How does glucagon affect liver glycogen?
What role does GLUT4 play in glucose regulation?
What role does GLUT4 play in glucose regulation?
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In insulin-resistant states, what happens to GLUT4?
In insulin-resistant states, what happens to GLUT4?
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What molecule primarily causes an increase in blood glucose levels through gluconeogenesis?
What molecule primarily causes an increase in blood glucose levels through gluconeogenesis?
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Which hormone is primarily responsible for reducing blood glucose levels?
Which hormone is primarily responsible for reducing blood glucose levels?
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What happens when insulin binds to its receptor on cell membranes?
What happens when insulin binds to its receptor on cell membranes?
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What are the two major transport mechanisms for monosaccharides across cell membranes?
What are the two major transport mechanisms for monosaccharides across cell membranes?
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Where does the absorption of dietary monosaccharides first occur in the enterocyte?
Where does the absorption of dietary monosaccharides first occur in the enterocyte?
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What is the function of SGLT1 in the enterocyte?
What is the function of SGLT1 in the enterocyte?
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Which glucose transporter is known to allow glucose to cross the blood-brain barrier?
Which glucose transporter is known to allow glucose to cross the blood-brain barrier?
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What type of transport do GLUTs utilize to facilitate glucose movement?
What type of transport do GLUTs utilize to facilitate glucose movement?
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What primarily determines the activity of SGLTs in monosaccharide transport?
What primarily determines the activity of SGLTs in monosaccharide transport?
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How are newly absorbed monosaccharides delivered to the liver?
How are newly absorbed monosaccharides delivered to the liver?
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What other molecules can GLUTs transport besides glucose?
What other molecules can GLUTs transport besides glucose?
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What is the primary function of glycogenesis?
What is the primary function of glycogenesis?
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Which enzyme is primarily responsible for phosphorylating glucose in muscle cells?
Which enzyme is primarily responsible for phosphorylating glucose in muscle cells?
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What is the primary storage location for glycogen in the body?
What is the primary storage location for glycogen in the body?
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Which metabolic process converts glucose into non-carbohydrate sources?
Which metabolic process converts glucose into non-carbohydrate sources?
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How does glucose-6-phosphate affect hexokinase activity in muscle cells?
How does glucose-6-phosphate affect hexokinase activity in muscle cells?
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Which metabolic pathway is responsible for the oxidation of acetyl-CoA?
Which metabolic pathway is responsible for the oxidation of acetyl-CoA?
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Where is glycogen primarily stored in the human body?
Where is glycogen primarily stored in the human body?
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What role does liver glycogen play in blood glucose homeostasis?
What role does liver glycogen play in blood glucose homeostasis?
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What is the primary function of carbohydrates in the human diet?
What is the primary function of carbohydrates in the human diet?
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Which statement correctly distinguishes between oligosaccharides and polysaccharides?
Which statement correctly distinguishes between oligosaccharides and polysaccharides?
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What substance primarily makes up the complex carbohydrates found in the human diet?
What substance primarily makes up the complex carbohydrates found in the human diet?
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What role do oligosaccharides play when conjugated to proteins and lipids in cells?
What role do oligosaccharides play when conjugated to proteins and lipids in cells?
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What is the composition of carbohydrates in terms of the elements they contain?
What is the composition of carbohydrates in terms of the elements they contain?
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What are microvilli and where are they located?
What are microvilli and where are they located?
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Which type of carbohydrate is considered a polymer of saccharide units linked by glycosidic bonds?
Which type of carbohydrate is considered a polymer of saccharide units linked by glycosidic bonds?
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What is the significance of the folds of Kerckring in the small intestine?
What is the significance of the folds of Kerckring in the small intestine?
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What is produced by gluconeogenesis from noncarbohydrate sources?
What is produced by gluconeogenesis from noncarbohydrate sources?
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Which enzyme is primarily responsible for the breakdown of glycogen?
Which enzyme is primarily responsible for the breakdown of glycogen?
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Which statement about glycogenolysis is accurate?
Which statement about glycogenolysis is accurate?
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What happens to glucose-6-phosphate in the liver after glycogenolysis?
What happens to glucose-6-phosphate in the liver after glycogenolysis?
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Which bonds can glycogen phosphorylase cleave?
Which bonds can glycogen phosphorylase cleave?
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Which of the following is true about glucose-6-phosphatase?
Which of the following is true about glucose-6-phosphatase?
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How does glycogen phosphorylase regulation differ in muscle compared to the liver?
How does glycogen phosphorylase regulation differ in muscle compared to the liver?
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What is the final product of glycogenolysis after glucose-6-phosphate is converted?
What is the final product of glycogenolysis after glucose-6-phosphate is converted?
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What is formed when uridine triphosphate (UTP) is hydrolyzed during glycogenesis?
What is formed when uridine triphosphate (UTP) is hydrolyzed during glycogenesis?
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What is the role of insulin in glycogenesis?
What is the role of insulin in glycogenesis?
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Which enzyme is responsible for creating branch points in glycogen?
Which enzyme is responsible for creating branch points in glycogen?
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What is the significance of branching in the glycogen molecule?
What is the significance of branching in the glycogen molecule?
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What structural requirement must glycogen synthase have to add UDP-glucose?
What structural requirement must glycogen synthase have to add UDP-glucose?
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What substrate is coupled with glucose-1-phosphate to form UDP-glucose?
What substrate is coupled with glucose-1-phosphate to form UDP-glucose?
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Which molecule serves as the initial primer for glycogen synthesis?
Which molecule serves as the initial primer for glycogen synthesis?
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What type of reaction does glycogenesis primarily consume?
What type of reaction does glycogenesis primarily consume?
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Study Notes
Carbohydrate Metabolism
- Carbohydrates are the most abundant organic molecules on Earth.
- They are the primary structural component of plants and the primary energy source for humans.
- Carbohydrates provide half or more of the food energy consumed by humans worldwide.
- They act as metabolic intermediates, components of RNA and DNA, structural elements of cells and tissues, and energy storage molecules.
- The functional diversity of carbohydrates is due to their structural diversity.
- Carbohydrates are composed of carbon, hydrogen, and oxygen atoms in a ratio of approximately (CH₂O)n.
- Carbohydrates are categorized into simple and complex carbohydrates.
Simple Carbohydrates
- Simple carbohydrates include monosaccharides and disaccharides.
- Monosaccharides—single sugar units (e.g., glucose, fructose, galactose).
- Disaccharides—two sugar units bonded together (e.g., sucrose, lactose, maltose).
Complex Carbohydrates
- Complex carbohydrates include oligosaccharides (3-10 sugar units) and polysaccharides (>10 sugar units).
- Oligosaccharides (e.g., raffinose, stachyose)
- Polysaccharides (e.g., starch, glycogen, dietary fiber).
Structure of Starch and Glycogen
- Amylose: A linear chain of glucose molecules linked by α(1-4) glycosidic bonds.
- Amylopectin: A branched chain of glucose molecules linked by α(1-4) and α(1-6) glycosidic bonds.
- Glycogen: A highly branched polysaccharide composed of glucose units, with more branches than amylopectin.
- Important for quick glucose release when needed.
Digestion of Complex Carbohydrates
- Digestion begins in the mouth with salivary α-amylase, which breaks down starch into dextrins.
- Gastric acidity in the stomach deactivates salivary amylase, and further digestion continues in the small intestine.
- Pancreatic α-amylase continues breaking down dextrins into smaller sugars like maltose, isomaltose, and maltotriose.
- Brush border enzymes (e.g., maltase, α-dextrinase) break down these sugars into glucose for absorption.
Small Intestine Structure
- The small intestine's mucosa contains folds (folds of Kerckring) increasing surface area.
- Villi, finger-like projections, further increase surface area.
- Microvilli, tiny hair-like projections on the surface of enterocytes (intestinal cells), form the brush border, maximizing absorption.
- Capillaries and lacteals absorb nutrients from enterocytes.
Membrane Transport
- Monosaccharides are absorbed into the bloodstream through specialized membrane transporters:
- SGLTs (Sodium-Glucose Co-Transporters): Active transport, using sodium gradient; primary mechanism for glucose and galactose absorption
- GLUTs (Glucose Transporters): Facilitated diffusion; transport glucose and other monosaccharides passively.
GLUTs
- GLUT1: Ubiquitous, transports glucose across the blood-brain barrier.
- GLUT2: Low affinity, high capacity; involved in glucose and fructose transport in liver, pancreas, and small intestine; regulates insulin release
- GLUT3: High affinity, specifically involved in brain glucose uptake
- GLUT4: Insulin-regulated; transports glucose into muscle and adipose tissue
- GLUT5: Fructose transporter.
Maintaining Blood Glucose Concentration
- The body regulates blood glucose levels through a coordinated effort of organs using hormones like insulin and glucagon.
- Insulin lowers blood glucose levels, promoting glycogenesis and glucose uptake through receptor-mediated translocation of GLUT4.
- Glucagon raises blood glucose levels via glycogenolysis.
- Glucocorticoids, like cortisol, affect blood glucose levels via gluconeogenesis.
Glycogenesis
- Synthesis of glycogen from glucose.
- Key enzyme is glycogen synthase.
- Branching enzyme creates branches in glycogen for rapid glucose release.
- Process consumes energy (ATP and UTP).
Glycogenolysis
- Breakdown of glycogen to glucose.
- Key enzyme is glycogen phosphorylase.
- Debranching enzyme is involved after glycogen phosphorylase.
- Process generates glucose-1-phosphate, which is converted to glucose-6-phosphate.
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Description
Explore the fascinating world of carbohydrate metabolism, the most abundant organic molecules on Earth. Learn about the different types of carbohydrates, their roles as energy sources, and their structural diversity in living organisms. This quiz will test your knowledge of simple and complex carbohydrates.
