CHO Metabolism Overview

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Questions and Answers

What is the net energy gain from aerobic glycolysis?

10 ATP

4 ATP

2 ATP

6-8 ATP (correct)

Which enzyme is NOT one of the key irreversible enzymes of glycolysis?

Hexokinase

Pyruvate kinase

Phosphofructokinase-1

Lactate dehydrogenase (correct)

What is the primary end product of glycolysis in mature red blood cells?

Ethanol

Pyruvate

Acetyl-CoA

Lactate (correct)

How does insulin affect the synthesis of key glycolytic enzymes?

It stimulates their synthesis Signup and view all the answers

Which of the following statements is true regarding 2,3 biphosphoglycerate in red blood cells?

It is produced during glycolysis Signup and view all the answers

Which of the following regulates phosphofructokinase-1 (PFK-1) through allosteric modulation?

Citrate Signup and view all the answers

What is the consequence of phosphorylating pyruvate kinase?

It inactivates the enzyme Signup and view all the answers

During anaerobic glycolysis, what happens to the 2 NADH produced?

They are consumed in the conversion of pyruvate to lactate Signup and view all the answers

What is the primary consequence of the absence of intestinal lactase?

Lactose accumulates in the intestine and is fermented by bacteria. Signup and view all the answers

Which pathway specifically produces pyruvate as a byproduct?

Glycolysis Signup and view all the answers

What is the net energy yield from anaerobic glycolysis?

2 ATP Signup and view all the answers

Which statement correctly describes the energy-requiring step of glycolysis?

One glucose molecule is converted into glyceraldehyde-3-P. Signup and view all the answers

Which of the following tissues is most reliant on glycolysis due to its lack of mitochondria?

Red blood cells Signup and view all the answers

What role does 2,3-bisphosphoglycerate play in the body?

It improves oxygenation of tissues by lowering hemoglobin's affinity for oxygen. Signup and view all the answers

Which is a characteristic of the citric acid cycle in terms of metabolic pathways?

It serves as an amphibolic pathway linking catabolism and anabolism. Signup and view all the answers

What is the metabolic significance of dihydroxyacetone phosphate in glycolysis?

It contributes to lipogenesis. Signup and view all the answers

What is the primary function of anabolic pathways in metabolism?

Synthesize complex molecules from simpler ones Signup and view all the answers

Which enzyme converts dextrins into maltose during carbohydrate metabolism?

Pancreatic amylase Signup and view all the answers

Which of the following best describes catabolic pathways?

They release free energy through the breakdown of complex molecules Signup and view all the answers

What role do amphibolic pathways play in metabolism?

They serve as a link between anabolic and catabolic pathways Signup and view all the answers

Which carbohydrate source constitutes the majority of dietary carbohydrates?

Starch from potatoes Signup and view all the answers

What is the consequence of a deficiency in lactase enzyme?

Lactose intolerance leading to gastrointestinal distress Signup and view all the answers

How much energy is released from the complete oxidation of 1 gram of carbohydrate?

4 kcal Signup and view all the answers

Which of the following statements regarding carbohydrate digestion is true?

Monosaccharides are the only form that can be absorbed Signup and view all the answers

Study Notes

CHO Metabolism

CHO metabolism is the study of how the body processes carbohydrates.
It involves the fate of food molecules after digestion and absorption.
It's a series of chemical and enzymatic reactions within the body, encompassing synthesis and breakdown of various substances.

Metabolic Pathways

Anabolic pathways: Synthesize complex molecules from simpler ones, requiring energy.
- Example: Protein synthesis
Catabolic pathways: Break down complex molecules into simpler ones, releasing energy.
- Example: Oxidative processes
Amphibolic pathways: Act as links between anabolic and catabolic pathways.
- Example: Citric acid cycle

Carbohydrate Metabolism

Carbohydrates provide 50% of daily calories.
Complete oxidation of 1 gram of carbs yields 4 kcal.
Sources of Carbohydrates (CHO) in food:
- Starch (50%, e.g., potatoes)
- Sucrose and lactose (remainder)
- Fructose and glucose (fruits, honey)

Digestion of CHO

Polysaccharides and disaccharides must be broken down into monosaccharides for absorption.
Enzymes involved:
- Salivary amylase: Breaks down starch and glycogen into dextrins.
- Pancreatic amylase: Breaks down dextrins into maltose.
- Intestinal disaccharidases:
  - Maltase: Converts maltose into glucose.
  - Sucrase: Converts sucrose into glucose and fructose.
  - Lactase: Converts lactose into glucose and galactose.

Lactose Intolerance

Definition: A condition where lactase enzyme is deficient, leading to lactose not being digested.
Cause: Deficiency of lactase enzyme.
Effects:
- Lactose accumulates in the intestine.
- Fermentation by intestinal bacteria.
- Production of acids and gases.
Symptoms: Abdominal distension, cramps, and diarrhea.
Treatment: Lactose-free milk formula.

Metabolic Pathways of Carbohydrates

Catabolic pathways:
- Glycolysis
- Hexose monophosphate shunt
- Uronic acid pathway
- Glycogenolysis
Anabolic pathways:
- Gluconeogenesis
- Glycogenesis
Amphibolic pathways:
- Citric acid cycle

Glycolysis

Definition: Oxidation of glucose to pyruvate in the presence of oxygen, or lactate in the absence.
Major pathway of glucose oxidation.
Site: Cytoplasm of all cells, with specific importance in:
- Cells lacking mitochondria (e.g., red blood cells)
- Tissues with frequent oxygen lack (e.g., skeletal muscles during exercise).
Steps:
- Stage 1: Energy-requiring step (glucose converted to glyceraldehyde-3-P).
- Stage 2: Energy-producing step (glyceraldehyde-3-P converted to pyruvate or lactate).

Glycolysis in Red Blood Cells

Mature RBCs lack mitochondria, relying solely on glycolysis.
Lactate is the final product.
Net energy yield: 2 ATP.
Glucose uptake is independent of insulin.
Critical in producing 2,3-biphosphoglycerate.

Regulation of Glycolysis

Key enzymes (irreversible): Hexokinase/glucokinase, Phosphofructokinase-1 (PFK-1), Pyruvate kinase
Hormonal regulation: Insulin promotes synthesis, glucagon inhibits.
Allosteric regulation:
- G-6-P inhibits hexokinase (not glucokinase).
- Fructose 2,6-bisphosphate stimulates PFK-1.
- Citrate inhibits PFK-1.
- Fructose 2,6-bisphosphate stimulates pyruvate kinase.
Covalent modification: Pyruvate kinase is inactivated by phosphorylation.
Energy regulation: ADP and AMP stimulate PFK-1; ATP inhibits PFK-1 and pyruvate kinase

In Vitro Inhibition of Glycolysis

Inhibitors:
- Arsenate (competes with inorganic phosphate).
- Iodoacetate (inhibits glyceraldehyde-3-phosphate dehydrogenase).
- Fluoride (inhibits enolase).
Clinical significance: Hemolytic anemia may result from insufficient pyruvate kinase activity in red blood cells.

Energy Production of Glycolysis

ATP consumption (both aerobic and anaerobic): 1 ATP for converting glucose to G-6-P, 1 ATP for converting fructose-6-P to fructose 1,6 biphosphate. Net energy consumed: 2 ATP.
ATP production (aerobic glycolysis):
- 4 ATP by substrate-level phosphorylation (e.g., conversion of 1,3-biphosphoglycerate to 3-phosphoglycerate).
- Other ATP from oxidative phosphorylation in mitochondria (from NADH). (either 4 or 6 ATP)
ATP production (anaerobic glycolysis): 2 ATP by substrate-level phosphorylation.

Substrate-level phosphorylation

Direct transfer of a phosphate group from a high-energy molecule to ADP.

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Description

This quiz dives into carbohydrate metabolism, exploring how the body processes carbohydrates after digestion and absorption. It includes key concepts like metabolic pathways, their functions, and the significance of carbohydrates as a primary energy source. Test your knowledge on anabolic, catabolic, and amphibolic pathways involved in energy production.