Carbo

Study Notes

Introduction to Carbohydrates

Carbohydrates are essential energy sources for metabolic activities.

Classification of Carbohydrates

Monosaccharides:
- Simplest sugar units; cannot be hydrolyzed.
- Classified by carbon number:
  - Trioses (C3H6O3): Glyceraldehyde (aldose), Dihydroxyacetone (ketose).
  - Tetroses (C4H8O4): Erythrose (aldose), Erythrulose (ketose).
  - Pentoses (C5H10O5): Ribose (aldose), Ribulose (ketose).
  - Hexoses (C6H12O6): Glucose (aldose), Fructose (ketose).
Disaccharides:
- Composed of two monosaccharides upon hydrolysis.
- Examples: Sucrose (table sugar), Lactose (milk sugar), Maltose (malt sugar).
Oligosaccharides:
- Yield 3-6 monosaccharides upon hydrolysis.
- Example: Maltotriose.
Polysaccharides:
- Composed of more than six monosaccharides.
- Examples: Starch (plant storage), Dextrin, Glycogen (animal storage).

Functions of Carbohydrates in Metabolism

Primary fuel source for energy-releasing processes, mainly in glucose form.
Main monosaccharides from digestion: Glucose, Fructose, Galactose.
Fructose and Galactose are converted to glucose by the liver.

Overview of Carbohydrate Metabolism Processes

Glycolysis:
- Breaks down glucose to pyruvate (aerobic) or lactate (anaerobic).
- Energy yield:
  - 2 ATP under anaerobic conditions, 7 ATP under aerobic conditions.
Glycogenesis:
- Synthesis of glycogen from excess glucose.
Glycogenolysis:
- Degradation of glycogen to release glucose during fasting or energy needs.
Pyruvate Oxidation to Acetyl-CoA:
- Prepared for the citric acid cycle; pathway for oxidation of all macronutrients.
Hexose Monophosphate Shunt:
- Alternative pathway for glucose metabolism.
- Functions: Produces NADPH for biosynthesis and ribose for nucleic acids.
Gluconeogenesis:
- Generates glucose from non-carbohydrate sources; vital during prolonged fasting.

Glycolysis Steps (Embden-Meyerhof Pathway)

Step 1: Glucose is converted to Glucose-6-phosphate using Hexokinase or Glucokinase, requiring ATP and magnesium.
Step 2: Glucose-6-phosphate transforms into Fructose-6-phosphate via Phosphohexose isomerase.
Step 3: Fructose-6-phosphate is converted to Fructose-1,6-bisphosphate by Phosphofructokinase-1 (requires ATP).
Step 4: Fructose-1,6-bisphosphate splits into Glyceraldehyde-3-phosphate and Dihydroxyacetone phosphate through Aldolase.
Step 5: Interconversion of Glyceraldehyde-3-phosphate and Dihydroxyacetone phosphate by Phosphotriose isomerase.
Step 6: Glyceraldehyde-3-phosphate leads to 1,3-Bisphosphoglycerate through oxidation and phosphorylation.
Step 7: 1,3-Bisphosphoglycerate generates ATP and converts to 3-Phosphoglycerate with Phosphoglycerate kinase (first ATP production).
Step 8: 3-Phosphoglycerate changes to 2-Phosphoglycerate via Phosphoglycerate mutase.
Step 9: 2-Phosphoglycerate yields Phosphoenolpyruvate and water through Enolase.
Step 10: Phosphoenolpyruvate produces Pyruvate and ATP via Pyruvate kinase (second ATP production).

Fate of Pyruvate

Anaerobic: Pyruvate is converted to Lactate by Lactate dehydrogenase, regenerating NAD+ for glycolysis.
Aerobic: Pyruvate enters the mitochondria for further oxidation.

Pyruvate Oxidation to Acetyl-CoA

Occurs in the mitochondria and is catalyzed by the Pyruvate dehydrogenase complex.
Steps: Decarboxylation of pyruvate, formation of hydroxyethyl-thiamine pyrophosphate, and transfer of the acetyl group to Coenzyme A to form Acetyl-CoA.

Energy Yield from Carbohydrate Oxidation

Complete oxidation of carbohydrates leads to significant energy production across various metabolic pathways.

Description

This quiz covers the fundamentals of carbohydrates, including their importance as an energy source and their classification. Explore the different types of carbohydrates such as monosaccharides, trioses, and tetroses, along with their characteristics. Test your knowledge of carbohydrate metabolism and classification.