Metabolism Overview Quiz

Overview of Metabolism & Metabolic Pathways

• Anabolic pathways construct larger molecules from smaller ones, consuming energy in the process.
• Catabolic pathways break down molecules into smaller units, releasing energy.
• Amphibolic pathways integrate both anabolic and catabolic processes, facilitating metabolic flexibility.

Metabolism of Major Nutrients

• Carbohydrate metabolism occurs primarily in the liver, involving breakdowns and conversions at the tissue and subcellular levels.
• Lipid metabolism is crucial for energy storage and release, facilitated by enzymes in adipose tissue and the liver.
• Amino acid metabolism plays a vital role in protein synthesis and energy production, occurring in various tissues.

Regulation of Metabolic Flux

• Metabolic pathways are regulated through feedback mechanisms, enzyme activity modulation, and substrate availability.
• Hormones like insulin and glucagon play significant roles in regulating the flow of metabolites.

Metabolic Fuels Supply in Fed and Fasting States

• In the fed state, carbohydrates, lipids, and proteins are digested and stored as metabolic reserves.
• During fasting, the body mobilizes stored fuels to maintain energy balance, utilizing glycogen and fat stores.

Digestion and Absorption of Carbohydrates

• Major dietary carbohydrates include starch, sucrose, and lactose.
• Key sites for carbohydrate digestion:
  • Mouth: Salivary enzyme a-Amylase initiates starch breakdown into shorter polysaccharides.
  • Stomach: Low pH halts salivary amylase activity.
  • Small Intestine:
    • Pancreatic a-Amylase further breaks down polysaccharides and disaccharides.
    • Membrane-bound enzymes such as maltase, lactase, and sucrase at intestinal cell walls convert disaccharides to monosaccharides (glucose, fructose, galactose).
  • Portal Circulation: Monosaccharides are absorbed into the bloodstream, transported to the liver.
  • Liver: Processes carbohydrates for energy use, storage, or metabolic pathways.

Enzyme Function in Carbohydrate Digestion

• Endoglycosidases: Hydrolyze internal glycosidic bonds in polysaccharides and oligosaccharides.
• Disaccharidases: Split disaccharides into their constituent monosaccharides.

Key Points about Carbohydrate Digestion Sites and Enzymes

• Digestion begins in the mouth and is completed in the small intestine.
• The small intestine's functional enzymes finalize carbohydrate breakdown, allowing efficient absorption into the bloodstream.