Overview of Metabolism

Study Notes

Overview of Metabolism

Metabolism encompasses all biochemical processes involving the conversion of food into energy and cellular components.
Metabolic pathways can be categorized into three types:
- Anabolic pathways: Build complex molecules from simpler ones, requiring energy (e.g., synthesis of proteins).
- Catabolic pathways: Break down complex molecules into simpler ones, releasing energy (e.g., glycolysis).
- Amphibolic pathways: Serve as both anabolic and catabolic processes, integrating metabolism (e.g., citric acid cycle).

Metabolism of Nutrients

Key macronutrients include carbohydrates, lipids, and amino acids, each metabolized in tissues and organs.
At the subcellular level, metabolism involves specific organelles (e.g., mitochondria for aerobic respiration).
Interconversion of metabolic fuels allows the body to adapt to different energy demands and nutrient availabilities.

Regulation of Metabolic Pathways

Flux of metabolites through pathways is regulated by:
- Enzyme activity, which can be modulated by allosteric effects and covalent modifications (e.g., phosphorylation).
- Hormonal signaling that influences enzyme expression and activity (e.g., insulin promoting glucose uptake).
- Availability of substrates and energy status within the cell.

Supply of Metabolic Fuels

In the fed state, the body stores excess energy as glycogen and fat.
Metabolic reserves are mobilized during the fasting state through hormone-regulated pathways:
- Glycogenolysis: breakdown of glycogen into glucose.
- Lipolysis: breakdown of triglycerides into fatty acids and glycerol.

Digestion and Absorption of Carbohydrates

Major dietary carbohydrates include starch, sucrose, and lactose.
Primary sites of carbohydrate digestion:
- Mouth: Salivary amylase begins starch breakdown.
- Intestinal lumen: Further digestion by pancreatic enzymes occurs here.
Digestion is rapid, facilitated by glycoside hydrolases (glycosidases) that hydrolyze glycosidic bonds.

Enzyme Functions in Carbohydrate Digestion

Endoglycosidases: Enzymes that hydrolyze internal glycosidic bonds within polysaccharides and oligosaccharides.
Disaccharidases: Enzymes that hydrolyze disaccharides into reducing sugars, necessary for absorption.

Description

This quiz covers the fundamental concepts of metabolism, including the various biochemical processes involved in converting food into energy. Explore the three types of metabolic pathways: anabolic, catabolic, and amphibolic, to understand how they contribute to cellular functions.