Macromolecules, Metabolism, and Cellular Respiration: Study Guide

Macromolecules and Nutrition

Macromolecular Structures of Carbohydrates, Proteins, and Lipids

Biological macromolecules are large, complex molecules essential for life. They include carbohydrates, proteins, and lipids, each with distinct structures and functions.

• Carbohydrates: Composed of monosaccharide monomers (e.g., glucose). Polysaccharides (e.g., starch, glycogen) are formed by dehydration synthesis of monosaccharides.

• Proteins: Polymers of amino acids linked by peptide bonds. The sequence and structure of amino acids determine protein function.

• Lipids: Include fats, oils, and phospholipids. Built from fatty acids and glycerol, they are hydrophobic and serve as energy storage and membrane components.

• Hydrolysis and Dehydration Synthesis: Dehydration synthesis forms bonds by removing water; hydrolysis breaks bonds by adding water.

Example: Starch (a polysaccharide) is a storage form of glucose in plants; triglycerides are a common lipid used for energy storage in animals.

Metabolism and Energy

Catabolism, Anabolism, and Metabolic Pathways

Metabolism encompasses all chemical reactions in an organism, divided into two main types:

• Catabolism: Breakdown of complex molecules into simpler ones, releasing energy (e.g., cellular respiration).

• Anabolism: Synthesis of complex molecules from simpler ones, requiring energy (e.g., protein synthesis).

Example: The hydrolysis of ATP to ADP is a catabolic reaction that releases energy for cellular processes.

Glucose Homeostasis

Regulation and Hormonal Control

Glucose homeostasis is vital for animal survival, ensuring a stable supply of energy. It is regulated by hormones:

• Insulin: Lowers blood glucose by promoting uptake into cells and storage as glycogen.

• Glucagon: Raises blood glucose by stimulating glycogen breakdown in the liver.

Homeostasis is maintained through feedback mechanisms involving the pancreas, liver, and muscle tissues.

Example: After a meal, insulin secretion increases to lower blood glucose; during fasting, glucagon secretion increases to raise blood glucose.

Cellular Respiration

Overview and Location

Cellular respiration is the process by which cells extract energy from glucose to produce ATP. It occurs mainly in the mitochondria of eukaryotic cells and consists of several stages:

• Glycolysis: Occurs in the cytoplasm; breaks down glucose into pyruvate.

• Citric Acid Cycle (Krebs Cycle): Occurs in the mitochondrial matrix; oxidizes acetyl-CoA to CO2.

• Oxidative Phosphorylation: Occurs across the inner mitochondrial membrane; produces most ATP via the electron transport chain (ETC).

Purpose: To generate ATP, the energy currency of the cell.

Inputs and Outputs of Major Pathways

• Glycolysis:

  • Input: 1 glucose, 2 NAD+, 2 ADP, 2 Pi

  • Output: 2 pyruvate, 2 NADH, 2 ATP (net)

• Citric Acid Cycle:

  • Input: 2 acetyl-CoA, 6 NAD+, 2 FAD, 2 ADP, 2 Pi

  • Output: 4 CO2, 6 NADH, 2 FADH2, 2 ATP

• Oxidative Phosphorylation:

  • Input: NADH, FADH2, O2, ADP, Pi

  • Output: NAD+, FAD, H2O, ATP (about 26-28 per glucose)

Equation for Cellular Respiration:

$\mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy (ATP + heat)}}$

Electron Transport Chain (ETC)

The ETC is a series of protein complexes in the inner mitochondrial membrane. It transfers electrons from NADH and FADH2 to oxygen, the final electron acceptor, creating a proton gradient that drives ATP synthesis.

• Electrons move through complexes I-IV, pumping protons into the intermembrane space.

• ATP synthase uses the proton gradient to convert ADP to ATP.

Example: Oxygen is essential as the final electron acceptor; without it, the ETC halts, and ATP production drops.

ATP Yield and Oxygen's Role

• Oxidative phosphorylation produces the most ATP (about 26-28 per glucose) compared to glycolysis and the citric acid cycle.

• Oxygen increases ATP yield by allowing the ETC to function efficiently, maximizing energy extraction from glucose.

Electron Carriers: NADH and FADH2 are critical for transferring electrons to the ETC, enabling ATP production.

Essential and Non-Essential Nutrients

Definitions and Examples

• Essential Nutrients: Must be obtained from the diet (e.g., certain amino acids, fatty acids, vitamins, minerals).

• Non-Essential Nutrients: Can be synthesized by the body.

Vitamins and Minerals: Required in small amounts for enzyme function, bone health, and other physiological processes.

Summary Table: Major Metabolic Pathways

Pathway	Main Location	Inputs	Outputs	ATP Yield
Glycolysis	Cytoplasm	Glucose, NAD+, ADP	Pyruvate, NADH, ATP	2 (net)
Citric Acid Cycle	Mitochondrial Matrix	Acetyl-CoA, NAD+, FAD, ADP	CO2, NADH, FADH2, ATP	2
Oxidative Phosphorylation	Inner Mitochondrial Membrane	NADH, FADH2, O2, ADP	NAD+, FAD, H2O, ATP	26-28

Additional info: This guide integrates foundational concepts from metabolism, nutrition, and cellular respiration, as outlined in the learning objectives. It is suitable for exam preparation in introductory college biology courses.