General Biology: Cellular Processes, Enzymes, and Respiration Study Guide

Cellular Transport and Membrane Dynamics

Diffusion and Factors Affecting It

Diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration. It is a fundamental process for the movement of substances across cell membranes.

• Definition: Diffusion is the net movement of molecules down their concentration gradient.

• Factors Influencing Rate:

  • Temperature

  • Concentration gradient

  • Molecule size

  • Pressure

• Osmosis: The diffusion of water across a selectively permeable membrane.

• Tonicity: Refers to the relative concentration of solutes in two solutions separated by a membrane.

  • Hypertonic: Higher solute concentration outside the cell; water moves out.

  • Isotonic: Equal solute concentration; no net water movement.

  • Hypotonic: Lower solute concentration outside; water moves in.

• Membrane Transport Proteins: Facilitate the movement of substances across membranes.

  • Channel proteins: Provide corridors for specific molecules.

  • Carrier proteins: Bind and transport substances.

• Peripheral vs. Integral Proteins:

  • Peripheral proteins are loosely attached to the membrane surface.

  • Integral proteins span the membrane and are involved in transport.

Thermodynamics in Biology

First and Second Laws of Thermodynamics

Thermodynamics governs energy transformations in biological systems.

• First Law: Energy cannot be created or destroyed, only transformed.

• Second Law: Every energy transfer increases the entropy (disorder) of the universe.

• Endergonic vs. Exergonic Reactions:

  • Endergonic: Absorb energy; products have more energy than reactants.

  • Exergonic: Release energy; products have less energy than reactants.

ATP and Energy Coupling

ATP: Structure and Function

ATP (adenosine triphosphate) is the primary energy currency of the cell.

• ATP Hydrolysis: The breakdown of ATP to ADP and inorganic phosphate releases energy.

• Energy Coupling: Cells use the energy from ATP hydrolysis to drive endergonic reactions.

Redox Reactions in Biology

Oxidation and Reduction

Redox reactions involve the transfer of electrons between molecules.

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Example: In cellular respiration, glucose is oxidized and oxygen is reduced.

Enzymes and Metabolic Pathways

Enzyme Function and Regulation

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy.

• Factors Influencing Enzyme Activity:

  • Temperature

  • pH

  • Substrate concentration

  • Presence of inhibitors or activators

• Allosteric Regulation: Enzyme activity is regulated by molecules binding at sites other than the active site, causing conformational changes.

• Coenzymes and Cofactors: Non-protein molecules that assist enzymes.

Cellular Respiration

Overview and Stages

Cellular respiration is the process by which cells extract energy from glucose to produce ATP. It consists of several stages:

1. Glycolysis

2. Pyruvate oxidation

3. Citric acid cycle (Krebs cycle)

4. Electron transport chain and oxidative phosphorylation

Glycolysis

• Occurs in the cytoplasm.

• Breaks down glucose into two molecules of pyruvate.

• Produces a net gain of 2 ATP and 2 NADH per glucose.

Citric Acid Cycle (Krebs Cycle)

• Occurs in the mitochondrial matrix.

• Completes the oxidation of glucose derivatives.

• Produces NADH, FADH2, ATP, and CO2.

• First Stable Intermediate: Citrate (formed from oxaloacetate and acetyl-CoA).

Electron Transport Chain and Oxidative Phosphorylation

• Located in the inner mitochondrial membrane.

• Electrons from NADH and FADH2 are transferred through protein complexes.

• Oxygen is the final electron acceptor, forming water.

• Proton gradient drives ATP synthesis via ATP synthase.

• Substrate-level Phosphorylation: Direct transfer of a phosphate group to ADP to form ATP.

• Oxidative Phosphorylation: ATP synthesis powered by the electron transport chain and chemiosmosis.

Fermentation

• Occurs when oxygen is not available.

• Allows glycolysis to continue by regenerating NAD+.

• Produces lactic acid (in animals) or ethanol and CO2 (in yeast).

• Importance: Prevents buildup of NADH and allows ATP production in anaerobic conditions.

Key Molecules and Intermediates

• ATP: Main energy carrier.

• NADH and FADH2: Electron carriers.

• Oxaloacetate: Regenerates in the citric acid cycle; combines with acetyl-CoA to form citrate.

Summary Table: Stages of Aerobic Cellular Respiration

Stage	Location	Main Inputs	Main Outputs	ATP Produced
Glycolysis	Cytoplasm	Glucose, 2 NAD+, 2 ADP	2 Pyruvate, 2 NADH, 2 ATP	2 (net)
Pyruvate Oxidation	Mitochondrial matrix	2 Pyruvate, 2 NAD+	2 Acetyl-CoA, 2 NADH, 2 CO2	0
Citric Acid Cycle	Mitochondrial matrix	2 Acetyl-CoA, 6 NAD+, 2 FAD, 2 ADP	4 CO2, 6 NADH, 2 FADH2, 2 ATP	2
Electron Transport Chain	Inner mitochondrial membrane	10 NADH, 2 FADH2, O2	H2O, NAD+, FAD	~26-28

Microscopy

Parts of the Microscope

Understanding the parts of a microscope is essential for laboratory work.

• Ocular lens (eyepiece): Where you look through to see the specimen.

• Objective lenses: Provide different magnification levels.

• Stage: Platform where the slide is placed.

• Light source: Illuminates the specimen.

• Coarse and fine focus knobs: Adjust the clarity of the image.

Additional info:

• Some questions in the original file were open-ended or required identification (e.g., "Be able to identify the parts of the microscope"). Academic context and standard answers have been provided for completeness.

• Where the original file listed only terms or brief prompts, full academic explanations and examples have been added to ensure the notes are self-contained and suitable for exam preparation.