General Biology: Cell Structure, Membrane Function, and Metabolism – Exam 2 Study Guide

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This section covers the tools and concepts used to study cells, as well as the fundamental differences between cell types.

Light Microscope: Used for viewing live cells and tissues at moderate magnification. Appropriate for general cell structure.
Transmission Electron Microscope (TEM): Provides detailed images of internal cell structures by passing electrons through thin sections.
Scanning Electron Microscope (SEM): Used to view cell surfaces in high detail by scanning the surface with electrons.
Eukaryotes vs. Prokaryotes:
- Eukaryotic cells have a nucleus and membrane-bound organelles (e.g., plants, animals, fungi, protists).
- Prokaryotic cells lack a nucleus and most organelles (e.g., bacteria, archaea).
Domains of Life: Classified as Bacteria, Archaea (both prokaryotic), and Eukarya (eukaryotic).
Common Structures: All cells have a plasma membrane, cytoplasm, ribosomes, and genetic material (DNA).
Differences in Plant, Animal, and Bacterial Cells:
- Plant cells: Have cell walls, chloroplasts, and large central vacuoles.
- Animal cells: Lack cell walls and chloroplasts, have centrioles.
- Bacterial cells: Have cell walls (different composition from plants), no nucleus.
Pathway Taken by a Newly Synthesized Protein: Typically, protein is synthesized on ribosomes, enters the endoplasmic reticulum, processed in the Golgi apparatus, and then transported to its destination.

This section explains the structure and function of biological membranes, focusing on their dynamic and selective nature.

Fluid Mosaic Model: Describes the plasma membrane as a flexible layer made of lipid molecules interspersed with proteins.
Membrane Components:
- Phospholipids: Form a bilayer with hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repelling) tails facing inward.
- Proteins: Embedded or attached to the membrane, serving as channels, receptors, or enzymes.
- Carbohydrates: Attached to proteins or lipids, important for cell recognition.
Hydrophilic vs. Hydrophobic Molecules: Hydrophilic molecules interact with water; hydrophobic molecules avoid water and are found in the membrane interior.
Diffusion and Osmosis:
- Diffusion: Movement of molecules from high to low concentration.
- Osmosis: Diffusion of water across a selectively permeable membrane.
Osmotic Environments:
- Isotonic: No net water movement; cell volume remains stable.
- Hypotonic: Water enters the cell; cell may swell or burst.
- Hypertonic: Water leaves the cell; cell shrinks.

This section introduces the principles of metabolism, including energy transformations and the laws governing them.

Metabolism: The sum of all chemical reactions in a cell, including catabolic (breakdown) and anabolic (synthesis) pathways.
Entropy: A measure of disorder; increases in spontaneous processes (e.g., diffusion, heat loss).
Dehydration Reactions: Synthesis reactions that remove water to form bonds.
Catabolism vs. Anabolism:
- Catabolism: Breaks down molecules, releasing energy (e.g., cellular respiration).
- Anabolism: Builds complex molecules, consuming energy (e.g., protein synthesis).
First and Second Laws of Thermodynamics:
- First Law: Energy cannot be created or destroyed, only transformed.
- Second Law: Every energy transfer increases the entropy of the universe.
Chemical Equilibrium: The point at which forward and reverse reactions occur at the same rate; no net change in concentrations.
ATP (Adenosine Triphosphate): The main energy currency of the cell; hydrolysis of ATP releases energy for cellular work.
Enzyme Function: Biological catalysts that speed up reactions by lowering activation energy; affected by cofactors, inhibitors, and environmental conditions.

This section covers how cells extract energy from nutrients through respiration and fermentation, including the key steps and molecules involved.

Oxidation and Reduction: Chemical reactions where electrons are transferred; oxidation is loss of electrons, reduction is gain of electrons.
Key Molecules: NAD+, NADH, FAD, FADH2, ATP.
Stages of Cellular Respiration:
- Glycolysis: Occurs in the cytoplasm; breaks glucose into pyruvate, producing ATP and NADH.
- Citric Acid Cycle (Krebs Cycle): Occurs in mitochondria; completes glucose breakdown, producing CO2, ATP, NADH, and FADH2.
- Electron Transport Chain: Uses electrons from NADH and FADH2 to create a proton gradient for ATP synthesis.
Fermentation: Anaerobic process that allows glycolysis to continue by regenerating NAD+.
- Lactic Acid Fermentation: Produces lactic acid as a byproduct (e.g., in muscle cells).
- Alcohol Fermentation: Produces ethanol and CO2 (e.g., in yeast).
Anaerobic Respiration: Uses a final electron acceptor other than oxygen; found in some bacteria and archaea.

Process	Oxygen Required?	Final Electron Acceptor	Main Products	ATP Yield (per glucose)
Cellular Respiration	Yes	O2	CO2, H2O, ATP	~30-32
Lactic Acid Fermentation	No	Pyruvate	Lactic acid, ATP	2
Alcohol Fermentation	No	Acetaldehyde	Ethanol, CO2, ATP	2
Anaerobic Respiration	No	Other (e.g., nitrate, sulfate)	Varies	Varies (less than aerobic)