Cell Biology Exam 2 Study Guide: Eukaryotic Cells, Membranes, Metabolism, and Photosynthesis

Chapter 6: A Tour of the Cell

Main Organelles in Eukaryotic Cells

Eukaryotic cells contain specialized organelles that perform distinct functions necessary for cellular life. Understanding their roles is fundamental to cell biology.

• Nucleus: Contains genetic material (DNA); site of transcription and RNA processing.

• Mitochondria: Site of cellular respiration; generates ATP through oxidative phosphorylation.

• Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; Smooth ER synthesizes lipids and detoxifies chemicals.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosomes: Contain hydrolytic enzymes for digestion of macromolecules.

• Peroxisomes: Break down fatty acids and detoxify harmful substances.

• Chloroplasts: (in plants) Site of photosynthesis.

• Vacuoles: Storage and maintenance of cell shape (large central vacuole in plants).

Example: The mitochondrion is often called the "powerhouse" of the cell due to its role in ATP production.

Subcellular Structures and Their Functions

Cells contain various structures that contribute to their shape, movement, and internal organization.

• Cytoskeleton: Network of protein filaments (microtubules, microfilaments, intermediate filaments) that provide structural support, facilitate intracellular transport, and enable cell movement.

• Flagella: Long, whip-like structures used for cell motility; composed of microtubules arranged in a "9+2" pattern.

• Cilia: Short, hair-like structures for movement or moving substances across cell surfaces.

Example: Sperm cells use flagella for motility, while amoebae use actin-based pseudopodia.

Cellular Motility and Energy

Cell movement requires energy, typically supplied by ATP. Different motility mechanisms involve distinct cellular components.

• Flagellar Motility: Driven by dynein motor proteins moving along microtubules; ATP is the energy source.

• Amoeboid Motility: Involves actin polymerization and myosin motors; enables cells to change shape and move by extending pseudopodia.

Comparison: Flagellar motility relies on microtubules and dynein, while amoeboid motility depends on actin and myosin.

Chapter 7: Membrane Structure and Function

Membrane Basics

Cell membranes are dynamic structures that regulate the movement of substances and maintain cellular integrity.

• Fluid Mosaic Model: Describes the membrane as a flexible bilayer of phospholipids with embedded proteins.

• Semi-permeability: Membranes allow selective passage of molecules based on size, charge, and polarity.

Example: Small, nonpolar molecules like O2 and CO2 diffuse freely, while ions require transport proteins.

Transport Across Membranes

Cells use various mechanisms to move substances across membranes.

• Passive Transport: Movement down a concentration gradient; includes diffusion, facilitated diffusion, and osmosis.

• Active Transport: Movement against a concentration gradient; requires energy (usually ATP).

• Osmosis: Diffusion of water across a semi-permeable membrane.

Equation: Osmotic pressure can be described by:

$\Pi = iMRT$

where $\Pi$ is osmotic pressure, $i$ is the van 't Hoff factor, $M$ is molarity, $R$ is the gas constant, and $T$ is temperature.

The Endomembrane System

The endomembrane system coordinates the synthesis, modification, and transport of cellular materials.

• Components: Nuclear envelope, ER, Golgi apparatus, lysosomes, vesicles, plasma membrane.

• Pathway: Proteins synthesized in the rough ER → transported to Golgi → sorted and packaged → sent to lysosomes, plasma membrane, or secreted.

• Production and Secretion of Proteins: Involves translation, modification, and vesicular transport.

• Endocytosis: Uptake of external materials by vesicle formation.

• Phagocytosis: "Cell eating"; engulfment of large particles.

• Autophagy: Degradation of internal cellular components.

Example: Macrophages use phagocytosis to ingest pathogens.

Chapter 9: Cellular Respiration and Fermentation

Free Energy and Modes of Metabolism

Metabolism involves energy transformations governed by free energy changes.

• Free Energy ($\Delta G$): Determines whether a reaction is spontaneous.

• Catabolism: Breakdown of molecules to release energy.

• Anabolism: Synthesis of molecules using energy.

Equation:

$\Delta G = \Delta H - T\Delta S$

where $\Delta H$ is enthalpy, $T$ is temperature, and $\Delta S$ is entropy.

Oxidation/Reduction Reactions and Electron Carriers

Cellular respiration relies on redox reactions and electron carriers to transfer energy.

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Electron Carriers: NAD+, FAD, NADP+ shuttle electrons during metabolic processes.

Example: NAD+ is reduced to NADH during glycolysis and the citric acid cycle.

Basics and Details of Cellular Respiration

Cellular respiration is a multi-stage process that converts glucose to ATP.

• Three Phases:

  1. Glycolysis (cytoplasm): Glucose → pyruvate

  2. Citric Acid Cycle (mitochondrial matrix): Pyruvate → CO2

  3. Oxidative Phosphorylation (inner mitochondrial membrane): Electron transport chain and ATP synthesis

• ATP Production: Substrate-level phosphorylation (glycolysis, citric acid cycle) and oxidative phosphorylation (ETC).

• Glucose Oxidation: Complete oxidation produces CO2 and water.

• Oxidative Phosphorylation: Electron transport chain creates a proton gradient; ATP synthase uses this gradient to produce ATP.

Equation:

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Energy (ATP)}$

Fermentation vs. Respiration

Cells can generate ATP anaerobically (fermentation) or aerobically (respiration).

• Fermentation: Occurs without oxygen; regenerates NAD+ by transferring electrons to organic molecules; produces less ATP.

• Respiration: Uses oxygen as the final electron acceptor; produces more ATP.

Example: Yeast cells perform alcoholic fermentation, producing ethanol and CO2.

Metabolic Regulation and Versatility

Cells regulate metabolism through feedback mechanisms and can utilize various substrates for energy.

• Allosteric Regulation: Enzymes are modulated by effectors.

• Versatility: Fats, proteins, and carbohydrates can enter metabolic pathways.

Chapter 10: Photosynthesis

Basics of Photosynthesis

Photosynthesis converts light energy into chemical energy in plants, algae, and some bacteria.

• Energetics: Light energy drives endergonic reactions; redox changes occur as electrons are transferred.

• Stages: Light reactions (thylakoid membrane) and Calvin cycle (stroma).

• Inputs/Outputs: Light reactions: water, light → O2, ATP, NADPH; Calvin cycle: CO2, ATP, NADPH → sugar.

Details of Photosynthesis

Light reactions and the Calvin cycle are tightly coordinated to produce organic molecules.

• Role of Light: Excites electrons in chlorophyll, initiating electron transport.

• Oxygen Production: Water is split during light reactions, releasing O2.

• ATP and NADPH Generation: Electron transport chain creates a proton gradient; ATP synthase produces ATP; NADP+ is reduced to NADPH.

Equation:

$6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Light Energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$

The Calvin Cycle

The Calvin cycle fixes carbon dioxide and synthesizes sugars using ATP and NADPH.

• Inputs: CO2, ATP, NADPH

• Outputs: G3P (a sugar), ADP, NADP+

• CO2 Fixation: Catalyzed by Rubisco enzyme.

• ATP and Electron Use: ATP provides energy; NADPH provides reducing power.

Comparison: Mitochondria vs. Chloroplasts

Mitochondria and chloroplasts are double-membraned organelles with distinct roles in energy metabolism.

Feature	Mitochondria	Chloroplasts
Main Function	Cellular respiration (ATP production)	Photosynthesis (sugar production)
Energy Source	Organic molecules (glucose)	Light energy
Key Processes	Glycolysis, Citric Acid Cycle, ETC	Light reactions, Calvin cycle
Byproducts	CO2, H2O	O2
Location	All eukaryotes	Plants and algae

Example: Both organelles use chemiosmosis to generate ATP, but mitochondria use organic substrates while chloroplasts use light energy.

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