Cellular Transport, Cell Structure, and Metabolism: Study Guide Notes

Chapter 6.2: Cellular Transport Mechanisms

Osmosis, Diffusion, Facilitated Diffusion, and Active Transport

Cells use various mechanisms to move substances across their membranes. Understanding these processes is essential for grasping how cells maintain homeostasis.

• Osmosis: The diffusion of water molecules across a selectively permeable membrane from an area of low solute concentration to high solute concentration.

• Diffusion: The passive movement of molecules from an area of higher concentration to an area of lower concentration.

• Facilitated Diffusion: Passive transport of substances across a membrane via transport proteins; does not require energy.

• Active Transport: Movement of substances against their concentration gradient, requiring energy (usually ATP).

Primary vs. Secondary Active Transport:

• Primary Active Transport: Direct use of ATP to transport molecules (e.g., Na+/K+ ATPase pump).

• Secondary Active Transport: Uses the energy from the electrochemical gradient created by primary active transport to move other substances.

Key Proteins in Transport:

• ATPase Transporters: Enzymes that hydrolyze ATP to provide energy for active transport (e.g., Na+/K+ ATPase).

• Aquaporins: Channel proteins that facilitate rapid water movement across membranes.

• Carrier Proteins: Proteins that bind specific molecules and change shape to shuttle them across the membrane.

Does Passive Transport Require Energy? No, passive transport (diffusion, osmosis, facilitated diffusion) does not require cellular energy.

Does Active Transport Require Energy? Yes, active transport requires energy, typically in the form of ATP.

Identifying Transport Types: If given a scenario, determine if the process is passive (no energy, down gradient) or active (requires energy, against gradient).

Chapter 7: Cell Structure and Function

Prokaryotes vs. Eukaryotes

Cells are classified as prokaryotic or eukaryotic based on their structural features.

• Prokaryotes: Lack a nucleus and membrane-bound organelles; DNA is in the nucleoid region (e.g., Bacteria and Archaea).

• Eukaryotes: Have a true nucleus and membrane-bound organelles (e.g., Animals, Plants, Fungi, Protists).

Comparison Table:

Feature	Prokaryotes	Eukaryotes
Nucleus	No	Yes
Membrane-bound organelles	No	Yes
Cell size	Small (1-10 μm)	Larger (10-100 μm)
Examples	Bacteria, Archaea	Animals, Plants, Fungi, Protists

Specialization: In multicellular organisms, different cell types have specialized functions (e.g., muscle cells, nerve cells).

Organelles and Their Functions

• Ribosomes: Sites of protein synthesis; can be free in the cytoplasm or bound to the rough endoplasmic reticulum (RER).

• Rough Endoplasmic Reticulum (RER): Studded with ribosomes; involved in protein synthesis and modification.

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

• Organelles with DNA: Mitochondria and chloroplasts contain their own DNA, supporting the endosymbiotic theory.

Endomembrane System: Includes the nuclear envelope, ER, Golgi apparatus, lysosomes, and vesicles; coordinates the synthesis and transport of cellular products.

Exocytosis and Endocytosis

• Exocytosis: Process by which cells expel materials in vesicles that fuse with the plasma membrane.

• Endocytosis: Process by which cells take in materials by engulfing them in vesicles; includes phagocytosis (solid particles), pinocytosis (liquids), and receptor-mediated endocytosis (specific molecules).

Chapters 9 and 10: Cellular Metabolism and Photosynthesis

Oxidation and Reduction (Redox Reactions)

Redox reactions are fundamental to cellular energy transformations.

• Oxidation: Loss of electrons from a molecule.

• Reduction: Gain of electrons by a molecule.

• Anabolic Pathways: Build complex molecules from simpler ones; require energy (endergonic).

• Catabolic Pathways: Break down complex molecules into simpler ones; release energy (exergonic).

Example Equation:

• Cellular respiration (glucose oxidation): $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy (ATP)}$

Cellular Respiration

Cellular respiration is the process by which cells extract energy from glucose.

• Stages: Glycolysis, Pyruvate Oxidation, Citric Acid Cycle (Krebs Cycle), Electron Transport Chain (ETC), and Oxidative Phosphorylation.

• ATP Production: Most ATP is produced during oxidative phosphorylation in the mitochondria.

• Oxygen's Role: Final electron acceptor in the ETC; combines with electrons and protons to form water.

• Location: Glycolysis occurs in the cytoplasm; other stages occur in the mitochondria.

Equation for Cellular Respiration:

• $\text{Glucose} + 6\ O_2 \rightarrow 6\ CO_2 + 6\ H_2O + \text{ATP}$

Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy.

• Light Reactions: Occur in the thylakoid membranes; convert solar energy to chemical energy (ATP and NADPH), release O2.

• Calvin Cycle (Dark Reactions): Occur in the stroma; use ATP and NADPH to fix CO2 into glucose.

• Relationship to Respiration: Photosynthesis stores energy in glucose; respiration releases energy from glucose.

Equation for Photosynthesis:

• $6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$

Comparison Table: Cellular Respiration vs. Photosynthesis

Process	Location	Reactants	Products	Energy
Cellular Respiration	Mitochondria	Glucose, O2	CO2, H2O	Released (ATP)
Photosynthesis	Chloroplasts	CO2, H2O, Light	Glucose, O2	Stored (in glucose)

Key Points:

• Photosynthesis and respiration are complementary processes in the global carbon and energy cycles.

• Both involve electron transport chains and chemiosmosis for ATP production.