Cell Structure, Membrane Function, and Energy Harvesting: Study Guide

Chapter 4: A Tour of the Cell

Basic Features Shared by All Cells

All cells, regardless of type, share several fundamental structures that are essential for life.

• Plasma Membrane: A selectively permeable barrier that encloses the cell, regulating the movement of substances in and out.

• Cytoplasm: The internal fluid of the cell, containing organelles and the cytosol.

• DNA/RNA: Genetic material responsible for storing and transmitting hereditary information.

• Ribosomes: Molecular machines that synthesize proteins by translating messenger RNA.

Eukaryotic Cellular Parts and Their Functions

Eukaryotic cells contain specialized organelles, each with distinct functions.

• Cell Wall: Provides structural support and protection (found in plants, fungi, and some protists).

• Cytoskeleton: Network of protein filaments (microfilaments, intermediate filaments, microtubules) that maintain cell shape, enable movement, and organize organelles.

• Cilia: Short, hair-like structures for movement or sensory functions.

• Flagella: Long, whip-like structures for cell locomotion.

• Nucleus: Contains genetic material; includes nuclear envelope, chromatin/chromosomes, and nucleolus (site of ribosome synthesis).

• Ribosome: Site of protein synthesis.

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

• Vesicle: Small membrane-bound sacs for transport and storage.

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

• Lysosome: Contains digestive enzymes for breaking down macromolecules.

• Peroxisome: Breaks down fatty acids and detoxifies harmful substances.

• Vacuole: Storage organelle; types include food, central (plants), and contractile (protists).

• Mitochondria: Site of aerobic cellular respiration and ATP production.

• Chloroplast: Site of photosynthesis in plant cells.

Distinguishing Plant Cells from Animal Cells

• Plant Cells: Have cell walls, chloroplasts, and large central vacuoles.

• Animal Cells: Lack cell walls and chloroplasts; may have small vacuoles.

Prokaryotic Cellular Parts

Prokaryotic cells lack membrane-bound organelles and have unique structures.

• Plasma Membrane: Controls entry and exit of substances.

• Slime Layer (Capsule): Provides protection and helps in adhesion.

• Fimbriae: Hair-like appendages for attachment.

• Plasmid (DNA): Small, circular DNA molecules for genetic exchange.

• Ribosomes: Protein synthesis (smaller than eukaryotic ribosomes).

• Cell Wall: Structural support and protection.

• Flagellum: Motility.

• Cytoplasm: Internal fluid.

• Nucleoid Region: Area containing the main DNA.

Distinguishing Prokaryotic from Eukaryotic Cells

• Prokaryotic Cells: No nucleus, no membrane-bound organelles, smaller size.

• Eukaryotic Cells: Nucleus present, membrane-bound organelles, larger size.

Types of Cellular Connections

• Anchoring Junctions: Attach cells to each other or to the extracellular matrix.

• Gap Junctions: Allow direct communication between cells via channels.

• Tight Junctions: Seal cells together to prevent leakage.

• Plasmodesmata: Channels between plant cells for transport and communication.

Chapter 5: The Working Cell

Major Functions of the Cell Membrane

The cell membrane is essential for maintaining cellular integrity and regulating interactions with the environment.

• Barrier: Separates internal cell environment from external surroundings.

• Selective Permeability: Controls which substances can enter or leave the cell.

• Communication: Contains proteins for signaling and interaction with other cells.

• Transport: Facilitates movement of molecules via proteins.

Selective Permeability of the Cell Membrane

The cell membrane allows certain molecules to pass while restricting others, based on size, charge, and solubility.

• Small, nonpolar molecules: Pass easily (e.g., O2, CO2).

• Large or charged molecules: Require transport proteins.

Fluid Mosaic Model Components

The fluid mosaic model describes the structure of the cell membrane as a dynamic combination of lipids and proteins.

• Phospholipids: Form a bilayer with hydrophobic (water-repelling) tails and hydrophilic (water-attracting) heads.

• Transport Proteins: Facilitate movement of substances across the membrane.

• Receptor Proteins: Receive and transmit signals from the environment.

• Enzymes: Catalyze reactions at the membrane surface.

• Glycoproteins: Proteins with carbohydrate chains for cell recognition.

• Attachment Proteins: Anchor the membrane to the cytoskeleton or extracellular matrix.

Key Terms and Concepts

• Concentration Gradient: Difference in concentration of a substance across a space.

• Diffusion: Movement of molecules from high to low concentration.

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Solvent: Substance in which solutes are dissolved (e.g., water).

• Solute: Substance dissolved in a solvent.

• Passive Transport: Movement without energy input (e.g., diffusion, osmosis).

• Active Transport: Movement against concentration gradient, requires energy (ATP).

• Simple Diffusion: Direct movement through the membrane.

• Facilitated Diffusion: Movement via transport proteins.

• Exocytosis: Export of materials via vesicles.

• Endocytosis: Import of materials via vesicles.

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

• Pinocytosis: "Cell drinking"; uptake of fluids.

• Receptor-Mediated Endocytosis: Uptake of specific molecules via receptor binding.

• Carrier Proteins: Bind and transport specific molecules.

• Channel Proteins: Form pores for passive movement.

• Aquaporins: Channel proteins specifically for water transport.

Effects of Tonicity on Cells

Tonicity describes the effect of solute concentration on cell volume.

• Hypotonic Solution: Lower solute concentration outside; cell gains water and may burst.

• Isotonic Solution: Equal solute concentration; cell maintains normal shape.

• Hypertonic Solution: Higher solute concentration outside; cell loses water and shrinks.

Chapter 6: How Cells Harvest Chemical Energy

Photosynthesis vs. Aerobic Cellular Respiration

These two processes are central to energy flow in biological systems.

Process	Reactants	Products	Energy Flow
Photosynthesis	CO2, H2O, light energy	Glucose, O2	Stores energy in glucose
Aerobic Respiration	Glucose, O2	CO2, H2O, ATP	Releases energy from glucose

Equations:

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

• Aerobic Respiration: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$

Glucose Metabolism and ATP Formation

Glucose is a primary energy source; its breakdown releases energy used to form ATP, the cell's energy currency.

• ATP: Adenosine triphosphate; stores and transfers energy for cellular processes.

Glycolysis

Glycolysis is the first step in cellular respiration, occurring in the cytoplasm.

• Location: Cytoplasm

• End Products: 2 pyruvate, 2 ATP, 2 NADH

Aerobic Cellular Respiration Steps

• Pyruvate Oxidation: Pyruvate enters mitochondria; converted to acetyl-CoA, producing NADH and CO2.

• Krebs Cycle (Citric Acid Cycle): Produces NADH, FADH2, and ATP.

• Electron Transport Chain: NADH and FADH2 donate electrons; energy used to pump protons.

• Oxidative Phosphorylation (Chemiosmosis): Protons flow back through ATP synthase, generating ATP.

Role of O2: Final electron acceptor in the electron transport chain; essential for ATP production.

Chapter 7: Photosynthesis: Using Light to Make Food

Autotrophs vs. Heterotrophs

Organisms are classified based on how they obtain nutrition.

• Autotrophs (Producers): Synthesize their own food from inorganic sources (e.g., plants).

• Heterotrophs (Consumers): Obtain food by consuming other organisms.

Photosynthesis Equation

The overall chemical reaction for photosynthesis is:

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

Structure and Function of Chloroplast

• Stroma: Fluid-filled space where the Calvin cycle occurs.

• Thylakoid: Membrane-bound sacs containing chlorophyll; site of light reactions.

• Granum: Stack of thylakoids.

Role of Chlorophyll

Chlorophyll is the pigment that absorbs light energy, initiating photosynthesis.

• Absorbs: Blue and red wavelengths; reflects green.

Light Reactions vs. Calvin Cycle

Aspect	Light Reactions (Light-Dependent)	Calvin Cycle (Light-Independent)
Location	Thylakoid membranes	Stroma
Inputs	Light, H2O, NADP+, ADP	CO2, NADPH, ATP
Outputs	O2, NADPH, ATP	Glucose, NADP+, ADP

• Light Reactions: Convert light energy to chemical energy (ATP, NADPH); release O2.

• Calvin Cycle: Uses ATP and NADPH to fix CO2 into glucose.