Chapter 4: A Tour of the Cell

Basic Features Shared by All Cells

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

• Cytoplasm: The jelly-like fluid inside the cell where organelles are suspended and most cellular activities occur.

• Genetic Material (DNA/RNA): Contains instructions for cell function and heredity.

• Ribosomes: Structures responsible for protein synthesis.

Eukaryotic Cellular Parts and Their Functions

• Cell Wall: Rigid outer layer found in plants, fungi, and some protists; provides support and protection.

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

• Cilia and Flagella: Hair-like structures for movement; cilia are short and numerous, flagella are longer and usually singular or few.

• Nucleus: Contains genetic material; includes the nuclear envelope (double membrane), chromatin/chromosomes (DNA), and nucleolus (site of ribosome assembly).

• Ribosome: Site of protein synthesis; found free in cytoplasm or attached to rough ER.

• Endoplasmic Reticulum (ER):

  • Rough ER: Studded with ribosomes; synthesizes and processes proteins.

  • Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies chemicals.

• Vesicle: Small membrane-bound sac for transport and storage of substances.

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

• Lysosome: Contains digestive enzymes to break down waste and cellular debris.

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

• Vacuole:

  • Food Vacuole: Stores and digests food.

  • Central Vacuole (plants): Maintains cell pressure, stores nutrients and waste.

  • Contractile Vacuole (protists): Expels excess water.

• Mitochondria: Site of aerobic cellular respiration; produces ATP.

• Chloroplast: Site of photosynthesis in plants and algae.

Distinguishing Plant and Animal Cells

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

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

Prokaryotic Cellular Parts

• Plasma Membrane: Controls entry and exit of substances.

• Slime Layer (Capsule): Protective outer layer; helps evade immune system.

• Fimbriae: Hair-like projections for attachment to surfaces.

• Plasmid (DNA): Small, circular DNA molecules; often carry antibiotic resistance genes.

• Ribosomes: Protein synthesis.

• Cell Wall: Provides shape and protection.

• Flagellum: Movement.

• Cytoplasm: Site of metabolic activities.

• Nucleoid Region: Area where the main DNA is located (not membrane-bound).

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: No nucleus, no membrane-bound organelles, generally smaller, single circular DNA.

• Eukaryotic Cells: Have nucleus, membrane-bound organelles, generally larger, linear DNA in chromosomes.

Types of Cell Connections

• Anchoring Junctions: Fasten cells together into strong sheets (e.g., desmosomes in animal tissues).

• Gap Junctions: Channels that allow molecules to pass between animal cells.

• Tight Junctions: Seal neighboring cells together to prevent leakage of extracellular fluid.

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

Chapter 5: The Working Cell

Major Functions of the Cell Membrane

• Acts as a barrier, maintaining the internal environment of the cell.

• Regulates transport of substances in and out (selective permeability).

• Facilitates communication with other cells via receptors.

• Provides structural support and enables cell recognition.

Selective Permeability of the Cell Membrane

• Allows some substances to cross more easily than others.

• Small, nonpolar molecules (e.g., O2, CO2) pass freely; ions and large polar molecules require transport proteins.

Fluid Mosaic Model Components

• Phospholipids: Form a bilayer with hydrophilic heads facing outward and hydrophobic tails inward, creating a semi-permeable membrane.

• Transport Proteins: Facilitate movement of substances across the membrane (channels, carriers).

• Receptor Proteins: Bind signaling molecules and initiate cellular responses.

• Enzymes: Catalyze reactions at the membrane surface.

• Glycoproteins: Proteins with carbohydrate chains; involved in cell recognition.

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

Key Terms and Comparisons

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

• Diffusion vs. Osmosis:

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

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

• Solvent vs. Solute:

  • Solvent: Substance that dissolves the solute (e.g., water).

  • Solute: Substance dissolved in the solvent (e.g., salt).

• Passive Transport vs. Active Transport:

  • Passive Transport: No energy required; moves substances down their concentration gradient (e.g., diffusion, osmosis, facilitated diffusion).

  • Active Transport: Requires energy (ATP); moves substances against their concentration gradient.

• Simple Diffusion vs. Facilitated Diffusion:

  • Simple Diffusion: Direct movement through the lipid bilayer.

  • Facilitated Diffusion: Movement via transport proteins.

• Facilitated Diffusion vs. Active Transport:

  • Facilitated Diffusion: No energy required; down gradient.

  • Active Transport: Requires energy; against gradient.

• Exocytosis vs. Endocytosis:

  • Exocytosis: Export of materials via vesicles fusing with the membrane.

  • Endocytosis: Import of materials by engulfing them in vesicles.

• Phagocytosis, Pinocytosis, Receptor-Mediated Endocytosis:

  • Phagocytosis: "Cell eating"; engulfing large particles.

  • Pinocytosis: "Cell drinking"; engulfing fluids.

  • Receptor-Mediated Endocytosis: Specific uptake of molecules via receptor proteins.

• Carrier Proteins, Channel Proteins, Aquaporins:

  • Carrier Proteins: Change shape to move molecules across membrane.

  • Channel Proteins: Form pores for specific molecules/ions.

  • Aquaporins: Channel proteins specifically for water transport.

Effects of Tonicity on Cells

Chapter 6: How Cells Harvest Chemical Energy

Photosynthesis vs. Aerobic Cellular Respiration

• Photosynthesis Equation:

• Aerobic Cellular Respiration Equation:

• Reactants and Products:

  • Photosynthesis: Reactants – CO2, H2O, light; Products – Glucose, O2

  • Respiration: Reactants – Glucose, O2; Products – CO2, H2O, ATP

• Energy Flow: Photosynthesis stores energy in glucose; respiration releases energy from glucose.

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 powers cellular work such as muscle contraction, active transport, and biosynthesis.

Glycolysis

• Occurs in the cytoplasm.

• Breaks one glucose molecule into two pyruvate molecules.

• End products: 2 pyruvate, 2 ATP (net), 2 NADH.

Aerobic Cellular Respiration Steps

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

• Krebs Cycle (Citric Acid Cycle): Produces NADH, FADH2, ATP, and CO2.

• Electron Transport Chain (ETC): NADH and FADH2 donate electrons to the ETC in the inner mitochondrial membrane.

• Oxidative Phosphorylation (Chemiosmosis): Electron flow drives proton pumping, creating a gradient used by ATP synthase to generate ATP.

Role of O2 in Aerobic Respiration

• Oxygen acts as the final electron acceptor in the ETC, forming water.

• Without O2, the ETC stops, and ATP production is severely reduced.

Chapter 7: Photosynthesis: Using Light to Make Food

Autotrophs vs. Heterotrophs

• Autotrophs (Producers): Organisms that make their own food from inorganic substances (e.g., plants, algae).

• Heterotrophs (Consumers): Obtain food by consuming other organisms (e.g., animals, fungi).

Photosynthesis Equation

Chloroplast Structure and Function

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

• Thylakoid: Membranous sacs containing chlorophyll; site of light reactions.

• Granum: Stack of thylakoids.

Role of Chlorophyll

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

Light Reactions vs. Calvin Cycle

• Light Reactions: Capture solar energy and convert it to chemical energy (ATP, NADPH); release O2 as a byproduct.

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

Example:

During photosynthesis, plants use sunlight to convert water and carbon dioxide into glucose and oxygen, providing energy for themselves and other organisms in the ecosystem.

Additional info: This guide expands on the learning objectives by providing definitions, comparisons, and context for each topic, ensuring a comprehensive review for exam preparation.