Ch 4: Cell Structure & Function

Cell Theory and Cell Types

The cell theory is a fundamental concept in biology that describes the properties and significance of cells in living organisms.

• Main Points of Cell Theory: All living things are composed of cells; the cell is the basic unit of life; all cells arise from pre-existing cells.

• Surface Area to Volume Ratio: This ratio affects the efficiency of material exchange in cells. Smaller cells have a higher ratio, allowing for more efficient transport.

• Prokaryotic vs. Eukaryotic Cells: Prokaryotic cells lack a nucleus and membrane-bound organelles; eukaryotic cells have both.

• Domain Bacteria: One of the three domains of life, consisting of prokaryotic microorganisms.

• Domain Archaea: Prokaryotes distinct from bacteria, often found in extreme environments.

• Major Differences: Prokaryotes have no nucleus, circular DNA, and simple structure; eukaryotes have a nucleus, linear DNA, and complex organelles.

Cell Structure and Organelles

Cells contain various structures and organelles that perform specialized functions necessary for life.

• Bacterial Cell Envelope: Consists of the plasma membrane, cell wall, and sometimes a capsule.

• Nucleoid: Region in prokaryotes where DNA is located.

• Ribosomes: Organelles responsible for protein synthesis.

• Plasmids: Small, circular DNA molecules in bacteria.

• Thylakoids: Membranous structures in cyanobacteria and chloroplasts for photosynthesis.

• Flagella and Fimbriae: Structures for movement and attachment in cells.

• Cell Wall: Provides structure and protection; found in plants, fungi, and bacteria.

• Cytoplasm: Gel-like substance inside the cell where organelles are suspended.

• Chromosome: DNA molecule containing genetic information.

• Nucleus: Organelle in eukaryotes that houses DNA.

• Nuclear Envelope: Double membrane surrounding the nucleus.

• Chromatin: DNA and protein complex in the nucleus.

• Endomembrane System: Includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, and vesicles.

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

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Vesicles: Small membrane-bound sacs for transport.

• Lysosomes: Organelles containing digestive enzymes.

• Peroxisomes: Organelles that break down fatty acids and detoxify harmful substances.

• Vacuole: Storage organelle, especially large in plant cells.

• Chloroplasts: Organelles for photosynthesis in plants and algae.

• Stroma: Fluid inside chloroplasts where the Calvin cycle occurs.

• Mitochondria: Organelles that produce ATP through cellular respiration.

• Cytoskeleton: Network of protein filaments for cell shape, movement, and division.

Ch 5 & 6: Cell Membrane

Structure and Function of Plasma Membrane

The plasma membrane is a selectively permeable barrier that regulates the movement of substances into and out of the cell.

• Fluid-Mosaic Model: Describes the membrane as a mosaic of proteins floating in or on the fluid lipid bilayer.

• Main Components: Phospholipids, proteins, cholesterol, and carbohydrates.

• Semi-permeable: Allows certain molecules to pass while restricting others.

• Cholesterol: Maintains membrane fluidity and stability.

• Integral and Peripheral Proteins: Integral proteins span the membrane; peripheral proteins are attached to the surface.

• Glycoproteins: Proteins with carbohydrate chains, important for cell recognition.

• Cell Junctions: Structures that connect cells (tight junctions, gap junctions, desmosomes).

Transport Across Membranes

Cells use various mechanisms to transport substances across their membranes.

• 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 membrane.

• Channel Proteins: Facilitate passive transport of molecules.

• Carrier Proteins: Bind and transport specific molecules.

• Active Transport: Movement against a concentration gradient using energy (ATP).

• Vesicle-Mediated Transport: Includes endocytosis (phagocytosis, pinocytosis, receptor-mediated) and exocytosis.

• Isotonic, Hypotonic, Hypertonic: Terms describing relative solute concentrations and their effects on cells.

• Cytolysis: Cell bursting due to excess water intake.

• Plasmolysis: Shrinking of cell membrane away from cell wall due to water loss.

Ch 7: Metabolism

Forms of Energy

Energy is the capacity to do work, and it exists in various forms relevant to biological systems.

• Kinetic Energy: Energy of motion (e.g., movement of molecules).

• Potential Energy: Stored energy (e.g., chemical bonds).

• Chemical Energy: Energy stored in chemical bonds.

• Electrical, Mechanical, Thermal, Electromagnetic Energy: Other forms relevant to biological processes.

Thermodynamics in Biology

Thermodynamics describes the principles governing energy transformations in living systems.

• 1st Law: Energy cannot be created or destroyed, only transformed.

• 2nd Law: Entropy (disorder) increases in closed systems.

• 3rd Law: As temperature approaches absolute zero, entropy approaches a minimum.

• Entropy: Measure of disorder or randomness.

• Ultimate Source of Energy: The sun provides energy for most life on Earth.

Metabolism and Enzymes

Metabolism encompasses all chemical reactions in a cell, including anabolic (building) and catabolic (breaking down) pathways. Enzymes are biological catalysts that speed up reactions.

• Metabolic Pathways: Series of chemical reactions in a cell.

• Anabolic Reactions: Build complex molecules from simpler ones.

• Catabolic Reactions: Break down complex molecules into simpler ones.

• Reactants and Products: Substances consumed and produced in reactions.

• Endergonic vs. Exergonic Reactions: Endergonic require energy input; exergonic release energy.

• Activation Energy: Minimum energy required to start a reaction.

• Enzyme Structure: Enzymes have an active site where substrates bind. Some enzymes require cofactors (non-protein helpers) or coenzymes (organic molecules).

• Enzyme Inhibition: Competitive inhibitors bind the active site; noncompetitive inhibitors bind elsewhere. Irreversible inhibitors permanently inactivate enzymes.

ATP and Redox Reactions

ATP is the primary energy currency in cells, and redox reactions are essential for energy transfer.

• ATP Structure: Composed of adenine, ribose, and three phosphate groups.

• ATP Cycle: ATP is hydrolyzed to ADP and inorganic phosphate, releasing energy; ADP is recharged to ATP.

• Functions of ATP: Powers cellular work such as muscle contraction, active transport, and biosynthesis.

• Redox Reactions: Involve transfer of electrons; oxidation is loss of electrons, reduction is gain of electrons.

• REDOX Carriers: Molecules like NAD+ and FAD that transport electrons and protons during metabolic reactions.

Additional info:

• Some questions reference specific examples (e.g., types of energy, enzyme inhibition) that can be expanded with textbook examples such as glucose metabolism, sodium-potassium pump, and competitive inhibitors like penicillin.

• Equations for energy transformations and ATP hydrolysis:

  • (Gibbs free energy equation)