BI102 General Cell Biology Study Notes

Structure of Phospholipids:
- Composed of two fatty acid tails (hydrophobic) and a phosphate group (hydrophilic) attached to glycerol.
- Essential for forming the lipid bilayer of cell membranes.
Function of Phospholipids:
- In water, phospholipids self-assemble into bilayers, with hydrophobic tails inward and hydrophilic heads outward.
- Critical for the existence of cells, serving as a barrier that regulates entry and exit of substances.
Characterization of Steroids:
- Steroids have a carbon skeleton made of four fused rings.
Functions of Cholesterol:
- Component of animal cell membranes and precursor for other steroids.
- High cholesterol levels may raise cardiovascular disease risk.

Plasma Membrane Composition:
- Separates cell from surroundings, made of lipids (mainly phospholipids), proteins, and carbohydrates.
Phospholipid Bilayer Formation:
- Composed of two layers of phospholipids with tails facing inward.
- Provides a semi-permeable barrier.
Features of the Plasma Membrane:
- Hydrophobic Interior: Tails repel water.
- Hydrophilic Surfaces: Heads interact with water.
- Cholesterol: Helps maintain fluidity of the membrane under different temperatures.
- Proteins: Facilitate membrane functions (e.g., transport proteins, enzymes).
- Glycolipids and Glycoproteins: Cell recognition and signaling.

Transport Proteins:
- Allow passage of hydrophilic substances; include channel and carrier proteins.
Enzymatic Activity:
- Enzymes catalyze reactions and increase rates of metabolic processes.
Signal Transduction:
- Process where cells respond to external signals through reception, transduction, and response.
Cell-Cell Recognition:
- Allows cells to identify each other; vital for immune response and tissue development.
Intercellular Joining:
- Facilitates adhesion and communication between adjacent cells.
Attachment to Cytoskeleton and ECM:
- Integrins connect cytoskeleton to ECM, supporting tissue integrity.

Sidedness of Membranes:
- Membranes have distinct inner and outer faces; asymmetric distribution established during synthesis.
Selective Permeability:
- Nonpolar molecules pass easily; polar molecules need transport proteins.

Passive Diffusion:
- Movement across membranes without energy input.
Facilitated Diffusion:
- Requires transport proteins to assist molecules across membranes.
Osmosis:
- Movement of water across a selectively permeable membrane.
Active Transport:
- Moves substances against concentration gradient; ATP-dependent. Example: Sodium-potassium pump.

Isotonic:
- Solute concentration is equal inside and outside the cell.
Hypertonic:
- Higher solute concentration outside the cell; causes cell to lose water.
Hypotonic:
- Lower solute concentration outside the cell; causes cell to gain water.

Definition:
- Voltage difference across a membrane due to ion distribution.
Electrogenic Pumps:
- Generate voltage (e.g., Na+-K+ pump) and store energy for cellular work.
Cotransport:
- Active solute transport indirectly drives the transport of other substances.

Exocytosis:
- Vesicles release contents outside the cell.
Endocytosis:
- Cells take in macromolecules through vesicle formation.
Types of Endocytosis:
- Phagocytosis: Cellular 'eating.'
- Pinocytosis: Cellular 'drinking.'
- Receptor-Mediated Endocytosis: Specific uptake triggered by binding to cell-surface receptors.

Types of Cells: Prokaryotic (no nucleus) and eukaryotic (nucleus).
Common Features: Plasma membrane, cytoplasm, ribosomes, chromosomes.
Prokaryotic Features: Nucleoid region contains DNA; lack membrane-bound organelles.
Eukaryotic Features: DNA in nucleus surrounded by a nuclear envelope; have organelles.
Organelle Functions:
- Nucleus: Houses genetic material; site of ribosomal RNA synthesis (nucleolus).
- Ribosomes: Sites of protein synthesis, found free or bound to ER.
- Rough ER: Assembles proteins; involved in glycoprotein synthesis.
- Smooth ER: Synthesizes lipids, detoxifies drugs, stores calcium ions.
- Golgi Apparatus: Modifies, sorts, packages proteins and lipids.
- Lysosomes: Digest macromolecules; operate in acidic environments.
- Mitochondria: Powerhouse of the cell, generating ATP via respiration.
- Chloroplasts: Sites of photosynthesis in plants; contain chlorophyll.
- Vacuoles: Storage and transport within cells (food vacuoles, contractile vacuoles, central vacuoles).
- Peroxisomes: Involved in lipid metabolism; contain enzymes that break down various compounds.

Components: A network of fibers (microtubules, microfilaments, intermediate filaments) maintaining cell shape and structure.
Motor Proteins: Facilitate movement within the cell using the cytoskeleton.
Microtubules: Guide organelle movements, separate chromosomes during division.
Microfilaments: Involved in muscle contraction, cell motility, and streaming in plants.
Intermediate Filaments: Support cell shape and anchor organelles.

Definition: The sum of all chemical reactions in an organism.
Metabolic Pathways:
- Catabolism: Breakdown of molecules, releasing energy.
- Anabolism: Build complex molecules, requiring energy.
Forms of Energy:
- Kinetic, potential, chemical energy, and heat.
Energy Conversions: Transformations between different energy forms.
Thermodynamics: Study of energy transformations.
- First Law: Energy cannot be created/destroyed.
- Second Law: Energy transformations increase entropy.

Exergonic Reactions: Release free energy; spontaneous.
Endergonic Reactions: Absorb free energy; nonspontaneous.
ATP Structure: Composed of ribose, adenine, and three phosphate groups.
ATP Regeneration: Powers cellular work through hydrolysis.
Factors Affecting Enzyme Function: Operating conditions (temperature, pH) and presence of inhibitors/regulators.
- Enzyme Inhibition: Competitive (competes with substrate) and non-competitive (binds elsewhere).

The end product inhibits the pathway, conserving resources and preventing overproduction.