Chapter 4: Cell Structure

Overview of Cell Types

Cells are the basic units of life, and they can be classified as prokaryotic or eukaryotic. Understanding their differences and similarities is fundamental in biology.

• Prokaryotic cells: Simple cells without a nucleus or membrane-bound organelles. Example: Bacteria.

• Eukaryotic cells: Complex cells with a nucleus and various organelles. Example: Animal and plant cells.

• Common features: Both types have plasma membranes, cytoplasm, ribosomes, and genetic material.

Key Cell Structures and Organelles

Each organelle within a cell has a specific function that contributes to the cell's overall operation.

• Nucleus: Contains genetic material (DNA) and controls cell activities.

• Chromosomes: Structures within the nucleus made of DNA and proteins.

• Ribosomes: Sites of protein synthesis; found free in cytosol or attached to the endoplasmic reticulum.

• Endoplasmic Reticulum (ER): Network for protein and lipid synthesis. Rough ER has ribosomes; smooth ER does not.

• Golgi apparatus: Modifies, sorts, and packages proteins and lipids for secretion or use within the cell.

• Lysosomes: Contain digestive enzymes to break down waste.

• Mitochondria: Powerhouse of the cell; site of cellular respiration and ATP production.

• Chloroplasts: Found in plant cells; site of photosynthesis.

• Cell wall: Provides structure and protection (plants, fungi, bacteria).

• Plasma membrane: Semi-permeable barrier controlling entry and exit of substances.

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

• Flagella and cilia: Structures for cell movement.

• Plasmodesmata: Channels between plant cells for communication.

Surface Area-to-Volume Ratio

The surface area-to-volume ratio affects the efficiency of diffusion and transport within cells.

• Smaller cells have a higher ratio, allowing for more efficient exchange of materials.

• As cells grow larger, the ratio decreases, limiting transport efficiency.

Formula:

Comparison Table: Prokaryotic vs. Eukaryotic Cells

Chapter 5: Membrane Transport

Structure and Properties of Cell Membranes

The plasma membrane is a selectively permeable barrier composed of a phospholipid bilayer with embedded proteins.

• Fluid mosaic model: Describes the dynamic nature of the membrane.

• Phospholipids: Form the bilayer; hydrophilic heads face outward, hydrophobic tails face inward.

• Marker proteins (glycoproteins): Involved in cell recognition.

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

Types of Membrane Transport

Cells use various mechanisms to move substances across membranes, depending on the properties of the molecules and the cell's needs.

• Passive transport: Movement without energy input; includes diffusion, osmosis, and facilitated diffusion.

• Active transport: Requires energy (ATP) to move substances against their concentration gradient.

• Endocytosis and exocytosis: Bulk transport mechanisms for large molecules or particles.

Key Terms and Concepts

• Selective permeability: Only certain substances can cross the membrane.

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

• Osmosis: Diffusion of water across a membrane.

• Isotonic, hypotonic, hypertonic: Terms describing relative solute concentrations and water movement.

• Facilitated diffusion: Passive transport via membrane proteins.

• Membrane potential: Electrical potential difference across the membrane.

• Aquaporins: Channel proteins for water transport.

Membrane Transport Table

Surface Area-to-Volume Ratio and Diffusion Efficiency

Cell shape affects the efficiency of diffusion. Higher surface area-to-volume ratios support more efficient exchange of materials.

Applications and Examples

Cell Specialization and Organelle Abundance

Different cell types require different organelles in varying quantities to perform specialized functions.

• Cardiac muscle cell: Needs many mitochondria for energy.

• Liver cell: Requires abundant lysosomes for detoxification.

• Glandular cell: Has extensive rough ER and Golgi for hormone production.

• Adipose cell: Contains many lipid droplets for energy storage.

• Muscle cell: Rich in structural proteins and mitochondria.

• Skin cell: Divides rapidly, needs many ribosomes and ER.

Membrane Adaptations for Transport

Cells adapt their membrane structure to facilitate specific transport functions.

• Microvilli: Increase surface area for absorption.

• Transport proteins: Enable active transport of nutrients.

• Enzyme synthesis: Ribosomes and ER are abundant in cells producing enzymes.

Antibiotics and Cell Structure

Antibiotics target specific cell structures, such as the cell wall or ribosomes, to inhibit bacterial growth.

• Vancomycin: Acts on bacterial cell walls; does not affect human cells (which lack cell walls).

• Tetracycline: Inhibits bacterial ribosomes, preventing protein synthesis.

Life Cycle of a Fly: Cellular Changes

During metamorphosis, cells undergo changes in organelle abundance to support tissue breakdown and rebuilding.

• Lysosomes: Increase in number to digest old tissues.

• Other organelles: ER and ribosomes may increase for new tissue synthesis.

Hormone Transport Across Membranes

Hydrophobic hormones like estrogens diffuse across the plasma membrane due to its lipid nature.

• Plasma membrane: Composed of phospholipids, allowing nonpolar molecules to pass.

• Diffusion: Passive movement down concentration gradient.

Active vs. Facilitated Transport

Active transport requires energy to move substances against their gradient, while facilitated diffusion does not.

• Active transport: Example: Proton pump inhibitors reduce stomach acid by blocking H+ transport.

• Facilitated diffusion: Example: Glucose transport via carrier proteins.

Key Equations and Calculations

• Surface Area of a Sphere:

• Volume of a Sphere:

• Surface Area-to-Volume Ratio:

Summary Table: Organelle Functions

Additional info:

• Some context and explanations have been expanded for clarity and completeness.

• Tables and diagrams have been recreated and summarized for study purposes.