Topic 1: Cell Structure and Function

Subcellular Components and Their Functions

Cells contain various subcellular components, each with specialized functions that contribute to the overall operation and survival of the cell.

• Ribosomes: Organelles responsible for protein synthesis. Found in both prokaryotic and eukaryotic cells.

• Endoplasmic Reticulum (ER): Network of membranes involved in protein and lipid synthesis. Rough ER has ribosomes attached and synthesizes proteins; Smooth ER lacks ribosomes and synthesizes lipids.

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

• Mitochondria: Site of cellular respiration and ATP production in eukaryotes.

• Chloroplasts: Organelles found in plant cells and some protists; site of photosynthesis.

• Lysosomes: Contain digestive enzymes for breaking down macromolecules.

• Vacuoles: Storage organelles; large central vacuole in plant cells maintains turgor pressure.

• Plasma Membrane: Selectively permeable barrier that regulates the movement of substances in and out of the cell.

Example: The mitochondrion is often called the "powerhouse" of the cell because it generates ATP through cellular respiration.

Cell Types and Structures

Cells are classified as prokaryotic or eukaryotic based on their structural features.

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles. Example: Escherichia coli.

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles. Example: animal and plant cells.

Additional info: Plant cells contain chloroplasts and a cell wall, which are absent in animal cells.

Vocabulary Table: Cell Structure

Topic 2: Membrane Structure

Phospholipid Bilayer and Fluid Mosaic Model

The plasma membrane is primarily composed of a phospholipid bilayer with embedded proteins, carbohydrates, and cholesterol, forming the fluid mosaic model.

• Phospholipids: Amphipathic molecules with hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.

• Embedded Proteins: Can be hydrophilic (interact with aqueous environment) or hydrophobic (interact with lipid core).

• Carbohydrates: Attached to proteins or lipids, function in cell recognition.

• Cholesterol: Modulates membrane fluidity and stability.

Example: Glycoproteins on the cell surface are important for cell-cell recognition.

Vocabulary Table: Membrane Structure

Topic 4: Membrane Permeability

Selective Permeability and Cell Function

The plasma membrane's selective permeability regulates the internal environment of the cell by controlling the movement of substances.

• Selective Permeability: Allows some molecules to pass while restricting others.

• Transport Proteins: Facilitate movement of ions and large molecules across the membrane.

• Cell Wall: Found in plants, fungi, and some bacteria; provides structural support and protection.

Example: Aquaporins are channel proteins that facilitate water transport across the membrane.

Topic 6: Facilitated Diffusion

Transport Mechanisms Across Membranes

Facilitated diffusion is a passive transport process where molecules move across the membrane via specific carrier or channel proteins, without energy input.

• Carrier Proteins: Bind and transport specific molecules.

• Channel Proteins: Form pores for molecules to pass through.

• Aquaporins: Specialized channels for water transport.

Equation:

Topic 8: Mechanisms of Transport

Active and Passive Transport

Cells use both active and passive transport mechanisms to move ions and molecules across membranes.

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

• Passive Transport: Includes diffusion, osmosis, and facilitated diffusion; does not require energy.

Equation: \text{ATPase:} \ 3\text{Na}^+ \text{out}, \ 2\text{K}^+ \text{in}$

Topic 10: Origin of Cell Compartmentalization

Prokaryotic vs. Eukaryotic Compartmentalization

Compartmentalization allows eukaryotic cells to carry out specialized functions in distinct regions, unlike prokaryotic cells.

• Endosymbiotic Theory: Suggests mitochondria and chloroplasts originated from free-living prokaryotes engulfed by ancestral eukaryotic cells.

• Internal Membranes: Partition the cell into specialized regions for different functions.

Example: Mitochondria have their own DNA and double membrane, supporting the endosymbiotic theory.

Additional Info: Surface Area to Volume Ratio

Importance in Cell Function

The surface area to volume (SA:V) ratio affects the efficiency of material exchange across the plasma membrane.

• Smaller cells have a higher SA:V ratio, allowing for more efficient exchange of nutrients and waste.

• As cells grow larger, the SA:V ratio decreases, limiting exchange efficiency.

Equation:

Summary Table: Cell Types and Features