Ch 5 review

Cell Structure and Function

Overview of Cell Types

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

• Prokaryotic cells: Lack a nucleus and membrane-bound organelles; examples include bacteria and archaea.

• Eukaryotic cells: Have a nucleus and various membrane-bound organelles; examples include plant, animal, fungal, and protist cells.

• Key difference: Eukaryotic cells are generally larger and more complex than prokaryotic cells.

• Cell size limitation: The size of a cell is limited by its volume-to-surface area ratio, which affects nutrient uptake and waste removal.

Organelles in Animal and Plant Cells

Organelles are specialized structures within cells that perform distinct functions.

• Animal cell organelles: Nucleus, mitochondria, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, peroxisomes, cytoskeleton.

• Unique plant cell organelles: Chloroplasts, central vacuole, cell wall.

• Endomembrane system: Includes the nuclear envelope, ER, Golgi apparatus, lysosomes, and vesicles.

Nucleus and Chromatin

The nucleus is the control center of the cell, containing genetic material and coordinating cellular activities.

• Main characteristics: Surrounded by a double membrane (nuclear envelope), contains nucleolus and chromatin.

• Nuclear lamina: A network of proteins providing structural support to the nucleus.

• Chromatin: DNA and associated proteins; condenses to form chromosomes during cell division.

• Nucleolus: Site of ribosomal RNA synthesis and ribosome assembly.

Endoplasmic Reticulum (ER)

The ER is a network of membranes involved in protein and lipid synthesis.

• Rough ER: Studded with ribosomes; synthesizes proteins for secretion or membrane insertion.

• Smooth ER: Lacks ribosomes; involved in lipid synthesis, detoxification, and calcium storage.

• Major functions: Protein and lipid synthesis, transport within the cell.

Golgi Apparatus

The Golgi apparatus modifies, sorts, and packages proteins and lipids for delivery to various destinations.

• Structure: Stacks of flattened membranous sacs (cisternae).

• Cis face: Receives vesicles from the ER.

• Trans face: Ships modified products to their destinations.

• Main function: Processing and packaging of macromolecules.

Lysosomes and Peroxisomes

Lysosomes and peroxisomes are involved in cellular digestion and detoxification.

• Lysosomes: Contain hydrolytic enzymes for breaking down macromolecules, old organelles, and pathogens.

• Enzymes in lysosomes: Proteases, nucleases, lipases, glycosidases.

• Peroxisomes: Break down fatty acids and detoxify harmful substances; contain catalase to decompose hydrogen peroxide.

Phagocytosis vs. Autophagy

Cells use different mechanisms to degrade materials.

• Phagocytosis: Engulfment of large particles or cells by the cell membrane.

• Autophagy: Degradation of the cell's own components via lysosomes.

• Main difference: Phagocytosis targets external material; autophagy targets internal components.

Mitochondria

Mitochondria are the powerhouses of the cell, generating ATP through cellular respiration.

• Structure: Double membrane, inner membrane folds (cristae), matrix, intermembrane space.

• Function: ATP production via oxidative phosphorylation.

• Tay-Sachs disease: Caused by a deficiency in a lysosomal enzyme, leading to accumulation of lipids in neurons.

Cytoskeleton

The cytoskeleton provides structural support, facilitates movement, and organizes cellular components.

• Main categories: Microtubules, microfilaments (actin filaments), intermediate filaments.

• Microtubules: Hollow tubes made of tubulin; involved in cell shape, transport, and division.

• Microfilaments: Thin filaments made of actin; involved in cell movement and shape.

• Intermediate filaments: Provide mechanical strength; made of various proteins (e.g., keratin).

• Motor proteins: Kinesin, dynein (move along microtubules); myosin (moves along actin).

Centrioles, Cilia, and Flagella

These structures are involved in cell movement and division.

• Centrioles: Cylindrical structures made of microtubules; organize spindle fibers during cell division.

• Cilia and flagella: Hair-like structures for movement; both have a "9+2" arrangement of microtubules.

• Similarity: Both are involved in movement; differ in length and number per cell.

Extracellular Matrix and Cell Junctions

The extracellular matrix (ECM) and cell junctions help cells interact and communicate.

• ECM components: Collagen, proteoglycans, fibronectin.

• Cell junctions: Tight junctions (seal cells), desmosomes (anchor cells), gap junctions (allow communication).

• Comparison: Tight junctions prevent leakage; desmosomes provide strength; gap junctions enable passage of ions and molecules.

Summary Table: Major Cell Organelles and Their Functions

Organelle	Main Function	Found in
Nucleus	Stores genetic material, controls cell activities	All eukaryotes
Rough ER	Protein synthesis	All eukaryotes
Smooth ER	Lipid synthesis, detoxification	All eukaryotes
Golgi apparatus	Modification and packaging of proteins/lipids	All eukaryotes
Lysosome	Digestion of macromolecules	Animal cells
Peroxisome	Breakdown of fatty acids, detoxification	All eukaryotes
Mitochondria	ATP production	All eukaryotes
Chloroplast	Photosynthesis	Plant cells

Key Equations

• Surface Area to Volume Ratio:

$\text{Surface Area to Volume Ratio} = \frac{\text{Surface Area}}{\text{Volume}}$

• ATP Production (Cellular Respiration):

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

Additional info:

• Some questions referenced specific diseases (e.g., Tay-Sachs) and cell junctions; brief academic context was added for completeness.

• Table entries and explanations were expanded for clarity and completeness.