Chapter 4: Organization of the Cell

Cell Theory:

  • All living things are composed of cells (unicellular or multicellular).

  • Cells are capable of growth and reproduction.

  • Cell size is limited due to surface area-to-volume ratio constraints (p. 75).

Basic Cell Features:

  1. Plasma Membrane – Phospholipid bilayer that encloses the cell.

  2. Organelles – Specialized structures within eukaryotic cells, enclosed by membranes.

Types of Cells:

  • Prokaryotic: No nucleus, no membrane-bound organelles (e.g., bacteria).

  • Eukaryotic: Contains a nucleus and membrane-bound organelles (e.g., plants, animals).

Genetic Material:

  • Both cell types have DNA.

  • In eukaryotic cells, DNA is in the nucleus.

Organelles and Their Functions (Table 4-1, pp. 90-91):

Nucleus: Large structure surrounded by double
membrane; contains nucleolus and chromosomes, Information in DNA is transcribed in RNA synthesis; specifies cell proteins
Nucleolus: Granular body within nucleus; consists of RNA and protein, Site of ribosomal RNA synthesis; ribosome subunit assembly
Chromosomes: Composed of chromatin, a complex of DNA and protein; condense during cell division, becoming visible as rodlike structures, Contain genes (units of hereditary information) that govern structure and activity of cell
Plasma membrane: Membrane boundary of cell Encloses cell contents; regulates movement of
materials in and out of cell; helps maintain cell shape; communicates with other cells (also present in prokaryotes)
Ribosomes: Granules composed of RNA and protein; some attached to ER, some free in cytosol Synthesize polypeptides in both prokaryotes and eukaryotes
Endoplasmic reticulum: (ER) Network of internal membranes extending through cytoplasm, Synthesizes lipids and modifies many proteins; origin of intracellular transport vesicles that carry proteins. Smooth; Lacks ribosomes on outer surface Lipid synthesis; drug detoxification; calcium ion storage. Rough; Ribosomes stud outer surface Manufactures proteins
Golgi complex: Stacks of flattened membrane sacs Modifies proteins; packages secreted proteins; sorts other proteins to vacuoles and other organelles
Lysosomes: Membranous sacs (in animals) Contain enzymes that break down ingested materials; break down damaged or unneeded organelles and proteins
Vacuoles: Membranous sacs (mostly in plants, fungi, algae) Store materials, wastes, water; maintain hydrostatic pressure
Peroxisomes: Membranous sacs containing a variety of enzymes, Site of many diverse metabolic reactions; e.g., break down fatty acids
Mitochondria: Sacs consisting of two membranes; inner membrane is folded to form cristae and encloses matrix, Site of most reactions of cellular respiration; transformation of energy originating from glucose or lipids into ATP energy
Plastids (e.g., chloroplasts): Double-membrane structure enclosing internal thylakoid membrane; chloroplasts, contain chlorophyll in thylakoid membrane. Chloroplasts are site of photosynthesis; chlorophyll captures light energy; ATP and other energy-rich compounds are produced and then used to convert CO2 to carbohydrate
Microtubules: Hollow tubes made of subunits of tubulin protein, Provide structural support; have role in cell and organelle movement and cell division; components of cilia, flagella, centrioles, basal bodies
Microfilaments: Solid, rodlike structures consisting of actin protein, Provide structural support; play role in cell and organelle movement and cell division
Intermediate filaments: Tough fibers made of protein, Help strengthen cytoskeleton; stabilize cell shape
Centrioles: Pair of hollow cylinders located near nucleus; each centriole consists of nine microtubule triplets (9 3 3 structure) Mitotic spindle forms between centrioles during animal cell division; may anchor and organize microtubule formation in animal cells; absent in most plant cells
Cilia: Relatively short projections extending from surface of cell; covered by plasma membrane; made of two central and nine pairs of peripheral microtubules (9 1 2 structure), Movement of some unicellular organisms; used to move materials on surface of some tissues; important in cell signaling
Flagella: Long projections made of two central and nine pairs of peripheral microtubules (9 1 2 structure); extend from surface of cell; covered by plasma membrane, Cell locomotion by sperm cells and some unicellular organisms

  1. Nucleus – Contains DNA (the blueprint of the cell).

  2. Mitochondria – Powerhouse of the cell, site of cellular respiration (found in both plant and animal cells).

  3. Chloroplasts – Site of photosynthesis (only in plants and algae).

  4. Endoplasmic Reticulum (ER) – Synthesis of lipids and proteins.

    • Rough ER: Has ribosomes, protein synthesis.

    • Smooth ER: No ribosomes, lipid synthesis.

  5. Golgi Complex – Modifies and packages proteins.

  6. Lysosomes/Peroxisomes – Contain enzymes for digestion and waste removal.

  7. Vacuoles – Store materials and help with water balance (mainly in plant cells).

Metabolism & Energy:

  • ATP = Energy currency of the cell.

  • Eukaryotic cells produce more ATP due to mitochondria.

Cytoskeleton (p. 98):

  1. Microtubules – Protein tubes made of tubulin for structure and organelle movement; also form cilia and flagella.

  2. Microfilaments – Rod-like actin fibers aiding in cell division and support.

  3. Centrioles – Help in chromosome movement during cell division.

  4. Cilia – Short, hair-like microtubule structures for movement (e.g., human respiratory tract cilia move mucus).

  5. Flagella – Longer, tail-like microtubules for propulsion (e.g., sperm cells).