ch 3

Reading Assignments: Critically read Chapter 3 and specifically focus on section 3.3 regarding Membrane Transport.
Terminology Master: Comprehend all terminology, especially terms highlighted in bold within the textbook.
Visual and Evaluative Study: Study all provided figures and answer the "Before You Go On" questions located at the end of each section.
Self-Assessment: Complete the end-of-chapter questions, specifically focusing on "Testing your recall 1."

Robert Hooke (1665): Observed cork (plant material) under a microscope and coined the term "cell."
Theodor Schwann (1800s): Concluded that all animals are composed of cells, contributing to the first major tenet of cell theory: All organisms are composed of cells.
Louis Pasteur (circa 1859): Conducted work with bacteria which disproved the idea of spontaneous generation (the belief that living things arise from nonliving matter).
Establishment of Biogenesis: By the end of the 19th century, the second major tenet was established: "Cells arise only from preexisting cells."

Fundamental Unit: All organisms are composed of cells.
Simplest Unit of Life: The cell is the simplest structural and functional unit of life.
Cellular Basis of Form and Function: An organism’s overall structure and functions are directly due to the collective activities of its individual cells.
Ancestry of Cells: Cells only arise from preexisting cells; therefore, all life traces its biological ancestry back to the same original cells.
Inherent Similarities: The cells of all species across biological domains share fundamental similarities in their basic chemistry and structure.

Definition of Resolution: The ability to reveal detail or distinguish between two separate points.
Naked Eye Resolution: The human eye can resolve details down to approximately $100\,\mu m$ .
Light Microscope (LM): - Resolution: Up to $200\,nm$ . - Visible Structures: Includes the surface membrane (plasma membrane), the nucleus, and the cytoplasm (including certain organelles).
Electron Microscope (EM): - Resolution: Reaches as fine as $1\,nm$ . - Visible Structures: Specifically used to view the cell ultrastructures within the cytoplasm.

Form Follows Function: Cell shape is intricately related to its specific physiological function. Common shapes include: 1. Squamous: Thin and flat. 2. Polygonal: Irregular angular shapes with four or more sides. 3. Cuboidal: Squarish or cube-shaped. 4. Columnar: Taller than they are wide, like columns. 5. Spheroid: Round to oval. 6. Discoid: Disc-shaped. 7. Stellate: Starlike with many projections. 8. Fusiform: Spindle-shaped; thick in middle and tapered at ends. 9. Fibrous: Thread-like.

Standard Human Cell Size: Most human cells range from $10\,\mu m$ to $15\,\mu m$ in diameter.
Extreme Cell Sizes: - Egg Cells: Represent very large cells at approximately $100\,\mu m$ in diameter (visible to the naked eye). - Muscle Cells: Can reach lengths of up to $30\,cm$ . - Nerve Cells: Can be elongated to lengths exceeding $1\,m$ .
Surface Area and Volume Relationship: - Small Cell: Possesses a high surface area-to-volume ratio, allowing efficient exchange of materials. - Large Cell: If a cell grows too large, it may have insufficient plasma membrane surface area to serve the metabolic needs of its significantly increased internal volume.

Plasma (Cell) Membrane: The outer boundary of the cell.
Cytoplasm: Also referred to as cytosol or Intracellular Fluid (ICF). It contains: - Organelles: Specialized structures performing specific tasks. - Cytoskeleton: The structural framework of the cell.
Extracellular Fluid (ECF): The fluid located outside of the cells.

Plasma Membrane: Defines cell boundaries.
Nucleus: Contains genetic material; enclosed by the Nuclear Envelope featuring Nuclear Pores.
Endoplasmic Reticulum (ER): - Rough ER: Studded with Ribosomes for protein synthesis. - Smooth ER: Involved in lipid synthesis and detoxification.
Golgi Complex: Processes and packages proteins into Golgi Vesicles or Secretory Vesicles.
Mitochondrion: The powerhouse of the cell producing ATP.
Lysosome: Contains digestive enzymes for waste processing.
Centrosome and Centrioles: Involved in cell division and microtubule organization.
Cytoskeletal Elements: Includes Microtubules, Microfilaments, and the Terminal Web.
Surface Extensions: Includes Microvilli for increasing surface area.
Inclusions: Such as Lipid Droplets free in the cytosol.
Cell Surfaces: Defined as Apical surface (top), Lateral surface (sides), and Basal surface (bottom, resting on the Basement Membrane).

Appearance: Often appears as a pair of dark parallel lines surrounding the cell with a total thickness of approximately $7.5\,nm$ .
Definition: The membrane defines the boundaries of the cell.
Key Functions: - Controls molecular and cellular interactions with neighboring cells. - Controls the passage of materials into and out of the cell (selective permeability).

Composition: Lipids constitute approximately $98\%$ of the molecules in the plasma membrane.
Phospholipid Bilayer ( $75\%$ of lipids): - Hydrophilic Heads: Located on each side of the membrane (facing ECF and ICF). - Hydrophobic Tails: Tucked away in the center of the bilayer.
Cholesterol ( $20\%$ of lipids): - Location: Interspersed between phospholipids. - Function: Affects the fluidity of the membrane (stiffens at higher temps, prevents freezing at lower temps).
Glycolipids ( $5\%$ of lipids): - Structure: Phospholipids with short carbohydrate chains attached. - Location: Found exclusively on the extracellular face. - Function: Help form the Glycocalyx, a fuzzy coat on the cell surface used for identification.

Relative Abundance: Proteins constitute only about $2\%$ of the total number of molecules in the plasma membrane, but they account for roughly $50\%$ of the membrane weight because they are much larger than lipids.
Integral (Transmembrane) Proteins: - Most are Glycoproteins. - They pass completely through the lipid bilayer. - They can drift freely in the "sea" of lipids or be anchored to the internal cytoskeleton.
Peripheral Proteins: - Location: Do not protrude into the phospholipid layer but typically adhere to either the extracellular or intracellular face. - Association: Often associated with integral proteins or the cytoskeleton.

(a) Receptor: A surface protein that binds to a chemical messenger (like a hormone) to trigger internal cell changes.
(b) Enzyme: Catalyzes chemical reactions, such as breaking down products at the cell surface.
(c) Ion Channel: A protein that is constantly open, allowing ions to pass in and out of the cell.
(d) Gated Ion Channel: A channel that opens and closes only at certain times (regulated by chemical or electrical signals) to allow ion flow.
(e) Cell-Identity Marker: A glycoprotein acting as a "tag" to distinguish the body's own cells from foreign cells.
(f) Cell-Adhesion Molecule (CAM): A protein that binds one cell to another cell or to extracellular material.