Cytology Part 1

Cell Membrane (Plasma Membrane)

The membrane surrounding the cell.

Fluid Mosaic Model

The model describing the structure of the cell membrane.

Passive Mechanisms

Do not require cellular energy.

Simple Diffusion

The passive process by which particles move from an area of high concentration to an area of lower concentration. Equilibrium.

Facilitated Diffusion

Diffusion through a channel protein (= channel mediated), which may involve a lipid-soluble carrier molecule (= carrier mediated).

Osmosis

The passive process by which solvent particles move through a semi permeable membrane to an area of greater solute concentration. Rate of osmosis increases as solute concentration increases.

Filtration

The passive process by which particles move into an area of lower pressure. Powered by hydrostatic (water) pressure.

Equilibrium

The state reached when particles become evenly distributed.

Kinetic Energy

The energy source used in simple diffusion, facilitated diffusion, and osmosis.

Hydrostatic Pressure

The pressure that powers filtration.

Simple Diffusion Example

Movement of O₂ through membrane.

Facilitated Diffusion Example

Movement of glucose into cells.

Osmosis Example

Movement of H₂O in & out of cells.

Filtration Example

Formation of kidney filtrate.

Isotonic

Solutions with the same solute concentration as that of the cytoplasm (= cytosol). No net change in cell.

Hypertonic

Solutions having greater solute concentration than that of the cytoplasm. Cell will shrink.

Hypotonic

Solutions having lesser solute concentration than that of the cytoplasm. Cell will swell.

Active Transport

Transport processes that use ATP.

ATP

The energy source used for active membrane transport.

Active Transport of Solutes

Movement of ions across membranes.

Primary Active Transport

Hydrolysis of ATP phosphorylates the transport protein causing conformational change.

Secondary Active Transport

Use of an exchange pump (such as the Na⁺-K⁺ pump) indirectly to drive the transport of other solutes.

Symport System

Two substances are moved across a membrane in the same direction.

Antiport System

Two substances are moved across a membrane in opposite directions.

Sodium-Potassium Pump

An example of primary active transport.

Vesicular Transport

Transport of large particles and macromolecules across plasma membranes.

Exocytosis

Moves substance from the cell interior to the extracellular space.

Endocytosis

Enables large particles and macromolecules to enter the cell.

Transcytosis

Moving substances into, across, and then out of a cell.

Vesicular Trafficking

Moving substances from one area in the cell to another.

Phagocytosis

Pseudopods engulf solids and bring them into the cell’s interior.

Fluid-Phase Endocytosis

The plasma membrane infolds, bringing extracellular fluid and solutes into the interior of the cell.

Receptor-Mediated Endocytosis

Clathrin-coated pits provide the main route for endocytosis and transcytosis.

Non-Clathrin-Coated Vesicles

Caveolae that are platforms for a variety of signaling molecules.

Three Types of Endocytosis

Phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Membrane Potential

Voltage across a membrane.

Resting Membrane Potential

The point where K⁺ potential is balanced by the membrane potential.

Range of Resting Membrane Potential

–20 to –200 mV.

Cause of Membrane Potential

Results from Na⁺ and K⁺ concentration gradients across the membrane.

Differential Permeability

Differential permeability of the plasma membrane to Na⁺ and K⁺.

Steady State

Potential maintained by active transport of ions.

Contact Signaling

Important in normal development and immunity.

Electrical Signaling

Voltage-regulated “ion gates” in nerve and muscle tissue.

Chemical Signaling

Neurotransmitters bind to chemically gated channel-linked receptors in nerve and muscle tissue.

G Protein-Linked Receptors

Ligands bind to a receptor which activates a G protein, causing the release of a second messenger, such as cyclic AMP.