Fluid Mosaic Model

Posits that the membrane contains many embedded structures (proteins) and is flexible (fluid), and that proteins move laterally along the membrane plane

Amphipathic

Containing a hydrophobic and hydrophilic portion

Phospholipid Movement

Laterally within the bilayer or Flip-flop transversely (rare) across the membrane

Membranes rich in unsaturated fatty acids

Are more fluid

Shorter fatty acid chains

Increase fluidity in cold environments.

How cholesterol affects membrane fluidity

At warm temperatures (such as 37°C), cholesterol restrains the movement of phospholipids; At cool temperatures, it maintains fluidity by preventing tight packing

Proteins

Determine most of the membrane's specific functions and contain hydrophobic and hydrophilic regions

Integral proteins

(intrinsic, transmembrane) are embedded into the cell membranes

Peripheral proteins

(extrinsic proteins) are attached to one side of the bilayer

Glycolipids and glycoproteins

Function in cell identification and signaling

Molecules that can pass through a cell membrane easily

Small and hydrophobic (nonpolar)

Molecules that require proteins

Ions and polar molecules

Permeable

Describes membranes through which substances can pass through

Semi (selectively) permeable

Describes membranes through which some molecules can pass and others cannot

Impermeable

Describes membranes through which no molecules can pass

Channel proteins

Allows molecules or ions through the membrane

Carrier Protein/Pumps

Hold onto the molecules and change shape in a way that shuttles it across the membrane

Ion channels

Channel proteins that transport ions; can be base on voltage or ligands

Aquaporins

Allows for water molecules to cross the membrane more efficiently

Passive transport

Movement across the cell membrane that does not require energy; includes: Diffusion (simple diffusion), Facilitated Diffusion, Osmosis

Active Transport

Movement across the cell membrane that does require energy (ATP) and includes: primary transport and secondary transport

Diffusion

The tendency for molecules to spread out evenly into the available space

Concentration gradient

The region along which the density of a chemical substance increases or decreases

Membrane potential

The voltage difference across a membrane

Electrochemical gradient

Driven by the diffusion of ions across a membrane determined by electrical and chemical forces

Facilitated Diffusion

Uses cell membrane protein channels to transport certain ions (Cl) and large molecules (sugars) from a high to low concentration

Osmosis

The diffusion of water through a selectively permeable membrane,

Tonicity

A measure of the osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane;

Hypotonic

When more water enters the cell than exits the cell causing cell to lyse (burst) or become turgid (plant cells)

Isotonic

When equal amounts of water enters and exits the cell; equilibrium, plant cells become flaccid

Hypertonic

When more water exits the cell than enters the cell causing cell to crenate (shrivel; animal cells) or plasmolyze (plant cells)

Osmoregulation

The control of solute concentrations and water balance

Electrogenic pump

A transport protein that generates voltage across a membrane to store energy

Primary Active Transport (Direct, Antiport)

Directly utilizes energy (ATP), to pump molecules across the membrane.

Secondary Active Transport (Indirect/Co-transport, Symport)

Uses the electrochemical gradient generated by primary active transport, rather than ATP, to move substances

Sodium-Potassium Pump

Moves 3 (Na+) ions out and 2 (K+) ions in, crucial for nerve cell function.

Proton pumps

Moves (H+) ions, common in plants and stomach acid production.

Phagocytosis

"Cell eating", engulf, ingest, and destroy large particles (bacteria, dead cells), wrapping it in a membrane to form a phagosome (vacuole), and digesting it via lysosomal fusion.

Pinocytosis

"Cell drinking", cells engulf extracellular fluids, dissolved solutes by folding inward to create a pocket (vesicle)

Receptor-Mediated Endocytosis

Enables a cell to take up large quantities of very specific substances by binding of ligands to receptors triggers vesicle formation (how cells take in cholesterol)

Pressure gradient

A passive process of moving material through a cell membrane from an area of higher pressure to an area of lower pressure.