Cell Membrane Structure and Transport: Key Concepts in Biology

Hydrophilic

A region that is polar and attracts water.

Hydrophobic

A region that is non-polar and repels water.

Phospholipid

A molecule consisting of two fatty acid tails and one phosphate group attached to a glycerol.

Phospholipid bilayer

A fluid membrane formed by the arrangement of phospholipids, constituting the cell membrane and organelle membranes.

Selectively permeable

A property of phospholipid bilayer membranes that allows certain molecules to pass while blocking others.

Small, nonpolar molecules

Molecules like oxygen and carbon dioxide that can pass easily through the membrane.

Small, polar molecules

Molecules that may pass through the membrane but often require assistance from proteins for efficiency, such as water.

Small, charged particles

Particles such as electrons and protons that cannot pass through the membrane without a specific protein.

Large particles

Particles that cannot pass through the membrane without the aid of a support protein.

Aquaporins

Integral membrane proteins that facilitate the passage of water through the cell membrane.

Osmosis

The movement of water from an area of high concentration of water to an area of low concentration of water.

Glycoproteins

Proteins that have carbohydrate groups attached to them, used for cell-to-cell recognition.

Cholesterol

A molecule that allows the membrane to be more fluid when colder and less fluid when warm.

Integral membrane proteins

Proteins that pass through the membrane, functioning like a piercing.

Peripheral membrane proteins

Proteins located on one surface of the membrane, which can attach to other cells.

Channel proteins

Proteins that facilitate the movement of particles from high to low concentration.

Pump proteins

Proteins that are involved in active transport across the membrane.

Facilitated diffusion

The process by which particles move from high to low concentration through a channel protein.

Active transport

The movement of molecules against their concentration gradient, requiring energy.

Kinetic energy

The energy that all particles possess, allowing for movement and diffusion.

Cell membrane

The boundary of a cell, composed of a phospholipid bilayer and proteins.

Fluid Mosaic Model

A representation of the cell membrane structure, including peripheral and integral proteins, glycoproteins, phospholipids, and cholesterol, indicating hydrophobic and hydrophilic regions.

Unsaturated Fatty Acids

Fatty acids in lipid bilayers that have lower melting points, contributing to membrane fluidity and flexibility at cell temperatures.

Saturated Fatty Acids

Fatty acids that have higher melting points, making membranes stronger at higher temperatures.

Lake Sturgeon Temperature Effect

When the temperature decreases from 16°C to 1°C, mono- and polyunsaturated fatty acids of phospholipids significantly increase while saturated fatty acids decrease.

Cholesterol in Membranes

A lipid in animal plasma membranes that disturbs the close packing of phospholipids, increasing membrane flexibility.

Cholesterol Modulation

Cholesterol stabilizes membrane fluidity at higher temperatures and prevents stiffening at lower temperatures.

Cholesterol and Fluidity

In mammals, cholesterol reduces fluidity and permeability to some solutes.

Cholesterol at Low Temperatures

At low temperatures, cholesterol maintains fluidity by forcing apart phospholipids.

Cholesterol at High Temperatures

At high temperatures, bonds between cholesterol and phospholipids maintain structural integrity and prevent the membrane from becoming too fluid.

Isotonic Solution

A solution where concentration is equal on both sides of the membrane, resulting in no net gain or loss of water and achieving dynamic equilibrium.

Hypertonic Solution

A solution outside the cell that is more concentrated than inside, causing water to move out of the cell and resulting in cell shrinkage.

Hypotonic Solution

A solution where concentration inside the cell is more concentrated than outside, causing water to move into the cell and resulting in cell swelling.

Red Blood Cells in Salt Solutions

Micrographs show changes in red blood cells placed in salt solutions of different concentrations.

Bulk Transport

Transport of materials by vesicles, a process known as cytosis, which requires ATP from metabolism.

Neurotransmitter Secretion

Neurotransmitters are secreted by cells using the fluidity of the membrane to fuse vesicles with the cell membrane.

Sodium-Potassium Pumps

An example of exchange transporters that help maintain cellular ion balance.

Gated Ion Channels

Voltage gated channels that open and close in response to changes in the cell's membrane potential.

Examples of Gated Ion Channels

Sodium channels and potassium channels that regulate ion flow across membranes.

Nicotinic Acetylcholine Receptor

A neurotransmitter gated ion channel that responds to acetylcholine.

Noncompetitive agonists (NCA)

Enhance the effect of the transmitter acetylcholine (Ach).

Local anesthetics (LA)

Reduce the effect of acetylcholine (Ach).

Sodium-dependent glucose cotransporters

An example of indirect active transport involving 2 Na+ for every glucose.

Cell Adhesion

The process by which cells adhere to each other to form tissues.

Tight junctions

Seal gaps between cells.

Adherin

Strengthen the adhesion between cells.

Gap junctions

Link the cytoplasm of adjacent cells.

Desmosome

Join cells by filaments.

Lipid Bilayers

Membrane barriers made of phospholipid molecules arranged in two sheets.

Plasma Membrane

The lipid bilayer membrane that surrounds all cells and regulates molecule entry and exit.

Integral Proteins

Proteins that span the membrane and are involved in transport and enzymatic activity.

Peripheral Proteins

Proteins that are attached to the exterior or interior surfaces of the membrane.

Aquaporin

An integral protein that acts as a pore in the membrane to speed the movement of water molecules.

Plasmodesmata

Structures specific to plants that link the cytoplasm between cells.