Cellular Membrane Structure and Function

Comprehensive vocabulary flashcards covering the fluid mosaic model, cell membrane components, cellular signaling, and mechanisms of substance transport.

Phospholipid Bilayer

The basic structural framework of the cellular membrane, approximately $7\,nm$ wide, formed by amphipathic molecules containing hydrophilic heads and hydrophobic tails.

Hydrophilic heads

Polar and phosphate-containing portions of phospholipids that face the aqueous environment inside and outside the cell.

Hydrophobic tails

Non-polar fatty acid chains that point inward, creating a core that acts as a barrier to water-soluble substances.

Cholesterol

A short, hydrophobic molecule found between phospholipid tails in animal cells that regulates fluidity, provides mechanical stability, and reduces permeability to ions.

Intrinsic (Integral) proteins

Proteins embedded in the membrane, many of which are transmembrane proteins (spanning the entire bilayer) like channel and carrier proteins.

Extrinsic (Peripheral) proteins

Proteins located on the inner or outer surface of the phospholipid bilayer.

Glycolipids

Lipids with branching carbohydrate chains attached that act as cell surface markers for cell-to-cell recognition.

Glycoproteins

Proteins with branching carbohydrate chains attached that function as receptors for hormones and neurotransmitters or as antigens.

Polyunsaturated fatty acids

Fatty acids with many double bonds that prevent tight packing of tails, increasing membrane fluidity.

Saturated fatty acids

Fatty acids with no double bonds and straight tails that pack tightly, decreasing membrane fluidity.

Glycocalyx

The collection of short carbohydrate chains on the outer surface of the membrane that help stabilize the structure by forming hydrogen bonds with water.

Cell signalling

The process of coordinating cellular activities by sending and receiving messages through a pathway of stimulus, receptor, transmission, target, and response.

Signal Transduction

The process of converting an original signal into a message that can be transmitted inside the cell.

Signaling Cascade

A chain of events where a signal is amplified at each stage, often involving G-proteins and second messengers, resulting in a cellular response.

Ligand

A signaling molecule that binds specifically to a receptor.

G-Protein

A protein that binds to $GTP$ (similar to $ATP$ but with guanine) and triggers the release of second messengers during cell signaling.

Simple Diffusion

The net movement of molecules like $O_2$ and $CO_2$ directly through the bilayer down a concentration gradient without energy expenditure.

Facilitated Diffusion

The passive movement of polar or large molecules across a membrane through specific channel or carrier proteins.

Channel Proteins

Water-filled pores that allow charged substances like ions to pass; many are "gated" and open or close in response to stimuli.

Carrier Proteins

Proteins that have a binding site and "flip" between two shapes to move specific molecules across the membrane.

Active Transport

The movement of ions or molecules through carrier proteins against their concentration gradient, requiring energy in the form of $ATP$.

Sodium-Potassium Pump

A carrier protein that uses $ATP$ to move $3\,Na^+$ out of the cell and $2\,K^+$ into the cell, maintaining a potential difference.

Osmosis

The net movement of water molecules from a region of high water potential to a region of low water potential through a partially permeable membrane.

Water Potential ($\psi$)

The tendency of water to move out of a solution; pure water has a value of $0$, and adding solutes makes it negative.

Solute Potential ($\psi_s$)

The effect of solutes on water potential, which is always a negative value.

Pressure Potential ($\psi_p$)

The pressure exerted by the cell wall on the cell contents; it is usually positive.

Turgid

The state of a plant cell in pure water where water enters until the protoplast pushes against the cell wall, creating pressure potential.

Plasmolysis

The process in concentrated solutions where water leaves the plant cell and the protoplast shrinks away from the cell wall.

Incipient plasmolysis

The specific point during the shrinking of a plant cell's protoplast at which the pressure potential ($\psi_p$) becomes $0$.