Membrane Structure and Function

Vocabulary flashcards covering membrane structure, phospholipid properties, transport mechanisms, organelles, and chemiosmosis.

Membrane

Sheets of tightly packed fatty acids that serve as a divider to define cell edges and organelle boundaries, consisting of a double layer of lipids that separates the interior of the cell from the outside environment.

Phospholipid

The primary lipid of cell membranes consisting of a hydrophilic polar head (polar group, phosphate, and glycerol) and hydrophobic non-polar tails made of two fatty acid chains.

Plasma Membrane

A semipermeable phospholipid bilayer that arranges itself in a double layer in water, acting as a barrier and gatekeeper between the inside and outside of a cell.

Aquaporins

Small transmembrane proteins that allow water molecules to travel through and diffuse across the plasma membrane down a concentration gradient.

Peter Agre & Roderick MacKinnon

Recipients of the 2003 Nobel Prize in Chemistry for structural and mechanistic discoveries concerning water channels (aquaporins) and membrane ion channels.

Simple Diffusion

The passive movement of non-polar, hydrophobic, or small uncharged molecules (such as fats, pesticides, $O_2$, and $CO_2$) down a concentration gradient from higher to lower concentration without using energy.

Osmosis

The diffusion of a solvent (such as water or alcohol) across a selectively permeable membrane down its concentration gradient.

Channel Protein

A membrane transport protein that facilitates passive transport down an electrochemical gradient by forming pores that discriminate solutes by size and/or charge.

Nucleoporins

Pore proteins that form the nuclear pore complex within the nuclear envelope to regulate the flow of macromolecules between the nucleus and cytoplasm.

Facilitated Diffusion

Passive transport of large or insoluble molecules across a membrane down their concentration gradient via a carrier protein without using energy.

Active Transport

The movement of molecules across a membrane against their concentration gradient (from low concentration to high concentration) using membrane protein pumps and energy in the form of ATP.

Sodium-Potassium Pump

A membrane protein pump that binds intracellular sodium ($Na^+$) and undergoes a conformational change upon phosphorylation by ATP to export sodium from the cell.

Endocytosis

An active membrane budding process used by cells to import large volumes of materials or whole particles into the cell.

Phagocytosis

A specific form of endocytosis ('cell-eating') that uses ATP and pseudopods to entrap large solid particles, whole substances, or organisms into a food vacuole for digestion by lysosomes.

Pinocytosis

A non-specific form of endocytosis ('cell-drinking') where the plasma membrane invaginates to take in extracellular fluids and dissolved, already broken-down substances into vesicles.

Exocytosis

The reverse of endocytosis, utilizing ATP to transport substances out of the cell via vesicle fusion with the plasma membrane.

Nuclear Envelope

A double-membrane structure comprising inner and outer nuclear membranes that compartmentalizes nuclear functions for complex gene expression and energy-efficient protein transport.

Nucleolus

A specialized region within the nucleus that serves as the site of assembly for ribosome subunits.

Chemiosmosis

The movement of ions across a selectively permeable membrane down their electrochemical gradient to generate ATP via oxidative phosphorylation.

Mitochondrion Structure

A double-membrane organelle consisting of an outer membrane, an inner membrane folded into cristae, an intermembrane space, and an internal matrix.

Chloroplast Structure

A double-membrane organelle consisting of an outer membrane, an inner membrane, a fluid stroma, stacked thylakoid membranes called grana, and an internal lumen.

Chemiosmotic Coupling in Mitochondria

The flow of electrons through complexes I, II, III, and IV pumps hydrogen ions ($H^+$) from the matrix into the intermembrane space; their return diffusion through ATP synthase produces ATP.

Chemiosmotic Coupling in Chloroplasts

Light-driven electron transport through photosystems II and I pumps hydrogen ions ($H^+$) into the thylakoid lumen; their diffusion back into the stroma via ATP synthase drives ATP synthesis.