Biology 1001 - Section 3 (Membrane Structure and Function)

Cellular Membrane

the most important component of the cell, composed by Phospholids, other Lipids, Proteins and Carbohydrates,

Bulk Transport

The transport of large molecules.

Amphipathic Molecules

Molecules with both hydrophilic and hydrophobic parts.

Fluid Mosaic Model

The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of individually inserted protein molecules drifting laterally in a fluid bilayer of phospholipids.

Cholesterol

Regulates membrane fluidity by reducing phospholipid movement; hinders solidification at low temperatures.

Integral Proteins

Proteins that penetrate the lipid bilayer.

Transmembrane Proteins

Proteins that span the membrane with hydrophilic regions extending outwards.

Functions of membrane proteins

transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to the cytoskeleton and extracellular matrix.

Enzymatic Protein

A protein that accelerates/catalyzes a specific reaction.

Signal Transduction Protein

A membrane protein (receptor) may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone. The external messenger (signaling molecule) may cause the protein to change shape, allowing it to relay the message to the inside of the cell, usually by binding to a cytoplasmic protein.

Cell-cell recognition Protein

Proteins that serve as identification tags that are specifically recognized by membrane proteins in other cells. Binding is typically short-lived.

Intercellular Joining Proteins

Membrane proteins of adjacent cells may hook together in various kinds of junctions that is more long-lasting than cell to cell recognition.

Attachment to the cytoskeleton and extracellular matrix

Proteins that covalently bond to the cytoskeleton or ECM that help maintain protein cell shape and stabilize the locations of certain membrane proteins.

Peripheral Proteins

Proteins that are outside the lipid bilayer.

Membrane Carbohydrates

Binds with other molecules on the extracellular surface to sort into tissues and organs or direct the immune system, usually involving glycolipids and glycoproteins. Also serve as identification markers for cells.

Glycoproteins

Membrane carbohydrates that are covalently bonded to proteins.

Glycolipids

Membrane carbohydrates that are covalently bonded to lipids.

Cytoplasmic Membrane

A phospholipid bilayer embedded with proteins that surrounds the cytoplasm and defines the boundary of the cell

Extracellular Membrane

Nonliving portion consisting of molecules that fill spaces between cells, consisting mostly of protein fiber networks

Selectively Permeable

An emergent property of cell membranes that allows some substances to pass through, while others cannot.

Transport Proteins

A protein that allows hydrophilic ions and polar molecules to pass through the lipid bilayer.

Channel Proteins

Proteins that provide passageways through the membrane for certain hydrophilic (water-soluble) substances such as polar and charged molecules.

Carrier Proteins

Proteins that change shape to transport a molecule through the lipid bilayer; specific to the substance they transport.

Diffusion

The spontaneous movement of a substance down its concentration or electrochemical gradient, from a region where it is more concentrated to a region where it is less concentrated.

Concentration Gradient

The region where the density of a substance increases or decreases.

Passive Transport

The diffusion of a substance across a biological membrane with no expenditure of energy.

Osmosis

Diffusion of water through a selectively permeable membrane.

Tonicity

The ability of a solution surrounding a cell to cause that cell to gain or lose water.

Isotonic

Describes a solution whose solute concentration is equal to the solute concentration inside a cell; no net movement of water.

Hypertonic

A solution with a higher concentration, in which a cell loses water.

Hypotonic

A solution with a lower concentration, in which a cell gains water.

Osmoregulation

Regulation of solute concentrations and water balance by a cell or organism.

Plasmolysis

A phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall; occurs when the cell loses water to a hypertonic environment.

Facilitated Diffusion

Movement of specific molecules across cell membranes through protein channels.

Active Transport

Moving a solute against its concentration gradient; requires energy and carrier proteins.

Sodium-Potassium Pump

A carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell.

Membrane Potential

The voltage across a cell's plasma membrane due to unequal distribution of anions and cations.

Electrochemical Gradient

Both the concentration gradient and membrane potential drive the diffusion of ions across the membrane.

Electrogenic Pump

An active transport protein that generates voltage across a membrane.

Proton Pump

An active transport protein in a cell membrane that uses ATP to transport hydrogen ions out of a cell against their concentration gradient.

Co-transport

Coupling diffusion of one solute down its concentration gradient with transport of another against its concentration gradient, using a cotransporter carrier protein.

Vesicles

Liquid or cytoplasm enclosed by a lipid bilayer; used as a package molecule for transport.

Exocytosis

Process by which a cell releases large amounts of material by fusing vesicles containing them with the plasma membrane.

Endocytosis

A process in which a cell engulfs extracellular material through an inward folding of its plasma membrane, forming vesicles or vacuoles.

Phagocytosis

A type of endocytosis in which a cell engulfs "cell eating" a molecule or particle by extending pseudopodia around it; packages matter into a food vacuole.

Food Vacuole

A membranous sac formed by phagocytosis of microorganisms or particles to be used as food by the cell.

Pinocytosis

A type of endocytosis in which the cell ingests extracellular fluid into small vesicles formed by infoldings of the plasma membrane.

Receptor-Mediated Endocytosis

A special type of pinocytosis that allows the cell to acquire bulk quantities of specific substances by clustering receptor molecules to form a vesicle.

Cross section of the phospholipid bilayer.

Current model of an animal cell's plasma membrane.

Osmosis.

The water balance of living cells.

Passive and active transport review

Exploring endocytosis in animal cells.