Chapter 7 Terms Flashcards
Selective permeability
a property of biological membranes that allows them to regulate the passage of substances across them
amphipathic
having both a hydrophilic region and a hydrophobic region
fluid mosaic model
the currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospolipids
Integral proteins
a transmembrane protein with hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane and with hydrophilic regions in contact with the aqueous solution on one or both sides of the membrane (or lining the channel in the case of a channel protein)
Peripheral proteins
a protein loosely bound to the surface of a membrane or to part of an integral protein and not embedded in the lipid bilayer
Functions of membrane proteins
- Transport
- Enzymatic activity
- Signal transduction
- Cell-cell recognition
- Intercellular joining
- Attachment to the cytoskeleton and extracellular matrix (ECM)
Transport
a protein that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute; other transport proteins shuttle a substance from one side to the other by changing shape. Some of these proteins hydrolyze ATP as an energy source to actively pump substances across the membrane
Enzymatic activity
a protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution. In some cases, several enzymes in a membrane are organized as a team that carries out sequential steps o of a metabolic pathway
Signal Transduction
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 shape, allowing it to relay message to the inside of the cell, usually by binding to a cytoplasmic protein
Cell-cell recognition
Some glycoproteins serve as identification tags that are specifically recognized by membrane proteins of other cells. This type of cell-cell binding is usually short-lived compared to that shown.
Intercellular joining
Membrane proteins of adjacent cells may hook together in various kinds of junctions, such as gap junctions or tight junctions. This type of binding is more long-lasting.
Attachment to the cytoskeleton and extracellular matrix (ECM)
Microfilaments or other elements of the cytoskeleton may be noncovalently bound to membrane proteins, a function that helps maintain cell shape and stabilizes the location of certain membrane proteins. Proteins that can bind to ECM molecules can coordinate extracellular and intracellular changes.
Glycolipids
a lipid with one or more covalently attached carbohydrates
Glycoproteins
a protein with one or more covalently attached carbohydrates
Transport protein
A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.
Aquaporin
A channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis, the diffusion of free water across the membrane
Diffusion
A channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis, the diffusion of free water across the membrane
Concentration gradient
A region along which the density of a chemical substance increases or decreases.
Passive transport
The diffusion of a substance across a biological membrane with no expenditure of energy.
Osmosis
The diffusion of free water across a selectively permeable membrane
Tonicity
The ability of a solution surrounding a cell to cause that cell to gain or lose water.
Isotonic
Referring to a solution that, when surrounding a cell, causes no net movement of water into or out of the cell.
Hypertonic
Referring to a solution that, when surrounding a cell, will cause the cell to lose water.
Hypotonic
Referring to a solution that, when surrounding a cell, will cause the cell to take up water
Osmoregulation
Regulation of solute concentrations and water balance by a cell or organism.
Turgid
Swollen or distended, as in plant cells. (A walled cell becomes turgid if it has a lower water potential than its surroundings, resulting in entry of water.)
Flaccid
Limp. Lacking turgor (stiffness or firmness), as in a plant cell in surroundings where there is a tendency for water to leave the cell. (A walled cell becomes flaccid if it has a higher water potential than its surroundings, resulting in the loss of water.)
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
The passage of molecules or ions down their electrochemical gradient across a biological membrane with the assistance of specific transmembrane transport proteins, requiring no energy expenditure.
Ion channel
A transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient.
Gated channel
A transmembrane protein channel that opens or closes in response to a particular stimulus.
Active transport
The movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins and requiring an expenditure of energy.
Sodium-potassium pump
A transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell.
Membrane potential
The difference in electrical charge (voltage) across a cell’s plasma membrane due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.
Electrochemical gradient
The diffusion gradient of an ion, which is affected by both the concentration difference of an ion across a membrane (a chemical force) and the ion’s tendency to move relative to the membrane potential (an electrical force).
Electrogenic pump
An active transport protein that generates voltage across a membrane while pumping ions.
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, generating a membrane potential in the process.
Cotransport
The coupling of the “downhill” diffusion of one substance to the “uphill” transport of another against its own concentration gradient.
Exocytosis
The cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane.
Endocytosis
Cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane.
Ligand
A molecule that binds specifically to another molecule, usually a larger one.
Three types of endocytosis
- Phagocytosis
- Pinocytosis
- Receptor-mediated endocytosis
Phagocytosis
A type of endocytosis in which large particulate substances or small organisms are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells)
Pinocytosis
A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes
Receptor-mediated endocytosis
The movement of specific molecules into a cell by the inward budding of vesicles containing proteins with receptor sites specific to the molecules being taken on; enables a cell to acquire bulk quantities of specific substances
