Chapter 7 Flashcards
Cellular Membrana is…
Selectively permeable
Amphipathic
Has both a hydrophilic and hydrophobic regions
Fluid mosaic model
The membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids
Evolution of Differences in Membrane Lipid Composition
Evolution led to differences in lipid composition (e.g. fish in icy-cold water have a high proportion of unsaturated hydrocarbon tails, enabling the membrane to stay fluid. Bacteria in extreme heats and their composition allows them to stay fluid in that heat. Some organisms can change their composition in places where temperatures vary)
Transmembrane Protein
Span the whole membrane
Integral Proteins
penetrate the bilayer but do not go all the way through
N-terminus
On the extracellular side of a transmembrane protein
C-terminus
On the cytoplasmic side of the transmembrane protein
Transport
Can consist of a transport channel protein or a protein that changes shape to move molecules across the membrane
Enzymatic activity
A protein in the membrane could be an enzyme with the active site exposed to the substances in the adjacent solution
Signal transduction
A membrane protein may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone which may cause the protein to change shape, allowing it to relay a message to the inside of the cell
Cell-cell recognition
some glycol-proteins serve as identification tags that are specifically recognized by membrane proteins of other cells (Shorter bonding)
Intercellular joining
membrane proteins of adjacent cells may hook together in various kinds of auctions (gap junctions or tight junctions) (Longer bonding)
Attachment to cytoskeleton and extracellular matrix (ECM)
Microfilaments or other elements of the cytoskeleton may be noncovalently bound to membrane proteins which helps maintain cell shape and stabilizes the location the location of certain membrane proteins. Proteins bound to ECM molecules can coordinate extracellular and intracellular changes
Peripheral Proteins
Proteins bound to the surface of the membrane
glycolipid
A membrane carbohydrate that is bound to a lipid
glycoprotein
A membrane carbohydrate that is bound to a protein
Synthesis and sidedness of membranes
Membranes have distinct inside and outside faces (the two lipid layers may differ in composition and each protein has directional orientation)
Selective permeability
The ability to allow some substances to cross the membrane more easily than others
Transport Proteins
allows the passage of hydrophilic substances through the membrane
aquaporins
Channels proteins that greatly facilitate the transport of water molecules
Carrier proteins
Bind to molecules and change their shape to get them across the membrane
Passive transport
Uses diffusion and requires no energy
diffusion
The movement of any substance so that they spread out into the available space
Concentration gradient
The region along which the density of a chemical substance increases or decreases
Osmosis
the diffusion of water across a selectively permeable membrane
Tonicity
the ability of a surrounding solution to cause a cell to gain or lose water.The tonicity of a solution depends on its concentration of solutes that cannot cross the membrane relative to that inside the cell
Isotonic
Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
Hypertonic
Solute concentration is greater than that inside the cell; the cell loses water
Hypotonic
Solute concentration is less than that inside the cell; the cell gains water
Osmoregulation
the control of solute concentrations and water balance
Facilitated diffusion
transport proteins speed the passive movement of molecules across the plasma membrane
Ion channels
channels that transport ions
Gated channels
open or close in response to a stimulus
Active transport
requires energy, usually in the form of ATP hydrolysis, to move substances against their concentration gradients
Sodium-potassium pump
an animal cell has a much higher potassium (K+) and a much lower sodium (Na+)concentration compared to its surroundings. This is controlled by the sodium-potassium pump, a transport protein that is energized by transfer of a phosphate group from the hydrolysis of ATP
Membrane potential
the voltage across a membrane (-50 to -200 millivolts (mV) and is negative relative to the outside). Voltage is created by differences in the distribution of positive and negative ions across a membrane. The cytoplasmic side of the membrane is negative in charge relative to the extracellular side
Electrochemical gradient
drive the diffusion of ions across a membrane (A chemical force [the ion’s concentration gradient] An electrical force [the effect of the membrane potential on the ion’s movement])
Proton pump
The main electrogenic pump of plants, fungi, and bacteria which actively transports hydrogen ions (H+) out of the cell
Cotransport
occurs when active transport of a solute indirectly drives transport of other substances
Exocytosis
When the cell secretes certain molecules by the fusion of vesicles with the plasma membrane
Endocytosis
The cell takes. in molecules and particulate matter by forming new vesicles form the plasma membrane
Phagocytosis
A cell engulfs a particle by extending pseudopodia around it and packaging it within a membranous sac called a food vacuole. The particle will be digested when the vacuole fuses with a lysosome containing hydrolytic enzymes
Pinocytosis
A cell continually “gulps” droplets of extracellular fluid into. tiny vesicles, formed by infolding of the plasma membrane. The cell obtains to molecules dissolved in the droplets. Nonspecific for the substances it transports
Receptor-mediated cytosis
A specialized type of pinocytosis that enables the cell to acquire bulk quantities of specific substances. Proteins with receptor sites in the membrane react when specific solutes bind to the receptors. The receptor proteins then cluster into coated pits and form vesicles containing the bound solute
