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Biology; Chapter Five

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phospholipid bilayer
the framework of the plasma membrane; consists of two layers of phospholipids
amphipathic
adjective describing molecules with a hydrophobic and hydrophilic region
fluid-mosaic model
name for the depiction of the membrane structure; it exhibits a fluid because lipids and proteins can move relative to each other within the membrane and is a basic mosaic of lipid, protein, and carbohydrate molecules
integral membrane protein
another name for the intrinsic membrane protein; cannot be released from the membrane unless the membrane is dissolved with an organic solvent or detergent
transmembrane protein
most common type of integral membrane protein; has one or more regions that are physically inserted into the hydrophobic region of the phospholipid bilayer
lipid anchored protein
a type of integral membrane that has a lipid molecule conveniently attached to an amino acid side chain within the protein
peripheral membrane proteins
extrinsic proteins; do not interact with the hydrophobic interior, but are non-covalently bound to regions of the integral membrane proteins that project outwards from the membrane or are bound to polar head groups of phospholipids
glycosylation
the process of covalently attaching a carbohydrate to a lipid or protein
glycolipid
a carbohydrate attached to a lipid
glycoprotein
a carbohydrate attached to a protein
membrane transport
the movement of ions and molecules across biological membranes
selective permeability
function of the plasma membrane which ensures that essential molecules like glucose and amino acids enter the cell while metabolic intermediates remain and waste is forced to exit
facilitated diffusion
a method of allowing substance to move across membranes; a transport protein provides a passageway for the substance to cross the membrane
passive transport
the transport of a substance across a membrane from a region of high concentration to a region of lower concentration; does not require input of energy
active transport
movement from an area of high concentration to low concentration or against a concentration gradient with the aid of a transport protein
transmembrane gradient
when a concentration of a solute is higher on one side of a membrane than the other
electrochemical gradient
a dual gradient that has both electrical and chemical components; occurs with solutes that have a net positive or negative charge
osmosis
the process in which water diffuses across a membrane from the hypotonic compartment into the hypertonic compartment
isotonic
when the solute concentrations on both sides of the plasma membrane are equal
hypertonic
when the solute concentration out the cell is higher (water is lower)
hypotonic
when the solute concentration outside the cell is lower (water is higher)
osmotic lysis
when a cell takes up so much water that it ruptures
crenation
when water exits the cells via osmosis and equalizes solute concentrations on both sides of the cell membrane, causing them to shrink
turgor pressure
osmotic pressure; the hydrostatic pressure required to stop the net flow of water across a membrane due to osmosis
transport protein
transmembrane protein that provides a passageway for the movement of ion and hydrophilic molecules across the membranes; play major role in selective permeability
channel
gated; forms an open passageway for the facilitated diffusion of ions or molecules across the membrane (solutes move directly through to get to the other side)
uniporter
binds a single ion or molecule and transports it across the membrane
symporter
cotransporter; binds two or more ions or molecules and transports the in the same direction
antiporter
binds two or more ions or molecules and transports them in opposite directions
primary active transport
involved the functioning of a pump (a type of transporter that directly uses energy to transport a solute against a gradient)
secondary active transport
involved the use of pre-existing gradient to drive the active transport of another solute
electrogenic pump
pump that generates an electrical gradient across the membrane
exocytosis
when material inside the cell is packaged into vesicles and then excreted into the extracellular environment (vesicles derived from Golgi apparatus)
endocytosis
the plasma membrane invaginates (fold inward) to form a vesicle that brings substances into the cell
receptor-mediated endocytosis
form of endocytosis; a receptor in the plasma membrane is specific for a given cargo
pinocytosis
formation of membrane vesicles from the plasma membrane as a way for cells to internalize the extracellular fluid (small substances)
phagocytosis
an extreme form of endocytosis involving the formation of an enormous membrane vesicle that engulfs a large particle