The Plasma Membrane Flashcards
The ______ membrane is the boundary that separates the living cell from its surroundings
plasma
The plasma membrane exhibits ______ ________ allowing some substances to cross it more easily than others
selective permeability
_______ are the most abundant lipid in the plasma membrane
phospholipids
Phospholipids are _______ molecules, containing hydrophobic and hydrophilic regions
amphipathic
The ____ ______ model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it
fluid mosaic
In 1935, Hugh Davson and James Danielli proposed a _______ model in which the phospholipid bilayer lies between two layers of globular proteins
sandwich
___________ studies of the plasma membrane supported the fluid mosaic model
freeze-fracture
Freeze-fracture is a specialized preparation technique that _____ a membrane along the middle of the phospholipid bilayer
splits
Phospholipids in the plasma membrane can move within the ____
bilayer
Most of the lipids, and some proteins, drift ______
laterally
As temperatures cool, membranes switch from a _____ state to a ____ state
fluid to solid
Membranes rich in unsaturated fatty acids are more _____ that those rich in saturated fatty acids
fluid
Membranes must be fluid to ____ properly; they are usually about as fluid as salad oil
work
At warm temperatures (such as 37°C), cholesterol ______ movement of phospholipids
restrains
At cool temperatures, cholesterol ______ fluidity by preventing tight packing
maintains
A _______ is a collage of different proteins embedded in the fluid matrix of the lipid bilayer
membrane
_______ determine most of the membrane’s specific functions
proteins
______ proteins are bound to the surface of the membrane
Peripheral
_____ proteins penetrate the hydrophobic core (they are ingrained in the membrane)
Integral
Integral proteins that span the membrane are called ______ proteins
transmembrane
The hydrophobic regions of an integral protein consist of one or more stretches of nonpolar amino acids, often coiled into _____ _____
alpha helices
Transport Enzymatic activity Signal transduction Cell-cell recognition Intercellular joining Attachment to the cytoskeleton and extracellular matrix
the 6 major functions of membrane proteins
Cells _______ each other by binding to surface molecules, often carbohydrates, on the plasma membrane
recognize
Membrane carbohydrates may be ________ bonded to lipids (forming glycolipids) or more commonly to proteins (forming glycoproteins)
covalently
Carbohydrates on the ______ side of the plasma membrane vary among species, individuals, and even cell types in an individual
external
The ___________ distribution of proteins, lipids, and associated carbohydrates in the plasma membrane is determined when the membrane is built by the ER and Golgi apparatus
asymmetrical
_________ (nonpolar) molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidly
Hydrophobic
_____ molecules, such as sugars, do not cross the membrane easily
polar
______ proteins allow passage of hydrophilic substances across the membrane
transport
Some transport proteins, called _____ proteins, have a hydrophilic channel that certain molecules or ions can use as a tunnel
channel
Channel proteins called _________ facilitate the passage of water
aquaporins
Other transport proteins, called ____ proteins, bind to molecules and change shape to shuttle them across the membrane
carrier
A transport protein is specific for the…
substance that it moves
Although each molecule moves _______, diffusion of a population of molecules may exhibit a net movement in one direction
randomly
At ______ _______, as many molecules cross one way as cross in the other direction
dynamic equilibrium
Substances diffuse _____ their concentration gradient, the difference in concentration of a substance from one area to another
down
No work must be done to move substances down the _______ _____
concentration gradient
The diffusion of a substance across a biological membrane is ______ transport because it requires no energy from the cell to make it happen
passive
______ is the diffusion of water across a selectively permeable membrane
Osmosis
Water diffuses across a membrane from the region of _____ solute concentration to the region of _____ solute concentration
lower;higher
______ is the ability of a solution to cause a cell to gain or lose water
tonicity
________ solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
isotonic
________ solution: Solute concentration is greater than that inside the cell; cell loses water
Hypertonic
________ solution: Solute concentration is less than that inside the cell; cell gains water
hypotonic
___________, the control of water balance, is a necessary adaptation for life in such environments
Osmoregulation
Cell walls help maintain _____ balance
water
A plant cell in a ______ solution swells until the wall opposes uptake; the cell is now turgid (firm)
hypotonic
If a plant cell and its surroundings are _______, there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt
isotonic
In a hypertonic environment, plant cells lose water; eventually, the membrane pulls away from the wall, a usually lethal effect called ________
plasmolysis
Passive Transport Aided by Proteins
Facilitated Diffusion
In facilitated diffusion, _______ ________ speed the passive movement of molecules across the plasma membrane
transport proteins
_______ proteins provide corridors that allow a specific molecule or ion to cross the membrane
channel
channel proteins for facilitated diffusion of water
aquaporins
channel proteins like Ion channels that open or close in response to a stimulus are called _____ _______
gated channels
Carrier proteins undergo a subtle change in shape that translocates the _____-______ _____ across the membrane
solute-binding site
Some diseases are caused by _________ in specific transport systems, for example the kidney disease cystinuria
malfunctions
Active Transport - uses energy to move solutes _____ their gradients
against
Facilitated diffusion is still ______ because the solute moves down its concentration gradient
passive
Some _______ proteins, however, can move solutes against their concentration gradients
transport
_____ transport moves substances against their concentration gradient
active
Active transport requires ______, usually in the form of ATP
energy
_____ transport is performed by specific proteins embedded in the membranes
active
Active transport allows cells to __________ concentration gradients that differ from their surroundings
maintain
Membrane ________ is the voltage difference across a membrane
potential
The sodium-potassium pump is one type of active ______ system
transport
______ is created by differences in the distribution of positive and negative ions
voltage
An _________ pump is a transport protein that generates voltage across a membrane
electrogenic
The sodium-potassium pump is the major electrogenic pump of _____ cells
animal
The main electrogenic pump of plants, fungi, and bacteria is a _____ pump
proton
_________ occurs when active transport of a solute indirectly drives transport of another solute
Cotransport
______ commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell
Plants
_____ transport across the plasma membrane occurs by exocytosis and endocytosis
Bulk
Small molecules and water enter or leave the cell through the _____ _____ or by transport proteins
lipid bilayer
______ molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles
Large
Bulk transport requires ______
energy
In _________, transport vesicles migrate to the membrane, fuse with it, and release their contents
exocytosis
Many _______ cells use exocytosis to export their products
secretory
In __________, the cell takes in macromolecules by forming vesicles from the plasma membrane
endocytosis
________ is a reversal of exocytosis, involving different proteins
Endocytosis
In ________ a cell engulfs a particle in a vacuole
The vacuole fuses with a lysosome to digest the particle
phagocytosis
In _________, molecules are taken up when extracellular fluid is “gulped” into tiny vesicles
pinocytosis
In __________________, binding of ligands to receptors triggers vesicle formation
receptor-mediated endocytosis
