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53 Cards in this Set
- Front
- Back
plasma membrane
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the outer layer of the cell
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selective permeability
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it allows some substances to cross it more easily than others
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amphipathic molecule
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has both hydrophobic and hydrophilic regions
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fluid mosaic model
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the membrane is a fluid structure with a "mosaic" of various proteins embedded in or attached to a double layer (bilayer) of phospholipids
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how is the membrane held together?
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through weak hydrophobic interactions which make it fluid
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When the temperature decreases, the fluidity of the membrane ....
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the membrane is liquid until the phospholipids are closely packed enough to form a solid
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unsaturated hydrocarbon tails make the temperature at which the phospholipid bilayer stays liquid ...
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lower
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steroid and membrane temperature
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it usually makes the membrane more solid at relatively warm temperatures
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Integral proteins
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penetrated the hydrophobic core of the lipid bilayer. They are transmembrane proteins which span the whole bilayer
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What do the hydrophobic regions of the integral proteins consist of?
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one or more nonpolar amino acids, usually coiled into alpha helixes
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Peripheral proteins
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are not embedded in the lipid layer at all,they are appendages loosely bound to the surface of the membrane
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What are the six major functions performed by proteins of the plasma membrane?
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Transport, Enzymatic activity, Signal Transduction, Cell-cell recognition, Intercellular joining, Attachment to the cytoskeleton and extracellular matrix(ECM)
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How are the proteins held in place on the cytoplasmic side of the plasma membrane?exterior side?
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by attachment to the cytoskeleton, are attached to fibers of the extracellular matrix
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Why is cell-cell recognition important to cells?
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sorting cells into tissues and organs, identifying foreign cells, etc
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carbohydrates on the membrane
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usually short branched chains of fewer that 15 sugar units
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glycolipids
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carbohydrate covalently bonded to a lipid on the membrane
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glycoproteins
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most carbohydrates are covalently bonded to proteins
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How do the inside and outside faces of the lipid bilayer differ?
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they have differ in specific lipid composition, each protein has directional orientation in the membrane
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For which kind of molecule is the membrane really hard to go through?
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hydrophilic molecules which find it hard to permeate through the hydrophobic core, so they need assistance to get through the plasma membrane
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What is one way for a hydrophilic molecule to get through the plasma membrane?
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transport proteins
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transport proteins
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some are called channel proteins as they serve as a tunnel for polar of ionic molecules to pass through
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aquaporins
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the passage of water molecules through the membrane in certain cells
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carrier proteins
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hold onto their passengers and change shape in a way that shuttles them across the membrane
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diffusion
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the tendency for molecules of any substance to spread out evenly into the available space
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concentration gradient
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a substance will diffuse from where it is more to where it is less
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diffusion: with or against concentration gradient?
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with concentration gradient
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What does diffusion eventually establish?
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An equilibrium, so it may be directional to establish an equilibrium
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passive transport
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diffusion is passive transport as the cell does not expend energy
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osmosis
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the diffusion of water through a selectively permeable membrane
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tonicity
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the ability of a solution to cause a cell to gain or lose water
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isotonic, apply to cell environment.
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the water and the solute concentrations are equal, so there will be equal movement across the membrane, and no net movement
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hypertonic, apply to cell environment
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the solute concentration is higher outside, which cause the water to travel outside of the cell and the cell will shrivel up and die
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hypotonic, apply to cell environment
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the solute concentration is lower outside and higher inside so the water will flow inside and the cell will probably swell and lyse
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osmoregulation
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the control of water balance, this is needed when organisms without a rigid cell wall live in a hypertonic or hypotonic environment
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turgid
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very firm, plant cells, when water enters the cell, the elastic wall will only stretch until it exerts back pressure on the cell and opposes further water uptake
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flaccid
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very limp, if a plant's cells and their surrounding are isotonic then there will be no net movement of water across the membrane which causes the cell to become very limp
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facilitated diffusion
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many polar molecules and ions diffuse passively with the help of transport proteins
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ion channels, gated channels
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there is a stimulus that causes the channels to open or close, the stimulus can be electrical or chemical
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active transport
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transport in which the cell expends energy
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sodium-potassium pump
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exchanges sodium for potassium across the plasma membrane of animal cells
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membrane potential
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ranges from about -50 to -200 millivolts (mV)
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charge of cytoplasm
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negative
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electrochemical gradient
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the combination of forces acting on an ion
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ions diffuse down their _______.
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electrochemical gradient
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electrogenic pump
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a transport protein that generates voltage across a membrane
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proton pump
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the main electrogenic pump of plants, fungi, and bacteria
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cotransport
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a substance that has been pumped across the membrane by diffusion
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exocytosis
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a cells secretes macromolecules by the fusion of vesicles with the plasma membrane
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endocytosis
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the cell takes in macromolecules and particular matter by forming new vesicles from the plasma membrane
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ligands
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any molecule that specifically binds to a receptor site of another molecule
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phagocytosis
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a cell engulfs a particle by wrapping pseudopodia around it and packaging it in the vacuole
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pinocytosis
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the cell "gulps" droplets of extra-cellular fluid into tiny vesicles
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receptor-mediated endocytosis
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the cells acquire bulk quantities of specific substances, even though those substances may not be very concentrated in areas of the extracellular fluid
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