Chapter 7 - Plasma Membrane

selectively permeable membrane

selectively permeable membrane

allows some substances to cross more easily than others

amphipathic

has a hydrophilic region and a hydrophobic region

• most membrane proteins

fluid mosaic model

the model of cell membrane structure where its membrane has a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids

• groups of proteins are in specialized patches

hydrophobic interactions

membrane fluidity is primarily held together by what?

temperature decreases and phospholipids settle into a tightly packed arrangement

Membranes remain fluid until ... and ... then the membrane solidifies

phospholipids with unsaturated hydrocarbon tails

What are membranes fluid with at a lower temperature?

Restricts phospholipid movement (less fluid)

What effect does cholesterol have at higher temperatures in membranes?

Lowers the temperature required to solidify

What effect does cholesterol have at lower temperatures in membranes?

can't support protein function

What happens when membranes are too fluid?

• fish in extreme cold: membranes with a high proportion of unsaturated hydrocarbon tails

• bacteria living in extreme heat: unusual lipids that prevent excessive fluidity

• plants that tolerate extreme cold: higher percentage of unsaturated phospholipids in autumn

What are some evolutionary differences in membrane composition?

membrane proteins

What determine most of the membrane's functions?

integral protein

penetrates the hydrophobic interior of lipid bilayer

• majority are transmembrane (span the membrane)

nonpolar amino acids (coiled into alpha helices)

What do hydrophobic regions consist of?

aqueous solutions on either or both sides of membrane

What are hydrophilic regions exposed to?

peripheral protein

not embedded in the lipid bilayer, but appendages are bound to the surface of the membrane

cytoskeleton

What are some membrane proteins attached to on the cytoplasmic (cell) side of the membrane?

extracellular matrix (ECM); gives animal cells a stronger framework

What are some membrane proteins attached to on the extracellular (outside of cell) side of the membrane? What benefit does that bring to animal cells?

transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to cytoskeleton

What are the six major functions of membrane proteins?

receptors of one cell bind to glycoproteins or glycolipids on another cells' surface

How does cell-cell recognition work?

glycolipid

a carbohydrate covalently bonded to a lipid

glycoprotein

a carbohydrate covalently bonded to a protein

• ions/polar molecules

• large molecules

What two molecules have trouble going through a plasma membrane?

transport protein

a transmembrane protein that helps a certain substance to cross the membrane

channel protein

a protein that has a hydrophilic channel that ions can go through

• hydrophilic

carrier protein

a protein that holds onto passengers and changes shape to bring molecule across the membrane

• change in shape results in the solute-binding site being translocated across the membrane

diffusion

the movement of particles of any substance so they spread out into the available space

• happens down its concentration gradient

• spontaneous process

passive transport

diffusion of a substance across a biological membrane with no expense of energy

• concentration gradient represents potential energy

osmosis

the diffusion of free water across a selectively permeable membrane

• more free water --> less free water

• less solute --> more solute

tonicity

the ability of a surrounding solution to cause a cell to gain or lose water

• depends on the concentration of solutes relative to the solutes inside the cell

isotonic

equal concentrations of solutes + no net movement of water

hypertonic

surroundings have a higher concentration of solutes

• cell loses water and shrivels

hypotonic

cell has a higher concentration of solutes

• cell absorbs the water and swells + lysing (bursting)

isotonic

Which tonicity are animal cells stable in?

hypotonic

Which tonicity is stable for plants cells?

osmoregulation

the control of solute concentrations and water balance in organisms

• plasma membrane may be less permeable to water

contractile vacuole

an organelle that functions as a pump to force water out as fast as it enters through osmosis

turgor pressure

the force directed against a plant cell wall after the influx of water and the swelling of the cell due to osmosis

• makes the cell firm and stable

it will become flaccid

What happens to a plant in an isotonic environment?

plasmolysis

cytoplasm shrivels and plasma membrane pulls away from the cell wall in a plant cell

facilitated diffusion

the passage of molecules or ions down their electrochemical gradient across a biological membrane with the assistance of specific transmembrane transport proteins

• no energy required

ion channel

a channel protein that transports ions

gated channel

a channel protein that opens or closes in response to a stimulus

active transport

the movement of a substance across a cell membrane against its concentration or electrochemical gradient by specific transport proteins

• requires energy (most from ATP)

transfer terminal phosphate group to the transport protein

What is one way to fuel active transport?

sodium-potassium pump

a pump that exchanges sodium for potassium across a membrane

membrane potential

the difference in electrical charge (voltage) across a cell's membrane due to the difference in distributions of cations and anions

negative charge

The cytoplasmic side of a membrane has what charge relative to the extracellular (outside) side of the cell?

electrochemical gradient

the combination of the concentration gradient and electrical force (membrane potential's effect) acting on an ion

electrogenic pump

a transport protein that generates voltage across a membrane

• ex: sodium-potassium pump (in animals)

proton pump

an active transport protein in a cell membrane that pumps hydrogen ions out of a cell against their concentration gradient

• generates membrane potential

• main electrogenic pump of plants, fungi, and bacteria

cotransport

the coupling of the downhill diffusion of one substance to the uphill transport of another against its gradient

• can take a partner across the membrane

exocytosis

cell secretes certain molecules by forming new vesicles from membrane

• used to export

endocytosis

cell takes in molecules by forming new vesicles from membrane

• used to import

phagocytosis

a cell engulfs a particle by extending pseudopodia around it and packaging it within a food vacuole (membrane sac)

• "cellular eating"

pinocytosis

a cell continuously collects droplets of extracellular fluid into coasted vesicles

• “cellular drinking”

receptor-mediated endocytosis

a specialized type of pinocytosis that enables the cell to acquire bulk quantities of specific substances

• receptor sites are embedded in the plasma membrane that are exposed to the extracellular fluid + specific solutes bind to the sites, causing the receptor proteins to cluster in coated [its that form a vesicle

receptor-mediated endocytosis

What process is used to collect cholesterol in human cells?