cell membrane and water movement

cell membrane

• membrane separate cells from their exterior environments

• define compartments within eukaryotic cells

• made of 2 layers of phospholipids and embedded proteins

• fluidity is determined by the lipid structure and temp

• selectively permeable

unsaturated fatty acids

• double bonds

• enhance fluidity

saturated fatty acids

• no double bonds

• hydrocarbon tails clustered together

• does not enhance fluidity

cholesterol

• animal cells

• prevents tails from coming together

• regulates fluid

• hydroxyl groups interact with the polar heads of phospholipids

hydrophilic regions

electrically charged head that links with the water molecules

hydrophobic regions

• nonpolar fatty acid tails

peripheral membrane proteins

• lacks hydrophobic group

• not embedded in the bilayer

integral/transmembrane proteins

• embedded in the phospholipid bilayer

• amphiphiles

• ex. channel proteins, carrier proteins, ligand gated ion channel

selective permeability

• membrane allows some substances but not others but not others, to pass

• high permeability= small hydrophobic molecules, ex. O2, CO2, N2

• low permeability= H20, glycerol, glucose, sucrose, charged particles

passive transport

• requires no energy(NO ATP)

• high to low concentration

• simple diffusion and facilitated diffusion

simple diffusion

• requires no energy

• high to low concentration

• down the concentration gradient

• increase in SA allows for simple diffusion ,ex. villi

• small nonpolar, lipid soluble molecules, steroids can directly diffuse through

facilitated diffusion

• requires no energy

• high to low concentration

• molecules diffuse through membrane through proteins

• larger, hydrophilic molecules/ions

channel proteins

• integral/transmembrane protein

• provides openings that allow specific molecules to pass through

• ex. aquaporins, ion channels

• channel protein changes when a ligand gated ion channel binds to it

aquaporins

• enhances movement of water

• more aquaporins- increases osmosis

carrier proteins

• changes shape/structure so molecule can move across the membrane

• specific molecules bind

ligand gated ion channel

integral protein that opens in response to a stimulus

glycoproteins

used for cell identification

active transport

• ATP is needed to move substances against their concentration gradient

• specific protein pumps move cells in or out of the cell-reset back to normal

primary active transport

• direct hydrolysis of ATP for energy

• ex. sodium potassium pump

electrogenic pump

• generate voltage across the membrane

secondary active transport/co transport

• uses energy from ion concentration gradient or electrical gradient

• established by primary active transport

• step 1= protons are pumped across the membrane using atp to cause the electrochemical gradient

• step 2= protons diffuse down their gradient and drive the movement against its concentration gradient

types of transporters

• uniporter= carries 1

• symporter= carries two in the same direction

• antiporter= carries two in different directions

exocytosis and endocytosis

• only in eukaryotes

• uses vesicles

• large molecule/proteins

• require energy, motor proteins, and dynamic cytoskeleton

• possible because of fluid and dynamic nature of membranes

exocytosis

• transport vesicles relocate to the membrane, fuse with it, and release their contents

• cells use exocytosis to secrete products, remove waste, deliver proteins to embed in cell membrane

endocytosis

• vesicle is formed by invagination of the cell membrane, leading to the uptake of molecules from the extracellular space

• 3 types=

  • phagocytosis= cellular eating

  • pinocytosis= cellular drinking

  • receptor mediated endocytosis= ligand binding to receptors triggers vesicle formation

application

signal transmission in a neuron

osmosis

• passive diffusion of water across membranes

• high water concentration to low water concentration

solute

dissolved substance

molarity

the concentration of a solute in a solution

osmotic pressure

• tendency of a solution to draw water in by osmosis; can be measured by the height of the water column and 2) apply the force to prevent the water from rising

• can modify the shapes of cells

• net water movement stops when pressure put by gravity(hydrostatic pressure) is equal to osmotic pressure

tonicity

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

• 1) if inside the cell and surrounding solution have the SAME solute concentration-EQUAL TONICITY

• 2) if the surrounding solution has a lower solute concentration- LOWER TONICITY

• 3) if surrounding solution has a higher solute concentration- HIGHER TONICITY

water potential

• physical property that predicts the direction in which water will flow

• quantity that includes the effects of solute concentration and physical pressure

• free water moves from higher water potential to lower water potential

• pure water has no solutes! has 0 MPa

pressure potential

• physical pressure

• can be positive or negative based on atmospheric pressure

solute potential

• effects of solutes on the movement of water

• can never be a positive number

free water

• moves from higher water potential to lower