Cell Membrane

what makes a phospholipid amphipathic?

it has both hydrophilic and hydrophobic components

cholestreol effect on membrane

• acts as fluidity buffer

• at lower temperature, increases fluidity

• at higher temperature, lowers fluidity

integral proteins (intrinsic)

penetrate hydrophobic interior of the lipid bilayer

peripheral proteins (extrinsic)

bound to the surface of the membrane

transmembrane proteins

span the entire lipid bilayer

lipid anchored protein

sit on one side of the membrane, firmly attached as they are covalently attached to a lipid molecule

permeability of cell membrane

selectively permeable, it will accept some molecules and reject others

glycolipids

membrane carbohydrates covalently bonded to lipids

glycoproteins

a protein with a carbohydrate chain covalently attached to it

types of molecules that easily pass through cell membrane

nonpolar molecules, hydrocarbons, CO2, O2, hydrophobic molecules

types of molecules that do not easily pass through cell membrane

polar molecules, ions, glucose, hydrophilic molecules

2 types of transport proteins

carrier proteins, channel proteins

channel proteins

proteins that transport hydrophilic molecules across the cell membrane by passive transport

aquaporins

proteins that facilitate the movement of water through the membrane

carrier proteins

proteins that change shape to transport specific solutes across a membrane by passive or active transport

diffusion

the movement of particles from an area of high concentration to an area of low concentration

osmosis

the diffusion of water across a selectively permeable membrane

isotonic

solute concentration in the cell and outside the cell is balanced, no net movement of water across the membrane

hypertonic

higher concentration of solutes outside the cell than inside the cell

hypotonic

a lower concentration of solutes outside the cell than inside the cell

animal cell in isotonic solution

no net movement of water, cell is normal

animal cell in hypertonic solution

water moves outside the cell, cell shrinks and dies

animal cell in hypotonic solution

water moves inside the cell, cell swells and bursts

plant cell in isotonic solution

cell becomes flaccid and wilts

plant cell in hypertonic solution

water leaves the cell, cell wilts and dies, plasmolysis

plant cell in hypotonic solution

water enters the cell, cell is turgid

type of solutions favourable for animal cell and plant cell

isotonic favours animal cell, hypotonic favours plant cell

osmoregulation

the control of solute concentrations and water balance

tugor pressure

the internal fluid pressure that pushes a plant’s membrane against its cell wall, keeping the plant turgid

facilitated diffusion

molecules blocked by the membrane diffuse passively via transport proteins

active transport

the movement of molecules across a cell membrane from low concentration to high concentration, requiring energy/ATP

electrochemical gradient

force that moves ions across a cell membrane, combining chemical force (particle concentration gradient) and electrical force (difference in charge)

main function of proton pump in plants, fungi, bacteria

active transport of protons out of the cell

exocytosis

cell secretes molecules by fusing vesicles with cell membrane

endocytosis

cell takes in molecules by forming vesicles from the cell membrane

3 types of endocytosis

phagocytosis, pinocytosis, receptor mediated cytosis

phagocytosis

cell engulfs large particles via pseudopodia, forms a membrane enclosed sac called food vacuole

pinocytosis

cell ingests extracellular fluid and small particles, forms a vesicle from the cell membrane

receptor mediated endocytosis

receptors on the surface on the cell membrane attach to ligand, move to an area concentrated with clathrin, and form a vesicle from the cell membrane, clathrin and receptors are reused

Sodium-potassium ATPase pump

3 Na out of the cell, 2 K into the cell

difference in charge between potassium and sodium in cells

more positive outside, less positive inside