biol1000 unit 3 chapter 2: membranes

plasma membrane

flexible boundary between the living cell and its surrounding environment

plasma membrane function

regulates the flow of material in and out of the cell

where are the hydrophobic and hydrophilic regions in the plasma membrane?

hydrophobic regions are embedded in the membrane, hydrophilic regions protrude into the aqueous solutions inside or outside the membrane

fluid mosaic model

diverse protein molecules suspended in a fluid phospholipid bilayer

selective permeability

some substances can cross the plasma membrane more easily than others

diffusion

the tendency for particles of any substance to spread out into the available space

passive transport

diffusion across a membrane with no energy investment

net movement of passive transport

from high to low concentration; down its concentration gradient

some molecules could still move in the opposite direction

equilibrium will be reached

substances move independently of each other

what substances can easily diffuse through a cell membrane using passive diffusion

small, non-polar molecules: O2 enters the cells and CO2 exits the cell

ions and polar molecules: diffuse freely using simple transport proteins; cannot pass directly through the phospholipid bilayer; must move down their concentration gradient

osmosis

diffusion of water across a membrane

water passes through the membrane until the concentration of a solute is equal on both sides

tonicity

the ability of a surrounding solution to cause a cell to gain or lose water; depends on the concentration of solutes in the environment compared to in the cell

isotonic

equal concentration of solutes

hypotonic

lower concentrations of solutes in the environment

hypertonic

higher concentration of solutes in the environment

if the animal cell swells too much, it will ______

lyse

lysis

breaking or bursting

turgor pressure

the cell swells as water enters but the cell wall exerts a back pressure

turgid cells

give support to non woody plants; this is the healthy, normal state for plants

isotonic solutions in animal cells

ideal type of solution; blood plasma is isotonic for red blood cells

isotonic solutions in plant cells

no build up of turgor pressure; the plant will wilt

hypertonic solutions in animal cells

the cells will shrivel and die

hypertonic solutions in plant cells

the cell shrivels up but the rigid cell wall cannot change its shape

plasmolysis

the plasma membrane pulls away from the cell’s wall; plant wilts and cells begin to die

osmoregulation

the control of water balance; prevention of excessive uptake or loss of water, and regulation of the solute concentrations in the body

transport proteins

passive transport; sugars, amino acids, ions, water

channel protein

simple channel for a molecule to pass through

carrier protein

solute binds the protein, causing it to change shape

aquaporin

allows the passage of water

active transport

a cell expends energy to move a solute against its concentration gradient

sodium-potassium pump

protein in the cell membrane that uses energy to move sodium out of the cell and potassium into the cell to keep the cell balanced and working properly

active transport steps

1) solute molecule binds to the transport protein

2) ATP provides energy for the transport protein to change shape

3) the solute is released to the opposite side

4) the transport protein returns to its original shape

exocytosis

larger molecules are excreted from the cell; transport vesicle buds off of the Golgi apparatus and fuses with the plasma membrane; contents of the vesicle are released from the cell

endocytosis

the process by which large molecules and fluids are taken up by the cell

phagocytosis

“cellular eating”; pseudopodia = extensions of the membrane that engulf a particle

particle is packaged in a vacuole which can fuse with a lysosome to digest the content… this is how the blood cells take in pathogens

receptor mediated phagocytosis

allows the cell to acquire specific solutes

receptor proteins

embedded in the membrane in an area lined by coat proteins; bind solutes and the plasma membrane indents to form a coated pit; the pit pinches closed to form a vesicle