BIOL Ch 5

functions of a plasma membrane

isolates cell contents from external environment, regulates exchange of essential substances, allows communication between cells, creates attachments within and between cells, regulates biochemical reaction

fluid mosaic model

1972, Singer and Nicolson, proposed “mosaics” or “a patchwork” of different proteins, selectively permeable, allows materials to move in/out of cell

phospholipid bilayer

fluid portion of plasma membrane, face both interior and exterior watery environments. Polar hydrophilic heads face outside and inside cell. Nonpolar hydrophobic tails face inside of membrane

cellular shape changes

phospholipid bilayer’s flexible, fluid membrane allows for …

are not

phospholipid molecules are/are not bonded to one another?

unsaturated fatty acids

presence of … cause kinks into phospholipid tails (kinks make membrane fluid)

O2, CO2, small nonpolar molecules; some water molecules

what can pass through the phospholipid bilayer?

glucose, larger polar water-soluble molecules; ions, most water molecules

what cannot pass through phospholipid bilayer?

more fluid = high temperature → more movement, less fluid = low temperature → less movement

temperature related to fluidity of plasma membrane

cholesterol

… stabilizes membranes, affecting fluidity and reducing permeability

variety of proteins. They are embedded within or attached to the phospholipid bilayer

what forms the mosaic within the plasma membrane? and where are they located?

proteins found within plasma membrane

receptor, recognition “name tag”, enzymatic, attachment, and transport

receptor proteins

trigger cellular responses upon binding of specific molecules (hormones) sent by other cells

recognition proteins

glycoproteins that serve as identification tags on the surface of a cell (i.e. “name tag”)

receptor protein activation

hormone binds to receptor, hormone binding activates receptor, changing the shape, activated receptor stimulates a response within the cell

enzymatic proteins

promote chemical reaction that synthesize or break apart biological molecules

attachment proteins

anchor the cell membrane to the inner cytoskeleton, to proteins outside the cell, and to other cells

transport proteins

regulate movement of hydrophilic molecules through plasma membrane. Types: channel and carrier

channel proteins

one of the types of transport proteins that form channels to allow specific ions or water molecules to pass through the membrane

carrier proteins

one of the types of transport proteins that have binding sites that can temporarily attach to specific molecules on one side of the membrane and them move them through the membrane to the other side

in response to gradients

how do substances move across membranes?

fluid

a substance whose molecules can flow past one another, no defined shape

solute

a substance that can be dissolved in a solvent (atoms, ions, or molecules)

solvent

a fluid capable of dissolving a solute

concentration of a substance

the amount of solute in a given amount of solvent

gradient

the physical different in temperature, pressure, charge, or concentration between two adjoining regions of space

molecules and ions in a solution are in constant random motion, increase of temperature increases rate of motion → net movement from regions of high concentration to those of low through diffusion

how do gradients cause molecules to move from one place to another?

drop of dye is placed in water, dye molecules diffuse into water, water molecules diffuse into dye, both dye and water molecules are evenly dispersed

diffusion of dye in water

passive transport and energy-requiring transport

how does movement through membrane occur?

passive transport

movement of substances across cell membranes down concentration gradients, no energy required (simple diffusion, facilitated diffusion, osmosis)

simple diffusion

substances move down their concentration gradients across a membrane

facilitated diffusion

substances move down their concentration gradients with the help of channel and carrier transport

osmosis

diffusion of water across selectively permeable membranes, from high concentration to low concentration

energy-requiring transport

movement of substances across cell membranes that requires the use of cellular energy (active transport, endocytosis, exocytosis)

active transport

proteins use energy to move substances across plasma membranes, against their concentration gradients “protein pumps”

endocytosis

cells engulf particles and transport them using vesicles. Types: pinocytosis and phagocytosis

pinocytosis

“cell drinking”, moves liquids into the cell

phagocytosis

“cell eating”, moves large particles into the cell

exocytosis

movement of material out of the cell by using energy and vesicles to dispose of waste products

isotonic solutions

have equal concentrations of water and dissolved substances. No net water movement occurs across the membrane

hypertonic solutions

have a greater solute concentration. Water moves across a membrane toward it

hypotonic solutions

have a lower solute concentration. Water moves across a membrane away from it

shrink, water loss

when cells are placed into a hypertonic solution, they … owing to …

swell, water entry

when cells are placed into a hypotonic solution, they … owing to …

unaffected

cells in isotonic solutions remain …

turgor pressure

water pressure within the central vacuole, provides support in plants

plasmolysis

when a plant cell’s membrane shrinks away from its cell wall. Occurs when water is drawn out of the cell and into the extracellular fluid

diffusion (a slow process) can take too long to supply important processes deep within the cell

what happens when a spherical cell gets too large?

if the radius increases by a factor of 3, then volume increased by a factor of 27, but surface area increases but factor of 9

surface area and volume relationships

desmosomes

attaches cells together, found where cells need to adhere tightly together under the stresses of movement (i.e. small intestine)

tight junctions

make cell attachments leakproof, found where tubes and sacs must hold contents without leaking (i.e. urinary bladder)

gap junctions

found in animal cells, allow direct communication between cells

plasmodesmata

found in plant cells, allow direct communication between cells