unit 5 - cell membrane & cellular transport

biology 9 honors

plasma membrane

• the movement of materials in/out of the cell

• key regulation of homeostasis of cell and maintenance of life functions

phospholipid

specialized triglyceride that makes up most of the membrane

• phospholipid structure leads to “phospholipids bilayer”

• polar/hydrophilic phosphate “head” attracts to water

• nonpolar/hydrophobic “tails” avoid water

• bilipid layer remains fluid while preventing polar molecules (like water) from crossing through

plasma membrane structure/proteins

multiple other structures reside within the plasma membrane to its function

phospholipid

• main structural component of cell membrane

• hydrophilic phosphate head

• hydrophobic fatty acid tails

cholesterol

• provides fluidity to membrane

• prevents phospholipid coagulation (solidifying/clotting)

membrane proteins

• perform various functions

• some are along the edge of the membrane (peripheral proteins)

• some are within the bilayer (integral proteins)

glycocalyx

• surface “fuzz” involved in cell to cell recognition

• made of short carbohydrate chains (oligosaccharides) attached to proteins (glycoproteins) and lipids (glycolipids)

• glycocalyx = glycoproteins + glycolipids

channel protein

• provides passage of small, polar molecules across membrane by simple diffusion

• substances pass through the channel unimpeded by nonpolar region

enzyme

• enzymes promote chemical reactions

• found as integral or peripheral proteins

carrier protein

• facilitate passage of large and/or polar molecules through membrane

• may function via simple diffusion (passive transport) or by ATP (active transport)

marker protein

• specialized protein involved in cell to cell recognition

  • help form the glycocalyx

receptor protein

specialized protein involved in “receptor-mediated endocytosis” (process by which cells absorb metabolites, hormones, proteins)

passive transport

movement of materials across a membrane which requires no energy other than kinetic energy of molecules

simple diffusion

• driven completely by kinetic energy of particles

• may or may not include a membrane

• movement of materials from area of high concentration to area of low concentration

concentration gradient

exists when there is a difference in concentrations over a distance or across a membrane

equilibrium

no concentration gradient; equal concentration

rate of diffusion

due to diffusion pressure, mass of molecule, and temperature

• low mass = fast diffusion

• high mass = slow diffusion

• low temp = slow diffusion

• high temp = fast diffusion

____ conc. gradient = ____ diffusion pressure = ____ rate of diffusion

greater ____ = greater ____ = greater ____

semi-permeable membrane

• lets only selected substances through

• based on size and polarity of molecules

what factors affect the rate of diffusion?

• mass of particle

• concentrations gradient

• temperature

what factors affect the ability to diffuse (across plasma membrane)?

• molecular size/volume

  • large = slow

  • small = fast

• polarity

  • polar = won’t cross membrane (H₂O, OH, H, Na, glucose)

  • non-polar = will cross membrane (O₂, CO₂)

facilitated diffusion

form of passive transport in which substances move from an area of high conc. to an area of low conc. with the assistance of proteins within the membrane

• ex. channel protein, carrier protein

what’s an example of facilitated diffusion?

glucose may need to be shielded from the hydrophobic portion of the lipid bilayer so that it can diffuse quickly.

osmosis

passive transport of water across a membrane from high conc. to low conc.

isotonic environment

• state of equilibrium

• equal concentrations throughout

• both inside and outside of cell

• no conc. gradient exists, zero diffusion pressure