CELL MEMBRANES

GUIDING QUESTION: HOW DOES A CELL MEMBRANE HELP A CELL STAY ALIVE?

Homeostasis- A stable internal condition inside of a living organism.

-Homeo= same

-Stasis= not moving

CELL MEMBRANE A phospholipid is a lipid

with a phosphate “head” and two fatty acid “tails”.

The head is attracted to water = Hydrophilic

The tail is not attracted to water = Hydrophobic

CELL MEMBRANE THOUGHT EXPERIMENT

1st Experiment

CELL MEMBRANE THOUGHT EXPERIMENT

2nd Experiment

CELL MEMBRANE THOUGHT EXPERIMENT

3rd Experiment

A phospholipid bilayer forms the basic unit of the cell membrane.

QUESTION # 1

Where in this diagram of a cell membrane would you expect to find the FEWEST water molecules?

A

B

C

The fatty acid “tails” of the phospholipids are hydrophobic. They would repel any water molecules that came into that area of the membrane.

SELECTIVE PERMEABILITY Cell membranes are said to be selectively

permeable membranes, meaning that they allow some, but not all, materials to simply pass through them.

http://www.johnkyrk.com/cellmembrane.html

http://www.youtube.com/watch?v=Rl5EmUQdkuI

QUESTION # 2

Which of the following is NOT an accurate analogy for a cell membrane?

A. a window screenB. the US – Mexico borderC. the Kansas – Colorado borderD. a university admissions department

QUESTION #3 WHICH OF THE FOLLOWING COULD NOT PASS THROUGH A CELL MEMBRANE WITHOUT THE HELP OF A PROTEIN?

A. Sugar B. Oxygen (O2) C. Carbohydrates D. Water

MEMBRANE COMPOSITION Proteins embedded in the bilayer help the cell

transport materials in and out. Carbohydrate chains (cell surface markers)

attached to some membrane proteins help the cell communicate with other cells.

Structure of the Cell Membrane

QUESTION # 4: WHAT TYPE OF MEMBRANE MOLECULES ARE RESPONSIBLE FOR CELL-TO-CELL COMMUNICATION?

A. lipidsB. proteinsC. phospholipidsD. carbohydrates

Carbohydrate chains act like “ID tags.” Different cell types have different kinds of carbohydrate chains on their surfaces.

CELL MEMBRANE ANALOGY

The cell membrane is similar to the walls that surround a house.

BOTH HELP PROTECT THE INSIDE FROM THE OUTSIDE.

outside

inside

A HOUSE NEEDS A WAY OF RECEIVING FUEL AND POWER FROM THE OUTSIDE. SUPPLY LINES PASS THROUGH THE WALLS OF THE HOUSE TO BRING IN THESE MATERIALS.

A CELL RECEIVES FUEL AND POWER FROM THE OUTSIDE THROUGH PROTEIN CHANNELS IN THE MEMBRANE.

PEOPLE IN A HOUSE ALSO NEED TO COMMUNICATE WITH THE OUTSIDE.

CARBOHYDRATES IN THE MEMBRANE ALLOW THE CELL TO COMMUNICATE WITH OTHER CELLS.

SENSING THE OUTSIDE ENVIRONMENT

People in a house need to know when deliveries or friends arrive.

RECEPTOR PROTEINS

These proteins let a cell sense its surroundings so that it can change and maintain homeostasis.

BACKGROUND INFORMATION

Most cells exist in liquid, making it easy for materials to move into and out of the cell.Every cell membrane is selectively permeable, meaning that some substances but not others can cross them.Particles have a tendency to move from a region where they are more numerous to a region where they are less numerous.

A CONCENTRATION GRADIENT IS…

…a difference in the number of particles of a substance in two neighboring regions.

Particles tend to move down their concentration gradients (higher to lower concentration).

PARTICLES OF A SUBSTANCE TEND TO GO FROM AREAS OF HIGHER CONCENTRATION TO AREAS OF LOWER CONCENTRATION.

A. TrueB. False

It's not simply a case of movement in one direction. Particles move in both directions, but because one side has more particles to start with, they are more likely to move in one direction than the other. When both sides have the same number of particles, they are just as likely to move one way as the other way, so there will be no change in amounts - both sides will stay equal.

DIFFUSION IS……the process by which particles of a substance move from areas of higher concentration to areas of lower concentration.

…the driving force behind the movement of materials across the plasma membrane.

A. A barrier separates two different substances.B. The barrier is removed, and the substances move

down their concentration gradients.C. Equilibrium is reached.

OSMOSIS IS…

…the diffusion of water molecules through a selectively permeable membrane from an area of greater concentration of water to an area of lesser concentration of water.

BASED ON THE CONCEPT OF OSMOSIS, WHAT WOULD YOU EXPECT TO HAPPEN IN THIS SETUP?

A. No movement of water will occur.B. Water will move in both directions equally.C. The net movement of water will be from side B to

side A.D. The net movement of water will be from side A to

side B.

OSMOSIS TERMINOLOGYWhen comparing two solutions……solutions with higher concentrations

of solute are hypertonic(hyper means "above").

…solutions with lower concentrations of solute are hypotonic(hypo means “below”).

…solutions in which the concentrations are equal are isotonic(isos means “equal”).

WHICH OF THE FOLLOWING CORRECTLY LABELS THIS SETUP?A. left: isotonic / right: isotonicB. left: isotonic / right: hypertonicC. left: hypertonic / right: hypotonicD. left: hypotonic / right: hypertonic

IMAGINE THAT THE MEMBRANE SHOWN BELOW IS IMPERMEABLE TO THE SOLUTE MOLECULES BUT PERMEABLE TO WATER. WHICH WAY WILL WATER FLOW?

A. left to rightB. right to left

NORMALLY, IN THE PROCESS OF OSMOSIS, THE NET FLOW OF WATER MOLECULES INTO OR OUT OF THE CELL DEPENDS UPON DIFFERENCES IN THE

A. rate of movement of molecules inside the cellB. concentration of water molecules inside and

outside the cellC. rate of molecular motion on either side of the

cell membraneD. concentration of enzymes on either side of the

cell membrane

FACILITATED DIFFUSION Diffusion of a substance through a transport protein embedded in a membrane.In facilitated diffusion, solute particles pass through a channel in a transport protein.

Facilitated Diffusion

Outside Cell

Inside Cell

TransportProtein

Higher Concentration of Molecules

Lower Concentration of Molecules

PASSIVE TRANSPORTDiffusion, osmosis, and facilitated diffusion are all forms of passive transport across the plasma membrane because energy is not required for them to happen.Like riding a bike down a hill, no energy is needed.

ACTIVE TRANSPORT…involves a substance being forced through a transport protein in the plasma membrane against the concentration gradient (from lower to higher concentration).

Like riding a bike up a hill, an energy boost is required.

Active Transport

Outside Cell

Inside Cell

TransportProtein

Higher Concentration of Molecules

ENERGY

Lower Concentration of Molecules

Molecule to be

carried

Active Transport

Outside Cell

Inside Cell

Molecule is transported to the other side of the membrane

WHICH OF THE FOLLOWING TYPES OF TRANSPORT ACROSS MEMBRANES WAS COMPARED TO RIDING A BIKE UP A HILL?

A. diffusionB. osmosisC. active transportD. facilitated diffusion

Like an enzyme, a transport protein recognizes a specific solute, molecule or ion. During active transport, the protein uses energy, usually moving the solute in a direction from lesser concentration to greater concentration.

ENDOCYTOSIS AND EXOCYTOSIS

…the processes of taking material into (endocytosis) or out of (exocytosis) the cell by means of pockets of the cell membrane.

WHAT PROCESS IS SHOWN HERE?

A. osmosisB. exocytosisC. endocytosisD. facilitated diffusion

INTERACTIVE VISUALS OF TRANSPORT ACROSS A MEMBRANE

OSMOSIS DEMOProcedure: The water surrounding an Elodea leaf will be replaced with salt water.Before the demo, write a paragraph describing what you expect to observe.After you have observed osmosis, write a paragraph describing what you observed and what caused it to happen.Correctly use the words equilibrium, hypertonic, hypotonic, and isotonic in your description.