MOVEMENT THROUGH THE MEMBRANE

•How do materials or substances enter or leave cells?

Cell Membrane

CELL MEMBRANE

•Function: The cell membrane encloses the cell.

•Function: It lets certain particles into and out of the cell.

•Surrounds all cells

THE CELL MEMBRANE IS PICKY!

•Selective Permeability - the membrane can pick and choose what particles can pass through it.

THE LIPID BILAYER

•A phospholipid - made up of a glycerol attached to 2 fatty acids and a phosphate group.

THE PHOSPHOLIPID

•The fatty acids are hydrophobic (hate water).

•The phosphate group is hydrophilic (likes water).

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THE BILAYER STRUCTURE

•The cell membrane is a bilayer of phospholipids.

THE BILAYER STRUCTURE

• The cell membrane is a bilayer of phospholipids.• Reference

OTHER STRUCTURES IN THE MEMBRANE...

•Some cell membranes have cholesterol embedded between phospholipids to restrict their movement.

MEMBRANE PROTEINS

•Proteins are embedded in membranes.

•Some are on the inner or outer surfaces, some go the entire way through the bilayer.

MEMBRANE PROTEINS’ JOBS

•Regulate which particles can pass through membrane

•Act as enzymes in chemical reactions

•Act as markers on outside and inside of cell to identify self

WAYS TO MOVE THROUGH THE MEMBRANE:

•1. Active transport requires energy to move the molecules through the cell membrane.

•2. Passive transport does not require energy, and occurs spontaneously.

PASSIVE TRANSPORT•The principle means of passive transport is diffusion.

•Diffusion is the movement of molecules from a HIGH concentration to a LOW concentration.

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•Equilibrium occurs when two opposing actions occur at the same rate.

•Diffusion occurs when a system is not at equilibrium.

FACTORS THAT AFFECT DIFFUSION:

•Temperature - higher temperature means more energy and molecules will diffuse faster.

•Size - Smaller molecules will move more rapidly than larger molecules

REAL-LIFE EXAMPLES•CO2 and O2 diffuse across cell membranes.

•Oxygen moves from an area of high concentration to an area of low concentration from your lungs to your blood to your cells.

•As chemical reactions in the cell use up oxygen they produce CO2.

•The concentration of CO2 inside the cell increases so that more CO2 is inside of the cell.

•Therefore CO2 diffuses into your blood and then into your lungs were it is exhaled.

OSMOSIS

•The movement of water from a high concentration to a low concentration.

•It is the diffusion of water.•This can cause cells to burst or shrink.

FACILITATED DIFFUSION

Helping diffusion along •Proteins help certain

chemicals pass through a cell membrane

•Requires no energy (still moves from high to low)

•Usually needed for slightly larger molecules like glucose

HighConcentration

LowConcentration

CellMembrane

Glucosemolecules

Proteinchannel

HighConcentration

LowConcentration

CellMembrane

Glucosemolecules

Proteinchannel

ACTIVE TRANSPORT

•When a cell needs energy to move from low to high concentration.

•Pumps - proteins bind to particles according to their shape

•The protein then uses energy to change its shape and release particle.

•Particles move against diffusion (from low to high concentration)

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OTHER WAYS CELLS GET MATERIALS...

•Endocytosis - cell membrane engulfs and takes in materials –Phagocytosis - solid material taken in

–Pinocytosis - liquid material take in

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•Exocytosis - vesicles with wastes move to cell membrane and fuse with membrane. The wastes are then released.

Exocytosis

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