Cellular transport

plasma membrane controls what enters and leaves the cell maintain homeostasis Selectively permeable The structure of the cell membrane determines what can enter or leave the cell

Cell membrane The cell membrane is a phospholipid bilayer with proteins embedded within The phospholipids are the round yellow structures with the blue tails, the proteins are the lumpy structures that are scattered around among the phospholipids.

phospholipid This is a simple representation of a phospholipid. the yellow structure represents the phosphate (hydrophilic or water loving section of the phospholipid). POLAR The blue tails that come off of the sphere represent the lipid (hydrophobic or water fearing end of the Phospholipid. NONPOLAR

Membrane proteins They communicate with the cell’s environment Proteins serve many functions within the cell membrane They communicate with the cell’s environment They allow the immune system to recognize the cell as foreign or not they control cell adhesion to form tissues They help with transport across the cell membrane

cholesterol Steroids are sometimes a component of cell membranes in the form of cholesterol. Maintains the shape (reduces the fluidity) of the membrane. Not all membranes contain cholesterol.

How molecules move in or out If they are small enough to pass through the spaces b/w the phospholipids (WATER) If they can be dissolved in the phospholipds (OXYGEN & CARBON DIOXIDE) Transported through membrane by carrier proteins or protein channels (GLUCOSE, AMINO ACIDS)

diffusion Random movement of molecules from a high concentration to a low concentration Concentration: (amount of solute in a solution) Molecules ‘spread out’ until they are evenly distributed No energy is required

Break it down… HIGH: lots of solute LOW: little solute GOAL: reach DYNAMIC EQUILIBRIUM CONCENTRATION GRADIENT: difference in concentration on each side of a membrane Factors that influence rate of diffusion: temperature pressure concentration

OTHER EXAMPLES OF DIFFUSION Diffusion explains how substances become dispersed in a solution

DYNAMIC EQUILIBRIUM Movement into the cell is at the same rate as the movement out of the cell The cell has achieved a “steady state”… HOMEOSTASIS Rate of water entering = Rate of water leaving Hence the level of water is constant

osmosis Movement of WATER from a HIGH to a LOW concentration Movement through a semi-permeable membrane Dilutes solutions Driven by CONCENTRATION GRADIENT Result: DYNAMIC EQUILIBRIUM

EFFECT OF OSMOSIS ON CELLS Higher water concentration OUTSIDE cell… cell GAINS…gets BIGGER Higher water concentration INSIDE cell… Cell LOSES…gets SMALLER Water concentration the same INSIDE and OUTSIDE… Water moves equally in and out; cell stays the same size

PASSIVE TRANSPORT Passive Transport requires NO ENERGY Molecules move from Higher conc. to Lower conc. (this is movement WITH the concentration gradient) EXAMPLES: DIFFUSION OSMOSIS FACILITATED DIFFUSION (CHANNEL PROTEINS)

Facilitated diffusion Movement of substances across the cell membrane through protein channels Molecules still move from higher concentration to lower conc. No energy is required This is how glucose & amino acids get into the cell

Channel proteins In some cases the channel proteins simply act as a passive pore. Molecules will randomly move through the opening in a process called diffusion. This requires no energy, molecules move from an area of high concentration to an area of low concentration

Carrier proteins These are carrier proteins. They do not extend through the membrane. They bond and drag molecules through the bilipid layer and release them on the opposite side. Requires energy

Active transport Movement of molecules from LOW to HIGH (against the concentration gradient) REQUIRES ENERGY (ATP) EXAMPLES: Ion pumps Contractile vacuole (pumps) Bulk Transport Endocytosis (in) Exocytosis (out)

endocytosis This is also how our WBC attack & destroy bacteria The cell membrane can also engulf structures that are much too large to fit through the pores in the membrane proteins… this process is known as endocytosis. In this process the membrane itself wraps around the particle and pinches off a vesicle inside the cell. In this animation an amoeba engulfs a food particle. This is also how our WBC attack & destroy bacteria PHAGOCYTOSIS

Passive vs. active transport What differences do you see in the diagrams b/w Active & Passive Transport? Active Transport uses ENERGY:ATP; and molecules are moving AGAINST concentration gradient (L-H) Passive Transport: no energy used; movement with conc.radient (H-L)