CHAPTER 7 CELL STRUCTURE AND FUNCTION Section 7

CHAPTER 7 CELL STRUCTURE AND FUNCTION Section 7. 3 - Cell Boundaries

Cell Membrane � Cell membrane � Border � Phospholipid bilayer

Cell Membrane � Fluid Mosaic Model � Proteins embedded in lipid bilayer Cell surface markers, pumps, channels, receptors

Cell Wall � � rigid layer made of cellulose

Passive Transport � What does passive mean? What does transport mean? � Passive Transport � � Movement of substances across a membrane “down” their concentration gradients without using energy

� � Diffusion Net flow from high conc. to low conc. Driven by kinetic energy (energy of motion)

Diffusion High [ ] Low [ ] � � Semipermeable Membrane Down Concentration Gradient Equilibrium “both sides are equal”

� � Diffusion of water across a membrane Direction of osmosis into or out of a cell depends on solute concentrations inside and outside the cell Osmosis Animation of Osmosis

Osmosis- Direction of Osmosis Isotonic � Hypertonic Hypotonic Salt is the solute �A solute is a substance that dissolves in a solvent

Facilitated Diffusion � Diffusion that requires the help of carrier proteins Animation of Facilitated Diffusion

Diffusion Through Ion Channels � � Ion channels are membrane proteins that allow only specific ions to pass through. Channels can be “open” or “gated” � If an ion channel is gated, it can be opened by stretching the cell membrane, a voltage, or a chemical

Active Transport � � Cell Membrane Pumps Movement in Vesicles

Active Transport � What does active mean? What does transport mean? � Active Transport � � Movement of substances across a membrane “up” their concentration gradients using energy

Cell Membrane Pumps � � Carrier proteins that move substances from areas of low concentration to areas of high concentration. Requires energy � What molecule furnishes the energy to power the pump? �ATP

Sodium-Potassium Pump � � Transports Na+ and K+ 3 Na+ out of cell / 2 K+ into cell

How Na+/K+ pump works: Animation of Sodium-Potassium Pump

Movement in Vesicles � � � What happens if substances are too large to pass through the cell membrane or carrier protein? What does the prefix endo- mean? What does the prefix exo- mean? What does cyto- mean? What does –osis mean?

Movement in Vesicles Endocytosis � Process by which cells ingest what they need. � Requires energy � Cell membrane folds and pinches off to form a vesicle

Endocytosis � 2 Types � Pinocytosis Endocytosis of solutes and fluids � Phagocytosis Endocytosis of large particles and whole cells Phagocytes

Movement in Vesicles Exocytosis � Process by which cells release unwanted substances. � Requires energy � Vesicles fuse to membrane to let substances out of cell