The Cell Membrane 1 Gateway Across the Cell

Functions of Plasma Membrane 2  Protective barrier Regulate transport in & out of cell (selectively permeable)

Importance of the Cell Membrane  Maintains HOMEOSTASIS  Balanced internal condition of cells…this is called reaching equilibrium 3

Structure of the Cell Membrane 4

Phospholipid Bilayer 5 Contains 2 lipid tails that are hydrophobic (nonpolar) Phosphate head is hydrophilic (polar)

6 Cell Membrane hydrophilic Polar heads are hydrophilic “water loving ” hydrophobic Nonpolar tails are hydrophobic “water fearing” Makes membrane “Selective” in what crosses

FLUID- FLUID- because individual phospholipids and proteins can move side-to-side within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above. 7 FLUID MOSAIC MODEL

Selective Permeability  Definition: the cell membrane only allows some, but not all, molecules to cross it  Also called semipermeable  Enables cells to maintain homeostasis  How molecules cross the cell membrane depend on it’s size and polarity NOT  Sometimes ENERGY is needed (ACTIVE transport), other times ENERGY is NOT needed (PASSIVE transport) 8

Types of Transport Across Cell Membranes 9

Passive Transport  Passive transport—movement of molecules across the cell membrane WITHOUT the use of energy  3 types:  Diffusion  Osmosis  Facilitated diffusion 10

Diffusion NO  Requires NO energy HIGH to LOW  Molecules move from an area of HIGH concentration to LOW concentration 11

12 Cell membrane Solutes move DOWN concentration gradient (HIGH to LOW)

Osmosis  Diffusion of water across a membrane  Moves from HIGH water potential (low solute) to LOW water potential (high solute) 13 Diffusion across a membrane Semipermeable membrane

Diffusion of Water Across A Membrane 14 High H 2 O potential Low solute concentration Low H 2 O potential High solute concentration

Cell in Isotonic Solution 15 CELL 10% NaCL 90% H 2 O 10% NaCL 90% H 2 O What is the direction of water movement? The cell is at _______________. equilibrium ENVIRONMENT NO NET MOVEMENT

Cell in Hypotonic Solution 16 CELL 10% NaCL 90% H 2 O 20% NaCl 80% H 2 O What is the direction of water movement?

Cell in Hypertonic Solution 17 CELL 15% NaCL 85% H 2 O 5% NaCL 95% H 2 O What is the direction of water movement? ENVIRONMENT

18 Isotonic Solution NO NET MOVEMENT OF H 2 O (equal amounts entering & leaving) Hypotonic Solution CYTOLYSIS Hypertonic Solution PLASMOLYSIS

19 Facilitated diffusion  Doesn’t require energy  Uses transport proteins to move high to low concentration

20 Active Transport  Requires energy or ATP  Moves materials from LOW to HIGH concentration  AGAINST concentration gradient

Active transport  Sodium Potassium Pump: Pumping Na + (sodium ions) out and K + (potassium ions) in against strong concentration gradients. 21

22 Moving the “Big Stuff” Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. Exocytosis moving things out. Exocytosis - moving things out.

23 Endocytosis – Phagocytosis Used to engulf large particles such as food, bacteria, etc. into vesicles