Plasma Membrane Structure and Function Homeostasis Balanced internal

Plasma Membrane Structure and Function

Homeostasis • Balanced internal condition of cells • Also called equilibrium • Maintained by plasma membrane controlling what enters & leaves the cell copyright cmassengale 2

Membrane Functions • Protective barrier • Communication • Regulate transport in & out of cell (selectively permeable) • Respond to environment • Recognition • Provide anchoring sites for filaments of cytoskeleton

Plasma Membrane • • • Boundary that separates the living cell from it’s non-living surroundings. Phospholipid bilayer Amphipathic - having both: hydrophilic heads hydrophobic tails Phospholipid ~8 nm thick Is a dynamic structure

Phospholipids Make up the cell membrane Contains 2 fatty acid chains that are nonpolar Head is polar & contains a –PO 4 group & copyright cmassengale glycerol 5

FLUID-MOSAIC MODEL 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.

Materials that are soluble in lipids can pass through the cell membrane easily

• Small molecules and larger hydrophobic molecules move through easily e. g. O 2, CO 2, H 2 O • Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own

Types of Transport Across Cell Membranes copyright cmassengale 9

Simple Diffusion • Requires NO energy • Molecules move from area of HIGH to LOW concentration copyright cmassengale 10

DIFFUSION Diffusion is a PASSIVE process which means no energy is used to make move, they natural molecules have a KINETIC ENERGY copyright cmassengale 11

Diffusion of Liquids copyright cmassengale 12

Diffusion through a Membrane Cell membrane Solute moves DOWN concentration gradient (HIGH to LOW) copyright cmassengale 13

Gas exchange in lungs by diffusion

Osmosis • Diffusion of water across a membrane • Moves from HIGH water potential (low solute) to LOW water potential (high solute) Diffusion across a membrane copyright cmassengale Semipermeable membrane 15

Osmosis The diffusion of water across a differentially permeable membrane due to concentration differences

Diffusion of H 2 O Across A Membrane High H 2 O potential Low solute concentration Low H 2 O potential High solute concentration copyright cmassengale 17

Cell in Isotonic Solution 10% Na. CL 90% H 2 O ENVIRONMENT CELL 10% Na. CL 90% H 2 O NO NET MOVEMENT What is the direction of water movement? equilibrium The cell is at ________. copyright cmassengale 18

Cell in Hypotonic Solution 10% Na. CL 90% H 2 O CELL 20% Na. CL 80% H 2 O What is the direction of water movement? copyright cmassengale 19

Cell in Hypertonic Solution 15% Na. CL 85% H 2 O ENVIRONMENT CELL 5% Na. CL 95% H 2 O What is the direction of water movement? copyright cmassengale 20

Isotonic Solution Hypotonic Solution NO NET MOVEMENT OF H 2 O (equal amounts entering & leaving) CYTOLYSIS copyright cmassengale Hypertonic Solution PLASMOLYSIS 21

Cytolysis & Plasmolysis Cytolysis copyright cmassengale Plasmolysi 22

What Happens to Blood Cells? copyright cmassengale 23

Three Forms of Transport Across the Membrane copyright cmassengale 24

Passive Transport Simple Diffusion üDoesn’t require energy üMoves high to low concentration üExample: Oxygen or water diffusing into a cell and carbon dioxide diffusing out copyright cmassengale 25

Passive Transport Facilitated diffusion üDoesn’t require energy üUses transport proteins to move high to low concentration üExamples: Glucose or amino acids moving from blood into a cell. copyright cmassengale 26

Proteins Are Critical to Membrane Function copyright cmassengale 27

Types of Transport Proteins • Channel proteins are embedded in the cell membrane & have a pore for materials to cross • Carrier proteins move material can change shape to from one side of the membrane to the other copyright cmassengale 28

Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins copyright cmassengale 29

Facilitated Diffusion • Some Carrier proteins do not extend through the membrane. • They bond and drag molecules through the lipid bilayer and release them on the opposite side copyright cmassengale 30

Carrier Proteins Other carrier proteins change shape move across to materials the cell membrane copyright cmassengale 31

Active Transport üRequires energy or ATP üMoves materials from LOW to HIGH concentration üAGAINST concentration gradient copyright cmassengale 32

Active transport ü Example: Pumping Na+ (sodium ions) out and K+ (potassium against ions) in strong concentration gradients. ü Called Na+-K+ Pump copyright cmassengale 33

Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped out; cmassengale 34 creates copyright a membrane potential

Exocytosis and Endocytosis • Exocytosis---Cellular secretion • Endocytosis— –Phagocytosis— “Cell eating” –Pinocytosis– “Cell drinking” –Receptor-mediated endocytosisspecific particles, recognition.

Exocytosis moving things out Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. This is how many hormones are secreted and how nerve cells copyright cmassengale 36 communicate with one another

Exocytosis

Phagocytosis

Pinocytosis

Receptor-mediated Endocytosis