Homeostasis Membrane Transport Copyright Pearson Prentice Hall Cell

Homeostasis & Membrane Transport Copyright Pearson Prentice Hall

Cell Boundaries All cells are surrounded by a thin, flexible barrier known as the cell membrane. Many cells also produce a strong supporting layer around the membrane known as a cell wall. Copyright Pearson Prentice Hall

The Plasma Membrane Outside of cell Proteins Cell membrane Inside of cell (cytoplasm) Protein channel Carbohydrate chains Lipid bilayer Gateway to the Cell copyright cmassengale 3

Cell Membrane The cell membrane regulates what enters and leaves the cell and also provides protection and support. Copyright Pearson Prentice Hall

Cell Walls Cell walls are found in plants, algae, fungi, and many prokaryotes. Copyright Pearson Prentice Hall

Cell Membrane The cell membrane is flexible and allows a unicellular organism to move copyright cmassengale 6

Homeostasis • Balanced internal condition of cells • Also called equilibrium • Maintained by plasma membrane controlling what enters & leaves the cell copyright cmassengale 7

Functions of Plasma Membrane ü Protective barrier ü Regulate transport in & out of cell (selectively permeable) ü Allow cell recognition ü Provide anchoring sites for filaments of cytoskeleton copyright cmassengale 8

Functions of Plasma Membrane ü Provide a binding site for enzymes ü Interlocking surfaces bind cells together (junctions) üContains the cytoplasm (fluid in cell) copyright cmassengale 9

Structure of the Cell Membrane copyright cmassengale 10

Membrane Components Phospholipids Cholesterol Proteins (peripheral and integral) copyright cmassengale 11 Carbohydrates (glucose)

Phospholipids Make up the cell membrane Contains 2 fatty acid chains that are nonpolar Head is polar & contains a –PO 4 group & glycerol copyright cmassengale 12

FLUID MOSAIC MODEL FLUID- because individual phospholipids and proteins can move around freely within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the copyright cmassengale 13 membrane is viewed from above.

Cell Membrane Polar heads are hydrophilic “water loving” Nonpolar tails are hydrophobic “water fearing” Makes membrane “Selective” copyright cmassengale in what crosses 14

copyright cmassengale 15

Cell Membrane The cell membrane is Hydrophobic made of 2 layers of molecules pass phospholipid called the easily; hydrophilic lipid bilayer copyright cmassengale 16 DO NOT

Solubility • Materials that are soluble in lipids can pass through the cell membrane easily copyright cmassengale 17

Semipermeable Membrane Small molecules and larger hydrophobic molecules move through easily. e. g. O 2, CO 2, H 2 O copyright cmassengale 18

Semipermeable Membrane Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own. copyright cmassengale 19

Types of Transport Across Cell Membranes copyright cmassengale 20

Measuring Concentration A solution is a mixture of two or more substances. The substances dissolved in the solution are called solutes. The concentration of a solution is the mass of solute in a given volume of solution, or mass/volume. Copyright Pearson Prentice Hall

Diffusion Particles in a solution tend to move from an area where they are more concentrated to an area where they are less concentrated. This process is called diffusion. When the concentration of the solute is the same throughout a system, the system has reached equilibrium. Copyright Pearson Prentice Hall

Simple Diffusion • Requires NO energy • Molecules move from area of HIGH to LOW concentration copyright cmassengale 23

DIFFUSION Diffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural KINETIC ENERGY copyright cmassengale 24

Diffusion of Liquids copyright cmassengale 25

Diffusion through a Membrane Cell membrane Solute moves DOWN concentration gradient (HIGH to copyright cmassengale 26 LOW)

Diffusion Through Cell Boundaries Copyright Pearson Prentice Hall

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 28

Diffusion of H 2 O Across A Membrane High H 2 O potential Low solute concentration Low H 2 O potential 29 High solute concentration

Aquaporins • Water Channels • Protein pores used during OSMOSIS WATER MOLECULES copyright cmassengale 30

Osmosis How Osmosis Works Copyright Pearson Prentice Hall

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 32

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 33

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 34

Water tends to diffuse from a highly concentrated region to a less concentrated region. If you compare two solutions, three terms can be used to describe the concentrations: hypertonic (“above strength”). hypotonic (“below strength”). isotonic (”same strength”) Copyright Pearson Prentice Hall

Cells in Solutions copyright cmassengale 36

Isotonic Solution Hypotonic Solution NO NET MOVEMENT OF H 2 O (equal amounts entering & leaving) CYTOLYSIS copyright cmassengale Hypertonic Solution PLASMOLYSIS 37

Cytolysis & Plasmolysis Cytolysis copyright cmassengale Plasmolysis 38

Osmosis in Red Blood Cells Isotonic Hypotonic copyright cmassengale Hypertonic 39

Osmotic Pressure Osmosis exerts a pressure known as osmotic pressure on the hypertonic side of a selectively permeable membrane. Copyright Pearson Prentice Hall

hypotonic hypertonic isotonic hypotonic copyright cmassengale 41

Three Forms of Transport Across the Membrane copyright cmassengale 42

Passive Transport Simple Diffusion v Doesn’t require energy v Moves high to low concentration v Example: Oxygen diffusing into a cell and carbon dioxide diffusing out. copyright cmassengale 43

Passive Transport Facilitated diffusion v. Doesn’t require energy v. Uses transport proteins to move high to low concentration Examples: Glucose or amino acids moving from blood into a cell. copyright cmassengale 44

Proteins Are Critical to Membrane Function copyright cmassengale 45

Types of Transport Proteins • Channel proteins are embedded in the cell membrane & have a pore for materials to cross • Carrier proteins can change shape to move material from one side of the membrane to the other copyright cmassengale 46

Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins. copyright cmassengale 47

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 48

Facilitated Diffusion Glucose molecules Facilitated Diffusion Protein channel Copyright Pearson Prentice Hall

Carrier Proteins • Other carrier proteins change shape to move materials across the cell membrane copyright cmassengale 50

Active Transport Sometimes cells move materials in the opposite direction from which the materials would normally move—that is against a concentration difference. This process is known as active transport. Active transport requires energy. Copyright Pearson Prentice Hall

Active Transport Molecular Transport In active transport, small molecules and ions are carried across membranes by proteins in the membrane. Energy use in these systems enables cells to concentrate substances in a particular location, even when diffusion might move them in the opposite direction. Copyright Pearson Prentice Hall

Active Transport Molecule to be carried Copyright Pearson Prentice Hall

Active Transport v. Requires energy or ATP v. Moves materials from LOW to HIGH concentration v. AGAINST concentration gradient copyright cmassengale 54

Active transport v. Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients. v. Called Na+-K+ Pump copyright cmassengale 55

Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped copyright cmassengale 56 out; creates a membrane potential

Moving the “Big Stuff” 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 copyright cmassengale 57 cells communicate with one another

Exocytosis Exocytic vesicle immediately after fusion with plasma membrane. copyright cmassengale 58

Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane. Inside Cell copyright cmassengale Cell environment 59

Moving the “Big Stuff” Large molecules move materials into the cell by one of three forms of endocytosis copyright cmassengale 60

Pinocytosis Most common form of endocytosis Takes in dissolved molecules as a vesicle copyright cmassengale 61.

Pinocytosis • Cell forms an invagination • Materials dissolve in water to be brought into cell • Called “Cell Drinking” copyright cmassengale 62

Example of Pinocytosis mature transport vesicle pinocytic vesicles forming copyright cmassengale Transport across a capillary cell (blue). 63

Receptor-Mediated Endocytosis Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol , etc. copyright cmassengale 64