Copyright Pearson Prentice Hall 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.

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

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

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

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

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

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

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

10 Structure of the Cell Membrane copyright cmassengale

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

12 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

13 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 membrane is viewed from above. FLUID MOSAIC MODEL copyright cmassengale

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

15copyright cmassengale

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

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

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

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

20 Types of Transport Across Cell Membranes copyright cmassengale

Copyright Pearson Prentice Hall 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.

23 Simple Diffusion NORequires NO energy HIGH to LOWMolecules move from area of HIGH to LOW concentration copyright cmassengale

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

25 Diffusion of Liquids copyright cmassengale

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

Copyright Pearson Prentice Hall Diffusion Through Cell Boundaries

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

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

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

Copyright Pearson Prentice Hall Osmosis How Osmosis Works

32 Cell in Isotonic Solution 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 copyright cmassengale

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

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

Copyright Pearson Prentice Hall 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”)

36 Cells in Solutions copyright cmassengale

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

38 Cytolysis & Plasmolysis Cytolysis Plasmolysis copyright cmassengale

39 Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic copyright cmassengale

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

41 hypotonichypertonic isotonic hypertonicisotonic hypotonic copyright cmassengale

42 Three Forms of Transport Across the Membrane copyright cmassengale

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

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

45 Proteins Are Critical to Membrane Function copyright cmassengale

46 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

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

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

Copyright Pearson Prentice Hall Facilitated Diffusion Protein channel Glucose molecules

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

Copyright Pearson Prentice Hall 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

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

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

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

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

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

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

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

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

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

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

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

65 Receptor-Mediated Endocytosis

66 Endocytosis – Phagocytosis Used to engulf large particles such as food, bacteria, etc. into vesicles Called “Cell Eating” copyright cmassengale

67 Phagocytosis About to Occur

68 Phagocytosis Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue) copyright cmassengale