1 The Plasma Membrane The Plasma Membrane - Gateway to the Cell

2 Photograph of a Cell Membrane

3 Cell Membrane flexible The cell membrane is flexible and allows a unicellular organism to move

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

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

6 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)

7 Structure of the Cell Membrane

8 Phospholipids Cholesterol Proteins ( peripheral and integral) Carbohydrates (glucose) Membrane Components

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

10 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

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

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13 Cell Membrane Hydrophobic molecules pass easily; hydrophillic DO NOT phospholipid bilayer The cell membrane is made of 2 layers of phospholipids called the lipid bilayer

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

15 Small molecules and larger hydrophobic molecules move through easily. e.g. O 2, CO 2 Semipermeable Membrane

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

17 Types of Transport Across Cell Membranes

18 Simple Diffusion NORequires NO energy HIGH to LOWMolecules move from area of HIGH to LOW concentration

19 DIFFUSION PASSIVE Diffusion is an example of PASSIVE TRANSPORT

20 Diffusion of Liquids

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

22 Osmosis Diffusion of water across a selectively permeable membraneDiffusion of water across a selectively permeable membrane Moves from HIGH to LOW water potentialMoves from HIGH to LOW water potential Diffusion across a membrane Semipermeable membrane

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

24 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

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

26 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

27 Cells in Solutions

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

29 Cytolysis & Plasmolysis Cytolysis Plasmolysis

30 Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic

31 hypotonichypertonic isotonic hypertonicisotonic hypotonic

32 Three Forms of Transport Across the Membrane

33 Passive Transport Simple Diffusion  NO energy is used  Moves high to low concentration Example: O 2, H 2 O, CO 2  Example: O 2, H 2 O, CO 2

34 Passive Transport Facilitated diffusion  NO energy  Uses proteins to move high to low concentration Examples: Glucose, and amino acids moving from blood into a cell.

35 4 functions of Proteins on the plasma membrane

36 Two Types of Proteins Channel proteins Carrier proteins

37 Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins.

38 Facilitated Diffusion Carrier proteins change the shape and transport substances across the membraneCarrier proteins change the shape and transport substances across the membrane

39 Carrier Proteins Change shapeChange shape

40 Active Transport  NEEDS energy (ATP)  Moves from LOW to HIGH concentration  AGAINST concentration gradient

41 Active transport  Example: Sodium- Potassium pump

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

43 EXOCYTOSIS Vesicles move substances out of the cell moving things out. Examples: Hormones, Nerve cell communication Examples: Hormones, Nerve cell communication.

44 Exocytosis Exocytic vesicle immediately after fusion with plasma membrane.

45ENDOCYTOSIS Large molecules enter the cell by endocytosis

46Pinocytosis Substances enter the cell as liquid drops Substances enter the cell as liquid drops.

47 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”

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

49 Receptor-Mediated Endocytosis Proteins receive and transport hormones and cholesterol into the cell

50 Receptor-Mediated Endocytosis

51 Endocytosis – Phagocytosis Used to engulf large particles such as food, bacteria, into vesicles Called “Cell Eating”

52 Phagocytosis About to Occur

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

54 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

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