Cells: The Living Units Part A

1. Cells: The Living Units Part A 3

2. Cell Theory • The cell is the basic structural and functional unit of life • Organism activity depends on individual and collective activity of cells • Biochemical activities of cells are dictated by subcellular structure • Continuity of life has a cellular basis

3. Structure of a Generalized Cell Figure 3.2

4. Plasma Membrane • Separates intracellular fluids from extracellular fluids • Plays a dynamic role in cellular activity • Glycocalyx is a glycoprotein area abutting the cell that provides highly specific biological markers by which cells recognize one another

5. Fluid Mosaic Model • Double bilayer of lipids with imbedded, dispersed proteins • Bilayer consists of phospholipids, cholesterol, and glycolipids • Glycolipids are lipids with bound carbohydrate • Phospholipids have hydrophobic and hydrophilic bipoles

6. Draw simple Phospholipid Bilayer

7. Fluid Mosaic Model Figure 3.3

8. Functions of Membrane Proteins • Transport • Enzymatic activity • Receptors for signal transduction Figure 3.4.1

9. Passive Membrane Transport: Diffusion • Simple diffusion – nonpolar and lipid-soluble substances • Diffuse directly through the lipid bilayer

10. Passive Membrane Transport: Osmosis • Occurs when the concentration of a solvent is different on opposite sides of a membrane • Osmosis: diffusion of water across a semi-permeable membrane • Osmolarity – total concentration of solute particles in a solution • Tonicity – how a solution affects cell volume

11. Effects of Solutions of Varying Tonicity • Isotonic – solutions with the same solute concentration as that of the cytosol • Hypertonic – solutions having greater solute concentration than that of the cytosol • Hypotonic – solutions having lesser solute concentration than that of the cytosol

12. Effect of Membrane Permeability on Diffusion and Osmosis Figure 3.8b

13. Passive Membrane Transport: Filtration • The passage of water and solutes through a membrane by hydrostatic pressure • Pressure gradient pushes solute-containing fluid from a higher-pressure area to a lower-pressure area

14. Diffusion Through the Plasma Membrane Figure 3.7

15. Passive Membrane Transport: Diffusion • Facilitated diffusion • Transport of glucose, amino acids, and ions • Transported substances bind carrier proteins or pass through protein channels • Are integral trans-membrane proteins • Show specificity for certain polar molecules including sugars and amino acids

16. Process of Facilitated Diffusion • Protein binds with molecule • Shape of protein changes • Molecule moves across membrane

17. Facilitated Diffusion Ion CHANNELS Membrane proteins create a tunnel through which Ions can pass. http://bio.winona.edu/berg/ANIMTNS/voltgate.htm

18. Active Transport Transport that require energy to move molecules against the concentration gradient. Cell example: Want to put MORE glucose into mitochondria when there is already glucose in there. Image from: http://www.biologyclass.net/mitochondria.jpg

19. Active Transport • Two Types of Active Transport. • Pumps • Cytosis.

20. Pumps • Carrier proteins that change shape for molecules that are not the correct shape. • Completely changing shape requires energy.

21. Sodium-Potassium Pump Extracellular fluid K+ is released and Na+ sites are ready to bind Na+ again; the cycle repeats. 6 Binding of cytoplasmic Na+ to the pump protein stimulates phosphorylation by ATP. 1 Cytoplasm Phosphorylation causes the protein to change its shape. 2 Concentration gradients of K+ and Na+ The shape change expels Na+ to the outside, and extracellular K+ binds. 3 Loss of phosphate restores the original conformation of the pump protein. 5 K+ binding triggers release of the phosphate group. 4 Figure 3.10

22. Vesicular Transport • Transport of large particles and macromolecules across plasma membranes • Exocytosis – moves substance from the cell interior to the extracellular space • Endocytosis – enables large particles and macromolecules to enter the cell

23. Vesicular Transport • Transcytosis – moving substances into, across, and then out of a cell • Vesicular trafficking – moving substances from one area in the cell to another

24. Exocytosis Figure 3.12a

25. Forms of Endocytosis • Phagocytosis – cell eating • Pinocytosis – cell drinking

26. WHITE BLOOD CELL ENGULFING BACTERIA(Phagocytosis) http://fig.cox.miami.edu/~cmallery/255/255ion/fig14x28.jpg

27. INSULIN being released by pancreas cells using exocytosis http://fig.cox.miami.edu/~cmallery/255/255ion/fig14x26.jpg

28. Passive Membrane Transport – Review

29. Active Membrane Transport – Review

30. Functions of Membrane Proteins • Intercellular adhesion • Cell-cell recognition • Attachment to cytoskeleton and extracellular matrix Figure 3.4.2

31. Plasma Membrane Surfaces • Differ in the kind and amount of lipids they contain • Glycolipids are found only in the outer membrane surface • 20% of all membrane lipid is cholesterol

32. Membrane Junctions • Tight junction – impermeable junction that encircles the cell • Desmosome – anchoring junction scattered along the sides of cells • Gap junction – a nexus that allows chemical substances to pass between cells

33. Membrane Junctions: Tight Junction Figure 3.5a

34. Membrane Junctions: Desmosome Figure 3.5b

35. Membrane Junctions: Gap Junction Figure 3.5c