1. Cells: The Living Units Part A3

2. The cell is the basic structural and functional unit of life
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. Separates intracellular fluids from extracellular fluids
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. Double bilayer of lipids with imbedded, dispersed proteins
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.

18. against the concentration gradient.
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:

19. Two Types of Active Transport. Pumps Cytosis.

20. Completely changing shape requires energy.
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 6
K+ is released and Na+ sites are ready to bind Na+ again; the cycle repeats. 1
Binding of cytoplasmic Na+ to the pump protein stimulates phosphorylation by ATP.
Cytoplasm 2
Phosphorylation causes the protein to change its shape.
Concentration gradients of K+ and Na+ 5
Loss of phosphate restores the original conformation of the pump protein. 3
The shape change expels Na+ to the outside, and extracellular K+ binds. 4
K+ binding triggers release of the phosphate group.
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. Phagocytosis – cell eating Pinocytosis – cell drinking
Forms of Endocytosis
Phagocytosis – cell eating
Pinocytosis – cell drinking

26. WHITE BLOOD CELL ENGULFING BACTERIA (Phagocytosis)

27. INSULIN being released by pancreas cells using exocytosis

28. Passive Membrane Transport – Review
Process
Energy Source
Example
Simple diffusion
Kinetic energy
Movement of O2 through membrane
Facilitated diffusion
Movement of glucose into cells
Osmosis
Movement of H2O in & out of cells
Filtration
Hydrostatic pressure
Formation of kidney filtrate

29. Active Membrane Transport – Review
Process
Energy Source
Example
Active transport of solutes
ATP
Movement of ions across membranes
Exocytosis
Neurotransmitter secretion
Endocytosis
White blood cell phagocytosis
Fluid-phase endocytosis
Absorption by intestinal cells
Receptor-mediated endocytosis
Hormone and cholesterol uptake
Endocytosis via caveoli
Cholesterol regulation
Endocytosis via coatomer vesicles
Intracellular trafficking of molecules

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. Tight junction – impermeable junction that encircles the cell
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