1. Cells: The Living Units Part A3

2. Structure of a Generalized Animal Cell
Figure 3.2

3. Plasma Membrane
Separates intracellular fluids from extracellular fluids
Bilayer consists of phospholipids, cholesterol, glycolipids and imbedded proteins

4. Functions of Membrane Proteins

5. Passive Membrane Transport: Diffusion
Simple diffusion –
nonpolar and lipid-soluble substances like steroids
Facilitated diffusion
Specific carries for some molecules
Protein channels

6. Diffusion 6 16 11
Membrane permeable to solute & H2O

7. Osmosis - Diffusion of water
Diffusion of water across a semipermeable membrane
Occurs when the concentration of a solvent is different on opposite sides of a membrane
Osmolarity – concentration of all solute molecules in a solution
Tonicity – term describing relative osmolarity of two solutions
Hypo – below (lower osmolarity)
Hyper – above (higher osmolarity)
Iso – equal (same osmolarity)

8. Osmosis
6 M
16 M
11 M
11 M
Membrane permeable only to H2O

9. Active Transport Uses ATP to move solutes across a membrane
Requires carrier proteins – pumps
Categories of Carrier Proteins
Uniport – a single substance
Symport system – two substances, simultaneously, same direction
Antiport system – two substances, simultaneously, opposite directions

10. Active Transport: Sodium-Potassium Pump6
K+ is released and Na+ sites are ready to bind Na+ again; the cycle repeats.
Extracellular fluid
Binding of cytoplasmic Na+ to the pump protein stimulates phosphorylation by ATP. 1
Cytoplasm
low
high 2
Phosphorylation causes the protein to change its shape.
low
high
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.

11. Types of Active Transport
Primary active transport –phosphorylation of the carrier protein by ATP causes conformational change
Secondary active transport – use of an exchange pump (such as the Na+-K+ pump) to indirectly drive the transport of other solutes

12. Membrane Potential Voltage across a membrane
Na+ and K+ concentration gradients
active transport of ions by pumps & diffusion of K+ through channels
Ranges from –20 to –100 mV

13. Roles of Membrane Receptors
Receive stimulus from outside cell and transmit signal into cell
Ligand
Proteins/peptides
Neurotransmitters
Ligand activates receptor
Receptor activates a signaling pathway inside the cell

14. Cytoplasm Cytoplasm – material between plasma membrane and the nucleus
Cytosol – aqueous solution of proteins, salts, sugars, etc..
Cytoplasmic organelles – metabolic machinery of the cell

15. Cytoplasmic Organelles
Membranous
nucleus
mitochondria
vesicles
endoplasmic reticulum
Golgi apparatus
Nonmembranous
cytoskeleton
centrioles
ribosomes

16. Nucleus
Figure 3.28a

17. Chromosomes Double stranded molecules of DNA
DNA compacted with proteins

18. DNA Replication
DNA polymerase replicates each strand of original double helix
Two copies are separated into daughter cells during mitosis
Figure 3.31

19. Cell Cycle Interphase Mitotic phase G1 DNA synthesis (S) G2 Prophase
Metaphase
Anaphase
Telophase
Figure 3.30

20. From DNA to Protein – Gene Expression
Regions of DNA constitute genes
Genes encode for RNA
RNA is produced by the biochemical process of transcription
RNA leaves the nucleus and is used to direct protein synthesis –translation - in the cytoplasm

21. RNA Synthesis - Transcription

22. Ribosomes Composed of rRNA and proteins Carry out protein synthesis
Cytoplasmic ribosomes synthesize soluble proteins
ER membrane-attached ribosomes synthesize proteins to be incorporated into membranes or secreted from cell

23. Protein Synthesis - Translation
Figure 3.37

24. Protein Synthesis by ER-bound Ribosomes
Figure 3.19

25. Endoplasmic Reticulum (ER)
Interconnected membrane compartments
Continuous with the outer nuclear membrane
rough ER and smooth ER

26. Golgi Apparatus Modification, concentration, and packaging of proteins
Vesicles from the ER fuse with the Golgi apparatus
Proteins pass through the Golgi apparatus
Secretory vesicles leave the Golgi and move to designated parts of the cell

27. The Endomembrane System – ER-Golgi-Vesicles
Figure 3.21

28. Vesicular Transport
Transport of large particles and macromolecules across plasma membranes
Exocytosis – out of cell
Endocytosis – into cell
Phagocytosis – large particles into cell
Vesicular trafficking – place to place within cell

29. Specialized Vesicles Lysosomes Peroxisomes
Vesicles containing digestive enzymes
Digest materials ingested by the cell during endocytosis & phagocytosis
Peroxisomes
Vesicles containing oxidases and catalases
Carry out biochemical reactions requiring O free radicals

30. Mitochondria Generates ATP by aerobic cellular respiration
Krebs’ Cycle
Oxidative-Phosphorylation

31. Cytoskeleton
Dynamic, rod-like proteins throughout the cytosol and underlying plasma membrane
Three major types
Microtubules
Intermediate filaments
Microfilaments

32. Microtubules Dynamic, hollow tubes made of tubulin proteins
Determine overall shape of cell and distribution of organelles
Organized by the centrioles

33. Centrioles Barrel-shaped organelles located near the nucleus
Pinwheel array of short microtubules
Organize mitotic spindle during mitosis

34. Motor Molecules & Microtubules
Examples: dyein, kinesin
Powered by ATP
Attach organelles to microtubules & microtubules to each other

35. Cilia & Flagella Whiplike, motile cellular extensions Cilia Flagella
Found in multiple arrays on apical surface of some epithelial cells
Respiratory tract
Fallopian tubes
Move substances in one direction across cell surfaces
Flagella
Single structure
Moves cell
Sperm are only human cell with flagellum

36. Cilia

37. Microfilaments Dynamic strands of the protein -actin
Attached to the inside of the plasma membrane
Braces and strengthens the cell surface
Function in endocytosis, exocytosis and cell movement

38. Intermediate Filaments
Tough, protein fibers resist pulling forces on the cell
Attaches to inside of membrane at desmosomes

39. Cell Adhesion Complexes
Anchor cells to each other
Desomsomes
Adherins junctions
Tight junctions
Allow cell motility by anchoring to the extracellular matrix
Focal adhesions
Allow cell-cell movement of relatively large molecules
Gap junctions
Cell adhesion molecules (CAMs)
desmin
cadherin
integrin

40. Tight Junction
Figure 3.5a

41. Desmosomes & Adherens Junctions
Figure 3.5b

42. Gap Junction
Figure 3.5c