General cell biology & physiology

1. General cell biology & physiology Paula Ingram Darasaw pmid2@aol.com

2. objectives • Be able to discuss the: • Principles of cell theory • General cellular anatomy • Lipid bilayer membrane and function • Overview of organelles • Cellular physiology • Overview of cell transport and diffusion • Vesicular transport

3. Six Principles of Cell Theory • The cell is the smallest structural and functional unit capable of carrying out life processes. • The functional activities of each cell depend on the specific structural properties of the cell. • Cells are the living building blocks of all plant and animal organisms. • All organism’s structure and function ultimately depend on the individual and collective structural characteristics and functional capabilities of its cells. • All new cells and new life arise only from pre-existing cells. • Because of this continuity of life, the cells of all organisms are fundamentally similar in structure and function.

4. Generalized cell • All cells have some common structures and functions • Human cells have three basic parts: • Plasma membrane—flexible outer boundary • Cytoplasm—intracellular fluid containing organelles • Nucleus—control center

5. Nuclear envelope Chromatin Nucleolus Nucleus Smooth endoplasmic reticulum Plasma membrane Mitochondrion Cytosol Lysosome Centrioles Centrosome matrix Rough endoplasmic reticulum Ribosomes Golgi apparatus Secretion being released from cell by exocytosis Cytoskeletal elements • Microtubule • Intermediate filaments Peroxisome

6. Plasma membrane • Bimolecular layer of lipids and proteins in a constantly changing fluid mosaic • Plays a dynamic role in cellular activity • Separates intracellular fluid (ICF) from extracellular fluid (ECF) • Interstitial fluid (IF) = ECF that surrounds cells

8. MEMBRANE PROTEINS • Integral proteins • Firmly inserted into the membrane (most are transmembrane) • Functions: • Transport proteins (channels and carriers), enzymes, or receptors • Peripheral proteins • Loosely attached to integral proteins • Include filaments on intracellular surface and glycoproteins on extracellular surface • Functions: • Enzymes, motor proteins, cell-to-cell links, provide support on intracellular surface, and form part of glycocalyx

9. FUNCTIONS OF MEMBRANE PROTEINS • Transport • Receptors for signal transduction • Attachment to cytoskeleton and extracellular matrix • Enzymatic activity • Intercellular joining • Cell-cell recognition

10. MEMBRANE JUNCTIONS • Three types: • Tight junction - Prevent fluids and most molecules from moving between cells • Desmosome - “Rivets” or “spot-welds” that anchor cells together • Gap junction - Transmembrane proteins form pores that allow small molecules to pass from cell to cell

11. Membrane transport • Passive processes • No cellular energy (ATP) required • Substance moves down its concentration gradient • Active processes • Energy (ATP) required • Occurs only in living cell membranes

13. Passive processes • Simple diffusion • Carrier-mediated facilitated diffusion • Channel-mediated facilitated diffusion • Osmosis

15. Simple diffusion

16. Facilitated diffusion

17. osmosis • Movement of solvent (water) across a selectively permeable membrane • Water diffuses through plasma membranes: • Through the lipid bilayer • Through water channels called aquaporins (AQPs) • Water concentration is determined by solute concentration because solute particles displace water molecules • Osmolarity: The measure of total concentration of solute particles • When solutions of different osmolarity are separated by a membrane, osmosis occurs until equilibrium is reached

18. TONICITY

19. (a) Membrane permeable to both solutes and water Solute and water molecules move down their concentration gradients in opposite directions. Fluid volume remains the same in both compartments. Right compartment: Solution with greater osmolarity Both solutions have the same osmolarity: volume unchanged Left compartment: Solution with lower osmolarity H2O Solute Solute molecules (sugar) Membrane Figure 3.8a

20. (b) Membrane permeable to water, impermeable to solutes Solute molecules are prevented from moving but water moves by osmosis. Volume increases in the compartment with the higher osmolarity. Both solutions have identical osmolarity, but volume of the solution on the right is greater because only water is free to move Left compartment Right compartment H2O Solute molecules (sugar) Membrane Figure 3.8b

21. SUMMARY OF PASSIVE PROCESSES

22. ACTIVE PROCESSES • Two types of active processes: • Active transport • Vesicular transport • Both use ATP to move solutes across a living plasma membrane

23. ACTIVE TRANSPORT • Requires carrier proteins (solute pumps) • Moves solutes against a concentration gradient • Types of active transport: • Primary active transport • Secondary active transport

25. Extracellular fluid Na+ Na+-K+ pump K+ ATP-binding site Cytoplasm 1 1 Cytoplasmic Na+ binds to pump protein. Cytoplasmic Na+ binds to pump protein. Figure 3.10 step 1

26. Na+ bound P ATP ADP 2 Binding of Na+ promotesphosphorylation of the protein by ATP. Figure 3.10 step 2

27. Na+ released P 3 Phosphorylation causes the protein tochange shape, expelling Na+ to the outside.

28. K+ P 4 Extracellular K+ binds to pump protein.

29. K+ bound Pi 5 K+ binding triggers release of thephosphate. Pump protein returns to itsoriginal conformation.

30. K+ released 6 K+ is released from the pump proteinand Na+ sites are ready to bind Na+ again.The cycle repeats.

32. VESICULAR TRANSPORT • Functions: • Exocytosis—transport out of cell • Endocytosis—transport into cell • Transcytosis—transport into, across, and then out of cell • Substance (vesicular) trafficking—transport from one area or organelle in cell to another

33. Coated pit ingestssubstance. 1 Extracellular fluid Plasmamembrane Protein coat(typicallyclathrin) Cytoplasm 2 Protein-coatedvesicledetaches. 3 Coat proteins detachand are recycled toplasma membrane. Transportvesicle Endosome Uncoatedendocytic vesicle 4 Uncoated vesicle fuseswith a sorting vesiclecalled an endosome. 5 Transportvesicle containingmembrane componentsmoves to the plasmamembrane for recycling. Lysosome 6 Fused vesicle may (a) fusewith lysosome for digestionof its contents, or (b) deliverits contents to the plasmamembrane on theopposite side of the cell(transcytosis). (b) (a)

34. The process of exocytosis Plasma membrane SNARE (t-SNARE) Extracellular fluid Fusion pore formed 1 The membrane- bound vesicle migrates to the plasma membrane. Secretory vesicle Vesicle SNARE (v-SNARE) 3 The vesicle and plasma membrane fuse and a pore opens up. Molecule to be secreted Cytoplasm 2 There, proteins at the vesicle surface (v-SNAREs) bind with t-SNAREs (plasma membrane proteins). 4 Vesicle contents are released to the cell exterior. Fused v- and t-SNAREs

35. Summary of active processess

36. Cytoplasm • Located between plasma membrane and nucleus • Cytosol • Water with solutes (protein, salts, sugars, etc.) • Cytoplasmic organelles • Metabolic machinery of cell • Inclusions • Granules of glycogen or pigments, lipid droplets, vacuoles, and crystals

37. Membranous Mitochondria Peroxisomes Lysosomes Endoplasmic reticulum Golgi apparatus Nonmembranous Cytoskeleton Centrioles Ribosomes Cytoplasmic Organelles

38. Mitochondria • Double-membrane structure with shelflike cristae • Provide most of cell’s ATP via aerobic cellular respiration • Contain their own DNA and RNA

39. Ribosomes • Granules containing protein and rRNA • Site of protein synthesis • Free ribosomes synthesize soluble proteins • Membrane-bound ribosomes (on rough ER) synthesize proteins to be incorporated into membranes or exported from the cell

40. Endoplasmic Reticulum (ER) • Interconnected tubes and parallel membranes enclosing cisternae • Continuous with nuclear membrane • Two varieties: • Rough ER • Smooth ER

41. Smooth ER Nuclear envelope Rough ER Ribosomes (a) Diagrammatic view of smooth and rough ER Figure 3.18a

42. Rough ER • External surface studded with ribosomes • Manufactures all secreted proteins • Synthesizes membrane integral proteins and phospholipids

43. Smooth ER • Tubules arranged in a looping network • Enzyme (integral protein) functions: • In the liver—lipid and cholesterol metabolism, breakdown of glycogen, and, along with kidneys, detoxification of drugs, pesticides, and carcinogens • Synthesis of steroid-based hormones • In intestinal cells—absorption, synthesis, and transport of fats • In skeletal and cardiac muscle—storage and release of calcium

44. Golgi Apparatus • Stacked and flattened membranous sacs • Modifies, concentrates, and packages proteins and lipids • Transport vessels from ER fuse with convex cis face of Golgi apparatus • Proteins then pass through Golgi apparatus to trans face • Secretory vesicles leave trans face of Golgi stack and move to designated parts of cell

45. 1 Protein- containing vesicles pinch off rough ER and migrate to fuse with membranes of Golgi apparatus. Rough ER Phagosome ER membrane Plasma mem- brane Proteins in cisterna Pathway C: Lysosome containing acid hydrolase enzymes 2 Proteins are modified within the Golgi compartments. Vesicle becomes lysosome 3 Proteins are then packaged within different vesicle types, depending on their ultimate destination. Secretory vesicle Pathway B: Vesicle membrane to be incorporated into plasma membrane Golgi apparatus Pathway A: Vesicle contents destined for exocytosis Secretion by exocytosis Extracellular fluid Figure 3.20

46. Lysosomes • Spherical membranous bags containing digestive enzymes (acid hydrolases) • Digest ingested bacteria, viruses, and toxins • Degrade nonfunctional organelles • Break down and release glycogen • Break down bone to release Ca2+ • Destroy cells in injured or nonuseful tissue (autolysis)

47. Endomembrane System • Overall function • Produce, store, and export biological molecules • Degrade potentially harmful substances The Endomembrane System includes the Endoplasmic Reticulum, Golgi Apparatus, Secretory Vesicles and Lysosomes as well as the Nuclear Envelope

48. Peroxisomes • Membranous sacs containing powerful oxidases and catalases • Detoxify harmful or toxic substances • Neutralize dangerous free radicals (highly reactive chemicals with unpaired electrons) • Oxidases convert free radicals to hydrogen peroxide, which is also reactive and dangerous but is quickly converted to water by catalase enzymes

49. Cytoskeleton • Elaborate series of rods throughout cytosol that support cellular structures and provide the machinery to generate various cell movements. There are three types of rods in the cytoskeleton, in order of increasing size: • Microfilaments • Intermediate Filaments • Microtubules

50. Microfilaments • Dynamic actin strands attached to cytoplasmic side of plasma membrane • Involved in cell motility, change in shape, endocytosis and exocytosis