Cell Structures & Types: A Detailed Overview

1. Chapter 3 Cells and Tissues

2. About this Chapter • Cell structure and types • Cell differentiation • Compartmentalization • Mechanical properties and cell functions • Cell junctions • Tissue types and characteristics

3. Overview: Cells to Organ Systems Figure 3-4d, e: Anatomy Summary: Levels of Organization—System to Cell

4. Cytosol Organelles Inclusion Dissolved Insoluble Cell Cytoplasm Figure 3-3: A map for the study of cell structure

5. Ribosomes Free Fixed Protein synthesis Vaults: large nucleoprotein particles (mostly protein) which have 39 fold symmetery. 3X the size of ribosomes and are present in many types of eukaryotic cells, Highly conserved among eukaryotes. Precise function unknown but they may play a role in protein synthesis; in transport of mRNA to cytoplasm, and may play a role in fighting pathogens Nonmenbranous Organelles

6. Nonmenbranous Organelles Figure 3-6: Ribosomes are nonmembranous organelles composed of RNA and protein

7. Internal lumen and membranes for protected reactions Mitochondria: Generates cell energy (ATP) , have DNA Membranous Organelles: Create cell compartments Figure 3-9: Mitochondria

9. Smooth ER: Lipid synthesis & conversion Rough ER: Ribosomes, protein assembly & transport vesicles Endoplasmic Reticulum (ER) ad Ribosomes Figure 3-10: The endoplasmic reticulum

11. Protein packaging Secretory vesicles Secreted to E C F Golgi Apparatus

12. Golgi Apparatus Figure 3-11: The Golgi apparatus

14. Lysosomes Enzymes Intracellular digestion Peroxisomes Hydrogen peroxide Detoxification Fatty acid degradation Cytoplasmic Vesicles Figure 3-12: Lysosomes and peroxisomes

15. Nuclear envelope Nuclear pore complex Chromatin DNA form genes Nucleoli DNA concentrations Control rRNA synthesis Nucleus

16. Nucleus Figure 3-13: The nucleus

17. Overview: Cells to Organ Systems Figure 3-4a-c: Anatomy Summary: Levels of Organization—System to Cell

18. Cell Membrane Figure 3-5: The cell membrane

19. The importance of selectively permeable membranes • Membranes are physical barriers of cells and subcellular compartments controlling material exchange between the internal environment and the extracellular environment • A membrane is essentially a hydrophobic permeability barrier consisting of phospholipids, glycolipids, and membrane proteins • Membranes contain amphipathic molecules such as phosphatidyl ethanolamine, an example of phosphoglycerides, the major class of membrane phospholipids in most cells. Polar head Nonpolar tail

20. Cell Junctions: • Gap Junctions: Simplest Cell-Cell Junction. Can open and close. Present in many tissues. Proteins associated with: Connexins • Tight Junctions: Cell-Cell Junction in Epithelial tissue that does not allow much movement of material between cells. Proteins associated with: Claudins and Occludins. Blood Brain Barrier • Anchoring Junctions: Attach cells to each other (cell-cell anchoring junction) or to the ECM (cell-matrix anchoring junction). Proteins associated with: Cadherins and integrins

21. Junctions Figure 3-14: Types of cell junctions

23. Key Junction Proteins: Connexin, cadherins, occludin & integrins Figure 3-15: A map of cell junctions

24. Junctions • Cell to cell • Gap junctions: between heart muscle cells • Tight junctions: blood brain barrier • Anchoring junctions: • Desmosomes- attach to intermediate filaments of cytoskeleton • Adherens Junctions- link actin in adjacent cells

25. Junctions • Cell to matrix: Anchoring Junctions • Focal Adhesions- junction between intracellular actin and matrix proteins • Hemidesmosomes- strong junction that ties a cell to the matrix proteins

26. Types of Anchoring Junctions • Cell- Cell Anchoring Junctions: Adherens Junction- links actin in adjacent cells and Desmosomes- attach to intermediate filaments of cytoskeleton • Cell-Matrix Anchoring Junctions: --Focal adhesions- bind intracellular actin to different matrix proteins such as fibronectin --Hemidesmosomes- strong junctions that anchor intermediate fibers of the cytoskeleton to matrix proteins such as laminin

27. Cytoskeleton • Three Dimensional Scaffold of Actin, Intermediate Filaments and Microtubules • Responsible for Cell Shape, internal organization, movement, intracellular transport and assembly of cells into tissue

28. Cytoskeleton Figure 3-7: The cytoskeleton and cytoplasmic protein fibers

29. Cytoskeleton • Strength • Support • Shape • Transport • Cell to cell links

30. Cytoskeleton • Microfilaments: Composed of Actin • Intermediate Filaments: Composed of Myosin, Keratin, Neurofilament and other proteins • Microtubules: Largest cytoplasmic protein fibers. Creates centrioles, cilia and flagella. Composed of tubulin (a globular protein) • Motor Proteins: Composed of multiple protein chains that bind to the cytoskeleton. Proteins involved include myosin, Kinesins and Dyneins

31. The Centrosome • The centrosome is located in the cytoplasm usually close to the nucleus. • It consists of two centrioles — oriented at right angles to each other — embedded in a mass of amorphous material containing more than 100 different proteins. • It is duplicated during S phase of the cell cycle. • Just before mitosis, the two centrosomes move apart until they are on opposite sides of the nucleus. • As mitosis proceeds, microtubules grow out from each centrosome with their plus ends growing toward the metaphase plate. These clusters of microtubules are called spindle fibers.

32. Centrosomes and Centrioles • Centrosomes are the microtubule organizing centers • Centrioles: bundles of microtubules • Centrioles are built from a cylindrical bundle of 27 microtubules arranged in nine triplets. Figure 3-8a,c: Centrioles, cilia, and flagella

33. Cilia and Flagella • Motor proteins • 2:9 microtubule pattern • Cilia move fluids • Flagella move sperm cell Figure 3-8c, d: Centrioles, cilia, and flagella

34. Extracellular Matrix • Extracellular material that is synthesized and secreted by the cells of a tissue. • Composed of Proteoglycans (glycoproteins or proteins covalently bound to polysaccharide chains) and Insoluble protein fibers such as collagen, fibronectin, laminin, fibrillin and elastin. • It provides strength and helps anchor cells to the Matrix • Attachments between the ECM and proteins in cell membrane or cytoskeleton are one means of communication between cell and environment

40. Proteoglycans • Proteoglycans are glycoproteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan (GAG) chain(s). • The point of attachment is a Ser residue to which the glycosaminoglycan is joined through a tetrasaccharide bridge (For example: chondroitin sulfate-GlcA-Gal-Gal-Xyl-PROTEIN). • The Ser residue is generally in the sequence -Ser-Gly-X-Gly- (where X can be any amino acid residue), although not every protein with this sequence has an attached glycosaminoglycan. • The chains are long, linear carbohydrate polymers that are negatively charged under physiological conditions, due to the occurrence of sulfate and uronic acid groups. Proteoglycans occur in the connective tissue.

41. Cell Membrane Proteins • Cell Adhesion Molecules (CAMS)- Membrane spanning proteins responsible for cell junctions and transient cell adhesions. Include Claudins, Occludins, Cadherins, Integrins and Selectins • Cell-Cell and Cell-Matrix Adhesions are mediated by these Cell Adhesion Molecules • Growing nerve cells move along ECM with help of nerve cell adhesion molecules (NCAM’s) • Cell Adhesions are not permanent so the bond between CAM’s may be weak

42. Cell Adhesion Molecules (CAM’s) • Attachments between ECM and Cell Membrane Proteins or Cytoskeleton are a means of communication between a cell and its external environment

43. Primary Tissue Types • Tissue defined: A collection of cells usually held together by cell junctions that works together to achieve a common purpose • Amount of Extracellular Matrix in a tissue is highly variable • Tissue types • Epithelial • Connective • Muscle • Nervous

44. Epithelial Tissue • Protects the internal environment of the body and regulates exchange of materials between the internal and external environment • Five Functional Types: Exchange, Transporting, Ciliated, Protective and Secretory

45. Epithelial Tissues Figure 3-17: Distribution of epithelia in the body

46. Exchange Epithelial Tissues • Leaky junctions • Rapid transport • Oxygen • Carbon dioxide • Ions & fluids • Capillaries • Lung alveoli Figure 3-18a: Movement of substances across tight and leaky epithelia

47. More Epithelia • Transport epithelium • Intestinal microvili • Tight junctions • Ciliated epithelium • Trachea • Sweep mucous out • Protective epithelium • Skin • Multiple cell layers • Prevent exchange Figure 3-18b: Movement of substances across tight and leaky epithelia

48. More Epithelia • Ciliated epithelium • Trachea • Sweep mucous out • Protective epithelium • Skin • Multiple cell layers • Prevent exchange Figure 3-19a: Ciliated epithelia

49. Secretory Epithelia • Exocrine tissues • Mucous glands- goblet cells • Sweat glands • Secreted externally • Endocrine tissues • Hormones • Secreted to ECF & blood

50. Secretory Epithelia Figure 3-20: Goblet cells