The Cell for upload.pptx cell and its organelles

An overview of the histology of the cell and its organelles. also mentions some clinical implications.

1. The Cell pt 1

2. Learning Objectives Understand: the major components of the cell and cytoplasm. Describe: the structure, function, and importance of membranous and non - membranous organelles. Recognize: key clinical correlations

3. Cell Types Prokaryotic cells: e.g., bacteria Eukaryotic cells: plants, animals, fungi What are they? Viruses? Prions?

4. Types of Cells Prokaryotes Eukaryotes

5. Specialized Cells Stem Cells Blood cells Skin cells Muscle cells Nerve cells Fat cells Bone cells Sex cells

6. Specialized cells

7. Overview of the Cell & Cytoplasm Cell: the basic structural and functional unit of life. Cytoplasm: everything inside the plasma membrane except the nucleus; includes organelles, cytoskeleton, inclusions, and cytosol. Cytosol (Cytoplasmic matrix): gel-like fluid where many metabolic reactions occur (glycolysis, protein synthesis initiation).

8. Overview of the Cell & Cytoplasm Organelles: specialized structures that perform a specific function. Inclusions: structures that are not usually surrounded by a plasma membrane, such as crystals, pigment granules, lipids, glycogen, and other stored waste products

9. Organelles Membranous Plasma membranes that separate the internal environment of the organelle from the cytoplasm Membranes increase the surface area on which physiological and biochemical reactions take place. Non-membranous no plasma membranes

10. Membranous Organelles Cell membrane rER sER Golgi apparatus Mitochondria Endosomes Lysosomes Transport vesicles Peroxisomes

11. Cytoplasmic Matrix (Cytosol) Structure: Water-based solution with ions, metabolites, enzymes, and ribosomes. Function: Site of many reactions (e.g., glycolysis); distributes molecules by diffusion. Importance : Provides the medium supporting organelles and rapid biochemical changes.

12. Rough Endoplasmic Reticulum (RER) Structure: flattened sacs studded with ribosomes. Function: synthesis of secret ory , membrane, and lysosomal proteins; protein modification ( initial glycosylation and folding ) . Quality control: misfolded proteins → ER-associated degradation (ERAD). Importance: highly developed in protein-secreting cells (e.g., plasma cells).

13. Rough ER: Microscopic View Size: 5-10 µm Often observed as a basophilic region of cytoplasm referred to as ergastoplasm under LM Flattened sheets, sacs, and tubes of membranes with attached ribosomes under EM

14. Smooth Endoplasmic Reticulum ( s ER ) Structure: tubular network without ribosomes. Function: lipid and steroid synthesis; detoxification; glycogen metabolism. Calcium storage: sarcoplasmic reticulum in muscle handles Ca²⁺ for contraction. Importance: abundant in hepatocytes and steroid-producing endocrine cells.

15. Smooth ER: Microscopic View Found throughout cytoplasm Not visible by LM, cytoplasm in the region of sER may exhibit distinct eosinophilia Flattened sheets, sacs, and tubes of membranes without attached ribosomes under EM

16. Golgi Apparatus Structure: Stacked cisternae: cis (entry), medial, trans (exit). Function: Modifies, sorts, and packages proteins; forms lysosomes. Why it matters: Addressing errors cause misdelivery (e.g., I-cell disease).

17. Microscopic View 5-10 µm Sometimes observed as a "negative staining" region on LM Appears as a network in heavy metal-stained preparations on LM Stack of flattened membrane sheets, often adjacent to one side of nucleus on EM

18. Electron Micrograph of Golgi Cisternae A. The trans-Golgi cisternae are in the process of coated vesicle formation. B. Incubation of the tflln9-Golgi cisternae with the coatomer-depleted cytosol shows a decrease in vesicle formation activity.

19. Mitochondria Structure: Double membrane; cristae; matrix with mtDNA and ribosomes. Function: Produces ATP via oxidative phosphorylation; mediates apoptosis. Why it matters: Maternal inheritance; dysfunction hits high-energy tissues.

20. Mitochondria: Microscopic View 0.2-7 µm On LM: Sometimes observed in favorable situations (e.g., liver or nerve cells) as minuscule, dark dots; visible in living cells stained with vital dyes ( e.g .Janus green) On EM: Two-membrane system: outer membrane and inner membrane arranged in numerous folds (cristae). In steroid-producing cells, inner membrane arranged in tubular cristae

21. Transport Vesic les Structure: pinocytic, endocytotic , and coated vesicles involved in endo cytosis and exocytosis , vary in shape and in material carried . Function: Moves bulk cargo in/out; recycles membrane and receptors. Why it matters: Essential for secretion (hormones, neurotransmitters) and nutrient uptake.

22. Endosomes Structure: Early, recycling, and late endosomes with increasing acidity. Function: Sort cargo; recycle receptors; deliver material to lysosomes. Why it matters: Prevents receptor overactivation and misrouting of cargo.

23. Microscopic View 0.02-0.5 µm N ot visible with LM O n EM: tubulovesicular structures with subdivided lumen containing electron-lucent material or other smaller vesicles.

24. Lysosomes Structure: Acidic, enzyme-filled vesicles; enzymes tagged with M6P in the Golgi. Function: Digest macromolecules and old organelles (autophagy). Why it matters: Defects cause lysosomal storage diseases and impaired cell cleanup.

25. Microscopic View 0.02-0.5 µm Visible only after special enzyme histochemical staining on LM Membrane-bounded vesicles, often electron dense

26. Clinical Correlation: Lysosomal Storage Diseases Tay-Sachs: Hexosaminidase A deficiency → GM2 ganglioside buildup; neurodegeneration, cherry-red spot. Gaucher: β-glucocerebrosidase deficiency → lipid-laden macrophages (Gaucher cells); hepatosplenomegaly. Pompe : acid maltase ( α-1,4- glucosidase) deficiency → cardiomyopathy, hypotonia. I-cell disease: defective M6P tagging → enzymes secreted; coarse facial features, skeletal abnormalities.

27. Peroxisomes (Microbodies) Structure: Contain oxidases and catalase. Function: break down free radicals, d etoxify H₂O₂; β-oxidation of very-long-chain fatty acids; plasmalogen synthesis. Why it matters: Biogenesis defects → Zellweger spectrum; protects from oxidative damage.

28. Peroxisomes Neutralize free radicals, which are molecules with an unpaired electron that can damage the cells by oxidizing lipids, proteins, and even the DNA. Free radicals get converted by an enzyme called oxidase into hydrogen peroxide. But since hydrogen peroxide is still dangerous, there’s another enzyme, called catalase, which safely converts it into water and oxygen. Another thing catalase can do is use that hydrogen peroxide to break down toxic substances like ethanol and formaldehyde.

29. Microscopic View 0.02-0.5 µm Visible only after special enzyme histochemical staining on LM Membrane-bounded vesicles, often electron dense

30. Non-Membranous Organelles Ribosomes Proteasomes Centrioles Filaments Microtubules

31. Ribosomes Structure: composed of a small and a large subunit; composed of ribosomal RNA (rRNA) and ribosomal proteins attached to membranes of the rER and proteins free in the cytoplasm. Function: protein synthesis by translating protein-coding sequence from mRNA I mportance : Ribosomal dysfunction in Alzheimer disease; Diamond- Biaclfan anemia ; some antibiotics act selectively on bacterial ribosomes

32. Ribosomes: Microscopic View 0.025 µm Not visible under LM Minute dark dots, often associated with the rER under EM

33. Proteasome-Mediated Degradation Structure: Ubiquitin tags proteins; 26S proteasome degrades them into peptides. Function: Controls protein quality and cell-cycle regulators; antigen processing. Why it matters: Cancer therapies (e.g., proteasome inhibitors) exploit this pathway.

34. Proteasomes Microscopic view 0.015 µm Not visible on LM Difficult to distinguish from other matrix proteins under the EM

35. Microtubules Structure: Hollow tubes of α /β-tubulin; polar; dynamic instability. Function: Tracks for kinesin/dynein transport; mitotic spindle; cilia/flagella. Why it matters: Drug targets ( taxanes , vinca ); defects → primary ciliary dyskinesia.

36. Actin Filaments (Microfilaments) Structure: F-actin polymers of G-actin; polar, dynamic. Function: Cell shape, movement, cytokinesis, microvilli; contraction with myosin. Why it matters: Toxins (phalloidin) bind actin; defects affect muscle/platelets.

37. Intermediate Filaments Structure: Rope-like fibers: keratin, vimentin, desmin , neurofilaments, lamins . Function: Provide tensile strength and structural stability. Why it matters: Useful in pathology as cell-type markers; mutations → fragility syndromes.

38. Clinical Correlation: Abnormalities in Microtubules & Filaments Structure: Dynein arm defects (primary ciliary dyskinesia); keratin mutations (epidermolysis bullosa simplex); tauopathies (microtubule-associated protein). Function: Chronic infections/infertility; skin fragility; neurodegeneration. Why it matters: Reveals how cytoskeletal integrity underpins tissue function.

39. Centrioles & Microtubule-Organizing Centers (MTOC) Structure: Centrioles: 9 microtubule triplets; a pair forms the centrosome (MTOC). Function: Nucleates microtubules; organizes mitotic spindle. Why it matters: Abnormal duplication → extra centrosomes and chromosomal instability.

40. Clinical Correlation: Abnormal Centriole Duplication & Cancer Structure: Excess centrosomes → multipolar spindles; mis-segregation of chromosomes. Function: Aneuploidy fuels tumor evolution Why it matters: Targeting centrosome clustering is under study.

41. Basal Bodies Structure: Centriole-derived structures at the base of cilia/flagella. Function: Template the axoneme and anchor ciliary apparatus. Why it matters: Defects impair mucociliary clearance and fertility.

42. Plasma membrane Not visible with LM and is seen only by EM. About 8-10 nm thick Also known as the UNIT membrane Composed of lipid (bilayer) arranged as a phospholipid bilayer + proteins + carbohydrates (glycolipids or glycoproteins). The phospholipid molecule has a hydrophilic head oriented towards extracellular or intracellular compartments, and a hydrophobic head oriented towards the inside of the membrane

43. Plasma Membrane

44. Functions of the Plasma Membrane Protect the structural integrity of the cell Control movements of substances in and out of the cell (selective permeability) Regulation of cell-cell interactions Recognition of antigens, foreign cells via receptors

45. Functions of the plasma membrane Establishing transport systems for specific molecules Signal transduction Membrane modifications help to form cellular junctions, microvilli, and cilia Phagocytosis, pinocytosis, and exocytosis

46. Plasma Membrane Structure: Phospholipid bilayer with cholesterol and integral/peripheral proteins (fluid mosaic). Function: Selective barrier; signaling platform; anchors cytoskeleton and cell junctions. Why it matters: Maintains homeostasis and communication; defects impair transport and immunity.

47. Independent Study Come prepared to discuss cell signaling and transport across the cell membranes. Read chapter 3 of Pawlina’s Histology.

48. References Ross and Pawlina’s Histology: Text and Atlas Junqueria’s Histology