The Cell part 2.pptx Cell membrane and components

An overview of the cell membrane and its components.

1. The Cell pt Dr. Keisha Westby Leonardo MEDI-3351 UBSOM

2. Learning Objectives Explain the fluid mosaic model of the plasma membrane . Differentiate passive vs active transport and give examples. Describe endocytosis (pinocytosis, receptor‑mediated , phagocytosis ) step by step. Describe exocytosis (constitutive vs regulated ) step by step. Outline major receptor types and common second messengers .

3. Plasma Membrane — 30‑Second Review Bilayer of phospholipids with cholesterol → fluid, flexible barrier. Integral & peripheral proteins = channels, carriers, receptors, enzymes. Glycocalyx (carb coat) = recognition/protection; microdomains: lipid rafts/caveolae .

4. Plasma Membrane

5. 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

6. 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

7. 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

8. 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.

9. Transport — Big Picture Passive transport : down a gradient; no ATP . Active transport : against a gradient; needs ATP (direct or indirect). Bulk (vesicular) transport : endocytosis/exocytosis in membrane packets.

10. Passive Transport (No ATP) Simple diffusion : small nonpolar (O₂, CO₂) slip through lipid. Facilitated diffusion : through channels (fast) or carriers (specific). Osmosis : water moves toward higher solute (via aquaporins ). Clinical Imp. : tonicity (hypo/iso/hyper) changes cell volume.

11. Vesicular Transport — Overview Endocytosis brings material in (pinocytosis, receptor‑mediated , phagocytosis ). Exocytosis sends cargo out ( constitutive vs regulated (Ca²⁺‑triggered) ). Vesicle coats help budding/targeting: clathrin , COPII (ER→Golgi), COPI (Golgi→ER).

12. Endocytosis During endocytosis, cells take in substances by invaginating a portion of the plasma membrane and forming a vesicle around the substance. Endocytosis occurs as: Phagocytosis: for solid particles. Pinocytosis: engulfing fluids (cell drinking). Receptor-mediated endocytosis: specific particles

13. Receptor‑Mediated Endocytosis (RME) — Step by Step 1) Ligand binds **receptor** concentrated in ** clathrin ‑coated pits** ( adaptins ). 2) **Dynamin** pinches off the clathrin ‑coated vesicle. 3) Vesicle uncoats → fuses with early endosome (slightly acidic). 4) Sorting: receptors often recycle; cargo can go to late endosome → lysosome**.

14. Phagocytosis

15. Pinocytosis

16. Pinocytosis (Cell Drinking) 1) Small invaginations take **fluid + small solutes** into tiny vesicles. 2) Often ** clathrin ‑independent**; continuous background uptake. 3) Vesicles fuse with **early endosomes** for sorting.

17. Exocytosis the biological process where a cell expels large molecules or waste byproducts out of the cell, involving the fusion of intracellular vesicles with the plasma membrane to release their contents to the exterior. Uses vesicles to deliver substances like hormones, neurotransmitters, and proteins, playing a vital role in cellular communication, waste removal, and maintaining the plasma membrane's structure.

18. Exocytosis

19. Quiz Check 1 — Membranes, Signaling, Vesicles 1) Which membrane component primarily maintains fluidity as temperature changes? A) Glycolipids B) Cholesterol C) Peripheral proteins D) Glycosaminoglycans

20. Quiz Check 1 — Membranes, Signaling , Vesicles 2) A ligand binds a GPCR and raises cAMP. Which enzyme most directly produces cAMP? A) Phospholipase C B) Adenylyl cyclase C) Guanylyl cyclase D) Protein kinase A

21. Quiz Check 1 — Membranes, Signaling , Vesicles 3) Receptor-mediated endocytosis commonly uses which coat protein? A) COPI B) COPII C) Clathrin D) Caveolin

22. Key Takeaways Structure predicts function: membranes signal and sort; organelles specialize tasks. Cytoskeleton provides routes (microtubules), force (actin–myosin), and strength (intermediate filaments). Clinical conditions often reflect failure of a specific structure or transport step.

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