Cytology Chapter 4.3 PDF

Chapter 4 Plasma Membrane and Other Cell Membranes Reem Dakhil M1 Biochemistry (Lebanese University) M2 Physiology, Epigenetics, Differentiation, and Cancer (Université Grenoble Alpes) FS.I Partial 2020 19.a 20.c 2...

Chapter 4 Plasma Membrane and Other Cell Membranes Reem Dakhil M1 Biochemistry (Lebanese University) M2 Physiology, Epigenetics, Differentiation, and Cancer (Université Grenoble Alpes) FS.I Partial 2020 19.a 20.c 22.a FS.I Partial 2019 16.c 17.b 18.b 20.b 27. proteins  III. Specialization of Plasma Membrane ✓ Specialized junctional regions ✓ Function: - Adhesion (cell-cell & cell-matrix) - Intercellular transport & communication - Wound healing ✓ Formed: in embryonic life & remain stable ✓ Involve: SAM & CAM membrane proteins – cytoskeleton components ✓ Proteins that function in adhesion → function in signaling III. Specialization of Plasma Membrane 1. Tight Junctions Narrowed / plugged intercellular space ✓ Function: Cell-cell adhesion + plugs intercellular space → barrier to flow of materials between cells → selective absorption by intestine (selective permeability at apical pole) ✓ Location: belt between the apical & lateral pole → Cell membranes of neighboring cells fuse → like 2 halves of a zipper → belt surrounds the cell ✓ Protein family involved: occludins ✓ Cytoskeleton component it’s associated with: actin filaments → determines cell shape ✓ Tissues: epithelia (eg: intestine enterocyte) – seminiferous tubules (sertoli cells) – endothelial cells (blood-brain) ✓ Control: dissociated by immune cells during an immune response to pass through epithelia III. Specialization of Plasma Membrane 1. Tight Junctions III. Specialization of Plasma Membrane 2. Intermediate Junctions / Belt Desmosomes / “Zonula Adherens” ✓ Function: adhesion of cells BUT: leaves intercellular space (doesn’t plug it) ✓ Location: just below tight junction belt – encircles the cell ✓ Protein: cadherins ✓ Cytoskeleton component: actin filaments – linked to cadherin by catenin → dense thick zone (network of protein filaments) ✓ Tissues: many, especially epithelia III. Specialization of Plasma Membrane 3. Spot Desmosomes “Macula Adherens” Punctual junctions → button-like attachment points → strongest junction ✓ Location: everywhere between 2 neighboring cells ✓ Function: connect intermediate filaments (keratin) by a 3D network → internal support → strength & resistance to pressure ✓ Proteins: cadherins ✓ Cytoskeleton component: intermediate filaments → interact with cadherins at a discoid dense region “cytoplasmic plaque” (anchorage proteins) ✓ Tissues: all, abundant in those subjected to mechanical pressure: skin epithelium – uterus – cardiac muscle III. Specialization of Plasma Membrane 3. Spot Desmosomes “Macula Adherens” Tight junction → III. Specialization of Plasma Membrane 4. Hemidesmosomes Half-desmosomes ✓ Location: basal pole of epithelia ✓ Function: attachment of epithelia to basement membrane (laminins) → adhesion between epithelia & connective tissue ✓ Proteins: integrins ✓ Cytoskeleton component: intermediate filaments attach to plectin plaques III. Specialization of Plasma Membrane 4. Hemidesmosomes III. Specialization of Plasma Membrane 5. Synaptic Junctions ✓ Function: signal transduction ✓ Location: contact point between axon & cell ✓ Protein involved: cadherin ✓ Function: transmission of action potential from presynaptic to postsynaptic 1. Action potential in presynaptic membrane 2. Change in presynaptic membrane permeability → release of neurotransmitters into synaptic cleft 3. Neurotransmitters bind to receptors in postsynaptic membrane 4. Change in postsynaptic membrane permeability 5. Postsynaptic message (action potential)  II. Fluid Mosaic Model 5. Synaptic Junctions III. Specialization of Plasma Membrane 6. Gap Junctions Pipline-like structures ✓ Location: between neighboring cells → extend from the cytosol of 1 cell to that of the other → narrow intercellular space (tightened) ✓ Proteins: connexins ✓ Function: transportation: exchange of molecules between neighboring cells ✓ Tissues: all except skeletal muscle & nerve cells III. Specialization of Plasma Membrane 6. Gap Junctions Structure: ✓ Aqueous channels in clusters ✓ 1 channel = 1 connexon = 6 connexin subunits ✓ Conexin: integral polytopic protein (4 transmembrane α-helices) ✓ Hydrophilic sides at channel center (2nm diameter) → passage of any hydrophilic moledule