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Lecture 20 - Chapter 19 - Junctions - March 28.docx

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York University
BIOL 2021
Patricia Lakin- Thomas

Lecture 20: March 28th, 2013  Figure 19-1 Chapter 19: Junctions, Adhesion Matrix  Architecture of animal tissues  2 basic strategies: 1. Extracellular matrix= ECM  Few cells, connective tissue, matrix of fibrous polymers carries stress 2. Cell-cell adhesion and cytoskeleton o Epithelial cells on basal lamina o Cytoskeleton carries stress  ECM  Proteins+ polysaccharides  Secreted locally by cells (+ minerals sometimes)  Examples of ECM: o Teeth(mineralized) o Cornea in eye o Insect carapace o Fungal + plant cell walls o Mollusc shells  Animal cells: basal lamina, connective tissue  Basal lamina: o Figure 19-40**, 19-54** o Also called basement membrane, found in all multicellular animals o Scaffold for regeneration if there is an injury o Functions: separates epithelium from connective tissue below it  Also provides mechanical support for epithelium and barrier to cell migration  Kidney: filter-molecular  Basal lamina can influence cell behaviour, polarity, proliferation, etc. o Lamin + collagen + others o Elastin= elasticity to skin  Connective tissue: o Bone, cartilage, tendon o Secreted by fibroblasts (which are in the matrix)  Molecules:  ECM: 1. Fibrous proteins, usually glycoproteins 2. Proteoglycans: proteins + polysaccharides  Major protein of connective tissue: collagen  Figure 19-41 (do not need to know the names)  Figure 19-62: collagen made of 3 chains  Figure 19-63  Figure 19-43  Figure 19-71: elastin molecules can stretch without breaking bonds Matrix Degradation:  For tissue repair + remodeling  Cells secrete proteases to degrade matrix  Cancer cells: matrix degradation allows cells to spread (metastasis) Cell Junctions:  Table 19-1  Figure 19-2 (occluding junctions)  Figure 19-23, 19-25, 19-34, 19-35 1. Occluding junctions: seal gap between epithelial cells  In animal epithelia= tight junctions, polarized cells (basal vs. Apical)  Epithelial becomes selective permeability barrier  Ex. Transcellular transport o Junctions keep proteins segregated  Structure= rows of sealing strands  Adhering proteins= Claudins  Figure 19-26 1. Channel Forming Junctions  Link cytoplasm of neighboring cells  Animal cells= gap junctions  Small molecules can pass directly between cells  Cells coupled metabolically and electrically  Channel protein= connexin  Six subunits will create one connexon  Transmembrane proteins in adjacent cells  Funct
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