SZL 201: Cell Biology Topic Nine: 

Cellular Communication/Interaction

 A. Introduction: In  this  topic  we  will  discuss  means  of  cell-to-cell communication  and  interaction. We will discuss the structures that link cells together in different tissues and sites of an organ. These structures play a role in conducting molecules from one compartment out of the cell to another or from one cell to another. In addition, we will discuss cell signalling, whereby there is no physical movement of molecules by activation of target molecules on the surface of the cell and transduction of the activation signal by other molecules into the cell. This is also a form of communication using chemical messengers. This will be an interesting discussion topic. Learning Objectives: By the end of this topic the learner should be able to; 

1. Discuss types of cell adhesion molecules.

 2. Discuss the role of tight junctions, gap junctions, desmosomes.

 3. Discuss the functions of extracellular matrix (ECM)

 4. Discuss cell signalling

. B. Requirements: 1 Time Recommended to complete this topic 3 hours 2 Hardware/software requirements: • Computer/Smart phone • Internet • Text books • Note Books 3 Core Textbook: 1. Bruce Alberts (2007). Molecular Biology of the Cell (5th edition). Garland Science Publishers. ISBN 978-0-8153-4106 General Textbooks: 1. Wayn M. Becker, Lewis J. Klein smith and Jeff Hardin (2006). The world of the cell (sixth edition). Pearson Benjamin Cummings Publishers. ISBN 0-321-31208-2. 2. Laddish, et al. Molecular Cell Biology. 5th ed. New York, NY: W.H. Freeman and Company, 2003. ISBN: 9780716743668. 3. David P. Clark, Molecular Biology. 2010 ELSEVIER Inc. ISBN 978-0-12-378589-3 C. Learning Activity: • Read notes in the section on topic content/notes • Read articles/notes on reading assignment • Read the literature in the required sections • Attempt the questions under assessment and assignments • Listen to any lectures on the university website D. Reading Assignment: Textbooks: 1. Bruce Alberts (2007). Molecular Biology of the Cell (5th edition). Garland Science Publishers. ISBN 978-0-8153-4106. 2. Wayne M. Becker, Lewis J. Klein smith and Jeff Hardin (2006). The world of the cell (sixth edition). Pearson Benjamin Cummings Publishers. ISBN 0-321-31208-2.2 3. Laddish, et al. Molecular Cell Biology. 5th ed. New York, NY: W.H. Freeman and Company, 2003. ISBN: 9780716743668. 4. David P. Clark, Molecular Biology. 2010 ELSEVIER Inc. ISBN 978-0-12-378589-3. E. Topic Contents/Notes SZL 201: Topic Nine: Cellular Communication/Interaction 1. Direct contact between membrane-bound cell-surface molecules (cell junctions, cell-cell recognition) e.g. Embryo development, immune response Local regulators - paracrine signalling Synaptic signalling - animal nervous system Cell-to-cell adhesions The life-sustaining activities of the body systems depend on the functions of the individual cells and on how these cells live and work together in tissue and organ systems. Cell adhesion is the binding of a cell to the surface of another cell using cell adhesion molecules (CAMs) such as integrins, selectins etc. Extracellular matrix (ECM) The ECM is an intricate meshwork of fibrous proteins embedded in a watery, gel-like substance composed of complex carbohydrates. The ECM serve as the biological “glue”. The watery gel provides a pathway for the diffusion of nutrients, wastes and other water-soluble traffic between the blood and the tissue cells. Plays a role in growth and differentiation. Cells can only survive in the ECM. Composition of the ECM varies according to the different tissues. Within the gel matrix are three major types of glycoprotein fibbers: collagen, integrins and fibronectin, embedded in a network of proteoglycans. Types of cellular attachments 1. Desmosomes (macula adherents) Disk-shaped adhesive junctions approximately 1 µm in diameter found in a variety of tissues. Dense cytoplasmic plaques form on the inner surface of the plasma membranes and serve as sites of anchorage for looping intermediate filaments similar to those of hemidesmosomes. Numerous in tissues that are subjected to mechanical stress, such as cardiac muscles and the epithelial layers of the skin and uterine cervix. Two cells involved are linked by cadherins (desmoglins and desmocollins) 1. Desmosome s 2. Tight Junctions 3. Gap Junctions 3 Circular, dense bodies that form at the site of attachment/ adhesion between adjacent cells. Anchoring junctions. Each consists of a dense plate in each joining cell separated by a thin layer of extracellular material. Anchor together two closely adjacent but non touching cells. Adhesion molecules such as cadherins are involved in cell attachment. A desmosome has two components: A pair of dense, button-like cytoplasmic thickenings known as plaque located on the inner surface of each of the two adjacent cells. Strong glycoprotein filaments that extend across the space between the two cells and attach to the plaque on both sides. Abundant in tissues subjected to considerable stretching e.g. skin, heart and uterus. In these tissues, the cells are joined together by desmosomes that extend from one cell to the next, then to the next and so on. A continuous network of strong fibbers extend throughout the tissue, both through the cells and between the cells. Provides tensile strength. Reduces the chances of tissue being torn when stretched. 2. Tight junctions (zonula occludes) It is an intercellular junction, where adjacent cells firmly bind with each other at points of contact to seal off the passageway between the two cells. The tight junctions are impermeable. Passage across the epithelial barrier, must take place through the cells, not between the cells. 4 The traffic across the cell is regulated by means of the carriers and channels present. Tight junctions thus prevent undesirable leaks within epithelial cells. - Linked by occluding and claudin molecules - Prevent paracellular movement of solutes - Prevent water loss from the skin - Participate in the formation of blood brain barrier to exclude toxic substances and drug