Lecture 15 Cell Biology
Lecture 15 Cell Biology BIOL 225
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This 3 page Class Notes was uploaded by MelLem on Thursday March 31, 2016. The Class Notes belongs to BIOL 225 at Simmons College taught by Dr. Lopilato in Fall 2016. Since its upload, it has received 20 views. For similar materials see Cell Biology in Biology at Simmons College.
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Date Created: 03/31/16
Lecture 15 Cell Biology Chapter 7 Interactions between cells and their environments Cell – Cell Adhesive Interactions Four distinct families of integral membrane proteins play a major role in mediating cell-cell adhesion. 1) selectins 2) certain members of the immunoglobulic superfamily (IgSF) 3) certain members of the integrin family, 4) Cadherins They are important in development, metastasis and inflammation. Cell – cell Adhesive Interactions Cadherins – integral membrane proteins Certain members of the IgSF and Integrins Selectins Selectins Selectins are a family of membrane glycoproteins that bind to specific oligiosaccharides on the surfaces of neighboring cells Lectin is a term for a compound that binds to specific carbohydrate groups. Selectins have a small cytoplasmic segment, a single membrane-spanning domain and a large extracellular portion. Three cell-specific selectin types: o E – Selectin – endotherlial cells o P – Selectin – platelets and endothelial cells o L – selectin – Leukocytes (white blood cells) Just have different carbohydrate groups attached The Immunoglobulin Super Family (IgSF) Antibodies are immunoglobulin proteins with Ig domains, 70 -110 a.a. organized into a tightly folded structure The human genome encodes 765 distinct Ig domains, making it the most abundant domain the human proteins. These proteins are members of the immunoglobulin super family, and most are involved with mediating interactions of lymphocytes with cells required for an immune response. (Macrophages, Lymphocytes, and target cells) 2 membrane proteins and 2 cells interacting through these proteins Cadherins Cadherins include 3 different types as well: o E – Cadherin – epithelial o N – Cadherin – Neural o P – Cadherin –Placental Cadherins have a large extracellular segment, a single transmembrane segment, and a small cytoplasmic domain The cytoplasmic domain is often associated with catenin proteins to tether the cadherins to the cytoskeleton and transmit signals Calcium ions maintain the extracellular portion of each cadherin in a rigid conformation required for cell adhesion Cadherins require calcium for a reaction. Interactions of cells with other cells Cadherins may mediate dynamic changes in adhesive contacts needed for morphogenesis. During embryonic development, cells can change from an epithelium to a mesenchyme or visa versa. This epithelia mesnechymal transition (EMT) is found during mesoderm formation. Migrating mesenchymal cells with eventually give rise to medodermal tissues such as blood, muscle and bone. Cell Junctions Anchoring cells to other cells – link epithelial cells together o Desmosomes o Adherens Junctions Tight junctions – sealing the extracellular space Cell communication o Gap junctions o Plasmodesmata Junctions for Communication Gap junctions – animal cells o Made of connexin protein o Passage of ions o Communication o Gap junctions – protein molecules of about 1000 Daltons can go through gap junctions. o Defects in gap junctions can cause deafness, blindness, cardiac problems, nerve degeneration and skin abnormalities. Plasmodemata – plant cells o Connect plant cells o Dilates for passage of macromolecules o Plasmodesmata - are cytoplasmic channels passing through cell walls of adjacent plant cells o Lined by the plasma membrane o Contain a central structure, the desmotubule o Dilate and up to 50 Kilo Daltons (50,000 Dalton) proteins can move through. o Both proteins and RNA (serving a signal molecule) move through plasmodesmata