Cell Cell Interactions 1 The Cell Surface Extracellular compartment Carbohydrate groups of glycoproteins Carbohydrate groups of glycolipids Cholesterol Integral protein Cytoplasm Peripheral proteins Phospholipids Cytoskeletal elements The extracellular matrix of the animal cells Almost all animal cells secrete a fiber know as the extracellular matrix The fibrous component of the ECM consist of protein fibers instead of polysaccharides How Variable is the ECM The amount of ECM varies from cell type to cell type in the same organism Examples bone and skin The composition also varies among cell types The structure of the cell s ECM correlates with their function However in every cell type the ECM will serve in structural support Each Type of Tissue produces its own unique ECM 6 What is the role of ECM in structural support The combination of protein filaments and surrounding polysaccharide gel creates a strong external layer because transmembrane proteins grabs proteins in the ECM Gel forming polysaccharides Collagen ECM Fibronectin Integrin Plasma membrane Cytoskeleton Actin filament How adjacent cells Connect and communicate Cell are not separate identities In multicellular organism there is a physical connection between the cells Most of the cell in multicellular organisms are held together somehow Because different type of cell specialized for particular task the cell must be able to communicate with each other to function as an integrated whole Cells are organized into functional units called tissues Tissues Consist of groups of similar cells that perform a similar function Several tissues combine to make up the integrated structures called organs Organs perform specialized functions such as reproduction digestion and support Examples of cellular structures that span the ECM to connect adjacent cells Tight junctions Desmosomes Gap junction 12 Tight Junction Is a cell to cell attachment composed of specialized proteins in the plasma membrane This proteins lined up and bind to one another Their form a watertight seal Is common in cells that form a barrier Is found in the cell lining the stomach and intestines Tight junctions are variable and dynamic Tight junction lining the bladder are much tighter than tight junction in the intestines because they consist of different proteins This difference will allows ions to pass through the small intestine but having a harder time passing through the surface of the bladder This will help to absorb ions present in the food But excess ions will be eliminated in the urine They can be loosened in some cases This will permit more transport between epithelial cell after enough ions have passed the tight junction can be retightened Desmosome Are common cell cell attachment in epithelial cell and in certain types of muscle cells At the center of the desmosome consists proteins that form a physical link between the cytoskeleton of the adjacent cells In addition to bind to each other these proteins bind to a larger protein that is anchored in the intermediate filaments in the cytoskeleton of the two cells In this way desmosomes bind together the cytoskeletons of the two cells Cell Cell Communication How plant cells communicate Gaps in the plant s cell walls create direct connections between the adjacent cells These connections are called plasmodesmata singular plasmodesma The plasma membrane of both cells are continuous Smooth endoplasmic reticulum runs through the plamodesmata Some evidence also suggest that plasmodesmata also contains proteins that regulate the passage of molecules This makes this structure similar to the nuclear pore Some of the proteins that cross this structure are involved in coordinating activities in adjacent cell Gap Junctions Most animal tissues are connected by gap junctions In the gap junction a unique protein creates channels between adjacent cells Gap junction will allow water ions and small molecules amino acids carbohydrates nucleotides to move between adjacent cells These molecules will assist in the coordination of adjacent cells activities buy allowing rapid passage of regulatory molecules More about animal cell cell communication Animal cells share most of their ions and or small molecules but retain their own organelles proteins and nucleic acids This communication is efficient This will allow the tissue to act as a whole because they are connected in their extracellular matrix How distant cells communicate Long distance organs in multicellular organisms have to coordinate their function They will use molecules that carry information about the conditions of our bodies This information will travel using our blood stream So a mechanism must exist that explain 1 How cells send long distance signals 2 How cells received the signals 3 How cells respond to these signals 26 How do distant cells communicate Long distance organs in multicellular organisms have to coordinate their functions They will use molecules that carry information about the conditions of our bodies This information will travel using our blood stream 27 What is a Hormone Hormones are information carrying molecules They are small molecules They are secreted by a cell In small amounts They circulate in the blood stream Acts in a target cell far from the original cell that sent the signal They have great impact on the activities of the target cells Lipid soluble hormones They cross the cell membrane Hydrophilic hormone They will be recognized by receptors in the cell membrane Signal reception They deliver their message by binding to the receptor molecule The presence of an appropriate receptor dictates which cell will be able to respond to a particular hormone In many cases many cells in different organs will respond to the same signal This happen because they all have the appropriate receptor for the same signal The important idea is that hormones coordinate the activities of cells through a multicellular organism How signal receptors work Signal receptor are proteins that change conformation shape or activity after binding to a signal molecule The signal receptor that respond to a steroid molecule are located inside the cells However most signal receptor hydrophilic are located in the plasma membrane because most hormones are not lipid soluble However both lipids and no lipids have two general qualities Receptor are dynamic Receptor can be blocked Most important characteristic of signal receptor They all change their conformation once the signal