Biol 118 1st Edition Lecture 9 Outline of Last Lecture I Energy Transformations II Role of Electrons III Definitions IV Oxidation Reduction V Phosphorylation 3 Types VI Ways ATP is Produced VII Key Players in the Processing of Glucose VIII Cellular Respiration has 4 Steps IX Fermentation Outline of Current Lecture I Review of Plasma Membrane Structure Function II Primary Cell Wall III Extracellular Matrix IV How Do Adjacent Cells Connect and Communicate V Connections Between Animal Cells VI Molecular Basis of Selective Adhesion VII Cell Communication via Cell Cell Gaps VIII Summary of Eukaryotic Cell Cell Attachments These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute IX How Do Distant Cells Communicate X Steps of Cell Cell Signaling Current Lecture Review of Plasma Membrane Structure Function The plasma membrane is made up of a phospholipid bilayer with many interspersed proteins o Generally consists of a fiber composite a cross linked network of long filaments surrounded by a stiff ground substance Rods filaments protect against tension Ground substance protects against compression The primary function of the plasma membrane is to create a different environment inside the cell Selective permeability of the membrane controls the flow of materials into and out of the cell Primary Cell Wall When new plant cells form they secrete a fiber composite called a primary cell wall composed of o Long strands of cellulose bundled into microfibrils that form a crisscrossed network Extracellular Matrix Most animal cells secrete a fiber composite called the extracellular matrix One of most important functions is structural support Amount and composition of the ECM depends on the cell type Consists of o A ground substance formed of gelatinous polysaccharide o A network of protein fibers Most common ECM protein fiber is collagen o Collagen is more elastic than cellulose o It forms a flexible extracellular layer ECM also helps cells o Stick together o Form protein protein attachments o Link the ECM directly to the cell s cytoskeleton Direct linkage between the cytoskeleton and ECM o Keeps individual cells in place o Helps adjacent cells adhere to each other o Breakdown can lead to metastasis of cancerous cell How do Adjacent Cells Connect Communicate Unicellular organisms do not connect to one another The basis of multicellularity is physical connections between cells Cells of multicellular organisms o Adhere to one another o Have specific distinct structures and functions Tissues are comprised of o Groups of similar cells o Performing similar functions The structures that hold cells together vary among multicellular organisms Connections Between Animal Cells A middle lamella like layer o Made of gelatinous polysaccharides o Exists between cells in many animal tissues The polysaccharide glue may be reinforced by cable like proteins that span the ECM to connect adjacent cells Epithelial tissue is composed of sheets of cells o Covers organs o Line body cavities Many types of structures connect neighboring epithelial cells o Tight junctions o Desmosomes Tight junctions o Are composed of specialized proteins in the plasma membranes of adjacent animal cells o These proteins line up and bind to each other o Stitching the two cells together to form a watertight seal between the 2 plasma membranes o Are usually found between cells in tissues that form a barrier such as the tissue lining the stomach or bladder Desmosomes o Made of proteins that link the cytoskeletons of adjacent cells o Common in epithelial and muscle tissue o Bind to each other and to the proteins that anchor cytoskeletal intermediate filaments Molecular Basis of Selective Adhesion Animal cells attach to each other selectively because o There are several classes of cell adhesion proteins o Each major cell type has its own cell adhesion proteins These cell cell connections are also species and tissue specific Cadherins are the adhesion proteins in desmosomes Cell Communication via Cell Cell Gaps Direct connections between cells in the same tissue o Allow cells to communicate o Work together in a coordinated fashion Plant cells are connected by plasmodesmata o Gaps in cell wall o Where the plasma membrane cytoplasm and smooth ER of two cells connect In animal tissues cell communications via cell cell gaps is through gap junctions o Connect adjacent cells by forming channels o Channels allow the flow of small molecules between cells Summary of Eukaryotic Cell Cell Attachments Bind adjacent cells to each other o Middle lamella o Continuous ECM o Tight junctions o Desmosomes o Cadherins Allow adjacent cells to communicate o Plasmodesmata in plants o Gap junctions in animals How do Distant Cells Communicate Hormones o Information carrying molecules o Secreted from a cell o Circulate in the body o Act on target cells far from signaling cell Hormones are usually o Small molecules o Typically present in minute concentrations o Have a large impact on the condition of the organism as a whole Function and chemical structure of hormones vary widely May be soluble or insoluble in lipids o Lipid Soluble hormones Usually diffuse across the plasma membrane and go into their target cells cytoplasm o Lipid Insoluble hormones Are large or hydrophilic Do not cross plasma membrane Instead bind to a receptor on the cell s plasma membrane Steps of Cell Cell Signaling 1 Signal Reception o Signal receptors are bound by Hormones Other cell cell signals o The presence of an appropriate receptor protein dictates which cells will be able to respond to a particular hormone o Identical receptors in diverse cells and tissues Allow long distance signals to coordinate the activities of cells throughout a multicellular organism o Signal receptors Are proteins that change their shape or activity after binding to a signaling molecule Are dynamic May change in their sensitivity to particular hormones Can be blocked o Signal receptors that bind to lipid soluble hormones are located inside the cell o Other signal receptors are located in the plasma membrane 2 Signal Processing o Lipid soluble hormones that cross the plasma membrane produce different cell responses that lipid insoluble hormones that bind to membrane receptors o Lipid soluble steroid hormones Bind to receptors inside the cell Trigger a change in the cell s activity directly o The hormone receptor complex Is
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