Cell Communication I PDF

Cell Communication  Session Learning Outcomes (SLOs) SLO# 1: Describe the importance of cell signaling in biology. SLO# 2: Explain the basic principles of cellular signal transduction. SLO# 3: Compare the main types of cell communication that exist in multicellular organisms....

Cell Communication  Session Learning Outcomes (SLOs) SLO# 1: Describe the importance of cell signaling in biology. SLO# 2: Explain the basic principles of cellular signal transduction. SLO# 3: Compare the main types of cell communication that exist in multicellular organisms.  Definitions Enger Ligand: the chemical signal that binds to a receptor. Receptor: a protein that can bind to the signal (in the case of a w̅ molecule) or detect a signal in the case of light or other non- molecule signals. Reception: when the receptor binds to the signal, causing the receptor to change shape. Kinase: an enzyme that attaches a phosphate to another protein (usually activating it) Phosphatase: an enzyme that removes phosphate from a protein (usually inactivating it) Second Messenger: a small non protein molecule that diffuses rapidly through the cell during signal transduction. Examples include cAMP, IP3, DAG, Ca2+. Signal Transduction: converting a signal into a cellular response.  Cell Communication The basics of cell communication are found in all living things. All living cells must respond appropriately to their environment. Importance of cell signaling in unicellular organisms In single-celled organisms, signal transduction pathways influence how the cell responds to its environment and signaling between organisms.  Unicellular organisms Example: Yeast cells identify their mates by cell * signaling factor Receptor 1 Exchange of mating factors: Each cell type secretes a mating a factor that binds to receptors on the other cell type. Yeast cell, a factor Yeast cell, mating type a mating type 2 Mating: Binding of the factors to receptors induces changes in the cells that a lead to their fusion. 3New a/ cell: The nucleus of the fused cell a/ includes all the genes from the a and α cells.  Importance of cell signaling in multicellular organisms Cell communication is necessary for the existence of multicellular organisms. lead communication Ina to enttiat gtatew.IE parliferates I Cell-cell signalling permits coordinated function of cells within and between tissues, up to the organism level Cells must interpret the multitude of signals they receive from other cells to help coordinate their behaviors. jw̅ Cells must communicate in order to proliferate, differentiate, migrate and maintain a functional state. Homeostasis 189bbacterial Most animal cells both send and receive signals. is Signals from other cells or the environment can be stimulatory (turn on a gene or protein) or inhibitory (turn off a gene or protein there something  g g eachpartwilldifferentiante todifferentcelltype toformdifferent differentorgansdifferentsystem tissuesform multicellular organisms Example: During animal development, cells in the embryo exchange signals to determine which specialized role each cell will adopt, what position it will occupy in the animal, and ofmembrane whether it will survive, divide, or die. apoptosis betweenthe fingers The ability of cells in multicellular organisms to perceive and correctly respond to their microenvironment is the basis of growth, development, tissue repair, and immunity as well as normal tissue homeostasis. Errors in cellular information processing are responsible for diseases such as cancer, autoimmunity, and diabetes.  General Principal of Cell Signaling - Cells in a multicellular organism communicate via chemical messengers. hormonesentropy cytokines inthe immune system - Communication between cells requires: Ligand: Extracellular signaling molecules that are produced and released by signaling cells. Receptor protein: the molecule to which the receptor binds and recognize the signaling molecules on the mm in surface of target cells where they cause a cellular response by means of a signal transduction pathway.  Signal transduction pathways A signal transduction pathway is a series of steps by which a signal on a cell’s surface is converted into a specific cellular response. receptor Figure 16-2 Essential Cell Biology (© Garland Science 2010) External signal is received and converted to another form to elicit a response insidethe ofsome expression nucleus genes  Methods used by Cells to Communicate There are different basic mechanisms for cellular communication: extracellular 1- Direct contact: Cell-cell or cell-matrix contact using membrane bound receptors. ciphysical no9h 2- Indirect: there are three kinds of chemical signaling: Extracellular signal molecules can act over either long or short distance secreted and some molecules A. Autocrine signaling work inthesamecellAuto B. Paracrine signaling signalingandtargetingcellare shortdistance neighbors C. Endocrine signaling Bigdistance  Types of signaling Cells that maintain an intimate membrane-to-membrane interface can engage in contact-dependent signaling. Cells may communicate by direct contact, or cell-cell recognition 1- Direct contact Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells Plasma membranes a in Gap junctions Plasmodesmata between animal between plant  Types of signaling went 2- Cell-cell recognition i IT ii The cells make direct physical contact through signal molecules lodged in the plasma membrane of i. si9np the signaling cell and receptor proteins embedded in the plasma membrane of the target cell. receptors feins signaling tail ce  collagen fibers Signaling by direct (cell-cell or cell-matrix) interactions plays a critical role in regulating the behavior of cells in animals tissues. Integrins cadenins thesamefunction cell extracellular linkconnection For example: receptors matrix The integrins and cadherins function not only as cell adhesion molecules but also as signaling molecules that regulate cell proliferation and survival in response to cell-cell and cell-matrix contacts. anlasiiive a.fi theyadhere only if for specialization ofthecell matrix toextracellular anddifferentiate During embryonic development, such contact-dependent signaling allows adjacent cells that are initially similar to become specialized to form different cell types  cell-cell recognition systemm Cell to Cell Contact: used to distinguish “self” from “other” Majorhistocompatibility complex Animal cells have MHC proteins on the surface of the cell to distinguish “self” from “other” Antigen Presenting Cells present antigen to T cells by cell- cell contact. pacteria macrophage dophagocytosis andpresent antigen macrophage willactivateTlymphocyte releasesomecytokines will YepR'plc Iffhg lymphocyte Im g e recognize secreteantibodies Recognition of foreign antigen causes T cell activation and signal to other immune cells to mature  TakeBacteria andpresentantigen withreceptors B Cells are antigen presenting cells to T helper cells B cells present antigen to TH cell. If the T cell receptor recognizes the antigen it will release lymphokines maturation The B cell matures into a plasma cell and releases antibodies into the blood plasma.  Three kinds of chemical signaling 1- Autocrine signaling: Cells respond to signaling molecules that they themselves produce. Examples: response of the immune system to foreign antigens, and cancer cells. cytokine jwjo.si or www.aijw mnawaaana.s Examples of an autocrine: interleukocytes orcytolenkin sjpsywreji.ae's 1- The cytokine interleukin-1 (IL-1) in monocytes: When interleukin-1 is produced in response to external stimuli, it can bind to cell-surface receptors on the same cell that produced it.  kinds of chemical signaling Short distance signaling: 2- Paracrine signaling: The signaling molecules released by one cell in the extracellular fluid act on neighboring target cells Examples: - Neurotransmitters at synapses in the nervous system. - Cytokines that cause an inflammatory response in the infection area. andworkin secreted signals frommonocyte endothelialcells * - Growth factors that control cell proliferation in a healing growth factorsfrom platelets will wound function. workonthe fibroplast Synaptic signaling: Neuronal signals are transmitted along axons to remote target cells. *  Three kinds of chemical signaling Long distance signaling: Long-distance signaling 3- Endocrine signaling: Blood Endocrine cell The signaling molecules are vessel hormones secreted by endocrine cells and carried through the circulation system to act on target cells at distant Hormone travels in bloodstream body sites. to target cells Examples: fromtheovary Target cell - Progesterone and testosterone. - Thyroid hormones.  Types of signaling The endocrine hormones FSH and LH are made by air on the pituitary gland in the brain. so - These hormones coordinate the maturation of ovules and and Endometrium Murat Figure 45.10 Glucose homeostasis maintained by insulin and glucagon  Each Cell Responds to a Limited Set of Signals A typical cell in a multicullar organism is exposed to hundreds of different signal molecules in its environment. solublesignalmolecule Hormones typesof nectin These may be free in the extracellular fluid, embedded in the flues extracellular matrix in which cell rest, or bound to the surface of the neighboring cells. onthetype ofthecell depends cellcellcommunication one inside receptor protein Each cell must respond selectively to a mixture of signal, disregarding some and reacting to others, according to the cell specialized function. Cell responds to a signal molecule depends on whether it possesses a receptor for that signal. If it has no receptor inoresponds Limited range of signals can still be used to control the behavior of cell in complex ways. change theshape megration The complexity is of two sorts:  specefity 1. Binding to one type of receptor protein, can cause a multitude of effects in the target cell. It can alter the cell’s shape, movement, metabolism, and gene expression. ontract increase same the ligand The information conveyed by the signal depends on how the target cell receives and interprets the signal. 2. A typical cell possesses a collection of different receptors. Such a variety makes the cell simultaneously be sensitive to many extracellular signals. these signal molecules work in combinations to regulate the behavior of the cell. communicate cellmust if itdidn't it willdie if itdidn't getanysignals Each cell is programmed to respond to specific combinations of extracellular signal molecules Extracellular signals alter the activity of a variety of cell proteins to change the behavior of the cell. Hormone Growthfactor The signal molecule binds to a cell- surface receptor protein. for The receptor protein activates an secondmassenger canbe intracellular signaling pathway that is quction mediated by a series of intracellular araha sieve's metdiated signaling proteins. Eating Some of these signaling proteins interact with target Sprotein proteins, altering them to target change the behavior of the cell. Signaling cascades of intracellular signaling molecules have several crucial functions. They transform the signal into a molecular form suitable for passing the signal along or passthesignal stimulating a response. Modulation They relay the signal from the point in the cell at by other which it is received to the point at which the factors response is produced. amplified tesp egod conferommotting willactiva Signaling cascades amplify the signals iii ii The signaling cascades can also distribute 3pathways activateone samemolecule if suitableresponses the signal so as to influence several ien iggggnqq.fi processes in parallel.  Session Learning Outcomes (SLOs) SLO# 1: List the major classes of signaling molecules and the receptor types upon which they act. SLO# 2: Compare the 2 types of receptors that are classified based on location in the cell SLO# 4: Describe how signal information is transduced into cellular responses in the cytoplasm and in the nucleus  Extracellular signals Extracellular signal molecules generally fall into two classes: 1- The most of the extracellular signal molecules are Hydrophylic molecules. bilayers phospholipid Can'tpassthroughthe Large polypeptide hormones (insulin, glucagon, growth hormones). Small charged compounds (Adrenaline). Unable to cross the plasma membrane of the target cell. Bind to cell surface receptors. nonprotein IP3 Calcuim Usually use a 2nd messenger. molecules Generate one or more signaling molecules inside the target cell. 2- Some of the extracellular signal molecules are: Small or hydrophobic. Diffuses through the plasma membrane. vitamin A Made from cholesterol, lipids, hydrophobic AAs, or Vit A. Very stable change = hours to days (slow and long-lasting cellular change). longer acting Activate intracellular enzymes directly or bind to intracellular receptors proteins in either the cytosol or the nucleus. longer gene expression short Both the cytosolic and nuclear receptors are referred to as nuclear receptors. bind to receptor dotheroleof transcription Most steroid receptors are transcription regulators, which bind to promoter and turn on specific genes. Regulates gene expression Transcription factor  - Cells in multicellular organisms use hundreds of kinds of extracellular molecules to send signals to one another. - Ligand can be: Proteins Peptide Amino acids, Nucleotides, Steroids Fatty acid derivatives, Dissolved gases  Extracellular signal molecules Extracellular signal molecules bind either to cell-surface receptors or to intracellular enzymes or receptors. cytosol inthe i L enticing transcription the do factor Extracellular signal molecules a cell’s response to a signal can be fast or slow Cell responses that need not involve changes in gene expression (changes in cell movement, secretion, or metabolism) occur more quickly. altered protein function change in the conformation Yin'sp factors altered protein synthesis Cell responses that involve changes in gene expression and the synthesis of new proteins (cell growth and division) occur relatively slowly.  Intracellular Receptors Intracellular receptors are cytoplasmic or nuclear proteins. Receptors are often in the cytoplasm until a ligand binds to them and then they move to the nucleus. hydrophopic Signal molecules are lipid-soluble molecules.  Intracellular Receptors A steroid receptor has 3 functional domains: receptor ligand dotheroleoftranscriptionfactors 1. Hormone-binding domain transcription factor toactivatethegeneexpression bind toDN 2. DNA binding domain to activate thegeneexpressionafter DNAbinding 3. Domain that interacts with coactivators 1 to affect gene expression to factor othertranscription Steroid Receptor Superfamily are transcription factors that function either as activators or repressors of transcription. inhibatory Cell Signaling by hydrophobic signals Nitric oxide (NO) triggers smooth muscle relaxation in a blood-vessel wall - Nitric oxide (NO), is able to diffuse across the membrane. - Nitric oxide gas signals by binding directly to an enzyme inside the target cell, and alters the activity of intracellular target enzymes.. w̅ Ex. It signals the dilation of blood vessels. The mechanism : 1. Acetylcholine is released from the terminus of nerve cell in the blood vessel wall. 6. the activated cyclase catalyzes the production of cGMp from Gtp. 5. NO bound to receptor guanylyl cyclase. agittitrace signals 3. The endothelial cells are stimulated to produce NO 7. cGMP causes 2. Acetylcholine (from arginine). muscle cells diffuses to reach relaxation acetylcholine receptors 4. The NO diffuses into adjacent smooth muscle cells. released fromonecell type of 8 paracrine molecules communication andworkinadjecent  Cell Signaling by hydrophobic signals One important class of signal molecules that rely on intracellular receptor proteins is the steroid hormones (cortisol, estradial, and testosterone) and the thyroid hormones (thyroxine). Thyroid Hormone Cell Signaling by hydrophobic signals  Steroid hormones bind to intracellular receptors 1. Hormone binds to a receptor protein in the 5. The mRNA is cytoplasm,. translated into a coactivator specific protein binding Hormone domain. Hormone passes through the plasma membrane. 1. Hormone-receptor complex enters the nucleus. 4. Hormone-receptor complex binds to target gene and stimulates the transcription of the gene into mRNA.