General principles and cell physiology LECTURE ONE DISSI, Gambo Mahdi Department of Human Physiology, Faculty of Basic Medical Sciences, College of Health Sciences, Bayero University, Kano. NIGERIA.the body is a social order of about 100 trillion cells Each functional structure contributes to the maintenance of homeostatic conditions in the extracellular fluid. As long as normal conditions of ECF are maintained, the cells of the body continue to live and function properly This reciprocal interplay provides continuous automaticity of the body until one or more functional systems lose their ability to contribute their share of function. When this happens, all the cells of the body suffer — Extreme dysfunction leads to death —Moderate dysfunction leads to sicknessINTRODUCTION * Clinicians often wish they knew more about the basic sciences, because it is through the science that they understand the complexities of the human body and thus have rational methods of diagnosis and treatment.INTRODUCTION Rational understanding of disease and plans for treatment are best acquired by learning about the normal human processes. There fore, the student of physiology should try to understanding the body in the context of molecular interactions, cellular adaptation, and responses by organ system.INTRODUCTION + Physiology gives the ability to appreciate the normal workings of the human body, whereas pathophysiology focuses on how disease or disruption of the normal state affects the same mechanisms.WHAT IS PHYSIOLOGY * The subject is vast and includes the whole of life. * Therefore the vast field of physiology can be divided into: * Viral physiology, * Bacterial physiology, * Plant physiology, * Animal physiology of which our focus is on the study of mammals, specifically, Human physiology.* Simply stated, physiology is the study of body functions. Function occurs at 3 levels: molecular, subcellular, and cellular. + Events at these levels in turn determine the activities of tissues, organs, and systems. * Understanding each level is necessary to appreciate the overall function or dysfunction of an individual. + The overriding principle of physiology is the integration of a variety of mechanisms.+ To study how the body works it is first necessary to know how it is built. Cells are the basic structural and functional living building blocks of the body. Cells of similar structure and specialized function grouped together to form tissues. The four primary tissues of the body are muscle, nervous, epithelial, and connective tissue. + Organs such as the brain, the heart, the lungs, are formed by the aggregation of different kinds of tissues that act together to perform one or more functions.+ The body organs are themselves parts of distinct physiological system. Body systems are collections of organs that perform related functions and interact to accomplish a common activity essential for survival of the whole body. + The heart and blood vessels form the cardiovascular system, the lung, trachea together with the chest wall and diaphragm form the respiratory system and so on. * Organ systems combine to formthe organism, or the whole body.CELLS All cells, whether they exist as solitary or as part ofa multicellular organism, perform basic functions essential for survival of the cell including: obtaining O and nutrients performing energy-generating chemical reactions eliminating wastes synthesizing proteins and other cell components controlling movement of material between the cell and its environment moving material throughout the cell responding to the environment and reproduction (some fully differentiated cells do not)CELLS + In addition to these basic functions, each cell in a multicellular organism performs a specialized function. * Unicellular organisms obtained the essential constituents to maintain life from the external environment. * In multicellular organisms most body cells are not in direct contact with the external environment.ORIGIN OF TISSUE FLUIDORIGIN OF TISSUE FLUID * Cells in the interior no longer remain in direct contact with external environment. + How then do every cell of the body obtain its needed requirement of O, and nutrients to maintain life?ORIGIN OF TISSUE FLUID * There is good evidence that our predecessors, the protovertebrates or prochordates, migrated from the seas into brackish or fresh water during the Cambrian period, almost 500 million years ago. * During that migration, which lasted some 200 million years, they locked" within themselves a fluid similar in composition to that of the seas from which they emerged.ORIGIN OF TISSUE FLUID In the course of that evolution, this problem was initially solved by having sea water run through the organism to bring sea water in direct contact with every cell. But this simple solution could not work since the number of cells in the organism had increased beyond a certain limitORIGIN OF TISSUE FLUID * Thus, since sea water could not be carried to each cell, each cell was furnished with a small private sea of its own. * This private sea or intercellular/interstitial (fluid whose composition is a reminder of origin in the sea) supplies cells with oxygen and nutrients and allow cells excrete their waste into it.ORIGIN OF VASCULAR SYSTEM * But this fluid is small in quantity so —Nutrients in it must be replenished and Waste products must be removed continuously and promptly + otherwise its pH will change and becomes unsuitable for optimal functioning of the cell. * Therefore, a set of tubes called capillaries are developedORIGIN OF CARDIOVASCULAR SYSTEM * Similarly, Fluid in the capillaries must be in constant exchange with the interstitial fluid which also must be in constant exchange with the cells. * The fluid in capillaries therefore, must be in constant motion, so that Continuous replenishment of nutrients And Prompt removal of waste products is accomplished. * This motion was possible by evolution of a pump to provide the force for the motion—the heart.ORIGIN OF OTHER SYSTEMS Also, to accomplish the task of living, these capillaries at least at few points in the circulatory system must come in close contact with the external environment for fresh supply of nutrients and disposal of waste. Structures were then evolved including: * Lungs: Where oxygen is taken up and CO2 is disposed * Kidneys: Nitrogenous waste products are disposed * Gut: Where nutrients are picked up. Thus, digestive system, excretory system and respiratory systems establish link between internal and external environment.ORIGIN OF OTHER SYSTEMS Nutrients Digestive system sak water NE > Nitrogenous waste a products salt, warer yt |FUNCTION OF ORGAN SYSTEMS The Ultimate aim of the work of all the systems Therefore, is to maintain constancy in the characteristics of the thin layer of fluid surrounding every cell of the body or internal environment or in other words all the systems work for homeostasis. * The musculoskeletal system provides support and protection for the soft tissues and organs , serves as storage site for calcium, all blood cells and is important in temperature regulation.FUNCTION OF ORGAN SYSTEMS * The integumentary system serves as an outer protective layer and also important in the regulation of body temperature. * The immune system defend the body against foreign invaders and body cancerous cells as well as repair or replace injured or warn out cells. + The Nervous system Controls and coordinates bodily activities that require rapid and fast responses. In addition to the Higher functions of consciousness, memory and creativity.FUNCTION OF ORGAN SYSTEMS * The Hormonal system Regulates activities that require duration rather than speed such as growth, Controlling the concentration of nutrients, volume of the internal environment and its electrolytes composition. * In nut shell, Chemical, thermal, and neural factors interact to maintain homeostasis.CONCEPTS OF HOMEOSTASIS If one had to describe, with a single word, what physiology is all about, that word would be homeostasis. This word was coined by the great American physiologist, Walter B. Cannon, in his book entitled The Wisdom of the Body (1939). The concept was first introduced by one of the founders of modern physiology, Claude Bernard, who made many contributions to our early understanding of digestion, metabolism, vasomotor activity of nerves, neuromuscular transmission, and other areas of physiology.CONCEPTS OF HOMEOSTASIS * Perhaps his greatest lasting contribution was the notion that all physiologic processes are designed to maintain the internal environment, the milieu interieur, that bathes our cells, tissues, and organs. The following is from his opening lecture in a course in general physiology given at the College de France in 1887:"The living body, though it has need of the surrounding environment, is nevertheless relatively independent of it. This independence which the organism has of its external environment derives from the fact that in the living being, the tissues are in fact withdrawn from direct external influences and are protected by a veritable internal environment which is constituted, in particular, by the fluids circulating in the body’. + In short, he suggested that we exist within our own ‘hot houses’ and that our existence depends on our abilities to maintain that ‘hot house.HOMEOSTASIS * These are mechanisms or processes of stabilizing the internal environment to nearly constant conditions (which is essential if the cells of the body are to function normally) despite variations in both the external world and the bodily activity. In other words homeostasis is a regulatory mechanisms by which biologic systems tend to maintain the internal stability necessary for survival while adjusting to internal or external threats to that stability. If homeostasis is successful, life continues; if it is unsuccessful, disease and perhaps death ensue.* The fact that the internal environment must be kept relatively stable does not mean that its composition, temperature, and other characteristics are absolutely unchanged. Thus homeostasis is not a rigid, fixed state but a dynamic steady state in which the changes that do occur are minimized by compensatory physiological responses.Examples of Homeostatically regulated variables Body Temperature Blood Composition of sugars, proteins e.t.c. Concentrations of O,, CO, and other waste products in the blood Acid-Base balance (pH) * concentration of water, salt and other electrolytes * Blood volume, pressure, cardiac output, cardiac rate * Respiratory rate and depth Secretions of endocrine glands Rate of chemical reactions intracellularly * The variable produces a change in the body —E.g. Increase in blood sugar levels or body temperatureHomeostatic Control Mechanisms/ systems * The control system consists of three interdependent components —Receptor — monitors the environments and responds to changes (stimuli) -> sensory input —Control center — determines the set point at which the variable is maintained->CNS — Effector — structures that provide the means to respond to the stimulus and restore the variables to the optimal physiological range.-> motor outputHomeostatic Control Mechanisms & Input: Information Orn em sent along along efferent afferent pathway to pathway 10 Effector @ change detected by receptor Response of effector feeds 5 back o influence lm magnitude of "eg stimulus and return | | variable to Variable (in homeostasis) homeostasis h me, cgControl systems/mechanisms * They work on the basis of feedback loops, Therefore, they are called feedback systems or feedback mechanism. For feedback systems to work there must be: + A detector (or sensor) + A regulator (or control systems) and for most variables there is * A set pointNEGATIVE FFEDBACK LOOPS * For variables that has a set point (such as body temperature), current value of the variable minus the set point = deviation or error. * This error triggers a response that acts to restore the factor to normal by moving the factor in the opposite direction of its initial change. * These loops are called negative feedback mechanism, as the effector response is negative to the initiating stimulus.Negative Feedback pancreas stimulated i. Foteas into the blood igh blood ‘lucose level ‘detected by Ineulin-secreting celle of pancreas e~ Liver takes up Glucose and stores itas glycogen ‘stimutus: Rising blood ‘lucose level ne Blood glucose level isos w set point; stimulus. {or glucagon’ body returns to homeostasis ‘Homeostasis: Nermal bod gluco evel (about mg/00 mt) a “sy Most body colle take Lup more glucose Blood glucose tevol declines toa set point: stimulus for insulin release diminishes and body returns to homeostasis ‘stim Declining biood ‘glucose level Low blood giucose level ‘detected by glucagon” Feteasng ets of pancreas Liver breaks down un pa yeneaatey soe ome Q pened A Giucagon-reteacing celle of ereas stimulated to release Glucagon into the blocd: target the liverrenve inear ate ! | § i i ‘A decrease in blood prosaure in dotectec Dy receplore inbvood veesele. Tha contol center n tne print regulates hear rate resyancs 100 trillion cells in body. — very small (10-5 m in diameter), hence very efficient. — highly organized. — variety of shapes & sizes. — each type of cells has a special fx.The Cell All Cells share certain characteristics: — general cell structure & components — general mechanisms for changing nutrients to Energy. — deliver end products into their surrounding fluid. — almost all have the ability to reproduce.The Cell Microscopes are required to visualize cells. Light microscopes can resolve structures that are 200nm apart. Electron microscopes can resolve structures that are 0.2nm apart.Observing Cells + Electron Microscopes —Images are black and white — may be colorized —Magnifcation up to ~100,000 * Transmission electron microscope (TEM) —2-D image * Scanning electron microscope (SEM) —3-D imageCell Theory Cell size is limited. -As cell size increases, it takes longer for material to diffuse from the cell membrane to the interior of the cell. Surface area-to-volume ratio: as a cell increases in size, the volume increases 10x faster than the surface areaCell Theory Copyright © The McGraw-Hill Companies, Ine. Permission roquired for reproduction er display. Coll radius (7) 1 unit 10 unit | ‘Surface area (42r?) 12.97 unit? 1257 unit@ Volume ($2r9) 4.189 unit® 4189 unit ‘Surface Area / Volume 3 03 | Siete th as ae as Shucawshnotake Bh tan Spl © Say Ml faate UeiaiodWhy Are Cells So Small? * Cells need sufficient surface area to allow adequate transport of nutrients in and wastes out. * As cell volume increases, so does the need for the transporting of nutrients and wastes.Why Are Cells So Small? + However, as cell volume increases the surface area of the cell does not expand as quickly. —If the cell's volume gets too large it cannot transport enough wastes out or nutrients in. + Thus, surface area limits cell volume/size.Why Are Cells So Small? * Strategies for increasing surface area, so cell can be larger: —“Frilly" edged....... —Long and narrow... * Round cells will always be small.Eukaryotic Cells Eukaryotic cells -possess a membrane-bound nucleus -are more complex than prokaryotic cells -compartmentalize many cellular functions within organelles and the endomembrane system -possess a cytoskeleton for support and to maintain cellular structureEukaryotic Cells Outer membrane Nuclear poreCell Components * What are the basic components of a cell? —Nucleus Cell —Cytoplasm = —Cell membraneCell Nucleus Is a large spheroid body. Largest of organelles. Contains the genetic material (DNA). Most cells have a single nucleus. Enclosed by inner & outer membrane (nuclear envelope). — Outer membrane is continuous w ER. Nuclear pore complexes fuse inner & outer membranes together. — Selective active transport of proteins & RNANucleus Surrounded by a bilaminar nuclear membrane or envelope with occasional pores One or more mobile nucleoli. The Nucleus contains almost all the DNA in the eukaryotic cell It is responsible for the synthesis of MRNA, tRNA and rRNA.Copy git The NeGuaw-Hil Corwperies, Ine, Peimlssion regula’ for ep1vOULvON O' splay. >.Outer membrane Inner membrane Nucleoplasm Nucleolus Chromatin Nuclear envelope Pore in nuclear envelopeNUCLEUS Nuclear Envelope double nuclear membrane each 2 nm thick The outer membrane is derived from the endoplasmic reticulum The inner membrane from the nucleus Each is a separate lipid bilayer A perinuclear space, 10-50 nm wide separate the two membranes.NUCLEUS + Nuclear Pores * The nuclear envelope has several circular nuclear pores (~1 nm wide). They occupy about 20% of the total surface area of the nuclear envelop. * Each pore is surrounded by 8 protein granules, which serve as molecular sieves, allowing the transport of materials such as RNANUCLEUS Nuclear Lamina * This is located between the inner nuclear membrane and the nuclear chromatin. + Itis composed of complex polypeptides known as laminins + They undergo phosphorylation and dephosphorylation at various stages of the cell cycle.NUCLEUS Nuclear Chromatin It is the Major constituent of the nucleus. It has a DNA: Proteins ratio of 1:2 Half of these proteins are histones, the other half are mainly transcription factors. Chromatin is made up of nucleosomes, each consisting of 8 histone molecules surrounded by DNA. Nucleosomes are joined together by an intervening length of DNA known as “linker-DNA".NUCLEUS * PML Nuclear Bodies— PML nuclear bodies (NBs) are spheres of 0.1—1.0 ym in diameter found in the nuclear matrix. * They anchor, regulate and fine-tune a wide variety of processes and functions including * DNA Replication * Transcription * Epigenetic silencing and cellular senescenceNUCLEUS Nucleolus * These are intranuclear structures which stain strongly for RNA and weakly for DNA. * They float in the nuclear fluid + It is the site for synthesis of ribosomal RNA (rRNA) + It is also the site for the assembly of ribosomal subunits.NUCLEUS Nuclear DNA Mammalian DNA is arranged in linear chromosomes It exists as a double helix held together by hydrogen bonds, with the two strands being complementary. It has Adenine being bound to Thymine (A-T) while Guanine is bound to Cytosine (G-C) Usually expressed as a number of nucleotide or base pairs (bp). Human haploid genome has 2.8 x 10: bp Only a small part of the genome contains actual ‘genes’DNA SYNTHESIS * Occurs before every cell division * Occurs during the S-phase of the cell cycle * Histone synthesis also occurs during the S- phaseDNA REPLICATION * Depends on the presence of DNA polymerases + Five main polymerases known: a, b, d, e and g. —Polymerase ‘a’ copies the lagging strand —Polymerase ‘b' copies the leading DNA strand —Polymerase ‘d’ and ‘e’ act with Endonuclease and DNA ligases to repair damaged DNA especially during cell division. —Polymerase 'g’ copies mitochondrial DNARNA SYNNTHESIS (TRANSCRIPTION) + Classes of RNAin Mammalian Cells: + —messenger RNA (mRNA) —ribosomal RNA (rRNA) + —transfer RNA (tRNA) + -small nuclear RNA (snRNA) + -heteronuclear RNA (hnRNA) Sites of Transcription + -Nucleus + —MitochondriaRNA POLYMERASES - Nuclear RNA Polymerases: —Polymerase | is located in the nucleolus and is responsible for the production of rRNA —Polymerase II is responsible for the transcription of protein-coding genes into mRNA and microRNAs —Polymerase III is responsible for the synthesis of tRNA and snRNA —Polymerases IV & V are found in plants and are responsible for synthesis of smal! interfering siRNA + Mitochondrial RNA Polymerase is responsible for the synthesis of mitochondrial RNATHE CYTOPLASM * The aqueous (fluid, jellylike substance) content of a cell, that lies b/w cell membrane & nucleus in which organelles are suspended. * Serves as matrix (ground substance) in which chemical reactions occur * Cytoplasm is divided functionally into —Cytosol (fluid portion of the cytoplasm) —Inclusions including non membranous organelles —Membranous Organelles (Functional units of the cell)Composition and function of cytosol * Dissolved glucose, proteins and electrolytes enzymes transport proteins (Steroid Hormones & Metals) glycogen granules triacylglycerol droplets (adipocytes) Cytosol functions (many in conjunction with other processes) —Cell signaling —Cytokinesis —Protein synthesis —many other chemical reactions e.g. Glycolysis, gluconeogenesisThe Inclusions —They have direct contact with the cytosol + Free Ribosomes — Involved in synthesis of proteins * Proteasomes — Involved in protein degradation + Protein fibers — Provide structure and movement within the cell + Vaults ~ They are large ribonucleoprotein about 3 times the size of a ribosome with incompletely determined functions. — They are however associated with lipid rafts hence may serve as organizing centers for the assembly of signaling molecules, and membrane protein trafficking. — By virtue of their octagonal shape, they has been associated with nuclear pore complexes, hence may play a role in transportation of molecules such as mRNA from the nucleus to parts of the cytoplasmMembranous organelles Mitochondria The Endoplasmic reticulum The Golgi complex Lysosomes Peroxisomes Phagosomes secretory vesicles Centrosome/CentriolesOuter Matrix ristae Inner mnelipae membraneMitochondria + Endosymbiotic theory — Believed to have been prokaryotes that formed a symbiotic relationship with precursor eukaryotic cells - Are have varied shapes ,sizes and location in the cell. They are usually elongated, tubular (spherical in stress) about 3m long and 0.5-1.5um wide Each has a continuous external limiting membrane and an inner membrane folded into septae (cristae) Cristae create partial subdivisions of the matrix Have their own DNA and Ribosomes —The mDNA encodes only some of the proteins found in mitochondria + Replicate independently of the nucleusTHE MITOCHONDRIA Serves as the "powerhouse of the cell” by generating chemical energy Site of the tricarboxylic acid cycle and production of NADH Oxidation of NADH in the electron transport chain to produce ATP (H+ concentration higher in the inter-membrane space than in the matrix) Stores energy as adenosine triphosphate (ATP) and subsequently releases it when required by the cellFunctions of the mitochondria B-Oxidation of fatty acids Synthesis of intermediate metabolites required for the biosynthesis of haem, glucose, steroids and urea Detoxification of ammonia Accumulation/storage of divalent cations such as Ca++ Is curial in apoptosis‘Rough endoplasmic pe reticulum ‘Smooth endoplasmic reticulumThe Endoplasmic reticulum * They are a complex network of membranes within the cytoplasm which are folded extensively to form vesicles, tubules and sacs usually as parallel pairs. —Continuous with the outer membrane of the nuclear envelope —Two forms - smooth and rough * When they have ribosomes attached to them, they are granular in appearance and are called rough ER * But when no/few ribosomes are present, they are referred to as smooth ER.RoughER + Network of flattened membrane sacs that create a network of channels throughout the cytoplasm. They contain enzymes that recognize and modify proteins + Ribosomes are attached to the outside of the RER and make it appear rough * They synthesize proteins to be secreted, sent to lysosomes or the plasma membrane + Proteins are modified as they move through the RER + Once modified, the proteins are packaged in transport vesicles for transport to the Golgi bodySmooth ER * Tubular membrane structure continuous with RER * The smocth ER has roles in gluconeogenesis, plasma lipoprotein production, synthesis of triacylglycerol, cholesterol, phospholipids and other membrane lipids. Formation of bile salts Synthesis, secretion and inactivation of steroid hormones detoxification of foreign compounds and conjugation reactions. sequestration of Ca2+ ions oxidative metabolism by the cytochrome P450 systemGolgi Apparatus Ba transCis face ‘Transport “receiving” side of vesicle from Golgi apparatus rough ER faa Cisternae forming Trans face “shipping” side of Golgi apparatus Secretory vesicle from the Golgi from trans face wThe Golgi complex Its structure is similar to that of smooth endoplasmic reticulum. It comprised of flattened stacks of interconnected membranes in cisternae or vesicular form, arranged like a stack of plates It forms a functional unit with the ER. Usually located near the nucleus. Some of its vesicles have special names such as endosomes (involved in endocytosis) and secretory vesicles (involved in hormone secretion).Functions of the Golgi Complex * Proteins (packaging Vesicle) formed in the rough ER passes through the cis-face and binds to the first layer of the Golgi body. * Its contents enter the Golgi complex for modification and subsequently exits through the trans-face into secretory channels, lysosomes, the plasma membrane or to become part of the GC itself. + The proteins and lipids are modified (as they pass through layers of the Golgi complex) through multiple post-translational modifications including further glycosylation (initial glycosylation occurs in the ER)Golgi Apparatus — Molecular tags are added to the fully modified substances + These tags allow the substances to be sorted and packaged appropriately. + Tags also indicate where the substance is to be shipped * Functionally, the Golgi apparatus completes the processing of substances received from the ER, Sorts them, tag them and package fully processed proteins and lipids into vesicles which are released via the trans face.Putting it all together —DNA directs RNA synthesis RNA exits nucleus through a nuclear pore ribosome protein is made _ proteins with proper code enter RER proteins are modified in RER and lipids are made inSER_ vesicles containing the proteins and lipids bud off from the ERPutting it all together ER vesicles merge with Golgi body roteins and lipids enter Golgi each is ully modified as it passes through layers of Golgi modified products are tagged, sorted and bud off in Golgi vesicles ... Golgi vesicles either merge with the plasma membrane and release their contents OR remain in the cell and serve a purposeAnatomy of the Lysosomelysosomes The lysosome is an example of an organelle made at the Golgi apparatus. —Golgi packages digestive enzymes in a vesicle. The vesicle remains in the cell (primary lysosome) They have the thickest membrane and contains a battery of hydrolytic enzymes (acid hydrolases). They are abundant in some cell types such as macrophages but scarce in others such as lymphocytes. Their enzymes are synthesized in the rough ER and processed through the Golgi complex before passage into the lysosomes.Functions of lysosome + The hydrolytic enzymes in lysosomes include nucleases, proteases (cathepsins), lipases and glycosidases. They generally have low degree of specificity. + These enzymes function best at a pH of between 4.0 and 5.5. They have a proton-pumping ATPase that allows its lumen to be acidified to a pH of 5. The enzymes help in digesting dead cells (endolysosomes), foreign cells and proteins (phagolysosome), albumin in the renal tubules and in the remodeling of bones and other tissuesTay-Sachs disease * This occurs when the lysosome is missing the enzyme needed to digest some lipids found in nerve cells. —As aresult the lipid accumulates and nerve cells are damaged as the lysosome swells with undigested lipid.Peroxisomes They are Spherical or spheroidal sacs, about 0.5-1.5 microns in diameter. Also bounded by a single membrane. Formed by division of pre-existing peroxisomes. Their proliferation is stimulated by certain drugs e. gclofibrates. They contain peroxidase and catalase enzymes which prevents the build-up of peroxides in cells. They are also capable of the B -oxidation of fatty acids They sub serve detoxification function Degrade purines to uric acid Formation of bile acids and myelin sheath of nerves.~~Pinocytic or Phagocytic vesicle Digestive vesiclo Figure 2-12. Digestion of substances in pinocytic vesicles by enzymes derived from lysosomes.Phagosomes + Are membrane bound bodies containing materials ingested by phagocytosis * To effect digestion they combine with lysosomes to produce phagolysosomes + Forms residual or dense bodies when ingestible material remains undigested/ partially digested* Read about —secretory vesicles —Centrosome and centrioles* Organelles without a limiting membrane + Ribosomes * cytoskeleton+ _Amode| structure of a ribosome. It is composed of two subunits: smaller (lighter) & larger (darker) subunits. The space between the two subunits accommodates a molecule of transfer RNA, needed to bring amino acids to a growing polypeptide chain.Ribosomes Are small granules of Ribonucleoprotein particles formed by the combination of rRNA and proteins in the nucleolus. + They are found embedded to the rough endoplasmic reticulum They control synthesis of proteins required for intracellular metabolism by forming complexes with mRNA during protein synthesis, creating polysomes (several ribosomes rolling along a strand of mRNA in the course of protein synthesis).[Transfer RNA JAmino acid & Messenger RNA Small suounit Brae chain © Elsevier. Guyton & Hall: Textbook of Medical Physiology 1 le - www.studentconsult.com Fibesome Large subunit eThe cytoskeleton * The cytoskeletal components help to — Maintain cell shape — Organize the internal compartment of the cell — Provide transport routes within cells — Aid in creation of tissues from cells — Create movement * Along with motor proteins such as Myosins — Actin motor protein Dyenins Kinesins Other cellular motor proteins include: ATP synthase, DNA & RNA polymeraseMicrotubules Are found throughout the cytoplasm * They are 20-27nm in diameter * Constitutes the mitotic spindle filaments * May also facilitate intracytoplasmic transport and maintain cell shape + Assembled from monomers of tubulin ( & ) + (& )monomers combine to form dimers + these assemble to create protofilaments (ingle tubes) which then assemble into the larger structures of —Centricles » Direct microtubule formation during the M phase of the cell cycle » Form basal bodies for flagella and cilia ~ flagella and cilia ~ provide motility » Using dyenin “motors”Microtubule; assembly of a ciliumMicrofilaments Smallest cytoskeletal filament Are long thread-like structures about 4-12nm in diameter They are made of anon contractile protein chiefly actin Contains binding sites for myosin Some converge on intercellular junctions to promote cell adhesion Functions also in the formation of microvilli. There are also unknown functions of microfilaments elsewheremicrofilament Actin Single actin subunit Spoons aa Actin ftament consisting ‘of multiple subunits aaa ag REIntermediate Filaments * Type | & Il Intermediate filaments — Hair/nails — keratin fibers + Type Ill Intermediate filaments —Desmin » Involved in structural support of sarcomeres » Connects z discs to subsarcolemmal cytoskeleton! > Involved in migration of cells during embryogenesis —Vimentin » Support cell membranes » Cytoskeletal component that anchors some organelles ~Peripherins & GFAP's (glial fibrillary acidic protein) » Intermediate filaments in nerves and glial cellsIntermediate Filaments —Type IV Intermediate filaments + Filament group that has types in neural tissue as well as muscle tissue —Type V Intermediate filaments + These are nuclear filaments, providing support for the nuclear membrane —Type VI Intermediate filaments + Aids in growth of axons