THE CELLLearning Objectives:1. Define organic and inorganic compounds and state examples of each. 2. List the components of the cell membrane and state it functions.3. Describe the organelles of the cell and the role each plays.4. Understand the significance of cellular inclusions and their role in cell function.5. Describe the surface specializations of the cell covered in lecture and their function. The cell is the fundamental structural and functional unit of all organisms.A. GENERAL STRUCTUREA wide variety of cells of different sizes and shapes are found in the human body. Many of these cells have very unique characteristics that allow them to perform their specific function. However, although they are morphologically different, most cells have three common components. These include a cell membrane, a nucleus and cytoplasm. These will be described in this lecture. Before doing this however some basic information related to the composition of cells will be reviewed. B. CHEMICAL COMPOSITIONThe body is composed, for the most part, of the following elements:Oxygen (O) 65%Carbon (C) 18%Hydrogen (H) 10%Nitrogen (N) 3% In addition it contains small amounts of elements such as Calcium (Ca), Potassium (K),Sodium (Na), Phosphorus (P), Magnesium (Mg), Chloride (Cl) and Sulfur (S).Many of these elements combine to form the various “macromolecules” or compoundswhich are the so-called “building blocks” of cell structure.In general, all cells contain the following: Inorganic compounds -Examples:a. waterb. electrolytes (acids, bases, salts)Cell I - Page 1 of 6Organic compounds -Types of Organic Compounds 1. ProteinThe structure and function of each protein is determined by the number and sequence of its amino acids. Examples include:- structural- enzymes- hormones2. Carbohydrates (CH0)Examples: monosaccharides, disaccharides, polysaccharides3. LipidsExamples: fats, cholesterol, phospholipids4. Nucleic acidsExamples: DNA (deoxyribonucleic acid), RNA (ribonucleic acid) C. MAJOR COMPONENTS OF CELLS 1. Cell Membrane (plasma membrane)a. Composed of: 1. 2. 3. b. General structure – “Fluid Mosaic Model” Cell I - Page 2 of 6Current theory for the arrangement of the components of the cell membrane:Lipid components (amphipathic molecules) are arranged in a bilayer which acts somewhat like a fluid. Proteins and carbohydrates float like icebergs in this sea of lipid. Note: Amphipathic molecules have a polar and nonpolar end.c. Function1. Compartmentalization2. Regulation of movement of materials from one area to another. Selectively permeable3. Provides for intercellular interactions allows communication between cells cell-cell recognition sites.4. Provides recognition sitesNote: Extracellular fluid is located outside of the cell membrane. The extracellular fluid located closest to the outer surface of the membrane is called interstitial fluid.2. Nucleus – cells “command center”a) structure 1. chromatin 2. nuclear envelope 3. nucleolus b) function 1.2.3.3. CYTOPLASM – substance located within the cell. This includes the following:Cell I - Page 3 of 6Cytosol – fluid within the cell. It varies in composition depending on the cell type.Organelles – small structures that perform specific cellular functionsInclusions – small components of cells related to the cell’s specific functionA. CYTOSOLB. ORGANELLES1. Ribosome “protein factories” of cella. structure b. function 2. Endoplasmic Reticuluma. structure b. function c. types 1. rough (RER) 2. smooth (SER)3. Golgi Complex a. structure b. function4. Mitochondria – “powerhouse” of the cellCell I - Page 4 of 6a. structure – b. functionC. CYTOPLASMIC INCLUSIONS – Includes a wide variety of chemical substances whose presence varies depending on the type cell. These will be discussed in detail in appropriate lectures. Some examples are:secretory granules lysosomeshemoglobin peroxisomeslipids droplets vacuolespigmentsD. CYTOSKELETON: Proteins arranged to perform specific cellular functions.1. Microtubules: Small, hollow tubules (formed by a protein called tubulin) which run throughout the cytoplasm. Functionally they act as:- a supporting network- conducting channels through which substances pass through the cytoplasm- structural component of centrioles and cilia2. Centrioles: Cylindrically shaped organelle composed of nine triplets of microtubules. - Two per cell, located near nucleus- They play an important role in cell division 3. Microfilaments: Thin strands of proteins - provide cytoskeletal support - associated with contractile activities and cell locomotion (movement) (abundant in muscle cells)Cell I - Page 5 of 6E. SURFACE SPECIALIZATIONS: These are located in cells in specific systems of the body. They will be discussed in detail in subsequent lectures.Examples include:1. Microvillia. Structure – finger-like projections of cell membrane made by in-foldingb. Function – increases surface area of cell membrane and facilitates transport2. Ciliaa. Structure – cytoplasmic projections made of microtubulesb. Function – move in a wave-like fashion to move mucous, etc.3. Cellular Adhesions: junctional complexes – specialized regions of contact. Examples:- Tight junctions – from a tight seal between cells- Desmosomes – “spot-weld” cells together- Gap junctions – allow for cell to cell exchange and communication.Cell I - Page 6 of