Chapter 3 The Cellular Level of Organization I An Introduction to Cells p 63 Cell theory Robert Hooke 1665 Cells are the building blocks of all plants and animals All cells come from division of preexisting cells Cells are the smallest units that perform all vital physiological functions Each cell maintains homeostasis at the cellular level An organism maintains homeostasis through the coordination of all its cells working individually and together Cytology the study of cell structure and function a division of cell biology Two classes of cells in the human body 1 sex cells germ cells reproductive cells male sperm female oocytes eggs 2 somatic cells soma body all body cells except sex cells Figure 3 1 Shows the general structure and typical organelles of a body cell Table 3 1 Summarizes the organelles and their functions Human body cells are surrounded by a cell membrane which separates the inside cytoplasm from the outside extracellular fluid Fluid between cells is called interstitial fluid interstitium something standing between Cell membrane is more than just a barrier it selectively transports nutrients into and cellular products and wastes out of the cell II The Cell Membrane p 63 Cell membrane or plasma membrane has 4 basic functions 1 Physical isolation forms a physical barrier between the inside and outside of the cell Keeps things in or out 2 Regulate exchange with the environment controls entry of ions and nutrients eliminates waste releases cellular products 3 Monitor the environment detects changes in composition concentration or pH of extracellular fluid Contains receptors that respond to chemical signals 4 Structural support keeps cells in place and stabilizes tissues Figure 3 2 The cell membrane is an active organelle containing lipids carbohydrates and several types of functional proteins Membrane Lipids p 66 Figure 3 2 The cell membrane is made up of a double layer of phospholipid molecules phospholipid bilayer with their hydrophilic heads toward the watery environment on both sides The hydrophobic fatty acid tails inside the membrane form a barrier to ions and water soluble compounds isolating the inside of the cell from the outside Membrane Proteins p 66 Figure 3 2 There are 2 structural classes of membrane proteins 1 integral proteins embedded within the membrane 2 peripheral proteins stuck to the inner or outer surface of the membrane These large protein molecules are divided into 6 specialized functions 1 anchoring proteins stabilizers attach cell membrane to inside or outside structures 2 recognition proteins identifiers label cells as normal or abnormal to the immune system 3 enzymes catalyze reactions inside or outside the membrane 4 receptor proteins bind and respond to extracellular molecules called ligands e g ions hormones 5 carrier proteins bind specific solutes and transport them through the cell membrane using energy 6 channels pores that regulate the flow of water and specific solutes through membrane Membrane Carbohydrates p 67 Carbohydrates in the cell membrane include proteoglycans glycoproteins and glycolipids Parts of these molecules extend outside the cell membrane to form a sticky sugar coat or glycocalyx Four main functions of the glycocalyx are 1 Lubrication and protection 2 Anchoring and locomotion 3 Specificity in binding receptors 4 Recognition immune response III The Cytoplasm p 68 Cytoplasm includes all materials inside the cell membrane but outside the nucleus The 2 components of cytoplasm are 1 cytosol intracellular fluid thick liquid with dissolved nutrients ions soluble and insoluble proteins waste products 2 organelles structures with specific functions inside the cell The Cytosol p 68 Cytosol differs from extracellular interstitial fluid in 3 ways 1 Potassium ions are concentrated inside and sodium ions outside the cell 2 Cytosol has a high concentration of suspended proteins 3 Cytosol stores some carbohydrates large amounts of amino acids and lipids Insoluble materials within the cytosol e g glycogen granules lipid droplets pigment granules are called inclusions The Organelles p 68 Each organelle has a specific function related to cell structure growth maintenance or metabolism Organelles are divided into 2 groups 1 nonmembranous organelles no membrane in direct contact with cytosol 2 membranous organelles isolated from cytosol covered with plasma membrane similar to cell membrane The 6 types of nonmembranous organelles are cytoskeleton microvilli centrioles cilia ribosomes and proteasomes Figure 3 3a 1 cytoskeleton structural proteins for shape strength and some metabolic functions All cells cytoskeletons have 3 elements microfilaments intermediate filaments and microtubules A microfilaments thin filaments the thinnest of all cytoskeleton protein strands typically composed of the protein actin Three major functions are 1 attachment and mechanical strength 2 interact with proteins to determine viscosity 3 in muscle cells actin pairs with thick filaments of the protein myosin to produce motion B intermediate filaments the most durable cytoskeleton elements e g collagen mid sized between microfilaments and thick filaments Three major functions are 1 strengthen cell and maintain shape 2 stabilize organelles 3 stabilize positions between cells C microtubules the largest cytoskeleton component hollow tubes made of the protein tubulin attach to the centrosome Five functions of microtubules are 1 primary structure of cytoskeleton cell strength rigidity anchor organelles 2 change shape of cell 3 form tracks to move vesicles and organelles within the cell molecular motors kinesin dynein 4 form spindle apparatus during cell division 5 form structural components of other organelles e g centrioles cilia Figure 3 3b 2 microvilli finger shaped projections on the surfaces of some cells increase surface area for absorption attached to cytoskeleton Figure 3 4a 3 centrioles form spindle apparatus during cell division only found in cells that divide Cytoplasm surrounding the centriole is the centrosome associated with the cytoskeleton Figure 3 4b c 4 cilia long extensions of cell membrane move fluids across the cell surface respiratory tract reproductive tract Made of microtubules anchored to a basal body below the cell surface 5 ribosomes carry out orders from the nucleus for protein synthesis Have 2 separate subunits the small ribosomal subunit and the large ribosomal subunit which contain special proteins and ribosomal RNA rRNA Protein