Chapter 3: The Living Units Objectives: 1. Define cell. 2. List the three major regions of a generalized cell and indicate the function of each. 3. Describe the chemical composition of the plasma membrane and relate it to membrane functions. 4. Compare the structure and function of tight junctions, desmosomes, and gap junctions. 5. Relate plasma membrane structure to active and passive transport mechanisms. Differentiate between these transport processes relative to energy source, substances transported, direction and mechanism. 6. Define membrane potential and explain how the resting membrane potential is maintained. 7. Describe the role of the glycocalyx when cells interact with their environment. 8. List several roles of membrane receptors and that of voltagesensitive membrane channel proteins. 9. Describe the composition of the cytosol; define inclusions and list several types. 10. Discuss the structure and function of mitochondria. 11. Discuss the structure and function of ribosomes, the endoplasmic reticulum, and the Golgi apparatus including function interrelationships among these organelles. 12. Compare the functions of lysosomes and peroxisomes. 13. Name and describe the structure and function of cytoskeletal elements. 14. Describe the roles of centrioles in mitosis and in formation of cilia and flagella. 15. Outline the structure and function of the nuclear envelope, nucleolus, and chromatin. 16. List the phases of the cell life cycle and describe the key events of each phase. 17. Describe the process of DNA replication. 18. Define gene and genetic code and explain the function of genes. 19. Name the two phases of protein synthesis and describe the roles of DNA, mrna, trna, and rrna in each phase. Contrast triplets, codons, and anticodons. 1
20. Describe the importance of ubiquitin degradation of soluble proteins. 21. Name and describe the composition of extracellular materials. 22. Discuss some theories of cell differentiation and aging. Cell: structural units of all living things I. Overview of the Cellular Basis of Life A. Robert Hooke 1. observed plant cells in 1600s B. Schleiden and Schwann 1. said living things were composed of cells in 1830s C. Virchow 1. said cells only come from other cells D. Cell Theory 1. A cell is the basic structural and functional unit of living organisms. So when you define cell properties you are in fact defining the properties of life. 2. The activity of an organism depends on both the individual and the collective activities of its cells. 3. According to the principle of complementarity, the biochemical activities of cells are dictated by the relative number of their specific subcellular structures. 4. Continuity of life has a cellular basis. E. Cell 1. varies in size, shape, function 2. Generalized, Composite Cell a. plasma/cell membrane b. cytoplasm c. nucleus II. The Plasma Membrane: Structure A. Plasma Membrane 1. separates the body s 2 major fluid compartments a. intracellular fluid b. extracellular fluid B. The Fluid Mosaic Model 1. Fluid Mosaic Model a. idea of plasma membrane as a think structure composed of a bilayer of lipid (phospholipids) molecules 2
b. protein molecules dispursed in bilayer constantly change c. hydrophilic 1. head of phospholipids 2. hydro = water 3. philic = loving d. hydrophobic 1. tail of phospholipids 2. phobic = hating e. integral proteins 1. proteins firmly inserted into the lipid bilayer 2. transmembrane go through the entire membrane layer 3. transporting things into & out of cell 4. channels pores formed in membrane 5. carriers bind to a substance and then movie it through membrane 6. signal transduction receptors that relay messages f. peripheral proteins 1. attached loosely to integral proteins or membrane lipid 2. supporting filaments 3. enzymes 4. mechanical functions III. Specializations of the Plasma Membrane A. Microvilli 1. minute fingerlike extensions of the plasma membrane project from free or exposed cell surface 2. increase surface area 3. often found on absorptive cells; intestinal cells B. Membrane Junctions 1. Tight Junctions a. series of integral protein fused together to form impermeable junction b. prevents molecules from passing through extracellular space c. found in epithelial cells lining the digestive tract 2. Desmosomes a. anchoring junctions b. spot welds between cells c. found in tissues subjected to great mechanical stress; skin, heart muscle 3
3. Gap Junctions a. communicating junction between adjacent cells b. found in heart and smooth muscle IV. The Plasma Membrane: Functions A. Membrane Transport 1. Interstitial Fluid a. extra cellular fluid our cells are bathed in b. helps to feed our cells 2. Selectively (differentially) Permeable Membrane a. allows some things to pass, but blocks others b. allows nutrients to enter cell c. allows cell proteins to stay in cell, lets waste out 3. Two ways things enter/exit cell a. Passive Processes 1. substances cross membrane without energy from cell a. Diffusion 1) tendency of molecules or ions to scatter evenly throughout the environment 2) molecules move from an area of higher concentration to an area of lower concentration 3) molecules move along or down a concentration gradient b. Simple Diffusion 1) unassisted diffusion of lipid-soluble or very small particles 2) Osmosis a) unassisted diffusion of a solvent (water) through membrane 3) oxygen, carbon dioxide, fat-soluble vitamins c. Facilitated Diffusion 1) type of diffusion of molecules that cannot pass through the membrane because they are dissolved in water 2) get help from carrier proteins or channels 3) carrier transmembrane integral protein 4) channel transmembrane tunnels d. Osmosis 1) diffusion of a solvent through a selectively permeable membrane 4
2) occurs when water concentration differs on both sides of cells 3) osmolarity the total concentration of all solute particles in a solution 4) if the membrane is impermeable to solute molecules the volume of the solution will change 5) hydrostatic pressure back pressure exerted by water against membrane 6) water will diffuse until hydrostatic pressure is equal to osmotic pressure 7) osmotic pressure cell s tendency to resist net water entry 8) tonicity ability of a solution to change shape or tone of cell by altering internal water volume a) isontonic solution with the same concentration of solute inside and outside of cell 1. 0.9% saline 2. 5% sucrose 3. no net loss or gain of water b) hypertonic solution with higher solute concentration outside cell 1. cells lose water 2. cell shrink c) hypotonic solution with lower solute concentration outside cell 1. cells gain water 2. cell burst (lyse) e. Flitration 1) process that forces water and solutes through a membrane or capillary wall by fluid or hydrostatic pressure 2) used pressure gradient pushes solutecontaining fluid from a higher-pressure area to a lower pressure area 3) not selective b. Active Processes 1. substances cross membrane with energy from cell 2. usually used with substances too large to pass through on their own 5
a. active transport requires carrier proteins to go against concentration gradient b. vesicular transport large particles and fluids are transported across plasma and intracellular membranes 1) exocytosis moving things out of the cell 2) endocytosis moving things into the cell 3) transcytosis moving substances into, across, and out of cell 4) trafficking moving substances from one part of the cell to another 5) phagocytosis cell eating 6) pinocytosis cell drinking V. The Cytoplasm A. cell-forming material B. cellular material between the plasma membrane and nucleus C. 3 parts 1. cytosol viscous, semi-transparent fluid, in which the other elements are suspended 2. cytoplasmic organelles metabolic machinery of the cell 3. inclusions chemical substances that may or may not be present D. Cytoplasmic Organelles 1. 2 types a. nonmembranous organelles lack membranes 1) cytoskeleton 2) centrioles 3) ribosome b. membranous organelles have membrane to maintain internal environment different than surrounding cytosol 1) mitochondria 2) peroxisome 3) lysosome 4) endoplasmic reticulum 5) Golgi apparatus c. helps to keep biochemical activity organized 2. Mitochondria a. threadlike or sausage-shaped membranous organelles b. change shape constantly c. power house of cell ATP supply 6
d. density in cell reflects energy requirement e. enclosed in 2 membranes 1) outside membrane not special 2) inside membrane folded in on itself forming cristae f. gel-like substance within Mitochondria called matrix g. site of cellular respiration 3. Ribosomes a. small granules composed of protein and DNA b. site of protein synthesis c. some free floating, some attached to membranes (RER) d. make 2 types of proteins 4. Endoplasmic Reticulum (ER) a. extensive system of interconnected tubes and membranes enclosing fluid filled cavities (cisternae) b. continuous with nuclear membrane c. 2 varieties 1) Rough Endoplasmic Reticulum (RER) a) external surface studded with ribosomes b) functions 1. manufacture proteins 2. form part of all cellular membranes 3. enzyme active sites on external face of ER membrane 2) Smooth Endoplasmic Reticulum (Smooth ER) a) enzymes catalyse reactions 1. lipid metabolism, cholesterol synthesis 2. synthesis of sex hormones 3. absorption, synthesis and transport of fats 4. detox of drugs, pesticides and carcinogens 5. breakdown of stored glycogen to form free glucose 5. Golgi Apparatus (Body) a. stacked and flattened membranous sacs b. modify, concentrate & package proteins & lipids made at RER c. secretory vesicles contain proteins destined for export 6. Lysosomes a. spherical membranous organelles containing digestive enzymes b. large & abundant in phagocytes c. functions to 7
1) digest particles taken in by endocytosis (bacteria, viruses, toxins 2) degrading warn-out or nonfunctional organelles 3) perform metabolic functions (glycogen breakdown/release) 4) break down nonuseful tissues 5) break down bone to release calcium ions 7. Endomembrane system a. system of organelles work together to 1) produce, store, export biological molecules 2) degrade potentially harmful substances b. organelles 1) ER 2) Golgi apparatus 3) secretory vesicles 4) lysosomes 5) nuclear membrane 8. Peroxisomes a. membranous sacs containing a variety of powerful enzymes b. neutralize free radicals highly reactive chemicals 9. Cytoskeleton a. cell skeleton b. 3 types of rods 1) microtubules a) element with largest diameter, hollow tubes b) radiate from a small region called centrosome c) determine overall shape of cell, distribution of organelles 2) microfilaments a) strengthens cell surface b) responsible for membrane changes of endocytosis and exocytosis 3) intermediate filaments a) tough insoluble protein fibers b) act as internal guy-wires to resist pulling motion on cell 4) centrosome a) microtubules anchored near nucleus b) containes paired centrioles small barrel-shaped organelles oriented at right angles forms mitotic spindle 8
E. Cellular Extensions 1. Cilia a. whiplike motile cellular extensions, occur in large numbers, on exposed surfaces of certain types of cells b. moves substances in one direction across cell surface 2. Flagella a. long singular cilia b. propels cell itself VI. The Nucleus A. Control center of cell B. Genetic Library 1. contains all instructions to build body s proteins 2. dictates kinds and amounts of proteins to be synthesized C. Most cells have one nucleus, some are multinucleate 1. skeletal muscle 2. bone desruction 3. liver cells D. Once cell is anucleate 1. mature red blood cell E. 3 structures 1. nuclear envelope 2. nucleoli 3. chromatin F. Nuclear Envelope (Membrane) 1. Double membrane barrier separated by fluid filled space 2. Outer membrane continuous with RER 3. Nuclear Pore areas where 2 membranes fuse 4. Selectively permeable 5. Contains nucleoplasm like cytoplasm/cytosol G. Nucleoli 1. Sites where ribosome subunits are assembled 2. Usually 1 or 2 per nucleus H. Chromatin 1. 30% DNA 2. 60% Histone Protein a. compact the DNA b. gene regulation 3. 10% RNA 4. Form chromosomes when cell is preparing to divide 9
VII. Cell Growth and Reproduction A. The Cell Life Cycle 1. Series of changes a cell goes through from the time it is formed until it reproduces 2. 2 Major Periods a. Interphase 1) cell growth 2) cell carries on normal activities b. Cell Division 1) Mitotic Phase 3. Interphase a. period from cell formation to cell division b. metabolic phase c. growth phase 4. Subphases a. G 1 (gap 1) 1) cell is metabolically active 2) synthesizing proteins 3) rapid growth b. G 0 1) phase for cells that permanently cease dividing c. S phase 1) DNA replicates 2) new Histone proteins formed d. G 2 1) final phase of interphase 2) enzymes, proteins (other organelles) are replicated 5. DNA Replication a. DNA helix begins to unwind b. Enzyme untwists double helix and separates DNA c. Free nucleotides serve as a template for a new DNA strand d. New DNA segments spliced together 6. Mitosis a. 4 phases 1) Prophase a) distinct pairs of chromosomes become apparent (tightly coiled DNA and protein) b) each pair of chromosomes is made of identical sister chromatids, held together by a centromer 10
c) pairs of centrioles migrate to opposite ends of the cell, form spindle fibers between them d) nuclear envelope and nucleolus disappear 2) Metaphase a) chromosomes line up midway between centrioles b) centromere holding each pair of chromosomes together attaches to spindle fiber between centrioles 3) Anaphase a) centromere holding chromosome pair together separates b) individual chromosomes migrate in opposite directions on the spindle fibers toward polar centrioles c) cytokinesis begins 4) Telophase a) chromosomes complete migration toward centrioles b) nuclear envelopes develop around each set of chromosomes c) nucleoli develop d) spindle fibers disappear e) cleavage furrow nearly complete 7. Cytokinesis a. division of the cytoplasm B. Protein Synthesis 1. Gene a. segment of DNA that carries instructions for creating one protein b. nucleotide bases are letters of DNA c. triplet sequence of 3 bases that form words or amino acids d. trna transfer RNA e. rrna ribosomal RNA f. mrna messenger RNA 2. Transcription a. the transfer of information from a DNA gene s base sequence to the complementary base sequence of an mrna molecule b. codon 3-base sequence of mrna 3. Translation a. language of nucleic acids is translated into the language of proteins b. anticodon 3-base sequence of trna 11