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Transcript
Anatomy & Physiology Lecture 3: Chapter 3 An Introduction To The Cellular Level of organization Pages: 62 - 105 Lecturer: Dr. Barjis Room: P313 / P307 Phone: (718) 260-5285 E-Mail: [email protected] Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Frederic H. Martini Fundamentals of Learning Objectives • List the main points of the cell theory. • Describe the chief structural features of the cell membrane. • Describe the organelles of a typical cell, and give their specific functions. • Summarize the process of protein synthesis. • Describe the various transport mechanisms used by cells, and relate this to the transmembrane potential. • Describe the cell life cycle, mitosis and cellular differentiation. An Introduction to Cells The cell theory states: • Cells are the building blocks of all plants and animals • Cells are produced by the division of preexisting cells • Cells are the smallest units that perform all vital physiological functions • Each cell maintains homeostasis at the cellular level • Homeostasis at higher levels reflects combined, coordinated action of many cells The Diversity of Cells in the Human Body Cell biology • Cytology, the study of the structure and function of cells • The human body contains both somatic and sex cells The Anatomy of a Representative Cell A typical cell • Is surrounded by extracellular fluid, which is the interstitial fluid of the tissue • Has an outer boundary called the cell membrane or plasma membrane The Cell Membrane Cell membrane functions include: • Physical isolation • Regulation of exchange with the environment • Structural support The Cell Membrane • The cell membrane is a phospholipid bilayer with proteins, lipids and carbohydrates. Membrane proteins include: • Integral proteins • Peripheral proteins • Anchoring proteins • Recognition proteins • Receptor proteins • Carrier proteins • Channels Membrane proteins Membrane carbohydrates form the glycocalyx • Proteoglycans • Glycolipids • Glycoproteins The Cytoplasm The cytoplasm contains: • The fluid (cytosol) • The organelles the cytosol surrounds Organelles • Nonmembranous organelles are not enclosed by a membrane and always in touch with the cytosol • Cytoskeleton, microvilli, centrioles, cilia, ribosomes, proteasomes • Membranous organelles are surrounded by lipid membranes • Endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, mitochondria The Anatomy of a Representative Cell Cytoskeleton provides strength and flexibility • Microfilaments • Intermediate filaments • Microtubules • Thick filaments Microvilli increase surface area The Cytoskeleton Centrioles • Direct the movement of chromosomes during cell division • Organize the cytoskeleton • Cytoplasm surrounding the centrioles is the centrosome Cilia • Is anchored by a basal body • Beats rhythmically to move fluids across cell surface Centrioles and Cilia Ribosomes • Are responsible for manufacturing proteins • Are composed of a large and a small ribosomal subunit • Contain ribosomal RNA (rRNA) • Can be free or fixed ribosomes Ribosomes Proteasomes • Remove and break down damaged or abnormal proteins • Require targeted proteins to be tagged with ubiquitin Endoplasmic reticulum • Intracellular membranes involved in synthesis, storage, transportation and detoxification • Forms cisternae • Rough ER (RER) contains ribosomes • Forms transport vesicles • Smooth ER (SER) • Involved in lipid synthesis The Endoplasmic Reticulum Golgi Apparatus • Forms secretory vesicles • Discharged by exocytosis • Forms new membrane components • Packages lysosomes The Golgi Apparatus Functions of the Golgi Apparatus Lysosomes and Peroxisomes • Lysosomes are • Filled with digestive enzymes • Responsible for autolysis of injured cells • Peroxisomes • Carry enzymes that neutralize toxins Lysosome Functions Membrane flow • Continuous movement and recycling of membranes • ER • Vesicles • Golgi apparatus • Cell membrane Mitochondria • Responsible for ATP production through aerobic respiration • Matrix = fluid contents of mitochondria • Cristae = folds in inner membrane The Nucleus The nucleus is the center of cellular operations • Surrounded by a nuclear envelope • Perinuclear space • Communicates with cytoplasm through nuclear pores The Nucleus Contents of the nucleus • A supportive nuclear matrix • One or more nucleoli • Chromosomes • DNA bound to histones • Chromatin Chromosome Structure The genetic code • The cells information storage system • Triplet code • A gene contains all the triplets needed to code for a specific polypeptide Gene activation and protein synthesis • Gene activation initiates with RNA polymerase binding to the gene • Transcription is the formation of mRNA from DNA • mRNA carries instructions from the nucleus to the cytoplasm An overview of Protein Synthesis Translation is the formation of a protein • A functional polypeptide is constructed using mRNA codons • Sequence of codons determines the sequence of amino acids • Complementary base pairing of anticodons (tRNA) provides the amino acids in sequence The Process of Translation The Process of Translation How Things Get Into and Out of Cells Permeability • The ease with which substances can cross the cell membrane • Nothing passes through an impermeable barrier • Anything can pass through a freely permeable barrier • Cell membranes are selectively permeable How Things Get Into and Out of Cells Diffusion • Movement of a substance from an area of high concentration to low • Continues until concentration gradient is eliminated Diffusion Diffusion across the Cell Membrane How Things Get Into and Out of Cells Osmosis • Diffusion of water across a semipermeable membrane in response to solute differences • Osmotic pressure = force of water movement into a solution • Hydrostatic pressure opposes osmotic pressure • Water molecules undergo bulk flow Osmosis Tonicity • The effects of osmotic solutions on cells • Isotonic = no net gain or loss of water • Hypotonic = net gain of water into cell • Hemolysis • Hypertonic = net water flow out of cell • Crenation Osmotic flow across a cell membrane transport • Carrier mediated transport • Binding and transporting specific ions by integral proteins • Cotransport • Counter-transport • Facilitated diffusion • Compounds to be transported bind to a receptor site on a carrier protein Facilitated Diffusion Active transport • Active transport • Consumes ATP • Independent of concentration gradients • Types of active transport include • Ion pumps • Secondary active transport The Sodium Potassium Exchange Pump Secondary Active Transport Vesicular transport: material moves into or out of cells in membranous vesicles • Endocytosis is movement into the cell • Receptor mediated endocytosis (coated vesicles) • Pinocytosis • Phagocytosis (pseudopodia) • Exocytosis is ejection of materials from the cell Receptor-Mediated Endocytosis Pinocytosis and Phagocytosis The transmembrane potential • Difference in electrical potential between inside and outside a cell • Undisturbed cell has a resting potential The Cell Life Cycle cell division • Cell division is the reproduction of cells • Apoptosis is the genetically controlled death of cells • Mitosis is the nuclear division of somatic cells • Meiosis produces sex cells The Cell Life Cycle Interphase • Most somatic cells spend the majority of their lives in this phase • Interphase includes • G1 • S • G2 The Cell Life Cycle DNA Replication Mitosis, or nuclear division, has four phases • Prophase • Metaphase • Anaphase • Telophase During cytokinesis, the cytoplasm divides and cell division ends Interphase, Mitosis, and Cytokinesis Interphase, Mitosis, and Cytokinesis Mitotic rate and cancer • Generally, the longer the life expectancy of the cell, the slower the mitotic rate • Stem cells undergo frequent mitoses • Growth factors can stimulate cell division • Abnormal cell division produces tumors or neoplasms • Benign • Malignant (invasive, and cancerous) • Spread via metastasis • Oncogenes Differentiation • Process of specialization • Results from inactivation of particular genes • Produces populations of cells with limited capabilities • Differentiated cells form tissues You should now be familiar with: • The main points of the cell theory. • The chief structural features of the cell membrane. • The organelles of a typical cell, and their specific functions. • The process of protein synthesis. • The various transport mechanisms used by cells, and how this relates to the transmembrane potential. • The cell life cycle, mitosis and cellular differentiation.