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Transcript
UNIT III – CELL STRUCTURE & FUNCTION • Hillis – Ch 4, 5 • Baby Campbell – Ch 4,5 • Big Campbell – Ch 6,7,11 Over 4 centuries ago von Leeuwenhoek and Hooke Stacked glass lenses together and took the first look At a world far too tiny for the naked eye to see And forever changed our understanding of Biology! I. DISCOVERY OF CELLS • History of Microscopes Anton van Leeuwenhoek - Used lenses and looked at pond water - described what he saw as small organisms Robert Hooke - looked at cork under a primitive microscope - described what he saw as “cells” which reminded him of the rooms in the monastery • Cell Theory All living things are made of cells. Cells are the smallest working unit. All cells come from pre-existing cells through cell division. I. DISCOVERY OF CELLS, cont. • Types of Microscopes Compound Light Microscope Magnification Resolution Advances in light microscopy include o o o o Confocal Fluorescent Phase Contrast Super-resolution Electron Microscope Scanning Electron Microscope (SEM) Transmission Electron Microscope (TEM) I. DISCOVERY OF CELLS, cont. • Cell Size o Metabolic needs impose both upper & lower limits on cell size o How small? Must have enough space for DNA, enzymes Mycoplasma sp. - < 1 μm o How large? Surface Area to Volume Ratio Adaptations II. CELL TYPES • Prokaryotic Cells Typically smaller than euks Bacteria Kingdom Archaebacteria Kingdom Eubacteria No true nucleus – DNA found as a single chromosome in region called nucleoid II. CELL TYPES, cont • Prokaryotic Cells 1. Cell wall 2. Capsule 3. Cell membrane 4. Chromatin 5. Ribosomes 6. Pili 7. Flagella II. CELL TYPES, cont • Eukaryotic Cells Larger, more complex Contain true nucleus, membranebound organelles suspended in cytosol Composed of Nucleus Ribosomes Endomembrane System o o o o ER Golgi Apparatus Lysosomes Vacuoles Mitochondria/Chloroplasts Peroxisomes Cytoskeleton III. EUKARYOTIC CELL STRUCTURES _Animal Cell _Plant_ Cell III. EUKARYOTIC CELL STRUCTURES, cont • Nucleus Control center of eukaryotic cell Nuclear Envelope Double membrane that protects nucleus; continuous with ER Contains pores Nucleolus Site of ribosome production Chromatin DNA wrapped in protein III. EUKARYOTIC CELL STRUCTURES, cont • Ribosomes Suspended in cytosol or found on rough ER Site of protein production in a cell III. EUKARYOTIC CELL STRUCTURES, cont • Endomembrane System Endoplasmic Reticulum Interconnected network continuous with nuclear envelope Rough ER modifies and transports proteins to the golgi Smooth ER detoxifies drugs, alcohol, poisons converts glycogen into glucose synthesizes lipids III. EUKARYOTIC CELL STRUCTURES, cont Endomembrane System, cont Golgi Apparatus “Cell postmaster” Receives transport vesicles from ER; modifies, stores, and ships products Receiving side is known as the cis face; shipping side is known as the trans face III. EUKARYOTIC CELL STRUCTURES, cont Endomembrane System, cont Lysosomes Sacs containing hydrolytic enzymes Used for recycling cellular materials, destroying pathogens III. EUKARYOTIC CELL STRUCTURES, cont Endomembrane System, cont Vauole Storage sac Plants typically have large, central vacuole surrounded by membrane called tonoplast. Absorbs water and helps plant cell to grow larger Some protists have contractile vacuole to pump out excess water III. EUKARYOTIC CELL STRUCTURES, cont • Mitochondria Site of oxidative respiration Contain own DNA, ribosomes Found in virtually all euk cells Enclosed by 2 membranes; inner membrane has folds called cristae to increase surface area III. EUKARYOTIC CELL STRUCTURES, cont • Chloroplast Type of plastid that carries out photosynthesis by converting solar energy to chemical energy (glucose) Contain membranous system of flattened sacs called thylakoids – stack is called a granum Fluid surrounding thylakoids is called stroma Contains DNA, ribosomes III. EUKARYOTIC CELL STRUCTURES, cont Endosymbiont Theory III. EUKARYOTIC CELL STRUCTURES, cont • Peroxisomes Membrane-bound compartments that use O2 to carry out metabolism H2O2 is produced; broken down by _perioxidase_ III. EUKARYOTIC CELL STRUCTURES, cont • Cytoskeleton Provides structural support to cell Allows for movement Attachment site for organelles, enzymes More extensive in animal cells Composed of three types of proteins Microtubules Microfilaments Actin Intermediate Filaments More fixed Keratin Cytoskeleton III. EUKARYOTIC CELL STRUCTURES, cont Cytoskeleton, cont IV. CELL BOUNDARIES • Cell Wall Found in bacteria, fungi, and plants Rigid structure; protects, maintains shape of cells Prevents excess water uptake Plant cell wall Cellulose Pectin - Sticky polysaccharide found between cell walls of adjacent cells Plasmodesmata - Perforations between adjacent cell walls that allow for movement of materials from one cell to another IV. CELL BOUNDARIES, cont • Extracellular Matrix of Animal Cells Holds cells together, protects & supports cells Allows for communication between cells Composed primarily of glycoproteins – proteins with covalently-bonded carbohydrate chains attached Must abundant glycoprotein in most animals is collagen IV. CELL BOUNDARIES, cont • Intracellular Junctions in Animal Cells Tight Junctions – Press membranes together very tightly; prevents leakage of fluid Desmosomes (Anchoring Junctions) – Fasten cells together in sheets Gap Junctions – Allow for movement of cytoplasm from one cell to another; important in communication between cells IV. CELL BOUNDARIES, cont • Cell (Plasma) Membrane Selectively-permeable barrier found in all cells Composed primarily of phospholipid bilayer (amphipathic) and proteins which are also amphipathic. Fluid Mosaic Model “Fluid” – Not a rigid structure. Organization due to high concentration of water inside & outside cell IV. CELL BOUNDARIES, cont • Organization of Plasma Membrane - membrane is held together by hydrophobic interactions; polar phosphate heads face internal and external environments; non-polar fatty acid tails face the interior of the bilayer. - proteins and lipids can shift laterally, but flip-flopping is rare. IV. CELL BOUNDARIES, cont • Fluidity of Plasma Membrane IV. CELL BOUNDARIES, cont • Cell Membrane, cont Proteins - “Mosaic” – Assortment of different proteins embedded in bilayer; determine most of membrane’s specific functions. Act as channels, pumps, enzymes in metabolism, binding sites, etc o Integral Proteins – Embedded in phospholipid layer o Peripheral Proteins – Bound to surface of membrane IV. CELL BOUNDARIES, cont Membrane Proteins IV. CELL BOUNDARIES, cont • Cell Membrane, cont Carbohydrates “ID tags” that identify cell. Enable cells to recognize each other and foreign cells. May be bonded to lipids (glycolipids) or proteins (glycoproteins) IV. CELL BOUNDARIES, cont V. CELL TRANSPORT V. CELL TRANSPORT, cont • Passive Transport – Movement of materials from high to low concentration. No energy output required. Diffusion Random movement of a substance across membrane down concentration gradient No net movement once equilibrium is reached Diffusion V. CELL TRANSPORT, cont • Passive Transport, cont Facilitated Diffusion Passive transport of molecules across cell membrane with the help of transport proteins Utilized by large molecules, charged particles, polar molecules Water Aquaporins V. CELL TRANSPORT, cont • Passive Transport, cont Osmosis – Diffusion of water across a membrane. Tonicity refers to tendency of cell to gain or lose water. If the solution is Isotonic relative to the cell – Solute concentration is same on both sides of membrane. No net movement of water. Hypertonic relative to the cell – Concentration of solute is greater outside cell → water moves out of cell until equilibrium is reached. Cell may shrivel. Hypotonic relative to the cell – Concentration of solute is lower outside cell → water moves into cell until equilibrium is reached. Cell may swell to bursting point. Osmosis V. CELL TRANSPORT, cont • Passive Transport / Osmosis, cont Water Potential Used to predict the passive movement of water Designated as Ψ (Greek letter psi) Water always moves from an area of higher water potential → lower water potential Ψ = ΨP + ΨS ΨS = -iCRT i = ionization constant (if NaCl, i = 2 because Na+ and Cl-) C = molar concentration R = pressure constant (R = .0831 liter bars/mole –K) T = temp K (273 + C) - Increase in solute lowers the water potential ΨP = 0 at atmospheric pressure; an increase in positive pressure raises the pressure potential, which raises water potential. Practice • Determine the water potential of a cell if ΨP = 0.3 MPa and ΨS = - 0.5 MPa. Ψ = ΨP + ΨS Ψ= Calculate the pressure potential in a cell if ΨW = 0 and ΨS = - 0.2. A dialysis bag is filled with sucrose solution of unknown concentration and then placed in a 0.6 M sucrose solution. The bag’s initial mass is 24 grams and the final mass is 22 grams. – What does this tell you about the molarity of the unknown solution in the dialysis bag? – Initially, is the unknown solution hyper, hypo, or isotonic relative to the solution in the beaker? – Calculate the initial water potential of the sucrose solution in the beaker. Assume the temperature is 28 degrees Celsius. Show your work! Ψ = ΨP + ΨS • Ψ = 0 + ΨS • ΨS • http://www.bozemanscience.com/waterpotential/ V. CELL TRANSPORT, cont • Passive Transport/Osmosis, cont Osmoregulation Cells must have mechanism to prevent excess loss, uptake of water Cell wall, contractile vacuole Plasmolysis – Seen in plants; excessive water loss causes cell membrane to pull away from cell wall V. CELL TRANSPORT, cont (crenated) V. CELL TRANSPORT, cont • Active Transport • Movement of materials against concentration gradient. Requires energy output by cell Carrier Proteins – Na+ / K+ Pump V. CELL TRANSPORT, cont • Active Transport, cont Proton Pump V. CELL TRANSPORT, cont • Active Transport, cont Exocytosis Secretion of biomolecules by fusion of vesicles with cell membrane. Biomolecules “spit out”. Hormones, neurotransmitters, etc V. CELL TRANSPORT, cont • Active Transport, cont Endocytosis – “Sucking In”. Cell membrane surrounds, engulfs particle or biomolecule, pinches in to form vesicle. Phagocytosis – “Sucking in” food particles Pinocytosis – “Sucking in” fluid droplets Receptor-mediated Endocytosis – Very specific Endocytosis VII. CELL SIGNALING VII. CELL SIGNALING, cont • Coordinates cell activities, development • Typically involves 3 steps: Reception – Target cell’s detection of signal molecule due to binding of signal molecule to receptor protein in cell membrane Transduction – Binding of signaling molecule changes receptor protein; triggers a sequence of events within cell Response – Results in specific cellular response; for example, activation of genes, enzyme catalysis, etc. VII. CELL SIGNALING, cont • Reception Typically involves G Proteins VII. CELL SIGNALING, cont • Transduction Typically multi-step pathway Relay molecules are usually protein kinases VII. CELL SIGNALING, cont • Transduction Non-protein molecule known as cAMP is often second messenger VII. CELL SIGNALING, cont • Response Nuclear May “turn on” or “turn off” genes Cytoplasmic May regulate enzyme activity Apoptosis Controlled cell suicide VI. CELL SIGNALING, cont • Regulation