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Chapter 7 Cellular Structure and Function 7.1 Cell Discovery and Theory 1 The History of the Cell Theory Cells are the basic units of living things Before microscopes people believed diseases were caused by curses and supernatural spirits (wrath of God) The idea that a living thing like a bacteria could cause disease or infection never occurred. Why? 2 Development of the Light Microscope Today's microscope is a compound microscope with two lenses Eyepiece lens Objective lens Can magnify 1500 times 3 Simple Light Microscope Developed by Anton van Leeuwenhoek in the mid 1600 One lens Much like a magnifying glass 4 The Cell Theory Robert Hook First to use the term “cell” Looked a cork under a microscope, saw the cell walls 5 Robert Hook Contemporary of Anton van Leeuwenhoek English Published and encouraged others to use microscopes 6 Matthias Schleiden 1838 German botanists Examined plants of all types All plants are made of cells 7 Theodore Schwann 1839 German zoologist Contemporary of Schleidens Examined animal tissues of many types All animals are made of cells 8 Rudolph Virchow 1855 German physician All cells come from preexisting cells 9 The Cell Theory 1. All organisms are composed of one or more cells 2. The cell is the basic unit of organization of all organisms 3. Unicellular or multicellular Structure Function All cells come from preexisting cells 10 Technology Since the 1800’s Compound light microscopes continued to improve so that bacteria were able to be classified Most magnification possible with light microscopes cannot see inner cell parts 11 Electron Microscopes Developed in the 1940’s Uses magnets to focus a beam of electrons (in place of light) Can magnify 500,000X Several types Scanning: looks at surface; get 3-D Transmission: looks at interior Scanning-Tunneling: atoms on surface 12 Microscope Aids Both light and electron microscopes use dyes and stains which helps to contrast cell and parts Most dyes and stains kill the cells Most specimens of electron microscopes need to be in a vacuum and/or coated with gold 13 Two Basic Cell Types Prokaryote Have plasma membrane No internal membrane bound structures Unicellular Smaller in size No specialization Example: bacteria Eukaryote Have plasma membrane Internal membrane bound structures Unicellular and multicellular Larger size Much specialization Example: animal 14 Two Basic Cell Types Prokaryote Eukaryote 15 Two Basic Cell Types 16 Chapter 7 Cellular Structure and Function 7.2 The Plasma Membrane 17 Plasma Membrane Diagram 18 Plasma Membrane Micrograph 19 Plasma Membrane Structure Made of phospholipid bilayer Polar ends are hydrophilic Nonpolar ends are hydrophobic 20 Plasma Membrane Function Job of plasma membrane is homeostasismaintain balance For cells to survive they must keep the inside in and the outside out, yet allow some materials to move into and out of the cell 21 Structure Fits Function The structure of the plasma membrane (how it is put together) allows the plasma membrane its function or job, selective permeability Selective permeability: the ability to allow some materials into or out of the cell but not other materials 22 Selective Permeability Out side of cell is different from inside of cell 23 Structure Fits Function Both the inside of the cell and the outside are water environment so the hydrophilic ends face in and out The hydrophobic fatty tails are in the middle so that materials can’t pass through easily 24 Structure Fits Function Role of proteins in plasma membrane Channels or tunnels for substances to pass through with specific fit Identification of organism and tissue type Signal sending proteins Provide support for the phospholipids 25 Plasma Membrane Proteins 26 Plasma Membrane Cholesterol stabilizes the plasma membrane in animal cells Animal cells have no cell wall as do plant cell High blood cholesterol is a risk factor for heart disease and stroke Animals (including us) produce cholesterol for the stabilization of the cell membrane 27 Fluid Mosaic Model 28 Fluid Mosaic Model FLUID: Plasma membrane in constant motion with the phospholipids of one layer moving one direction and the phospholipids of the other layer moving in the opposite direction MOSAIC: something consisting of a number of different things of different types 29 Chapter 7 Cellular Structure and Function 7.3 Structures and Organelles 30 Cellular Boundaries Plant Cell outer most part is the cell wall; plasma membrane is inside of the cell wall Also fungi, algae and other Kingdom Protista organisms Animal Cell outer most part is the plasma membrane Also protozoans (Kingdom Protista) 31 Cell Wall Functions to protect and support NOT selectively permeable Porous: let anything in Plant cell wall made of cellulose (wood) 32 Plant Cell Wall 33 Nucleus Controls all cell activities Contains information to make proteins; all parts of the cell depend on proteins to do its job 34 Nucleus Contains DNA in strands known as chromatin (chromosomes are chromatin that is condensed and visible during cell reproduction) 35 Nucleolus Found in the nucleus Organelle that makes ribosomes Ribosomes are sites where proteins are manufactured 36 Ribosomes Ribosomes are unique because they do not have a membrane around them Found in prokaryotes and eukaryotes Look like pepper on the ER (spaghetti) 37 Nuclear Membrane Also called Nuclear Envelope Surrounds the nucleus Same composition as the plasma membrane Contains pores to allow large materials to pass out (ribosomes and RNA) 38 Cytoplasm All the gelatinous material with the organelles inside the cell between the nucleus and the cell membrane Cytosol is that part of the cytoplasm that is liquid 39 Organelles for Assembly, Transport and Storage Endoplasmic Reticulum (ER) Golgi Apparatus Vacuoles Lysosomes All have phospholipid bilayer membrane structure 40 Endoplasmic Reticulum (ER) Folded membrane like an accordion for workspace Rough ER contains ribosomes for protein production Smooth ER (No ribosomes) for lipid production Tube-like for transport of materials 41 Golgi Apparatus Takes protein from the ER and makes it ready to be transported Like UPS, packages it and gives it a destination address 42 Vacuoles Large central vacuole in plant cells to store water Smaller vacuoles for storage of food, waste, water, enzymes and other substances in both plant and animal cells 43 Lysosomes Double membrane bound sac containing digestive enzymes Digests food particles, engulfed viruses and bacteria, and worn out cell parts Can fuse with vacuole to digest contents of vacuole 44 Energy Transformers Chloroplasts Mitochondria Both have phospholipid bilayer membrane structure 45 Chloroplasts Capture light energy and produce food to be used later Pigment chlorophyll give plants their green color Other plastids store starch, lipids and other pigments 46 Chloroplasts Double membrane Clear outer Folded inner: thylakoid Stacks of membranes sacs grana and liquid stroma Site of photosynthesis 47 Mitochondria Break down food to release energy Found in eukaryotes 48 Mitochondria Double membrane Outer Folded Inner to increase membrane space Some cells need much energy and have hundreds of mitochondria; other cell have few mitochondria because these cells use little energy Site of cellular respiration 49 Structures for Support and Locomotion Cytoskeleton Cilia Flagella 50 Cytoskeleton Internal framework in the cell to keep the organelles in place Maintains the cell’s shape Made of microtubules (hollow) and microfilaments (solid) protein fibers Shown in green 51 Centrioles Made of groups of microtubules Function in cell division (Ch. 9) 52 Cilia and Flagella Enclosed by plasma membrane Used for locomotion and feeding Made of pair of microtubules surrounded by 9 additional pairs 53 Cilia Short numerous hair like projections Beat like oars on a boat Line our respiratory system 54 Flagella Tail like structure that is whip like May have one flagella or several Mostly used for locomotion 55 Chapter 7 Cellular Structure and Function 7.4 Cellular Transport 56 Passive Transport NO energy expended by cell Diffusion Facilitated diffusion Osmosis 57 Diffusion All molecules are in constant motion; called Brownian Motion The high the temperature the faster the motion because they have more energy Diffusion is the net movement of particles from higher concentration to lower concentration because of this movement of particles Diffusion is slow because it is a random process 58 59 Rates of Diffusion Concentration of substances involved 1. More concentrated substances speed up rate of diffusion Energy by temperature or agitation 2. Increased temperature speeds up rate of diffusion Agitation or stirring speeds up rate of diffusion Pressure 3. Increased pressure speeds up diffusion because pressure increases molecular movement 60 Dynamic Equilibrium Equilibrium is reached when there is no net concentration change Dynamic because Brownian motion continues 61 Diffusion in Living Systems In living things materials must diffuse into and out of cells all the time Concentration gradient exists so that substances will move into the cell until there is the same number on each side Liquids, solids and gasses can diffuse into and out of a cell 62 Facilitated Diffusion Diffusion of materials through proteins in cell membranes NO energy required Common for sugars and amino acids 63 Osmosis Diffusion of water through a cell membrane Cell membranes are selectively permeable NO energy expended by the cell Moves water from high concentration to low concentration Must occur for homeostasis to occur 64 Control of Osmosis Unequal distribution of particles on either side of a selectively permeable membrane Water moves through the membrane until equilibrium is reached (no net change) 65 Cells in Solutions Isotonic Solution = same solutes Hypotonic Solution = lower solutes Hypertonic Solution = higher solutes 66 Cells in Isotonic Solutions Isotonic solutions have the same solute concentration as the cell, so water moves in and out at the same rate; no osmosis; no net change Dissolved substances outside the cell equals dissolved substances inside the cell Examples: Normal saline IV solution (0.9% salt) and tap water in most areas 67 Cells in Hypotonic Solutions Dissolve substances lower outside the cell than inside the cell Water moves into the cell; cell swells Animal cell bursts Plant cell becomes more firm (higher turgor pressure); reason why plants are sprayed at grocery store Example: Distilled water 68 Cells in Hypotonic Solutions 69 Cells in Hypertonic Solutions Dissolved substances higher outside the cell than inside the cell Water leaves the cell; cell shrinks Animal cell wrinkled (reason why meat is salted after cooking) Plant cell plasmolyzed; cell membrane moves away from cell wall Example: salt water, syrup 70 Cells in Hypertonic Solutions 71 Cells in Solutions 72 Comparing Plant and Animal Cells 73 Active Transport ENERGY used by the cell Carrier proteins with a SPECIFIC FIT with a specific molecule Bringing substances into the cell against the concentration gradient 74 Active Transport When molecule fits with carrier protein the carrier protein molecule changes shape to allow the molecule to move into or out of the cell When movement complete, the carrier protein changes back to original shape for another molecule 75 Active Transport Also used to rid the cell of materials against the concentration gradient Takes energy to use a pump Much of your cell’s energy is expended in the sodium-potassium pump (2 K+ in 3 Na+ out) 76 Large Materials Into Cells Endocytosis, getting large materials INTO the cell Cell expends energy Engulfs and forms a vacuole Example: white blood cells engulfing a bacteria 77 Large Materials Out of Cells Exocytosis: large materials out of a cell Cell expends energy Example: secretions or hormones Example: waste products 78 79 Pseudopodia Structure of locomotion Used for capture of food Extensions of the cell contents within the cell membrane Example: Amoeba 80 81
