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Transcript
Cell Structure and Function Chapter 3 Part A Introduction • In the image of a wall, what is the basic building block? • If you look closely enough at living organisms you can see that the basic building block is cells o There are many kinds of cells with specific purposes • Just like a house is made with a variety of building materials Microscopy • Because cells are so small microscopes are needed to view them o Light microscopes • • Use a beam of light Used for viewing o o o • • Small, thin or translucent specimens Living organisms Stained cells (ususally dead) Images are inverted Up to about 400X magnification Microscopy • Because cells are so small microscopes are needed to view them o Dissecting microscopes • Used for viewing o o o • • Larger, thick specimen Tissue structure and overall anatomy Living organisms Images are three dimensional Up to about 40X magnification Microscopy • Because cells are so small microscopes are needed to view them o Transmission electron microscopes • • • • o Use a beam of electrons transmitted through the cell Higher magnification More internal detail No live cells Scanning electron microscopes • • Use a beam of electrons reflecting off the specimens’ surfaces Details of surface characteristics Scanning Electron Microscopy • Tip of a straight pin with rodshaped bacteria Robert Hooke saw “cells” in thin sections of cork Cell Theory 1. 2. 3. 4. All organisms consist of one or more cells The cell is the basic unit of life All cells arise from pre-existing cells Cells contain hereditary material which they pass to their offspring Comparing Prokaryotic and Eukaryotic Cells • All cells share four common components o Plasma membrane • Separates cell from surroundings • Communicates with surroundings o DNA • Free-floating (nucleoid) • Membrane bound (nucleus) o Cytoplasm • Semifluid mixture filling the cell o Ribosomes • Protein synthesis Comparing Prokaryotic and Eukaryotic Cells • Prokaryotes o No nucleus • Prokaryotes have a nucleoid region where DNA is located (not enclosed in a membrane) o No membrane bound organelles o Small (1-10 micrometers) o Most have a cell wall around their cell membrane o Many produce a capsule • Slime layer for protection o Some have flagella, pili, or fimbriae Comparing Prokaryotic and Eukaryotic Cells • Prokaryotes include organisms from o Domain Bacteria • Kingdom Eubacteria o Domain Archae • Kingdom Archaebacteria Comparing Prokaryotic and Eukaryotic Cells • Eukaryotes o Contain a nucleus • Membrane surrounding the DNA • Keeps the DNA separated from the cytoplasm o Contain many organelles • Structures that have specific metabolic functions • Often surrounded by phospholipid membrane o Larger size (0.1-1 millimeter) Comparing Prokaryotic and Eukaryotic Cells • Eukaryotes Include organisms from o Domain Eukarya • Kingdoms Protista, Plantae, Fungi, and Animalia Comparing Prokaryotic and Eukaryotic Cells • Cell size and shape o When a cell grows, the volume increases faster than the surface area • The cell membrane becomes too small relative to the volume o Can’t move enough nutrients into the cell or wastes out of the cell • Surface-to-volume ratio • Limits growth o Alternate shapes can result in larger cells • Long and thin (neuron) or frilly surfaced (intestinal villi) Questions • • • • What is one of the four tenets of the cell theory? Why are most cells very small? What is one type of microscope? If you found a cell that was very small what type of cell would you expect it to be? Would you expect it to have a nucleus? • Which type has a nucleus? • Which kingdoms have prokaryotic cells? Eukaryotic Cells • The following slides will discuss the different cells structures, organelles, and components of eukaryotic cells Plasma Membrane • Phospholipid bilayer o With embedded proteins • All cells have a plasma membrane o Distinct identity o Communicates with surroundings o Controls what enters or exits the cell Cytoplasm • Metabolic activities occur and organelles are suspended in the cytoplasm • Contents of a cell between the plasma membrane and the nucleus • Consists of o Cytosol: A semi-fluid gel-like matrix o Nutrients, enzymes, and organelles Cytoplasm Dynamic Cytoskeleton • System of interconnected protein fibers o Maintain shape o Secure certain organelles in specific positions o Movement • Intracellular: cytoplasm, vesicles, organelles • Extracellular: flagella and cilia • Unicellular organisms move independently Dynamic Cytoskeleton • Components of the cytoskeleton o Microtubules • Long hollow cylinders made of tubulin subunits • Temporary scaffolding for many processes o Rapidly assembling and disassembling as needed • Mitosis and Flagella/cilia • Centrosomes made up of two centrioles direct assembly Microtubules Centrioles Dynamic Cytoskeleton • Components of the cytoskeleton o Microfilaments • Fibers consisting of actin subunits • Strengthen and affect shape • Myosin and actin filaments produce muscle contractions o Intermediate filaments • Mechanical strength • Underlie and reinforce membranes Dynamic Cytoskeleton • Components of the cytoskeleton o Motor proteins (kinesin and dynein) • Drag cellular structures along microtubules and microfilaments • Requires ATP Dynamic Cytoskeleton • Components of the cytoskeleton o Motor proteins (kinesin and dynein) • Flagella and cilia o Microtubules are arranged lengthwise in a 9 + 2 array • A basal body (a specialized centriole) controls microtubule lengths o Dynein “walks” along the microtubules causing them to bend back and forth Flagella and cilia Flagella and Cilia 2 Dynamic Cytoskeleton • Components of the cytoskeleton o Motor proteins (kinesin and dynein) • Flagella and Cilia o Flagella: long, few/cell o Cilia: short, many/cell Dynamic Cytoskeleton • Components of the cytoskeleton o Pseudopods or “false feet” • Microfilaments build scaffolding which support temporary, irregular membrane lobes • Motor proteins drag the plasma membrane along with them Dynamic Cytoskeleton • Components of the cytoskeleton o Pseudopods or “false feet” • Pseudopodal movement o Amoeba creeping along • Phagocytosis o White blood cell engulfing a bacterium o White blood cell engulfing bacteria Endomembrane System • A series of membranous compartments that work together to modify, package, label, and ship proteins and lipids • Consists of o o o o o Nuclear envelope Lysosomes Vesicles Endoplasmic reticulum Golgi apparatus Endomembrane System • The nucleus o Contains DNA in the form of chromatin o Directs the synthesis of ribosomes and proteins Nucleus Endomembrane System • Nuclear envelope o Two phospholipid bilayers o Pores control the passage of ions, molecules, and RNA • Chromosomes o Double-stranded DNA molecule with attached proteins o Codes for the genetic/hereditary material o Chromatin is the name for all of the chromosomal DNA and associated proteins • Nucleolus o A region where ribosome subunits are assembled Endomembrane System • Endoplasmic Reticulum (ER) o Series of interconnected membranous tubules • Continuous with the nuclear envelope • Two types of ER