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Biology Chapter 6

by: Alexis Elston

Biology Chapter 6 BSC 114

Alexis Elston
GPA 4.0

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Complete coverage of chapter 6 from book and class powerpoints
Principles Of Biology I
Daryl W. Lam
Class Notes
Biology, Chapter6, week6, notes
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This 5 page Class Notes was uploaded by Alexis Elston on Friday September 23, 2016. The Class Notes belongs to BSC 114 at University of Alabama - Tuscaloosa taught by Daryl W. Lam in Fall 2016. Since its upload, it has received 5 views. For similar materials see Principles Of Biology I in Biology at University of Alabama - Tuscaloosa.


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Date Created: 09/23/16
Chapter 6 A Tour of the Cell  Historical: o Cell theory:  All living things are composed of one or more cells  Cells are the basic units of structure and function in living things  Every cell originates from another cell; therefore, all cells are related by their descent  from earlier cells o Basic Features of All Cells  Plasma Membrane: phospholipid bilayer embedded with many proteins  Chromosomes: DNA and proteins associated with DNA  Ribosomes: very large protein­RNA complexes that carry out protein synthesis  (translation) o Visualizing Cells  Microscope: optical instrument used to visualize cells and other objects too small to see  with the naked eye.  Three factors that affect microscope: o Magnification: the ratio of an object’s image size to its actual size o Resolution: measure of the clarity of an image  Two dots on board example o Contrasts: degree of difference between the lightest and darkest parts of a sample  Light Microscopy:  o Light Microscope: visible light passes through a specimen and then  through glass lenses, which magnify the image  Can magnify effectively to about 1000 times the size of the  specimen  Minimum resolution is about 200 nm o Types of Light Microscopy:  Bright Field Microscopy: simplest  Light passes directly through specimen, then through  glass lenses  Image has little contrast unless sample is naturally  pigmented or artificially stained  Phase­Contrast Microscopy  Specialized optics enhance contrast in cells by  amplifying variations in sample density  Living cells can be observed without staining  Differential Interference Contrast Microscopy  Use polarizers to exaggerate differences in the optical density of a specimen  Samples have a 3D­like appearance  Fluorescence Microscopy  UV light is transmitted through a specimen  Fluorescently tagged molecules absorb UV light and  emit visible light  Confocal Microscopy:  Lasers and special optics are used to image  specimens within a very narrow focal plane  Images are acquired point­by­point and reconstructed with a computer  Most often used with fluorescently stained specimens  Electron Microscopy:  Chapter 6 o Electron Microscope: can be used to visualize surface or intracellular  features of a specimen  Scanning electron microscopes:   Focus a beam of electrons onto the surface of a  specimen, resulting in images with a 3D appearance  Transmission Electron microscopes:  Focus a beam of electrons through a specimen  Mainly used to study internal ultrastructure of cells  Prokaryotes and Eukaryotes: o Prokaryotes: Bacteria and Archaea  No membrane bound organelles  DNA, typically double stranded and circular in structure, is contained in a non­membrane bound region called the nucleoid  Cytoplasm is bound only by a plasma membrane o Eukaryotic Cells:  DNA, double stranded and usually linear in structure, is contained in a membrane­bound  organelle called the nucleus  Other membrane­bound organelles are found in cell  Cytoplasm is the region between the plasma membrane and nucleus  Generally, much larger than prokaryotic cells  Parts of the Cell: o Nucleus and Ribosomes:   A eukaryotic cell’s genetic instructions are housed in nucleus and carried out by the  ribosomes  Nucleus contains most DNA in a eukaryotic cell  Ribosomes use the information from DNA to make proteins o DNA (gene) to mRNA to Protein  Nucleus contains of the cell’s genes and is most conspicuous organelle  Enclosed by the nuclear envelope, which separates it from the cytoplasm o Nuclear envelope is a double membrane (2 phospholipid bilayers) o Nuclear pores regulate the entry and exit of many molecules from the  nucleus o Shape of the nucleus is maintained by the nuclear lamina, which is  composed of protein filaments called intermediate filaments and  membrane­associated proteins  DNA is organized into chromosomes o Each chromosome is composed of a single DNA molecule associated  with proteins o DNA and proteins of chromosomes are together called chromatin  Condenses to very compacted form as cell prepares to divide o Nucleolus:  Roughly spherical “sub­organelle” of the nucleus  Site of rRNA synthesis and assembly of large and small ribosomal subunits o These subunits exit the nucleus through nuclear pores  Then enter the cytoplasm where they assemble into functional  ribosomes during protein synthesis o Ribosomes:   Responsible for all protein synthesis in a cell  Large, macromolecular complexes made of rRNA and multiple polypeptide  subunits  Two types: o Free ribosomes: suspended in cytoplasm Chapter 6  Make proteins that function within the cytoplasm o Bound Ribosomes: attached to ER  Make proteins that will be part of cell membranes, packaged  inside other organelles, or exported  Endomembrane System: internal membranes that partition the cell into organelles  o Includes:  Nuclear envelope  Endoplasmic reticulum  Consists of flattened sacs, called cisternae, and interconnected tubules o ER membrane is continuous with nuclear envelope o Accounts for more than half of the total membrane in eukaryotic cells o Two distinct, interconnected regions  Rough: cytoplasmic surface is studded with ribosomes  Functions: o Final steps in processing of membrane,  organelle­targeted, and secreted proteins o Distributes transport vesicles o Membrane factory of the cell  Smooth: lacks ribosomes on cytoplasmic surface  Functions: o Lipid synthesis o Carbohydrate metabolism o Calcium storage o Detoxification of poisons and drugs  Golgi apparatus  Consists of cisternae o Major shipping and receiving center of the cell  Modifies products of ER  Manufactures certain macromolecules  Sorts and packages materials into transport vesicles  Cis Face: receives transport vesicles o Usually located near ER  Trans Face: ships materials out  Lysosomes  Membranous sac of hydrolytic enzymes that can break down macromolecules  and organelles that are damaged or no longer needed o Lumen: space bounded by the lysosome membrane  More acidic than the cytosol  Lysosomal enzymes work best in the acidic  environment inside the lysosome o Breakdown products are used to synthesize new macromolecules  Functions: o Phagocytosis: some types of cells can engulf other cells and cell debris  Results in formation of a food vacuole in engulfing cells  Lysosomes fuse with food vacuoles to break down  their contents o Autophagy: lysosomes use enzymes to recycle the cell’s own  organelles and macromolecules  Tay­Sachs Disease is caused by lysosomal disorder  Vacuoles:  Membrane­bound sacs within the cell that are larger than vesicles  Plant cell or fungal cell may have several vacuoles Chapter 6  Types: o Central: plants use these as storage o Contractile: pumps excess water out of the cell o Food: formed by phagocyrtosis  Fungal vacuoles have hydrolytic functions comparable to those of lysosomes in  animal cells  Transport vesicles  Plasma/cell membrane:  Selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of the cell  General structure of a biological membrane is a bilayer of phospholipids  embedded with proteins.   Organelles not in Endomembrane System: o Mitochondria: sites of cellular respiration  Found in vast majority of eukaryotic cells  Have smooth outer membrane and an inner membrane folded into cristae  Cristae provides large surface area for enzymes involved in the synthesis of ATP  Inner membrane creates two compartments o Intermembrane space o Mitochondrial matrix o Chloroplasts: sites of photosynthesis in plants and algae o Peroxisomes: involved in breakdown of long­chain fatty acids and other metabolic processes via  oxidative reactions  Found in all eukaryotic cells  Contain enzymes that transfer hydrogen from various substances to oxygen  Producing hydrogen peroxide o Highly reactive and toxic to cells, but is contained and rapidly  converted to water and oxygen  Break down fats into smaller molecules that can be used as fuel.  Peroxisomes in liver detoxify alcohol and other harmful compounds  Cytoskeleton: o Network of protein fibers extending throughout the cytoplasm of a cell  Organizes the cell’s structures and activities  Provides mechanical support for cells needed to maintain and alter cell shape  Anchors organelles in eukaryotic cells  Enables cellular motion  Plays important role in intracellular transport o Highly dynamic and can be quickly disassembled and reconstructed  Consists of:  Microfilaments (actin filaments)  Intermediate filaments  Microtubules (tubulin polymers) o Centrosomes and Centrioles:   Microtubules are nucleated and grow out from centrosome, located near nucleus  Centrosome referred to as microtubule organizing center  Centrosome consists of amorphous material called pericentriolar matrix o Surrounds a pair of centrioles, each with 9 triplets of microtubules  arranged in a ring  Cilia and Flagella:  o Microtubules control locomotor appendages o Share common ultrastructure:  Chapter 6  Core of microtubules sheathed by plasma membrane  Basal body anchors cilium or flagellum  Motor proteins called dynein drive he bending  movements o Motor proteins powered by ATP o Microfilaments function in cell motility contain the motor protein  myosin as well as actin  Thicker myosin interdigitates with thinner actin  Extracellular Structures: o Most cells synthesize and secrete materials that are external to plasma membrane  Cell walls: plants  Protect cells, maintain cell shape, prevent excess uptake of water o Primary cell wall, middle lamella, secondary cell wall  Plasmodesmata: channels between adjacent plant cells  Extracellular matrix: animals  Provides structural support for cells, segregates tissues from one another,  contributes to regulation of intercellular communication o Made up of glycoproteins and other macromolecules  Collagen: most abundant  Forms strong fibers outside the cells  Embedded in proteoglycans, another glycoprotein  Intercellular Junctions:   Facilitate cell adherence, interaction, and communication o Uses direct physical contact  Intercellular junctions facilitate this contact:  Plasmodesmata: Plants o Channels that perforate plant cell walls o Water and small solutes can pass from cell  to cell  Tight junction: o Membranes of neighboring cells are pressed  together by interactions between  transmembrane proteins, preventing leakage  of extracellular fluid  Desmosomes o Spot­like transmembrane protein­based  adhesions that fasten cells together  Gap junctions o Cytoplasmic channels between adjacent  cells


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