Cell structure and function Chapter 3

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Cell structure and functionChapter 3
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Processes of Life

• Growth
• Reproduction
• Responsiveness
• Metabolism

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Prokaryotes

• Do not have membrane surrounding their DNA no
  nucleus
• Lack various internal structures bound with
  phospholipid membranes
• Small 1.0 µm in diameter
• Simple structure
• Comprised of bacteria and archaea

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Eukaryotes

• Have membrane surrounding DNA have nucleus
• Have internal membrane-bound organelles
• Are larger 10-100 µm in diameter
• Have more complex structure
• Comprised of algae, protozoa, fungi, animals, and
  plants

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Comparing Prokaryotes and Eukaryotes
Figure 3.2a
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Comparing Prokaryotes and Eukaryotes
Figure 3.2b
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External Structures of Prokaryotic Cells

• Glycocalyces
• Flagella
• Fimbriae and pili

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Glycocalyces

• Gelatinous, sticky substance surrounding the
  outside of the cell
• Composed of polysaccharides, polypeptides, or
  both
• Two types
• Capsule
• Slime layer

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Capsule

• Composed of organized repeating units of organic
  chemicals
• Firmly attached to cell surface
• Protects cells from drying out
• May prevent bacteria from being recognized and
  destroyed by host

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Example of Capsule
Figure 3.4a
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Slime Layer

• Loosely attached to cell surface
• Water soluble
• Protects cells from drying out
• Sticky layer that allows prokaryotes to attach to
  surfaces

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Example of Slime Layer
Figure 3.4b
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Flagella

• Are responsible for movement
• Have long structures that extend beyond cell
  surface
• Not all prokaryotes have flagella

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Bacterial Flagella Structure

• Composed of filament, hook, and basal body
• Flagellin protein (filament) is deposited in a
  helix at the lengthening tip
• Base of filament inserts into hook
• Basal body anchors filament and hook to cell wall
  by a rod and a series of either two or four rings
  of integral proteins
• Filament capable of rotating 360º

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Bacterial Flagella Structure
Figure 3.5a
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Bacterial Flagella Structure
Figure 3.5b
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Arrangements of Bacterial Flagella
Figure 3.6a
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Arrangements of Bacterial Flagella
Figure 3.6b
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Arrangements of Bacterial Flagella
Figure 3.6c
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Function of Bacterial Flagella

• Rotation propels bacterium through environment
• Rotation can be clockwise or counterclockwise
  reversible
• Bacteria move in response to stimuli (taxis)
• Runs movements of cell in single direction for
  some time due to counterclockwise flagellar
  rotation increase with favorable stimuli
  (positive chemotaxis, positive phototaxis)
• Tumbles abrupt, random, changes in direction
  due to clockwise flagellar rotation increase
  with unfavorable stimuli (negative chemotaxis,
  negative phototaxis)

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Bacterial Movement
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Fimbriae and Pili

• Nonmotile extensions
• Fimbriae
• Sticky, proteinaceous, bristlelike projections
• Used by bacteria to adhere to one another, to
  hosts, and to substances in environment
• May be hundreds per cell and are shorter than
  flagella
• Serve an important function in biofilms

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Fimbriae Versus Flagella
Figure 3.9
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Pili

• Long hollow tubules composed of pilin
• Longer than fimbriae but shorter than flagella
• Bacteria typically only have one or two per cell
• Join two bacterial cells and mediate the transfer
  of DNA from one cell to another (conjugation)
• Also known as conjugation pili or sex pili

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Pilus Versus Fimbriae
Figure 3.10
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Prokaryotic Cell Wall

• Provides structure and shape and protects cell
  from osmotic forces
• Assists some cells in attaching to other cells or
  in eluding antimicrobial drugs
• Animal cells do not have can target cell wall of
  bacteria with antibiotics
• Bacteria and archaea have different cell wall
  chemistry

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Bacterial Cell Wall

• Most have cell wall composed of peptidoglycan a
  few lack a cell wall entirely
• Peptidoglycan composed of sugars, NAG, and NAM
• Chains of NAG and NAM attached to other chains by
  tetrapeptide crossbridges
• Bridges may be covalently bonded to one another
• Bridges may be held together by short connecting
  chains of amino acids
• Scientists describe two basic types of bacterial
  cell walls gram-positive and gram-negative

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Gram-Positive Cell Wall

• Relatively thick layer of peptidoglycan
• Contains unique polyalcohols called teichoic
  acids
• Some covalently linked to lipids, forming
  lipoteichoic acids that anchor peptidoglycan to
  cell membrane
• Retains crystal violet dye in Gram staining
  procedure appear purple
• Acid-fast bacteria contain up to 60 mycolic
  acid helps cells survive desiccation

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Gram-Negative Cell Walls

• Have only a thin layer of peptidoglycan
• Bilayer membrane outside the peptidoglycan
  contains phospholipids, proteins, and
  lipopolysaccharide (LPS)
• May be impediment to the treatment of disease
• Following Gram staining procedure, cells appear
  pink

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LPS

• Union of lipid with sugar
• Also known as endotoxin
• Lipid portion known as lipid A
• Dead cells release lipid A when cell wall
  disintegrates
• May trigger fever, vasodilation, inflammation,
  shock, and blood clotting
• Can be released when antimicrobial drugs kill
  bacteria

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Periplasmic Space

• Located between outer membrane and cell membrane
• Contains peptidoglycan and periplasm
• Contains water, nutrients, and substances
  secreted by the cell, such as digestive enzymes
  and proteins involved in transport

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Bacterial Cell Walls
Figure 3.13a
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Bacterial Cell Walls
Figure 3.13b
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Archael Cell Walls

• Do not have peptidoglycan
• Cell walls contain variety of specialized
  polysaccharides and proteins
• Gram-positive archaea stain purple
• Gram-negative archaea stain pink

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Prokaryotic Cytoplasmic Membrane

• Referred to as phospholipid bilayer composed of
  lipids and associated proteins
• Approximately half the membrane is composed of
  proteins that act as recognition proteins,
  enzymes, receptors, carriers, or channels
• Integral proteins
• Peripheral proteins
• Glycoproteins
• Fluid mosaic model describes current
  understanding of membrane structure

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Phospholipid Bilayer of Cytoplasmic Membrane
Figure 3.14
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Cytoplasmic Membrane Function

• Controls passage of substances into and out of
  the cell selectively permeable
• Harvests light energy in photosynthetic
  prokaryotes

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Control of Substances Across Cytoplasmic Membrane

• Naturally impermeable to most substances
• Proteins allow substances to cross membrane
• Occurs by passive or active processes
• Maintains a concentration gradient and electrical
  gradient
• Chemicals concentrated on one side of the
  membrane or the other
• Voltage exists across the membrane

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Passive Processes of Transport

• Diffusion
• Facilitated diffusion
• Osmosis
• Isotonic solution
• Hypertonic solution
• Hypotonic solution

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Effects of Solutions on Organisms
Figure 3.18
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Active Processes of Transport

• Active Transport
• Utilizes permease proteins and expends ATP
• Uniport
• Antiport
• Symport
• Group Translocation
• Substance chemically modified during transport

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Cytoplasm of Prokaryotes

• Cytosol liquid portion of cytoplasm
• Inclusions may include reserve deposits of
  chemicals
• Ribosomes sites of protein synthesis
• Cytoskeleton plays a role in forming the cells
  basic shape
• Some bacterial cells produce dormant form called
  endospore

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External Structure of Eukaryotic Cells

• Glycocalyces
• Never as organized as prokaryotic capsules
• Helps anchor animal cells to each other
• Strengthens cell surface
• Provides protection against dehydration
• Function in cell-to-cell recognition and
  communication

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Eukaryotic Cell Walls

• Fungi, algae, plants, and some protozoa have cell
  walls but no glycocalyx
• Composed of various polysaccharides
• Cellulose found in plant cell walls
• Fungal cell walls composed of cellulose, chitin,
  and/or glucomannan
• Algal cell walls composed of cellulose, proteins,
  agar, carrageenan, silicates, algin, calcium
  carbonate, or a combination of these

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Eukaryotic Cytoplasmic Membrane

• All eukaryotic cells have cytoplasmic membrane
• Is a fluid mosaic of phospholipids and proteins
• Contains steroid lipids to help maintain fluidity
• Controls movement into and out of cell
• Uses diffusion, facilitated diffusion, osmosis,
  and active transport
• Performs endocytosis phagocytosis if solid
  substance and pinocytosis if liquid substance
• Exocytosis enables substances to be exported from
  cell

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Cytoplasm of Eukaryotes Nonmembranous Organelles

• Flagella
• Cilia
• Ribosomes
• Cytoskeleton
• Centrioles and centrosome

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Flagella

• Shaft composed of tubulin arranged form
  microtubules
• 9 2 arrangement of microtubules in all
  flagellated eukaryotes
• Filaments anchored to cell by basal body no hook
• Basal body has 9 0 arrangement of
  microtubules
• May be single or multiple generally found at one
  pole of cell
• Do not rotate, but undulate rhythmically

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Cilia

• Shorter and more numerous than flagella
• Composed of tubulin in 9 2 and 9 0
  arrangements
• Coordinated beating propels cells through their
  environment
• Also used to move substances past the surface of
  the cell

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Eukaryotic Flagella
Figure 3.27a
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Eukaryotic Cilia
Figure 3.27c
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Eukaryotic Flagella and Cilia
Figure 3.27b
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Ribosomes

• Larger than prokaryotic ribosomes (80S versus
  70S)
• Composed of 60S and 40S subunits

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Cytoskeleton

• Extensive
• Functions
• Anchor organelles
• Cytoplasmic streaming and movement of organelles
• Movement during endocytosis and amoeboid action
• Produce basic shape of the cell
• Made up of tubulin microtubules, actin
  microfilaments, and intermediate filaments
  composed of various proteins

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Centrioles and Centrosome

• Centrioles play a role in mitosis, cytokinesis,
  and in formation of flagella and cilia
• Centrioles composed of 9 0 arrangement of
  microtubules
• Centrosome region of cytoplasm where centrioles
  are found

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Cytoplasm of Eukaryotes Membranous Organelles

• Nucleus
• Endoplasmic reticulum
• Golgi body
• Lysosomes, peroxisomes, vacuoles, and vesicles
• Mitochondria
• Chloroplasts

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Nucleus

• Often largest organelle in cell
• Contains most of the cells DNA
• Semiliquid portion called nucleoplasm
• One or more nucleoli present in nucleoplasm RNA
  synthesized in nucleoli
• Nucleoplasm contains chromatin masses of DNA
  associated with histones
• Surrounded by double membrane composed of two
  phospholipid bilayers nuclear envelope
• Nuclear envelope contains nuclear pores

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Endoplasmic Reticulum

• Netlike arrangement of flattened, hollow tubules
  continuous with nuclear envelope
• Functions as transport system
• Two forms
• Smooth endoplasmic reticulum (SER) plays role
  in lipid synthesis
• Rough endoplasmic reticulum (RER) ribosomes
  attached to its outer surface transports
  proteins produced by ribosomes

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Rough and Smooth Endoplasmic Reticulum
Figure 3.32
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Golgi Body

• Receives, processes, and packages large molecules
  for export from cell
• Packages molecules in secretory vesicles that
  fuse with cytoplasmic membrane
• Composed of flattened hollow sacs surrounded by
  phospholipid bilayer
• Not all eukaryotic cells contain Golgi bodies

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Golgi Body
Figure 3.33
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Lysosomes, Peroxisomes, Vacuoles, and Vesicles

• Store and transfer chemicals within cells
• May store nutrients in cell
• Lysosomes contain catabolic enzymes
• Peroxisomes contain enzymes that degrade
  poisonous wastes

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Mitochondria

• Have two membranes composed of phospholipid
  bilayer
• Produce most of cells ATP
• Interior matrix contains 70S ribosomes and
  circular molecule of DNA

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Chloroplasts

• Light-harvesting structures found in
  photosynthetic eukaryotes
• Have two phospholipid bilayer membranes and DNA
• Have 70S ribosomes

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Endosymbiotic Theory

• Eukaryotes formed from union of small aerobic
  prokaryotes with larger anaerobic prokaryotes
  smaller prokaryotes became internal parasites
• Parasites lost ability to exist independently
  retained portion of DNA, ribosomes, and
  cytoplasmic membranes
• Larger cell became dependent on parasites for
  aerobic ATP production
• Aerobic prokaryotes evolved into mitochondria
• Similar scenario for origin of chloroplasts