Prokaryotic and Eukaryotic Cellular Structure

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Prokaryotic and Eukaryotic Cellular Structure
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Prokaryotic Eukaryotic Cells An Overview

• Prokaryotes
• Do not have membrane surrounding their DNA
• lack a nucleus
• Lack various internal structures bound with
  phospholipid membranes
• Are small, 1.0 µm in diameter
• Have a simple structure
• Composed of bacteria and archaea

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Prokaryotic Eukaryotic Cells An Overview

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

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Prokaryotic Eukaryotic Cells An Overview
INSERT FIGURE 3.1
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Prokaryotic Cell Membrane

• Structure
• Referred to as phospholipid bilayer composed of
  lipids and associated proteins
• Approximately half 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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Cell Membrane

• Membranes contain a hydrophilic and hydrophobic
  side
• Composed of many different types of proteins
• Proteins in the lipid bilayer move freely within
  the membrane

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Cell Membrane

• Thin pliable lipid and protein envelope
• that defines a cell.
• Phospholipid bilayer
• Functions
• Regulates nutrient and water intake
• Regulates waste removal
• Site of prokaryotic respiration
• Site of prokaryotic flagella attachment
• Involved in the distribution of genetic material
  during binary fission

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Prokaryotic Cytoplasmic Membranes

• Function
• Energy storage
• Harvest light energy in photosynthetic
  prokaryotes
• Selectively permeable
• Naturally impermeable to most substances
• Proteins allow substances to cross membrane
• Occurs by passive or active processes
• Maintain concentration and electrical gradient
• Chemicals concentrated on one side of the
  membrane or the other
• Voltage exists across the membrane

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Cell Membrane
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External Structures of Prokaryotic Cells

• Glycocalyces
• Gelatinous, sticky substance surrounding the
  outside of the cell
• Composed of polysaccharides, polypeptides, or
  both

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External Structures of Prokaryotic Cells

• Types of Glycocalyces
• 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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Capsule

• Polysaccharides or polypeptides in composition.
• Surround the cell wall in some bacteria.
• Function
• Protection from phagocytosis
• Osmotic barrier
• Reservoir for nutrients
• Virulence factor

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Capsule Stain
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Slime Layer

• Consist of polysaccharide fibers that extend
  form the bacterial surface
• Functions
• Protection
• Attachment
• Associated with biofilms

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External Structures of Prokaryotic Cells

• Types of Glycocalyces
• 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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Bacterial Appendages

• Flagella
• Axial Filaments
• Pili (Fimbriae)

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Bacterial Appendages

• Flagella

• Structures of locomotion
• Originate in the plasma membrane
• In bacteria rotate like a propellar
• Many different arrangements

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External Structures of Prokaryotic Cells

• Flagella
• Are responsible for movement
• Have long structures that extend beyond cell
  surface
• Are not present on all prokaryotes

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External Structures of Prokaryotic Cells

• Flagella
• Structure
• Composed of filament, hook, and basal body
• Flagellin protein (filament) 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 Appendages

• Arrangements of Flagella

• Monotrichous
• Lophotrichous
• Amphitrichous
• Peritrichous

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Bacterial Appendages

• Axial filament (endoflagella)
• Originates in the cell membrane and transverses
  the length of the cell in the periplasmic space.
• As the endoflagella rotate to move the cell the
  characteristic shape is formed .
• Endoflagella are associated with spirochetes.

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External Structures of Prokaryotic Cells

• Endoflagellum is also know as an
• axial filament.
• Attached to the plasma embrane
• and transverses the entire cell.
• Responsible for the spirochete
• morphology.

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External Structures of Prokaryotic Cells

• Flagella
• Function
• Rotation propels bacterium through environment
• Rotation reversible, can be clockwise or
  counterclockwise
• Bacteria move in response to stimuli (taxis)
• Runs
• Tumbles

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Bacterial Appendages

• Fimbriae and Pili
• Rod-like proteinaceous extensions

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Bacterial Appendages

• Fimbriae

• Hollow tubes that protrude from some bacteria
• Compose of protein

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External Structures of Prokaryotic Cells

• Fimbriae
• Sticky, bristlelike projections
• Used by bacteria to adhere to one another, to
  hosts, and to substances in environment
• Shorter than flagella
• May be hundreds per cell
• Serve an important function in biofilms
• Virulence factor

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External Structures of Prokaryotic Cells

• Pili
• Tubules composed of pilin
• Also known as conjugation pili
• Longer than fimbriae but shorter than flagella
• Bacteria typically only have one or two per cell
• Mediate the transfer of DNA from one cell to
  another (conjugation)

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• Bacterial Conjugation

• Transfer of plasmid DNA from a donor to a
  recipient.
• Process strengthens the bacterial cell and alows
  for survival in a competitive environment.

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Bacterial Inclusion Bodies

• 1. poly-Beta-hydroxybutyric acid - stores lipids
  for use in plasma membrane
•  
• 2. glycogen - stores starch like polymer of
  sugar for energy production
•  
• 3. Polyphosphate granules (metachromatic
  granules) - storage for phosphates for plasma
  membrane and the formation of ATP from ADP.
•  
• 4. Sulfur granules - stores sulfur which is
  necessary for the metabolic reactions in
  biosynthesis.

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5. Mesosome

• Mesosomes - invagination of the plasma membrane
  that increases the surfaces area of the plasma
  membrane during binary fission.
• The mesosome also serves as a site for the
  attachment and distribution of genetic material
  during binary fission.

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Mesosome

• In prokaryotic cell division, called binary
  fission.
• A diagram of the attachment of bacterial
  chromosomes, indicating the possible role of the
  mesosome (an inward fold of the cell membrane) in
  ensuring the distribution of the "chromosomes" in
  a dividing cell.
• Upon attachment to the plasma membrane, the DNA
  replicates and reattaches at separate points.
  Continued growth of the cell gradually separates
  the chromosomes and allocates chromosome copies
  to the two daughter cells.

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Inclusion Bodies

• 6. gas vacuoles - storage of metabolic gases
  such as methane or hydrogen gas. The gas
  vacuoles help in the buoyancy of the cell and
  aids in it motility.
•  
• 7. ribosomes - responsible for the synthesis of
  proteins.
•  
• 8. nucleoid material - the genetic material of
  bacteria, which usually is balled up in the cell.
  During binary fission the nucleoid material
  unravels within the cell in order to be copied
  and distributed to the daughter cells.
•  
• 9. Plasmid - small fragments of
  self-replicating extrachromosomal DNA that codes
  for the resistance to antibiotics or for the
  productions of a specific metabolite, i.e.
  toxins, pigments. These plasmids may be
  transferred from one bacterial cell to another by
  the F-pili.

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Inclusion Bodies

•  9. Plasmid - small fragments of
  self-replicating extrachromosomal DNA that codes
  for the resistance to antibiotics or for the
  productions of a specific metabolite, i.e.
  toxins, pigments. These plasmids may be
  transferred from one bacterial cell to another by
  the F-pili.

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Inclusion Bodies

•  
• These plasmids may be transferred from one
  bacterial cell to another by the
• F-pili.

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Inclusion Bodies

• Endospores - a survival mechanism of certain
  genera of bacteria such as Clostridium and
  Bacillus.
• The endospores are composed of a complex of
  dipicolinc acid and calcium and the function of
  the endospore is to protect the bacterial
  chromosome.
• The endospores are very resistant to heat,
  desiccation, freezing, and other physical
  properties such as pesticides, antibiotics, dyes,
  and acids.

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Inclusion Bodies

• The endospores may remain dormant for many years
  until the environment becomes suitable to sustain
  the life of the bacteria.
• The endospore will then germinate to form an
  exact copy of the parent cell that produced it.
•  

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Eukaryotic Cell Walls Cytoplasmic Membranes

• 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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Cell Walls

•  

• Three different types of cell walls and their
  compositions
•  
• Fungal cell walls are composed of cellulose
  and/or chitin.
•  
• Plant cell walls are composed of cellulose.
•  
• Algal cell walls are composed of cellulose,
  silicon, and calcium carbonate.

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Plasma Membrane

•  
• Consist of a lipid bilayer and associated
  proteins. The Plasma Membrane of Eukaryotic
  cells resembles and functions in the same manner
  as the prokaryotic plasma membrane with the
  following exceptions
•  
• Contains high levels of sterols such as
  cholesterol.
•  
• No respiratory enzymes are located in the
  eukaryotic plasma membrane.
• Respiration occurs in the mitochondria.

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External Structure of Eukaryotic Cells

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

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Eukaryotic Appendages

•  
• Flagella
•  
• There are several different arrangements of
  flagella in eucaryotes.
•  
• This diagram represents a biflagellated
  eukaryotic cell.
• One of the flagella aids in movement laterally
  and the other aids in up and down movement.
• The eukaryotic flagella move like a whip.
• See Flagellar handout.
•  

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Eukaryotic Appendages

• Flagella
• Function
• Do not rotate, but undulate rhythmically

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Eukaryotic Appendages

• Cilia
•  
• Similar to flagella both structurally and
  functionally but are much shorter and more
  numerous.
• Cilia are found peritrichously to the cell.
• Move in an undulating manner and motility by
  those organisms with cilia is much more rapid
  than those with flagella.
•  
•  

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Intracellular Structures of Eukaryotic Organisms
(organelles)

• Membranous Organelles
• Nucleus
• Often largest organelle in cell
• Contains most of the cells DNA
• Semi-liquid 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 nuclear envelope double membrane
  composed of two phospholipid bilayers
• Nuclear envelope contains nuclear pores

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Intracellular Structures of Eukaryotic Organisms
(organelles)

• Nucleus - double membraned organelle that houses
  the genetic material of cell.
• Nuclear membrane contains numerous pores through
  which proteins and RNA can move.

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Intracellular Structures of Eukaryotic Organisms
(organelles)

• Membranous Organelles
• 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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Intracellular Structures of Eukaryotic Organisms
(organelles)

• Endoplasmic reticulum - network of cytoplasmic
  membranes where lipids and proteins are produced.
•  
• Smooth ER - synthesis of lipids
•  
• Rough ER - associated with ribosomes and is
  responsible for the synthesis of proteins.
• .

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Intracellular Structures of Eukaryotic Organisms
(organelles)

• Membranous Organelles
• 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 in all eukaryotic cells

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Intracellular Structures of Eukaryotic Organisms
(organelles)

• Golgi apparatus (dictyosome) is associated with
  the ER.
• It modifies and packages the lipids and proteins
  manufactured by the ER and places them in
  vesicles for cellular use.

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Intracellular Structures of Eukaryotic Organisms
(organelles)

• Membranous Organelles
• 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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Intracellular Structures of Eukaryotic Organisms
(organelles)

• Membranous Organelles
• 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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Intracellular Structures of Eukaryotic Organisms
(organelles)

• mitochondria - involved in the production of
  chemical energy in the form of ATP.
• Consist of convoluted inner membrane and outer
  membrane. Invaginations are called cristae and
  contain enzymes used to synthesis ATP.
• All respiratory enzymes are located in the inner
  membrane of the mitochondria.

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Cytoplasm of Eukaryotes

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

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Cytoplasm of Eukaryotes

• 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
• Not universally accepted

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Cytoplasm of Eukaryotes
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Cytoplasm of Eukaryotes
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Eukaryotic Cell Walls Cytoplasmic Membranes
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