Download Cell Structure and Taxonomy

Cell Structure and
Taxonomy
Hani Masaadeh, MD, Ph.D
Structure and Taxonomy
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Compound light microscope role.
Electron Microscope role.
Cell. (The fundamental unit of any living
organism).
Metabolism.
DNA.
Species.
Procaryotes and Eucaryotes.
Viruses, viroides (Kuru disease) and virions
(Creutzfeldt–Jakob disease).
Selective toxicity.
Cytology.
Types of Living Cells
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All living cells can be classified into two groups: Prokaryotes and
Eukaryotes.
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Prokaryote comes from the Greek words for prenucleus.
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Eukaryote comes from the Greek words for true nucleus.
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Plants and animals are entirely composed of eukaryotic cells.
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In microbial world, bacteria and archaea are prokaryotes.
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Other cellular microbes – fungi (yeasts and molds), protozoa, and
algae (Sea weeds) are eukaryotes.
Viruses are noncellular elements.
Eucaryotes Cell structure
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Cell membrane. Both eucaryotic and procaryotic cells
possess a cell membrane. Cell membranes have
selective permeability, allowing only certain
substances to pass through them.
proteins and phospholipids.
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True nucleus.
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Motile eucaryotic cells possess either cilia or flagella.
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Cell Structure
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Cytoplasm.
Endoplasmic reticulum.
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Rough.
Smooth.
Ribosomes.
Golgi apparatus.
Lysosomes and Peroxisomes.
Mitochondria.
Plastids.
Cytoskeleton.
Cell wall.
Flagella and Cilia.
Nucleus
Command center.
 Nucleoplasm.
 Chromosome.
 Nuclear membrane.
 Genes.
 RNA.
 Genotype.
 Nucleolus.
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The Prokaryotic Cell: Size, Shape
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1 µm wide and 2 to 3 µm long.
Basic shapes: 1. Spherical coccus
2. rod-shaped
bacillus 3. Spiral : have one or more twists, called
vibrios when they look like curved rods, and spirilla when
they look like a corckscew, spirochetes if helical and
flexible.
Figures 4.1a, 4.2a, 4.2d, 4.4b, 4.4c
The Prokaryotic Cell: Size, Shape
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Unusual shapes
 Star-shaped (rectangular) Stella
 Square Haloarcula
Most bacteria are monomorphic (maintain a single shape)
A few are pleomorphic (have many shapes, not just one)
Figure 4.5
The Prokaryotic Cell: Arrangements
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Cocci and bacilli
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Pairs: Diplococci, diplobacilli
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Chains: Streptococci, streptobacilli
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Tetrads: division in 2 planes and
remain in groups of four.
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Sarcinae: division in 3 planes and
remain attached in cubelike groups of
eight.
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Clusters: division in multiple planes
forming clusters called Staphylococci
Figures 4.1a, 4.1d, 4.2c
Plasma Membrane
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Selective permeability allows passage of some molecules.
 Permeability depends on:
 Size: large molecules (Proteins) can not pass while small
molecules (H20, O2, C02, simple sugars) pass easily.
 Solubility: Lipid soluble molecules (02, CO2, nonpolar organic
molecules) pass easily.
 Presence of transporter proteins.
Enzymes for ATP production
Photosynthetic pigments on foldings called chromatophores or
thylakoids
Damage to the membrane by alcohols, quaternary ammonium
(detergents), and polymyxin antibiotics causes leakage of cell contents
Cytoplasm: Composition and
Functions
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Cytoplasm is the substance of the cell inside the plasma membrane.
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80% water and contains proteins (enzymes), carbohydrates, lipids, and
inorganic ions.
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It is thick, aqueous, semitransparent, and elastic.
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Major structures: Nucleoid, ribosomes, inclusion bodies, protein filaments
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Nucleoid, the nuclear area, contains a single long, continuous, circular thread
of double stranded DNA called the bacteria chromosome which carries the
genetic information rquired for the cell’s sturctures and functions.
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Moreover, bacteria often contain an extrachromosomal, small circular,
double stranded DNA molecules called Plasmids.
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Plasmids usually contain 5 to 100 genes responsible for antibiotic resistance,
production of toxins, and synthesis of enzymes.
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Cytoplasm:
Ribosomes
Ribosomes
The sites of protein synthesis.
 Composed of two subunits, each consists of protein and ribosomal RNA.
Prokaryotic ribosomes differ from eukaryotic ribosomes
 in number of proteins and rRNA molecules.
 Smaller and less dense
 70S ribosomes in prokaryotes and 80S ribosomes in eukaryotes.
Several antibiotics work by inhibiting protein synthesis on prokaryotic
ribosomes
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Figure 4.19
Cytoplasm: Inclusions (Reserve
deposites)
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Metachromatic granules
(volutin)
Polysaccharide granules
Lipid inclusions
Sulfur granules
Carboxysomes
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Phosphate reserves
Energy reserves
Energy reserves
Energy reserves
Ribulose 1,5-diphosphate
carboxylase for CO2 fixation
The Cell Wall
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A complex, semirigid structure
responsible for the shape of the cell,
surrounding the plasma membrane.
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CW prevents osmotic lysis of bacteria.
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CW maintain the shape of a bacterium
and anchors the flagella.
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Clinically, CW increases the ability of
some bacteria to cause disease and it is
the site of action of some antibiotics.
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CW is used to differentiate major types
of bacteria.
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Made of peptidoglycan (in bacteria)
Figure 4.6a–b
Gram-Positive Cell Walls
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Teichoic acids
 Lipoteichoic acid links to plasma membrane
 Wall teichoic acid links to peptidoglycan
Negatively charged, may regulate movement of cations.
Polysaccharides provide antigenic variation.
Figure 4.13b
CW of Gram +ve and Gram –ve
bacteria
Figure 4.13b–c
Gram-Negative Outer
Membrane
Figure 4.13c
Gram-Negative Outer
Membrane
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Lipopolysaccharides (LPS), lipoproteins, phospholipids
Forms the periplasm between the outer membrane and the
plasma membrane.
Protection from phagocytes and complement.
Porins (proteins) form channels through membrane permit the
passage of molecules (nutrients)
O polysaccharide antigen, e.g., E. coli O157:H7
Lipid A is an endotoxin and is toxic in the host’s bloodstream
or gastrointestinal tract.
CW of Gram +ve and Gram –ve bacteria
Gram +ve CW
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Thick peptidoglycan composed
of many layers.
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Contains teichoic acids
In acid-fast cells, contains
mycolic acid
Gram –ve CW
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Thin layer of peptidoglycan
No teichoic acids
Surrounded by outer membrane
Peptidoglycan layer is connected
to the outer membrane via
lipoproteins.
A periplasm (gel like fluid) is found
between the outer membrane and
plasma membrane.
Atypical Cell Walls
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Mycoplasmas
Lack cell walls
 Sterols in plasma membrane to protect them
from lysis.
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Archaea
May lack walls, or unusual walls composed of
polysaccharides and proteins but not
peptidoglycan.
 Archaea can not be Gram stained.
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External Structures: Glycocalyx
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Located outside cell wall
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Viscous (sticky), consists of gelatinous polysaccharide,
polypeptide, or both.
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It is made inside the cell and secreted to the cell
surface.
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If it is organized and firmly attached to the cell wall, it is
called Capsule.
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Capsules increase bacterial virulence by preventing
phagocytosis
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Extracellular polysaccharide (EPS) allows cell to attach to
various surfaces
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Some bacteria use its capsule as a source of nutrition to
produce energy.
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A glycocalyx can protect a cell against dehydration.
Figure 4.6a–b
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External
Structures:
Flagella
Located outside cell wall
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Long filamentous appendages that
propel bacteria.
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It has 3 basic parts:
1.
The filament: made of chains of
flagellin
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The hook: consisting of
different protein
3.
The basal body: Anchors the
flagellum to the cell wall and
plasma membrane.
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Flagellum moves the cell by rotating
from the basal body.
Figure 4.8a
Axial Filaments and Fimbriae
Endoflagella
 In spirochetes
 Anchored at one end of a cell
 Rotation causes cell to move
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Fimbriae allow attachment
 Pili are used to transfer DNA
from one cell to another
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Cytoplasm:
Endospores
Resting cells formed when essential nutrients are depleted.
Bacillus (anthrax and food poisoning), Clostridium (gangarene,
tetanus, botulism, and food poisoning)
Highly durable dehydrated cells with thick walls and additional
layers, formed internal to the bacterial cell membrane.
Resistant to desiccation, heat,
chemicals, radiation.
Sporulation: Endospore formation
Germination: Return to vegetative
state
Figure 4.21b