The Bacterial Cell
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THE BACTERIAL CELL: Classification and Morphology ARTHUR C. BENIGNOS II M.D. Department of Microbiology and Parasitology Davao Medical School Foundation
Differences between Prokaryote and Eukaryote Prokaryote
Eukaryote
DNA free in the cytoplasm
DNA is contained with a membrane-bound nucleus
Cell division by binary fission Energy metabolism associated with the cytoplasmic membrane
Cells divide by mitosis Mitochondria present in most cases
Differences between Prokaryote and Eukaryote Flagella consist of one protein
Ribosomes are of 70S type Peptidoglycan cell walls
Flagella have a complex structure with 9+2 microtubular structure Ribosomes are of 80S type Polysaccharide cell walls, where present, are generally either cellulose or chitin
Bacterial Forms Spheres or Cocci Singly, in pairs with both apposing sides flattened (diplococci), in chains (streptococci), groups of fours (tetrads), or in grape-like clusters (staphylococci)
Rods or Bacilli Very short (coccobacilli), long filaments (incomplete separation), fusiform (tapered ends), club-shaped, comma-shaped (vibrioid)
Spiral or Spirilli
Bacterial Forms
Bacterial Forms Pleomorphism
Lack rigid cell wall No defined shape Variation of size and shape Assymetric growth of cell wall
Aggregation properties
Long chains, irregular clustering, etc Determined by orientation of cell division planes and tendency to adhere
Bacterial Size
Vary in size from 0.4 – 5 µm Hundred-fold larger than virus Ten-fold smaller than eukaryotic cell Spirillar forms can be many times longer than their cross-sectional diameter
Bacterial Ultrastructure
Cell envelope Cytoplasmic structures External appendages
Cell Envelope
Term applied to the material external to and enclosing the cytoplasm
Most prominent layers:
Cell wall Cell membrane
Cell Wall Functions:
Prevent from exploding in hypotonic solutions due to its high internal osmotic pressure Determines the shape of bacterial cell
Cell Wall
Also known as peptidoglycan layer Peptido portion: short string of amino acids cross-linking the carbohydrate units Glycan portion: linear polymer of alternating monosaccharide subunits of
N-acetylglucosamine (NAG) N-acetylmuramic acid (NAM)
Cell Membrane
Composed of phospholipids forming two parallel layers (lipid bilayer) Polar phosphate groups: facing outside Non-polar lipid chains: on the inside Does not differ from human cell
Cell Membrane
Selective permeability: easily allows lipid-soluble small molecules (O2, CO2)
Specific protein contents:
Porins – channels Permeases – carriers for specific substances
Contains the ATP-producing mechanism
Gram-positive Cell Envelope
Thick multilayered peptidoglycan cell wall external to the bacterial cell membrane Teichoic acids
Polymer of glycerol units Present in all Gram-positive organisms Major cell surface antigens
Gram-negative Cell Envelope Outer membrane
Contain lipopolysaccharides which is antigenic (O-polysaccharide portion) and toxic (lipid portion) Lipid A: endotoxin of Gram-negative organisms
Periplasmic space
Contains the thin peptidoglycan cell wall Also contain enzymes and other various substances
External Capsule and Glycocalyx Capsule
Usually polysaccharide but sometimes made of protein Tightly bound to the bacterial cell and has organized structure
Glycocalyx
Loosely bound to bacterial cell and amorphous
External Capsule and Glycocalyx Functions
Allow bacterial cells to adhere to surfaces Protection from antibodies and phagocytosis Diffusion barriers against some antibiotics
Appendages Flagella
Long semi-rigid, helical, hollow tubular structures composed of flagellin For motility Responds to chemotactic stimulus Attached to cell wall and cell membrane by a basal body that rotates the flagellum Highly antigenic (H-antigen)
Appendages Pili or fimbriae
Shorter and thinner than flagella Attachment organs for cell-to-cell contact
Bacterium-mucosal cells (Neisseria gonorrhea) Bacterium-bacterium (Eschericia coli) through sex pili for donation of DNA molecules
Cytoplasmic Structures
Cytoplasm Nucleoid Ribosomes Inclusions Endospores Plasmids Mesosomes
Cytoplasm
Complex mixture of substances enclosed by the cell envelope Consists of amorphous aqueous fluid Where suspended or dissolved are
Enzymes, ions, metabolites, storage granules Fibrous mass of densely packed DNA, RNA and proteins, also plasmids
Nucleoid
Fibrous mass of genetic material
Double-stranded circular DNA composing the bacterial singular chromosome Associated RNA and proteins
No discernible membrane enclosure
Plasmids
Small fraction of circular doublestranded DNA molecules that exists and replicates autonomously Carry genes for a variety of functions not essential for bacterial cell viability Enhance bacterial survival by
conveying antibiotic resistance enhancing mating ability making possible toxin production
Ribosomes
Responsible for polymerization of amino acids into proteins (as in eukaryotes) Differ in composition and size from eukaryotic ribosomes
70S (50S, 30S) as against 80S (60S, 40S) of eukaryotes 53 proteins as against 80+ proteins among eukaryotes
Cytoplasmic Inclusions
Accumulations of food reserves
Polysaccarides Lipids Polyphosphates
Maybe membrane-bound or scattered in the cytoplasm
Endospores
Dormant form within vegetative cell Can be released as free spores Rich in calcium dipicolinate Most resistant life forms known
Heat (survive boiling) Dessication Ultraviolet light Bacteriocidal chemical agents Destroyed by autoclaving
Sporulation
Formation of spore within vegetative cell Process
Invagination of parent cell membrane Isolation of copy of bacterial DNA Formation of new cell wall (peptidoglycan) Formation of outer keratin-like external coat Formation of external lipoprotein layer
Spore Germination
Return of spore form to vegetative state Occurs in nutritionally-rich environment Process
Destruction of cortex by lytic enzymes Uptake of water Release of dipicolinate from the cell
Medical Significance of Sporulation
Most notorious pathogens are spore-formers
Bacillus anthracis (Anthrax) Clostridium botulinum (Botulism) Clostridium perfringens (Gas gangrene)
Spores can remain viable for many years
Mesosomes
Complex invaginations of bacterial cell membrane Seem to be involved in chromosome separation May be evolutionarily related to nuclear envelope of eukaryotes
Nucleoid
GOOD MORNING.
Differences between Prokaryote and Eukaryote Prokaryote
Eukaryote
DNA free in the cytoplasm
DNA is contained with a membrane-bound nucleus
Cell division by binary fission Energy metabolism associated with the cytoplasmic membrane
Cells divide by mitosis Mitochondria present in most cases
Differences between Prokaryote and Eukaryote Flagella consist of one protein
Ribosomes are of 70S type Peptidoglycan cell walls
Flagella have a complex structure with 9+2 microtubular structure Ribosomes are of 80S type Polysaccharide cell walls, where present, are generally either cellulose or chitin
Bacterial Forms Spheres or Cocci Singly, in pairs with both apposing sides flattened (diplococci), in chains (streptococci), groups of fours (tetrads), or in grape-like clusters (staphylococci)
Rods or Bacilli Very short (coccobacilli), long filaments (incomplete separation), fusiform (tapered ends), club-shaped, comma-shaped (vibrioid)
Spiral or Spirilli
Bacterial Forms
Bacterial Forms Pleomorphism
Lack rigid cell wall No defined shape Variation of size and shape Assymetric growth of cell wall
Aggregation properties
Long chains, irregular clustering, etc Determined by orientation of cell division planes and tendency to adhere
Bacterial Size
Vary in size from 0.4 – 5 µm Hundred-fold larger than virus Ten-fold smaller than eukaryotic cell Spirillar forms can be many times longer than their cross-sectional diameter
Bacterial Ultrastructure
Cell envelope Cytoplasmic structures External appendages
Cell Envelope
Term applied to the material external to and enclosing the cytoplasm
Most prominent layers:
Cell wall Cell membrane
Cell Wall Functions:
Prevent from exploding in hypotonic solutions due to its high internal osmotic pressure Determines the shape of bacterial cell
Cell Wall
Also known as peptidoglycan layer Peptido portion: short string of amino acids cross-linking the carbohydrate units Glycan portion: linear polymer of alternating monosaccharide subunits of
N-acetylglucosamine (NAG) N-acetylmuramic acid (NAM)
Cell Membrane
Composed of phospholipids forming two parallel layers (lipid bilayer) Polar phosphate groups: facing outside Non-polar lipid chains: on the inside Does not differ from human cell
Cell Membrane
Selective permeability: easily allows lipid-soluble small molecules (O2, CO2)
Specific protein contents:
Porins – channels Permeases – carriers for specific substances
Contains the ATP-producing mechanism
Gram-positive Cell Envelope
Thick multilayered peptidoglycan cell wall external to the bacterial cell membrane Teichoic acids
Polymer of glycerol units Present in all Gram-positive organisms Major cell surface antigens
Gram-negative Cell Envelope Outer membrane
Contain lipopolysaccharides which is antigenic (O-polysaccharide portion) and toxic (lipid portion) Lipid A: endotoxin of Gram-negative organisms
Periplasmic space
Contains the thin peptidoglycan cell wall Also contain enzymes and other various substances
External Capsule and Glycocalyx Capsule
Usually polysaccharide but sometimes made of protein Tightly bound to the bacterial cell and has organized structure
Glycocalyx
Loosely bound to bacterial cell and amorphous
External Capsule and Glycocalyx Functions
Allow bacterial cells to adhere to surfaces Protection from antibodies and phagocytosis Diffusion barriers against some antibiotics
Appendages Flagella
Long semi-rigid, helical, hollow tubular structures composed of flagellin For motility Responds to chemotactic stimulus Attached to cell wall and cell membrane by a basal body that rotates the flagellum Highly antigenic (H-antigen)
Appendages Pili or fimbriae
Shorter and thinner than flagella Attachment organs for cell-to-cell contact
Bacterium-mucosal cells (Neisseria gonorrhea) Bacterium-bacterium (Eschericia coli) through sex pili for donation of DNA molecules
Cytoplasmic Structures
Cytoplasm Nucleoid Ribosomes Inclusions Endospores Plasmids Mesosomes
Cytoplasm
Complex mixture of substances enclosed by the cell envelope Consists of amorphous aqueous fluid Where suspended or dissolved are
Enzymes, ions, metabolites, storage granules Fibrous mass of densely packed DNA, RNA and proteins, also plasmids
Nucleoid
Fibrous mass of genetic material
Double-stranded circular DNA composing the bacterial singular chromosome Associated RNA and proteins
No discernible membrane enclosure
Plasmids
Small fraction of circular doublestranded DNA molecules that exists and replicates autonomously Carry genes for a variety of functions not essential for bacterial cell viability Enhance bacterial survival by
conveying antibiotic resistance enhancing mating ability making possible toxin production
Ribosomes
Responsible for polymerization of amino acids into proteins (as in eukaryotes) Differ in composition and size from eukaryotic ribosomes
70S (50S, 30S) as against 80S (60S, 40S) of eukaryotes 53 proteins as against 80+ proteins among eukaryotes
Cytoplasmic Inclusions
Accumulations of food reserves
Polysaccarides Lipids Polyphosphates
Maybe membrane-bound or scattered in the cytoplasm
Endospores
Dormant form within vegetative cell Can be released as free spores Rich in calcium dipicolinate Most resistant life forms known
Heat (survive boiling) Dessication Ultraviolet light Bacteriocidal chemical agents Destroyed by autoclaving
Sporulation
Formation of spore within vegetative cell Process
Invagination of parent cell membrane Isolation of copy of bacterial DNA Formation of new cell wall (peptidoglycan) Formation of outer keratin-like external coat Formation of external lipoprotein layer
Spore Germination
Return of spore form to vegetative state Occurs in nutritionally-rich environment Process
Destruction of cortex by lytic enzymes Uptake of water Release of dipicolinate from the cell
Medical Significance of Sporulation
Most notorious pathogens are spore-formers
Bacillus anthracis (Anthrax) Clostridium botulinum (Botulism) Clostridium perfringens (Gas gangrene)
Spores can remain viable for many years
Mesosomes
Complex invaginations of bacterial cell membrane Seem to be involved in chromosome separation May be evolutionarily related to nuclear envelope of eukaryotes
Nucleoid
GOOD MORNING.
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