GENETICS OF BACTERIA
Structure
● Capsule (polysaccharides)
● Peptidoglycan cell wall
○ “glycan” - linear polymer of alternating monosaccharide subunits
(N-acetylglucosamine/NAG and N-acetylmuramic acid/NAM) linked by
β(1,4)-glycosidic bonds
○ “peptido” - short string of amino acids that cross-link adjacent polysaccharide
strands at NAM subunits to form a network with high tensile strength
● Cell membrane
● Flagellum (motility)
● Pilus (for conjugation)
● Ribosomes (70S)
Gram-positive bacteria Gram-negative bacteria
thick, multi-layered peptidoglycan cell wall thin peptidoglycan cell wall (more susceptible to
physical damage)
only one cell membrane two membranes: outer membrane and inner
membrane
cell wall exterior to membrane cell wall between two membranes (periplasmic
space)
peptidoglycan covalently linked to teichoic acid
(major cell surface antigens)
outer membrane contains various embedded
lipopolysaccharides
● Polysaccharide portion
(O-polysaccharide is antigenic
● Lipid portion (lipid A) is toxic to
humans/animals (endotoxin)
stained purple (Gram staining) stained red (Gram staining)
Endosymbiosis theory
● Early ancestor of eukaryotic cell engulfed an oxygen-using non-photosynthetic prokaryotic
cell and formed a mutually beneficial relationship
● Over the course of evolution the host cell and its endosymbiosis merged into a single
organism (eukaryotic cell with mitochondrion)
● Mitochondria evolved before plastids (e.g. chloroplast) through a sequence of endosymbiosis
events (serial endosymbiosis)
● Evidence for endosymbiotic origin of mitochondria and plastids:
Copyright © 2019 tonyndr
Structure
● Capsule (polysaccharides)
● Peptidoglycan cell wall
○ “glycan” - linear polymer of alternating monosaccharide subunits
(N-acetylglucosamine/NAG and N-acetylmuramic acid/NAM) linked by
β(1,4)-glycosidic bonds
○ “peptido” - short string of amino acids that cross-link adjacent polysaccharide
strands at NAM subunits to form a network with high tensile strength
● Cell membrane
● Flagellum (motility)
● Pilus (for conjugation)
● Ribosomes (70S)
Gram-positive bacteria Gram-negative bacteria
thick, multi-layered peptidoglycan cell wall thin peptidoglycan cell wall (more susceptible to
physical damage)
only one cell membrane two membranes: outer membrane and inner
membrane
cell wall exterior to membrane cell wall between two membranes (periplasmic
space)
peptidoglycan covalently linked to teichoic acid
(major cell surface antigens)
outer membrane contains various embedded
lipopolysaccharides
● Polysaccharide portion
(O-polysaccharide is antigenic
● Lipid portion (lipid A) is toxic to
humans/animals (endotoxin)
stained purple (Gram staining) stained red (Gram staining)
Endosymbiosis theory
● Early ancestor of eukaryotic cell engulfed an oxygen-using non-photosynthetic prokaryotic
cell and formed a mutually beneficial relationship
● Over the course of evolution the host cell and its endosymbiosis merged into a single
organism (eukaryotic cell with mitochondrion)
● Mitochondria evolved before plastids (e.g. chloroplast) through a sequence of endosymbiosis
events (serial endosymbiosis)
● Evidence for endosymbiotic origin of mitochondria and plastids:
Copyright © 2019 tonyndr
