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Bacterial Ultrastructure and
Reproduction
Medical Microbiology
Spring 2010
Cytoplasmic Structures
• Cytoplasm of a bacterial cell includes:
– DNA chromosome
– mRNA
– Ribosomes
– Proteins
– Metabolites
• Very simple inside as compared to a
eukaryotic cell
Bacteria’s genetic material
• DNA chromosome that is found in an area called
the nucleoid (nucleus-like). It is not contained
within a nucleus.
• This chromosome is a single, double-stranded
circle with no histones
• Some bacteria have plasmids- smaller, extra
chromosomal DNA (usually in G-)
– Non-essential for survival, but aide in conferring
resistance to antibiotics
eukaryotic DNA and cell structure
Prokaryotic DNA and cell structure 
• With no nucleus, protein synthesis is much
simpler
– Transcription and translation are coupledribosomes(which are much smaller than their
eukaryotic counterparts) bind straight to the
mRNA and proteins are made while the
mRNA is still attached to the DNA
Cytoplasmic membrane
• Lipid bi-layer similar to that of your cell
membranes without the cholesterol
Cytoplasmic membrane
• Since prokaryotic cells lack organelles,
this is where most of the cell’s functions
happen
– Energy production (e- transport chain)
Cell Wall
• Distinguishing characteristic between G+ and Gbacteria.
• Peptidoglycan (also called murein) surround the
cytoplasmic membrane of most prokaryotes.
– Function: provides rigidity, determines the shape of
the bacteria; protection
• Lysozyme found in tears and mucus degrades this leaving a
protoplast….will lyse since its no longer protected!
– Porous (mesh-like) to allow diffusion of particles
Gram + Bacteria
• Thick, multilayered cell wall made up of
mostly peptidoglycan.
• Cell wall may also include teichoic and
lipoteichoic acids which can serve as
antigen surface markers (aides in
virulence)
Gram - bacteria
• Cell walls are more complex than G+ cell
walls.
– 2 layers external to the cytoplasmic
membrane separated by what’s called the
periplasmic space
• 1 thin peptidoglycan layer
• Outer membrane
– extra barrier to block entry of large molecules
– Extra protection from harsh environments like stomach
• No teichoic or lipoteichoic acids
G- bacteria
• The outer membrane is composed of LPS
(lipopolysaccharide) also called endotoxin,
which stimulates the immune systems of
organisms
• Cell walls have porins, pores that allow the
passage of metabolites and some other
materials (like antibiotics)
G- bacteria
• Structural proteins that serve as receptor
and adhesion sites
• If the outer membrane of G- bacteria is
weakened, lysozyme can come and
degrade the bacteria
– Here, its called a spheroplast which like
protoplasts are osmotically sensitive
External Structures: capsule
• Some bacteria (both g+ and g-) are surrounded
by a capsule
– Sometimes referred to as a slime layer, slime coat, or
glycocalyx
• Unnecessary for growth, but help the bacteria
survive
– Poorly antigenic, antiphagocytic so it’s a major
virulence factor.
• Barrier to toxic materials
• Aides in adhesion: ex. Streptococcus mutans
(biofilm)
Flagella
• May have one or several; used for
movement (chemotaxis)
• Bacteria swim to find food or avoid poison
External structure: fimbrae
•
•
•
•
= “fringe”
Also called pili
Smaller than flagella
Promote adherence (increase virulence)
Cell Division
• DNA replicates
• Growth of cell wall
• Septum (cleavage) formation
– Incomplete cleavage leads to formation of
chains (strepto-) or clusters (staphylo-)
• Bacterial cell division = binary fission
Spores
• Some G+ can form these (never G-)
• Allows bacterial cells to survive harsh
environments for long periods of time.