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Prokaryotes (Bacteria & Archaea)
Prokaryotic cells (“before” nucleus)
• lack a nucleus & other organelles
• small, single-celled
• organisms of the following types:
Bacteria
(diameter ~1-10 mm)
Archaea
Bacterial Cell Structures
Ribosome
Cytoplasm
Nucleoid
Glycocalyx
Cellwall Cell
membrane
Flagellum
Inclusions
Peptidoglycan layer of cell wall
Lipopolysaccharide
(LPS)
Outermembraneof cell wall
Cell membrane
n
O side chain(varies inlength andcomposition)
Gram-negative cell wall
Lipid A(embeddedin outermembrane)
Fatty acid
Porin
(sectioned)
Periplasmic space
Phospholipid layers
Integral
proteins
Corepolysaccharide
Porin
• thin layer of peptidoglycan
Gram-negative Cell Wall
• outer membrane containing
lipopolysaccharide (LPS)
• Lipid A (endotoxin) + polysaccharide
Peptidoglycan layer(cell wall)
Cell membrane
Teichoic acid
Integralprotein
Lipoteichoic acid
Gram-positive cell wall
Gram-positive Cell Wall
• thick-layered peptidoglycan cell wall
• NO outer membrane
Bacterial Growth Curve
Viruses
Viruses are extremely small intracellular parasites with no
metabolic ability of their own.
• have none of the characteristics of living cells
• do NOT reproduce or metabolize on their own
• do NOT respond to their environment or
• depend on host cells for their reproduction(which are typically destroyed in the process)
**It’s hard to “kill” something that’s not really alive, so
antibiotics that kill bacteria, fungi, etc, do NOT harm viruses**
E. coli (bacterium)(1000 nm x 3000 nm)
Red blood cell (10,000 nm in diameter)
Smallpox virus(200 nm x 300 nm)
Tobacco mosaic virus(15 nm x 300 nm)
Bacterialribosomes
(25 nm)
Poliovirus(30 nm)
Bacteriophage T4(50 nm x 225 nm)
Bacteriophage MS2(24 nm)
Size of Viruses
• almost all
viruses are
smaller than
the smallest
bacteria
What’s a Virus made of?
All viruses consist of at least 2 components:
Genetic Material
• usually a single DNA or RNA molecule
• can be single or double stranded, linear or circular
A Capsid• a hollow protein capsule which houses the
genetic material
Some viruses also contain:
An Envelope
• membrane from host cell with viral proteins (spikes)
that surrounds the capsid
• contains the viral genes
The Viral Capsid
Capsids are hollow, protein “shells” that:
• are an array of
protein subunits
called capsomeres
• house the genetic
material (DNA/RNA)
• are frequently
involved in host
recognition & entry
• vary in shape, size
among viruses
The Viral EnvelopeThe capsid of some viruses
is enclosed in a phospholipid
membrane called an
envelope containing viral
proteins called “spikes”:
• membrane comes
from host cell
• “spike” proteins involved
in attachment and entry
into host cell
Viral MorphologyViruses come in 4 basic morphological types:
1. Polyhedral Viruses
• capsomeres in capsid have a
“polyhedral” arrangement
2. Helical Viruses
• capsomeres in capsid have a
“helical” arrangement
4. Complex Viruses
• consist of multiple
types of structures
3. Enveloped Viruses
The Viral Reproductive CycleVIRUS
2
1
3
4
Attachment& Entry
Replication ofViral Gemone
Expression ofViral Genes
Self-assembly ofnew virus particles
DNA
Capsid
HOSTCELL
Viral DNA
ViralDNA
mRNA
Capsidproteins
5 Release from the host cell
• attachment requires highly
specific interactions between
viral capsid or envelope
proteins and host cell surface
molecules
• attachment determines the
host cells a virus can infect