1. Bacteria and Viruses
Katie Burke & Aliya Alidina

2. Contents
• What is bacteria?
• What are the components of bacteria?
– Cell wall
– Capsule
– Cell surface membrane
– Flagellum
– Pilus
– Mesosome
– DNA and Plasmids
• What is a virus?
• The life cycle
• Similarities and differences

3. Back to Contents
What is Bacteria?
• They are prokaryotic
organisms
• Many are pathogens
• But many are
beneficial to
organisms
– In the human gut
– The carbon cycle
– The nitrogen cycle

4. Cell wall
Gram-Positive Gram-Negative
• The cell wall has a thick layer • The cell wall has a thin layer of
of peptidoglycan peptidioglycan
• This layer has teichoic acid • There is no teichoic acid
• The cell wall also contains • There is an outer and inner
surface proteins and a plasma membrane with inner and outer
membrane membrane proteins
• The crystal violet bind to the • There are lipopolysaccharides
teichoic acid to give it the • The cells appear red in crystal
purple/blue colour violet
Back to Contents

5. Back to Contents
Capsule
• Otherwise known as a
slime layer if it is very
thin
• This is around the cell
wall
• It protects the bacteria
from phagocytosis by
white blood cells
• However it also helps
the bacteria stay
hydrated

6. Back to Contents
Cell Surface Membrane
• This is similar in the
structure and function
to that of a eukaryotic
cell

7. Back to Contents
Flagellum
• This provides the
bacteria with
movement
• It does this due to
rapid rotations

8. Back to Contents
Pilus
• These are protein
projections from the
surface of bacteria
• They attach to the host
cell but also to each
other
• It can be used for
sexual reproduction
• But it can cause an
entry point for
bacteriophages

9. Back to Contents
Mesosome
• This is an infolding
part of cell membrane
• This is thought to be
the site of respiration
• However there is still
some debate of their
full function

10. Back to Contents
DNA and Plasmids
• DNA comes in the
form of a single
circular piece
• Smaller pieces are
known as plasmids
• DNA is free in the
cytoplasm

11. Back to Contents
What is a Virus
• There is much debate
over this
• Overall it is a micro-
organism
• They only contain
nucleic acid and a
protein coat although
some have an
envelope

12. Back to Contents
The Life Cycle
Lysogenic Pathway Lytic Pathway

13. Back to Contents
Organelles of Bacterium vs. Viruses
Bacterium Viruses
• Cell wall • Nucleic Acid (possibly
• Capsule DNA)
• Cell surface membrane • A protein coat or capsid
• Ribosomes
• Flagellum • Some have an envelope
• Pilus
• Mesosome
• DNA and Plasmids