Welcome to
Microbiology
Learning Objectives:
To be able to describe
characteristics of bacteria and
the functions of each structure
What can you remember?
• ALL bacteria are prokaryotes. What does this mean?
• Without nucleus
• Compare prokaryotes and eukaryotes:
Prokaryotes
Eukaryotes
Small – less than 5 µm
Always unicellular
No nucleus or any membrane
bound organelles
DNA is circular, without proteins
Large cells (>10 µm)
Often multicellular
Always have a nucleus and other
membrane bound organelles
DNA is linear and associated with
proteins to form chromatin
Ribosomes are large (80S)
Ribosomes are small (70S)
No cytoskeleton
Motility by rigid rotating flagellum
Cell division by binary fision
Reproduction is always asexual
Huge variety of metabolic
pathways
Always has a cytoskeleton
Motility by flexible waving
undulipodium made of tubilin
Cell division by mitosis or meiosis
Reproduction is sexual or asexual
Common metabolic pathways
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How big?
A metre (m) contains an thousand millimetres (mm)
A millimetre contains a thousand micrometres (µm)
A micrometre contains a thousand nanometres (nm)
The size of an animal cell and some of its contents, in micrometres
and nanometres is given below.
Animal cell 20µm; mitochondrion 1µm; cell membrane (width) 8nm;
nucleus 5µm; ribosome 15nm
Imagine an animal cell is 5 metres across. How big would the various
organelles inside it be?
Real animal cell = 20µm. 5 metres = 5000 000µm, so the cell has been
magnified 5000 000/20 = 250 000
– Size of nucleus
• 5 µm x 250 000 = 1.25m
– Size of mitochondria
• 1 µm x 250 000 = 250 mm
– Size of ribosome
• 15nm x 250 000 = 3.75mm
– Width of cell membrane
• 8nm x 250 000 = 2mm
Bacteria are classified according
to their shape:
Make a list of the shapes of bacteria
that you can remember
Cocci – spherical bacteria:
•Cocci – smallest bacteria, occur as single
spheres.
•Diplococci – pairs of spheres, e.g. Diplococcus
pneumoniae (pneumonia).
•Staphylococci – clusters of spheres, e.g.
Staphylococcus aureus (boils and food
poisoning).
•Streptococci – chains of spheres, e.g.
Streptococcus pyogenes (sore throats).
Bacilli – rod-shaped bacteria:
•Individual rods – e.g. Escherichia coli, Salmonella typhi
(typhoid fever).
•Chains of rods – e.g. Azotobacter, Bacillus anthracis (anthrax).
Spirilla – large, spiral-shaped bacteria (motile with flagella),
e.g. Treponema pallidum (causes syphilis).
Vibrio – crescent-shaped bacteria (motile),
e.g. Vibrio cholerae (causes cholera).
Structure
Function
Ribosomes
Carries out protein synthesis
Mesosome
Site of respiration (formed by the intucking of
the plasma membrane)
Slime Capsule
Physical barrier to predatory protazoa, white
blood cells or bacteriophages
Cell Wall
Provides structure
Flagellum
Organelle of propulsion
Pili or Fimbriae
Bristle like projections that allow bacteria to
stick to surfaces
Cell surface
membrane
Plasmid
Barrier between cell and environment
Regulates transport of substances
Loops carrying 10-30 genes enable production
of antibiotics, or resistance to antibiotics
Nuclear material
within the
nuclear zone
Carries genetic material
• Give four features that most bacteria have in
common
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Cell wall made of peptidoglycan
Reproduce asexually by binary fission
No membrane bound organelles
DNA is a circular molecule
• Give three features that are only present in some
bacteria
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Presence of flagella
Mesosomes
Pili or fimbriae
Slime layer or capsule
• The mitochondria found in eukaryotic cells contain
their own loop of DNA as well as 70S ribosomes.
Given this information suggest how mitochondria
may have originated