PHCY219 – Microbiology Section 2 – Lecture 4 Keith Ireton
Lecture 4 – Cell Structure and Function of Prokaryotes
Need to learn about bacterial cell structure and function so that we can understand pathogens and normal
Phylogenetics = study of evolutionary relationship (evolutionary tree).
Three branches 1) Bacteria 2) Archaea 3) Eukarya
Prokaryotes vs. eukaryotes: Prokaryotes don’t have nuclei; usually they have a chromosome (circular).
Archaea and bacteria look the same, but they are distantly related. Archaea more closely related to eukarya.
Has a nucleus
Lacks nucleus o Ribosomes
Lacks organelles o Golgi
Has cell wall o Endoplasmic Reticulum
Lacks cell wall
A chromosome is present; it is not in a true nucleusMultiple chromosomes are present DNA replication
But it IS ORGANISED. mRNA is transported out. Compartments are
physically separated. Plants chloroplasts vs.
mitochondria in other species.
The red stars indicate pathogens. Examples of
Proteobacteria gram –ve bacteria = salmonella
and E. coli. Example of gram +ve = S. aureus.
Examples of Spirochete = syphilis.
Staining can differentiate between gram –ve and
gram +ve organisms. PHCY219 – Microbiology Section 2 – Lecture 4 Keith Ireton
Gram staining process
Initially all the cells are stained purple. After alcohol is
introduced, only gram +ve cells are stained. Gram –vecells
are not stained. At the last stage of this procedure gram –ve
cells are pink due to safranin.
Gram +ve bacteria have peptidoglycan layer which is thicker
than gram –ve. So when crystal violet is present, it’s harder
for it to leave again. So stains the gram +ve cells and not the
gram –ve cells.
Archaea can be found in extreme places (high salt, low pH,
high temperatures etc). They also have metabolisms that
are different. For example methanogens, they degrade
organic material into methane. Archaea haven’t been found
to be pathogenic to us so far.
Size and Shape
Bacteria can come in different shapes (morphology).
Coccus Staphylococcus aureus.
Rod E. coli
Spirillum Helicobacter pylori
Spirochete Borrelia burgdorferi
Stalks & Hyphae Caulobacter crescentus
Size – Bacteria range in size. The smallest is Mycoplasma
pneuomoniae (0.2 µm). Conversely, the largest is
Thiomargarita namibiensis (750 µm).
Advantage of being small: surface area:volume ratio
stays small absorbing nutrients and excreting waste
becomes more efficient.
Surface area is related to square of the radius. PHCY219 – Microbiology Section 2 – Lecture 4 Keith Ireton
Bacteria – made of phospholipid bilayer.
Glycerol and phosphates found facing outwards
Two fatty acids found facing inwards.
This arrangement has the hydrophobic and hydroph