1. The microbial world & Bacteria
• Classification, the 3 domains
• The prokaryotic/eukaryotic divide
• Bacteria, gram positive or negative
2. Common properties of all cell types
(discussed in first lecture)
highly organised, cytoplasmic membrane
growth and reproduction
DNA as hereditary information, express
genes by transcription and translation
cellular metabolism, use energy to transform
simple materials into cellular structures
Redox reactions generates electrochemical
gradient (H+) used to make ATP.
3. Living diversity
(subject of the course essay
• Lack of gross morphology in microbes
problematic for descriptive taxonomy.
• Most unicellular, some form multicellular
associations, none form tissues.
• As microscopy developed, scientists saw
intracellular structures, e.g. nuclei, in animal
and plant cells. In late 1920s Chatton
reported that bacteria do not have nuclei.
• Stanier & van Niel (1962) proposed eukaryote
(true nucleus) for animal and plant cells,
prokaryote (before nuclei) for bacteria.
4. 5 Kingdoms
• 1969 Whittaker 5-kingdom classification, plants, fungi,
animals, single cell eukaryotes, and monera (prokaryotes)
• prokaryotes form distinct evolutionary group envisaged to be
common ancestor of other four groups.
5. A Tree of Life.
1985 Woese 3 domains based on gene sequencing.
7. Bacteria Archaea Eukaryotes
Single celled Single celled Single/multicellular
No nucleus No nucleus Nucleus
Ester linked Ether linked isoprenyl Ester linked alkane phospho
Alkane phospholipid phospholipids lipids
DNA replication DNA replication DNA replication
Gene expression Gene expression Gene expression
Ribosomes, protein Ribosomes, protein Ribosomes, protein
Synthesis bacterial Synthesis eukaryotic Synthesis archaeal
Interesting chimeric mix of properties?
8. The ring of life?
An anaerobic Archaea engulfed an aerobic Bacteria, eventually
giving rise to the Eukaryotes?
Bacterial lipids were preferred, archaeal genome formed a
nucleus and much of the cell biology, the bacteria became a
mitochondrion ‘exporting many genes to the new nucleus.
9. • Classification, the 3 domains
• The prokaryotic/eukaryotic divide
(flawed but integral to curent
thinking)
• Bacteria, gram positive or negative
12. The eukaryote/prokaryote divide
(a controversial distinction)
• Eukaryotic cells nuclei, nuclear membrane
around DNA-histone complexes
(chromosomes); prokaryotes no nucleus,
DNA tightly coiled with associated RNA and
proteins (nucleoid).
• Eukaryotes have membrane-bound
organelles (chloroplasts, mitochondria,
endoplasmic reticulum, Golgi apparatus,
vacuoles); prokaryotes do not, although
specialised groups have internal membranes
where ATP is generated (e.g.
photosynthetic bacteria).
13. Transcription and translation
differ
in eukaryotes, transcription in nucleus, translation in
the cytoplasm; in prokaryotes the two processes
occur concurrently.
prokaryotes have sigma subunit of RNA polymerase
for recognition of promoters, sigma binding necessary
for pol to interact with promotor; in eukaryotes RNA
polymerase and transcription factors bind directly to
promoter sequences independently.
Bacterial cell walls contain peptidoglycan (murein), a
polymer specific to prokaryotes; plant cells and some
eukaryotic micro-organisms have cellulose; animal cells
do not have cell walls.
14. Differences (cont)
ribosomes have the same basic structure but different sizes and
different sizes of rRNA components (some organelles in
eukaryotic cells have prokaryote-like ribosomes.); eukaryotic
ribosomes are larger, prokaryote ribosomes sensitive to
aminoglycoside antibiotics.
Type Size Large subunit Small subunit
prokaryotic 70S
50S
(5S, 23S RNAs)
30S
(16S RNA)
eukaryotic 80S
60S
(5S, 5.8S, 28S RNAs)
40S
(18S RNA)
15. less widespread differences:
• Some bacteria make endospores for surviving
hostile conditions, germinate to vegetative cells
when conditions improve.
• Some aquatic photosynthetic bacteria have gas
vesicles of protein rather than lipid membranes
(adjust buoyancy, maintain optimum depth for
light capture).
• Bacteria have flagella( flagellin) for motility;
eukaryotic microbes have cilia (tubulins).
• Bacteria usually 100-1000 times smaller than
eukaryotic cells (e.g. E. coli typically 2x1 um).
BUT
16. 1999. Biggest bacteria in world
• Thiomargarita namibiensis the “Sulphur Pearl of Namibia.”
1mM long. oxidises H2S and
store elemental sulphurjust
under the cell wall using
nitrate in a huge central sac
which shines blue-green
whiteness. Making it a ????
Pics from Science
17. Bacteria
• prokaryotes.
• No nucleus, genome is present in cytosol
cytoplasm.
• small
• simple cellular organization
• strong cell walls
• binary fission.
18. • Classification, the 3 domains
• The prokaryotic/eukaryotic divide
• Bacteria, gram positive or negative
major historical divide but many are atypical
19. • Membrane is a lipid bilayer, with proteins but
lacks sterols. Active transport functions.
20. 2 fundamental types of
Bacteria
Gram positive
Gram negative
Differ in cell wall
structure
21. • Christian Gram 1884, bright-field light microscopy, still an
important taxonomic identifier.
• Heat-fix to glass slide, stain crystal violet (purple), wash.
Potassium iodide added, ethanol rinse, counterstain with
safranin (red).
• Crystal violet enters all bacteria. Gram’s iodine clusters stain in
large precipitates, cannot be removed from cell unless cell wall
broken down. Ethanol rinse doesn’t affect cell wall of Gram-
positive bacteria, cells remain purple.
• In Gram-negative the outer and plasma membranes dissolve in
alcohol, purple stain washed away and safranin counterstains
red.
+
-
23. Peptidoglycan
• linear polymer made up of about 50 N-
acetylglucosaminyl b(14)-linked N-
acetylmuramyl dimers attached in a row.
24. Diaminopimelic acid linked
to Ala by peptide bond.
Less extensive. Less
sensitive to penicillin
Extensive cross-linking
Transpeptidase penicillins and
lysosyme.
25. • peptidoglycan makes up the rigid
framework of the Gram-positive
wall: the primary polymer.
• additional macromolecules,
secondary polymers, can be
attached to the primary framework
• Bacillus spp can have ~50% of the
dry weight of its cell wall as
teichoic acid. Glycerol backbone
with the 3C units connected by
phosphates. Fill in the
interpeptidoglycan spaces of the
cell wall.
26. G+ve walls are
thicker, 20-50 nm
stronger and
contain more
peptidoglycan than
Gram-negative
walls.
G-ve outer
membrane,
capsule
attached to
peptidoglycan.
LPS layer,
endotoxin. NAGs,
with fatty acids linking it
to membrane and
complicated CBH
assembly
27. • Periplasmic space. Gap between membrane
and cell wall. Full of enzymes, transport
proteins
• Periplasm consists of periplasmic space and
peptidoglycan
Gram negative
28. Description of LPS beyond our scope.
NAGs, with fatty acids linking it to membrane and complicated CBH assembly
Gram negative Gram positive
Editor's Notes
English: Structure and shape of the E.coli 70S ribosome. The large 50S ribosomal subunit (red) and small 30S ribosomal subunit (blue) are shown with a 200 Ångstrom (20 nm) scale bar. For the 50S subunit, the 23S (dark red) and 5S (orange red) rRNAs and the ribosomal proteins (pink) are shown. For the 30S subunit, the 16S rRNA (dark blue) and the ribosomal proteins (light blue) are shown.
