Ch 27: Prokaryotes - Bacteria and Archaea Great Salt Lake – pink color from living prokaryotes; survive in 32% salt • Prokaryotes are divided into two domains – bacteria and archaea • thrive in diverse habitats – including places too acidic, salty, cold, or hot for most other organisms • Most are microscopic – but what they lack in size they make up for in numbers – For example: more in a handful of fertile soil than the number of people who have ever lived
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Ch 27: Prokaryotes - Bacteria and Archaea Great Salt Lake – pink color from living prokaryotes; survive in 32% salt Prokaryotes are divided into two domains.
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Ch 27: Prokaryotes - Bacteria and Archaea
Great Salt Lake – pink color from living prokaryotes; survive in 32% salt
• Prokaryotes are divided into two domains– bacteria and archaea
• thrive in diverse habitats– including places too acidic,
salty, cold, or hot for most other organisms
• Most are microscopic– but what they lack in size
they make up for in numbers
– For example: more in a handful of fertile soil than the number of people who have ever lived
Prokaryotes• Single cell
– Some form colonies• Very small
– 0.5–5 µm (10-20 times smaller than Eukaryotes)
• Lacks nucleus and most other membrane bound organelles
• Reproduce very quickly– Asexual binary fission– Genetic recombination
• variety of shapes– spheres (cocci)– rods (bacilli)– spirals
• Cell wall
More structural & functional characteristics in (Ch.27)
Bacilli
• Rod shaped– Example: E. coli
• Usually solitary• Sometimes chains– streptobacilli
Cocci
• Spherical– Clumps or clusters (like
grapes)• E.g. Staphylococcus aureus
– Streptococci – chains of spheres
– Diplococci – pairs of spheres• E.g. Neisseria gonnorheae
Streptococcus 1
Streptococcus 2
Diplococcus 1
Diplococcus 2
Spiral prokaryotes
• Spirilla – spiral shaped– With external flagella– Variable lengths
• Spirochaetes– Internal flagella– Corkscrew-like
• Boring action• E.g. Treponema pallidum (Syphilis)
Cell-Surface Structures• Cell wall is important
– maintains cell shape– protects the cell– prevents it from bursting in a
hypotonic environment• Eukaryote cell walls are
made of cellulose or chitin• Bacterial cell walls contain
peptidoglycan– network of sugar polymers
cross-linked by polypeptides• Archaea cell walls
– polysaccharides and proteins but lack peptidoglycan
• Scientists use the Gram stain to classify bacteria by cell wall composition– Counter stains to differentiate between cell wall
characteristics
– Gram-positive bacteria• simpler walls with a large amount of peptidoglycan
– Gram-negative bacteria• less peptidoglycan and an outer membrane that can be toxic
Gram-positivebacteria
10 m
Gram-negativebacteria
Gram positive bacteria
• Thick layer of peptidoglycans
• Retains crystal violet– Doesn’t wash out– Masks red safranin
• Stains dark purple or blue-black
Gram negative bacteria
• Thin sandwiched layer of peptidoglycans
• Rinses away crystal violet
• Stains pink or red OutermembranePeptido-glycanlayer
Plasma membrane
Cellwall
Carbohydrate portionof lipopolysaccharide
(b) Gram-negative bacteria: crystal violet is easily rinsed away, revealing red dye.
• Extra capsule covers many prokaryotes– polysaccharide or protein
layer
• Some also have fimbriae– stick to substrate or other
individuals in a colony
• Pili (or sex pili)– longer than fimbriae– allow prokaryotes to
exchange DNA
Bacterialcell wall
Bacterialcapsule
Tonsilcell
200 nm
Fimbriae
1 m
Diverse nutritional and metabolic adaptations have evolved in prokaryotes
• Prokaryotes can be categorized by how they obtain energy and carbon
– Phototrophs obtain energy from light– Chemotrophs obtain energy from chemicals– Autotrophs require CO2 as a carbon source
– Heterotrophs require an organic nutrient to make organic compounds
• Energy and carbon sources are combined to give four major modes of nutrition
The Role of Oxygen in Metabolism
• Prokaryotic metabolism varies with respect to O2
– Obligate aerobes require O2 for cellular respiration
– Obligate anaerobes are poisoned by O2 and use fermentation or anaerobic respiration
– Facultative anaerobes can survive with or without O2
Nitrogen Metabolism
• Nitrogen is essential for the production of amino acids and nucleic acids – nitrogen fixation– some prokaryotes convert atmospheric
nitrogen (N2) to ammonia (NH3)– Some cooperate between cells of a colony
• allows them to use environmental resources they could not use as individual cells– E.g. cyanobacterium Anabaena, photosynthetic
cells and nitrogen-fixing cells called heterocysts (or heterocytes) exchange metabolic products
Photosyntheticcells
Heterocyst
20 m
Molecular systematics led to the splitting of prokaryotes into bacteria and archaea
Eukaryotes
Korarchaeotes
Euryarchaeotes
Crenarchaeotes
Nanoarchaeotes
Proteobacteria
Chlamydias
Spirochetes
Cyanobacteria
Dom
ain BacteriaD
omain ArchaeaUNIVERSAL
ANCESTOR
Gram-positive
Clades of Domain Bacteria
• Fig 27.18 (27.13 in 7th ed.)• Proteobacteria– diverse & includes gram-negatives– Subgroups: α, β, γ, δ, ε