ProkaryotesChapter 23

Features of Prokaryotes Cellular organisms In one of two domains: Archaea and Eubacteria Generally smaller than eukaryotes Most are unicellular, some form colonies or

filaments No membrane-enclosed organelles Ribosomes are located in the cytoplasm In some – the inner plasma membrane is

extensively folded inward to provide reaction sites

Most have a cell wall

Shapes of Prokayrotes Cocci – spherical

• Single cells• Groups of two: diplococci• Long chains: streptococci• Clumps: staphylococci

Bacilli – rod-shaped• In single rods or long chains

Spiral:• Spirochete – flexible spiral• Spirillum – rigid spiral

Vibrio – spirillum shaped like a comma

Bacterial Shapes

Cell Wall Provides shape and stability Allows the cell to inhabit hypotonic

surroundings without bursting Does not help in hypertonic solutions

– most bacteria do not grow well in foods preserved with high sugar or salt content

In eubacteria the cell wall contains peptioglycan

Gram staining Gram-positive bacteria:

• Appear blue or violet• Cell walls with a very thick layer of peptidoglycan• Disease causing gram-positive bacteria are easily

killed by penicillin which interferes with peptidoglycan production

Gram-negative bacteria:• Appear red or pink• Cell walls have two layers: a thin peptidoglycan

layer and a thick outer membrane

Other bacterial structures Capsule – a slime layer that surrounds

the cell wall in some species• May provide pathogenic bacteria protection• May also allow some bacteria to attach to

surfaces (e.g.: to cause dental plaque) Pili – short, hair-like projections of

protein which allow bacteria to adhere to each other or other surfaces

Flagella – longer projections found in mobile bacteria

Bacterial structures

Prokaryote DNA In cytoplasm, not surrounded by a

membrane In most, a singular circular

chromosome Most bacteria also contain smaller

circular plasmids which may contain genes that code for enzymes, genetic exchange, or antibiotic resistance

Bacterial DNA

Bacterial Reproduction Asexual:

• Binary fission – DNA replication followed by a transverse wall separating the two new cells

• Budding – a bulge forms and matures, eventually separating from the original cell

• Fragmentation – walls develop within a single cell which then separates into several different cells

Genetic exchange:• Transformation – fragments of DNA released by one cell

are picked up by another• Transduction – a phage (form of a virus) carries bacterial

DNA from one to another• Conjugation – two different bacterial cells exchange

genetic material

Bacterial Reproduction

Endospore Formation Some bacterial form dormant,

extremely durable cells in response to unfavorable environmental conditions

Tetanus, gas gangrene, anthrax can all form endospores

Prokaryotic Metabolism Heterotrophs – most bacteria obtain

energy from surroundings:• Chemoheterotrophs – decomposers and

pathogens• Photoheterotrophs – get carbon from other

organisms but have chlorophyll to trap sunlight energy

Autotrophs – manufacture their own organic molecules• Photoautotrophs – use photosynthesis• Chemoautotrophs – use chemosynthesis

Prokaryote Classification Archaea:

• No peptidoglycan in cell walls• Many live in extremely harsh environments:

no oxygen, high salt, or high temperatures Eubacteria:

• Peptidoglycan in cell walls• Widely distributed and better known

Ecological Significance Decomposers

• Recycle chemical nutrients necessary for life• Especially important in the nitrogen cycle

Pathogens• Exotoxins - poisons produced by the bacteria that cause the

damage• Endotoxins – components of the cell walls that affect the

host only when released from the dead bacteria Food production

• Microbial fermentation – yogurt, pickles, olives, sauerkraut, vinegar, soy sauce

Antibiotic production Genetic engineering Bioremediation