Chapter 27

• Prokaryotes!• Wow!

Some Interesting Info…*The biomass of all the prokaryotes of the world is

10 times that of eukaryotes!

*The # of prokaryotes in a handful of soil is greater than all the humans who have EVER lived!

*Don’t think you’re more unique than a bacterium – they are VERY genetically diverse. 2 different strains of the E. coli species are more genetically different than a human & platypus!

*Very successful – live in almost ANY environment!

Remember…

All prokaryotes are classified into 2 domains:

1.) Bacteria

2.) Archaea

Prokaryotic Structures

1.) All have cell walls (plus a plasma membrane) to maintain shape & protect.

a.) Bacteria have peptidoglycan (a sugar polymer) in their cell walls.

b.) Archaebacteria do NOT have peptidoglycan in their cell walls.

Prokaryotic Structuresc.) Gram Stain: technique

used to stain bacteria based on properties of cell wall.

i.) Gram +: simpler cell walls with large

amount of peptidoglycan

ii.) Gram -: less peptidoglycan, more complex cell walls.

iii.) Gram (–) pathogenic species

are usually more threatening to us because the molecules on their

cell walls are generally more toxic

Prokaryotic Structures2.) Cell membrane & cell wall is surrounded by a

capsule (polysaccharide and/or protein layer).

a.) Protects & helps adhere to surfaces

Internal Organization

1.) May have infoldings of plasma membrane that serve as compartments to perform specialized functions.

2.) All have ribosomes for protein synthesis.

a.) Protein & rRNA content differs from eukaryotes.

Genomic Organization

1.) Have much less DNA than eukaryotes

2.) DNA exists in a circular piece located in a nucleoid region of cytoplasm.

3.) Usually have plasmids (small rings of DNA) which replicate on their own & are separate from chromosome.

Reproduction1.) Divide (reproduce) by binary

fission.

2.) Some bacteria can form endospores: bacterium copies its chromosome & surrounds it with a thick, tough wall.

a.) This protects chromosome in harsh conditions when rest of cell disintegrates – can even withstand boiling water!

b.) Endospores can remain viable for centuries! They can rehydrate & resume metabolism when environment is favorable.

Reproduction

3.) Bacteria can exchange plasmid genes through conjugation.

4.) Because of their ability to reproduce rapidly they can undergo natural selection & adapt rapidly too.

Nutritional/Metabolic Adaptations

4 Major Modes of Nutrition among Prokaryotes:

1.) Photoautotrophs: conduct photosynthesis (cyanobacteria)

2.) Chemoautotrophs: Oxidize hydrogen sulfide or ammonia and make own food (use chemicals for energy instead of light)

Nutritional/Metabolic Adaptations

3.) Photoheterotrophs: Use light for energy but must get carbon from an organic source (can’t use carbon dioxide to make own sugars)

4.) Chemoheterotrophs: must consume organic molecules for both energy & carbon…this is us too (just a fancy way of saying it).

Nutritional/Metabolic Adaptations

Relationships to Oxygen:

1.) Obligate aerobes: require oxygen for cellular respiration

2.) Facultative anaerobes: use oxygen if it’s there but can survive without it by fermentation.

Nutritional/Metabolic Adaptations

3.) Obligate anaerobes: poisoned by oxygen – can survive by fermentation or…

a.) Anaerobic respiration: do “cellular respiration” but use another molecule (instead of oxygen) as the final e- acceptor in the ETC.

Nutritional/Metabolic Adaptations

Nitrogen Metabolism:

1.) Certain prokaryotes carry out nitrogen fixation – converts atmospheric N to ammonia.

2.) Prokaryotes can use/incorporate N in a wide variety of forms (unlike plants & animals).

Molecular Systematics – Comparing the Gene Sequences of Prokaryotes

1.) Bacteria & Archaea were originally separated due to comparing ribosomal RNA sequences.

a.) Archaebacteria are more closely related to eukaryotes than bacteria!!

2.) Domain Bacteria: includes the majority of common prokaryotes – pathogens, beneficial species.

Molecular Systematics – Comparing the Gene Sequences of Prokaryotes

3.) Many Archaebacteria are classified as extremophiles: “lovers” of extreme conditions.

a.) Thermophiles: thrive in hot environments

b.) Halophiles: live in highly saline environments

c.) Methanogens: use carbon dioxide to oxidize hydrogen and release methane – poisoned by oxygen.

i.) Some species live in intestines of cattle & termites. Used in sewage treatment as well!

Halophiles:

Have pigments of various colors!

Prokaryotic Roles in the Biosphere1.) As decomposers, responsible for much of our chemical

cycling in ecosystems.

a.) Also make N available through N fixation.

b.) Oxygen released by those that do photosynthesis.

2.) Involved in many necessary symbiotic relationships:a.) There are 10 times more bacteria in your

body than there are cells belonging to you! Many live in intestines & help digest your food.

Impacts on Humans1.) ½ of all human disease are caused by

pathogenic prokaryotes.

2.) Usually cause illness by producing toxins:a.) Exotoxins: proteins secreted by prokaryotesb.) Endotoxins: components of the cell walls of gram (-) bacteria that cause disease.

3.) Positive impacts: used for genetic engineering, bioremediation, food production (turning milk into cheese & yogurt)