Overview of the chapter Prokaryotes are microscopic. They have a biomass that is ten times larger than all eukaryotes. Think of this; The amount of prokaryotes on a handful of soil is greater than the number of people who have ever lived. In this chapter, prokaryotes are classified into two domains: Bacteria and Archaea.

Prokaryotes live almost everywhere! Including hot geysers!

Ch 27.1: Structural, functional, and genetic adaptations contribute to prokaryotic success. Cell Surface Structures One of the most important features of prokaryotes is their cell wall. It maintains shape, provides protection, and prevents the cell from bursting in a hypotonic environment, an environment where the solute concentration is higher on the inside. Most Prokaryotes lose water and shrink away from their cell wall, which means to plasmolyze, like other walled cells. Severe water loss activates the reproduction of prokaryotes.

The 3 most common shapes (: 1  m 2  m 5  m (a) Spherical (cocci) (b) Rod-shaped (bacilli) (c) Spiral

EukaryotesProkaryotes Have chromosomes located in a membrane-enclosed organelle called the nucleus. Has membrane bound organelles in the cytoplasm. Cell walls made of cellulose or chitin. The DNA is concentrated in a region called the nucleoid, but there is no membrane that separates it from the rest of the cell. Lacks organelles in cytoplasm. Cell walls made of peptidoglycan. * Peptidoglycan- a network of modified- sugar polymers cross-linked by short polypeptides

The Gram Stain Using a technique called the Gram stain, developed by Hans Christian Gram, scientists can classify many bacterial species into two groups based on their differences in cell wall composition. Gram-Positive bacteria have simple walls and a large amount of peptidoglycan. Gram-Negative bacteria have less peptidoglycan and are more complex and contain lipopolysaccharides, which are carbohydrates bonded to lipids.

(a) Gram-positive. Gram-positive bacteria have a cell wall with a large amount of peptidoglycan that traps the violet dye in the cytoplasm. The alcohol rinse does not remove the violet dye, which masks the added red dye. (b) Gram-negative. Gram-negative bacteria have less peptidoglycan, and it is located in a layer between the plasma membrane and an outer membrane. The violet dye is easily rinsed from the cytoplasm, and the cell appears pink or red after the red dye is added. Peptidoglycan layer Cell wall Plasma membrane Protein Gram- positive bacteria 20  m Outer membrane Peptidoglycan layer Plasma membrane Cell wall Lipopolysaccharide Protein Gram- negative bacteria

Applications Gram Staining is a valuable tool in medicine. Among disease causing bacteria, gram- negative bacteria are often more threatening than gram-positive species. Some drugs destroy species of bacteria without affecting human cells.

Capsule, Fimbriae, and Pili The cell wall of most prokaryotes is covered by a capsule, a sticky layer of polysaccharide or protein.  Capsules shield the cell from attacks of the hosts immune system, and they enable prokaryotes to stick to their substrate or to other individuals in a colony. Some prokaryotes stick to their substrate or to another because of hair like appendages called fimbrae and pili.

200 nm Capsule

Motility About half of all prokaryotes are capable of directional movement. Some species can move at speeds up to 50 times their body length per second! Flagella is the main structure that helps the prokaryotes to move. In a heterogeneous environment, many prokaryotes exhibit taxis, movement toward or away from a stimulus. (site that influences activity)

Flagellum Filament Hook Cell wall Plasma membrane Basal apparatus 50 nm

Internal and Genomic organization Prokaryotic cells are simpler than eukaryotic cells. In their internal structure and genomic organization. Prokaryotic cells lack complex compartmentalization. ( the ability of a cell to make cellular compartments such as membranes) T he typical prokaryotic genome is a ring of DNA that isn’t surrounded by a membrane. There is a nucleoid region which is lighter than the surrounding cytoplasm. Some species also have smaller rings of DNA called plasmids.

Reproduction and Adaptation Prokaryotes reproduce quickly by binary fission. Many form endospores, which can remain viable in harsh conditions for centuries. Rapid reproduction and horizontal gene transfer facilitate the evolution of prokaryotes in changing environments. Endospore 0.3  m

Concept 27.2: a great diversity of nutritional and metabolic adaptations have evolved in prokaryotes. Examples of all four models of nutrition-photoautotrophy, chemoautotrophy, photoheterotrophy, and chemoheterotrophy- are all found among prokaryotes!

Metabolic Relationships to Oxygen Obligate aerobes require O 2, Obligate anaerobes are poisoned by O 2, Faculative anaerobes can survive with or without O 2 Anaerobic respiration-substances other than O 2, accept electrons at the “downhill” end of electron transport chains.

Nitrogen Metabolism Prokaryotes can metabolize a large variety of nitrogenous compounds. Some can turn atmospheric nitrogen into ammonia in a process called nitrogen fixation, which is the assimilation or “fixing” of nitrogen by prokaryotes.

Metabolic cooperation Cooperation between prokaryotes allows them to use environmental resources they could not use as individual cells. Prokaryotes depend on the metabolic activities of other prokaryotes. In Anabaena, photosynthetic cells and nitrogen fixing cells exchange their metabolic products. Biofilms are surface-coating colonies, which may include different species.

A Biofilm 1  m

Molecular Systematics Leading to a phylogenetic classification of prokaryotes. Allows systematists to identify new clades, or a group of organisms. Concept 27.3 Molecular systematics is illuminating prokaryotic phylogeny

Domain Bacteria Domain Archaea Domain Eukarya Alpha Beta Gamma Epsilon Delta Proteobacteria Chlamydias Spirochetes Cyanobacteria Gram-positive bacteria Korarchaeotes Euryarchaeotes Crenarchaeotes Nanoarchaeotes Eukaryotes Universal ancestor

Bacteria When we think of bacteria we think of it as only being harmful and disease causing. They cause strep throat and other diseases. Some “beneficial” species are used to make Swiss cheese.

Bad Bacteria  Good Bacteria

Archaea Share some traits with bacteria. Some are different though… Extremophiles- love extreme conditions Extreme thermophiles- thrive in hot environments Extreme halophiles- live in highly saline (salty) environments. Methanogens obtain energy by using carbon dioxide to oxidize hydrogen, and releases methane as waste.

Proteobacteria A clade, or group of Gram- negative bacteria. It includes photoautotrophs, chemoautotrophs, and heterotrophs. There are 5 subgroups : alpha, beta, gamma, delta, and epsilon. They each do their own things, such as producing nitrate, or sulfur as wastes.

Rhizobium (arrows) inside a root cell of a legume (TEM) Nitrosomonas (colorized TEM) Chromatium; the small globules are sulfur wastes (LM) Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM) Bdellovibrio bacteriophorus Attacking a larger bacterium (colorized TEM) Helicobacter pylori (colorized TEM).

Chlamydias Parasites that can only survive in animal cells. Lack peptidoglycan. Peptidoglycan- a network of modified-sugar polymers cross-linked by short polypeptides Spirochetes Like living flagellum Some are free-living, but some are parasites. Cause syphilis

Gram positive bacteria Form chains of cells Cause tuberculosis and leprosy Lack cell walls. They are very tiny cells

Cyanobacteria The only prokaryotes that use photosynthesis. Abundant in water or wherever there is food, like freshwater. They also have cells that do nitrogen fixation, the process that converts nitrogen into other molecules

If humans disappeared tomorrow, life on Earth for other species would go on. Prokaryotes are so important on Earth that if they disappeared, any other life surviving is impossible. Concept 27.4 Prokaryotes play crucial roles in the biospere

Chemical Recycling Ecosystems depend on recycling of chemical elements between the living and nonliving parts of the environment, and prokaryotes have a major job in this process. Example: Chemoheterotrophic prokaryotes function as decomposers, they break down dead corpses, waste products, and dead vegetation.

Symbiotic Relationships Symbosis- an ecological relationship between organisms of different species that live together. Host- larger organism Symbiont- smaller organism Mutualism- both symbiotic organisms benefit. Parasitism- one organism, the parasite, benefits from the host.

The best known prokaryotes are those that cause diseases in humans. But, these only are a small part of prokaryotes. Some have good interactions with humans. Concept 27.5 Prokaryotes have both harmful and beneficial impacts on humans.

Pathogenic prokaryotes Cause half of all human diseases! Like lyme disease and tuberculosis Exotoxins are proteins secreted by prokaryotes. Endotoxins are lipopolysaccharide components of the outer membrane of gram-negative bacteria.

5 µm

Prokaryotes in research and technology Experiments using prokaryotes have led to important advances in DNA technology Prokaryotes are the principal agents in bioremediation the use of organisms to remove pollutants from the environment

Prokaryotes also… Are good in mining Making new medicines and antibiotics Synthesizing vitamins Genetic engineering!