Prokaryotes

AP BiologySpring 2011

Domains the two domains of prokaryotes

Describe the unique characteristics of prokaryotes and their metabolic diversity

Discuss how prokaryotes reproduce Give examples of positive and

negative impacts of bacteria on humans

Viruses

Read chapter 21.1-21.2 Good refresher on viruses Remember:

StructureViral replication

http://www1.teachertube.com/viewVideo.php?title=Viral_infection_and_replication&video_id=50887

Viroids and Prions

Since the 1970’s about 30 viroids have been identified

A viroid is a small circle of RNA that can affect organisms

Most affect plants; only one viroid known to affect humans

Prions are misfoldings of proteinsAccumulate in nervous system cellsCause cell death and a spongiform

pathology in the brain cell

Prokaryotes- Enduring, Abundant, and Diverse

The earliest cells were prokaryotes, cells with no nucleus

Bacteria:Classified based on shape, cell wall

properties, metabolism, and other properties

Automated gene sequencing has elucidated prokaryote diversity

Shortly after life began there was a branching between bacteria and Archae Which eventually led

to Eukaryote lineage Despite estimates of

millions of species of bacteria, only about 5,000 named

Bacteria are very successful and terms of reproduction

Metabolic diversity is key to reproductive success in bacteria

Metabolic diversity:Photoautotrophs are

photosynthetic Cyanobacteria

Chemoautotrophs use electrons that they strip from inorganic compounds and use that energy to build organic compounds from CO2 and water

Photoheterotrophs use light energy and obtain carbon from organic compounds from their environment

Chemoautotrophs get both their carbon and their energy by breaking down organic compounds This group includes many prokaryotes, some

protists, and all animals and fungi Usually parasites- get butrients from living host

Prokaryotic Structure and Function

Modern prokaryotes include bacteria and archeansThey are unicellular and do not enclose

their DNA in a nucleus All prokaryotes have ribosomes Some have infoldings of their

membrane Nearly all have a cell wall, some have an

external slime coat that helps them adhere to surfaces

Gram staining: can identify many bacteria species by their wall staining properties

Unknown species exposed to purple dye, then iodine, then alcohol wash, and finally a counterstain

Gram-positive: stays purple Gram-negative: loses colour

at first, then counterstain turns it pink

Glycocalyx: sticky mesh, consists of polysaccharides, polypeptides, or both Capsule: when highly organized and

attached firmlySlime layer: when less organized, and

loosely attached

Three basic shapes:Coccus:

Spherical Bacillus:

Rod Cylindrical

Spirillum: Helical

Two kinds of filamentous structures may be attached to the cell wallBacterial flagellum: rotates like a

propeller to pl the cell along Pili: help bacteria attach to another in

conjugation (exchange of DNA), or help them attach to surfaces

Reproductive rates in prokaryotes are high, some species can reproduce every 20 minutes

Some species reproduce using a budding mechanism

More commonly, reproduce with fission that is similar to mitosis

Some bacteria can also pass along genes without reproducing

During conjugation a plasmid, a small, self-replicating circle of DNA containing only a few genes, can be passed to another cell

Some F (fertilty) plasmids allow bacteria to engage in bacterial conjugation in which a pilus joins two prokaryotic cells to permit the transfer of plasmid DNA

Prokaryotic Growth and Reroduction

When a bacterium divides, each daughter cell inherits a single chromosomeCircular double-stranded DNA molecule

Bacteria reproduce by prokaryotic fissionResults in two genetically identical daughter

cellsOnly bacteria and archaens reproduce by

this type of cell division

A plasmid is small, self-replicating circle of DNA containing only a few genes

Some F (fertility) plasmids allow bacteria to engage in bacterial conjugation in which a pilus joins two prokaryotic cells to permit transfer of plasmid DNA

Conjugation

The Bacteria

Thermophiles exist in extreme environments

Members of the genus Aquifex include bacteria that live in volcanic spring, thermal vents, and hot springs

Chloroplast-containing bacteria Anabaena: by means of heterocysts, can

fix nitrogen

Make up largest, most diverse bacterial group (gram negative)

Theiomargarita namibiensis:Chemeoautotroph that lives in marine

environments and gets its energy from striping electrons from sulfur

Rhizobium: fixes nitrogen on roots of legumes

E. Coli & H. Pylori:Live in human digestive system

E. Coli

Some free living, chemoautotrophic proteobacteria exhibit complex behavior Magnetoacteria: attracted by magnetic

fields

Myxobacteria: move as a group and feed on soil bacteria

Gram Positive: Not a monophyletic group

If all organisms in that group are known to have developed from a common ancestral form, and all descendants of that form are included in the group

Most are chemioheterotrophs with thick cell walls that retain gram stain

Lactobacillus: used in dairy product conversions such as yogurt

L.acidophilus: lowers the pH of skin and vaginal linings

Some form resistant endospores that can survive harsh environmental conditionsEx. Clostridium tetani (tetnus)

Tetnus

Spirochetes: resemble a springResposible for causing Lyme diseaseFree living parasites or symbionts

Clamydias: intracellular parasites that affect animal cellsCannot make DNA, pilfer it from cells

Archaeans

Archaeans: differ in their ribosomal DNA and cell wallsResemble eukaryotic cells

by making histones and sharing the same start codon for transcription

Some may resemble first cells on Earth

Recently this group has been subdivided into 3 major groups

Methane makers Inhabit swamps, mud, sewage, and animal guts Make ATP anaerobically by converting carbon

dioxide and hydrogen to methane Free oxygen kills them

Salt lovers Can tolerate high salt environments

such as brackish ponds, salt lakes, volcanic vents on seafloor, and the like

Most are heterotrophic aerobes, some can switch to a special photosynthesis, using bacteriorhodopsin to produce ATP Light activating pigment embedded in

plasma membrane, when it absorbs sunlight energy, changes shape and pumps H+ out from cell. H+ flows back into it, through ATP synthase and drives ATP formation

Heat lovers Live in hot springs and other very hot

places such as thermal vents of the sea floor where temps exceed 250 degrees C

Use sulfur as source of electrons for ATP formation