Biology 112

 Smallest and most common microorganisms
 Unicellular organisms that lack a nucleus
 They can be divided into two separate groups
 Eubacteria
 Archaebacteria

 Live almost everywhere
 Usually surrounded by a cell wall that protects it from injury as well as determines its shape
 Cell wall contains peptidoglycan, a carbohydrate
 Cell membrane inside the cell wall that surrounds the cytoplasm
 Some have a second membrane which further protects it from damage

 Have cell walls, lack nuclei and lack the peptidoglycan that is present in eubacteria
 There are different lipids existing in their cell membranes
 The DNA sequencing is more similar to eukaryotes than prokaryotes
 May be the ancestors of eukaryotes
 Most live in harsh environments, including mud, digestive tracts, volcanoes

 Shape
 Rod-shaped (bacilli), spherical (cocci), spiral/corkscrew (spirilla)
 Composition of Cell Walls
 Thick peptidoglycan walls (gram positive) or thinner walls with a second outer lipid layer (gram negative)
 Movement
 Some do not move at all, others have flagella, which are whiplike structures while others still lash, snake, spiral and glide

Heterotrophs (ex. E coli )
Autotrophs (ex.
Cyanobacteria)

 Heterotrophic Prokaryotes
 Eat other organisms for energy as well as a supply of carbon
 Called chemoheterotrophs
 Others are autotrophs to obtain their energy but also eat other organisms for their necessity for carbon
 Called photoheterotrophs

 Use light energy to convert carbon dioxide and water to carbon compounds and oxygen
 Found where light is available
 Photoautotrophs
 Make organic carbon molecules from carbon dioxide but do not require light
 Use energy from chemical reactions involving ammonia, hydrogen sulfide, nitrites, sulfur or iron
 Present in harsh environments
 Chemoautotrophs

 They undergo cellular respiration, fermentation or both
 Those that require a constant supply of oxygen are called obligate aerobes
 Those that do not require it (or may even be killed by the presence of oxygen) are called obligate anaerobes
 Those that can survive with or without oxygen are called facultative anaerobes
 Do not require it but are not harmed by it either
 As a result, they can survive almost anywhere

 How fast they grow and reproduce depends mostly on availability of food and the production/elimination of waste products
 When a prokaryote has doubled in its size, it may divide in half through a process called binary fission (daughter cells are identical to single parent cell – asexual reproduction)
 Conjugation occurs when a bridge forms between two cells and genetic material can be passed between the two
 Spore formation, called endospores, may form within a prokaryote
 A thick wall forms around the DNA and a portion of the cytoplasm
 Spore may remain dormant until more favorable conditions occur

 Critical for maintaining the living world
 Some are producers as well as decomposers
 Others have uses in human survival
 Decomposers
 Bacteria recycles nutrients which maintains balance in the environment
 Without them, sewage systems would not be able to eliminate all its waste and disease would spread

 Nitrogen fixers
 Plants need nitrogen to make amino acids
(building blocks of protein)
 Nitrogen (N
(NH
3
2
) must be changed to ammonia
) or other nitrogen compounds (nitrates) before it can be used by living things
 This process is known as nitrogen fixation

 Human uses
 Food industry
 Lactobacillus is used for the preservation of dairy
 Industry
 Sulfate-reducing bacteria in the petroleum industry
 Waste removal
 Bacteria that converts waste into fuel
 Mining
 Bacteria that leaches copper from mines
 Synthesize drugs and chemicals for improved health
 Vaccines

 Viruses are composed of parts of nucleic acid, protein and lipids
 Reproduction only occurs by infecting living cells
 Great variety in their size and appearance
 All viruses infect cells the same way – by entering healthy cells and once inside, use the organelles of the infected cell to produce more viruses
 It is typically composed of DNA, RNA and a protein coat

 Protein coat is also called a capsid
 Contains proteins that enable the virus to enter the host cell
 Binds to receptors on a healthy cell and “tricks” the cell into allowing it to enter
 Once inside, viral genes are exposed to the cell
 The healthy cell ‘reads’ the genetic information and then may, as a result, get destroyed in the process
 The host cell may also make copies of the virus

 Viruses are highly specific to the host cell it is infecting
 As a result, viruses which target plants may not contain the proteins in their capsids to gain entry to an animal cell
 Viruses that attack bacteria are called bacteriophages

 Some viruses replicate themselves immediately once inside the host cell and kill the cell
 Others do not replicate in such a way that destroys the host cell immediately
 Lytic Infection
 Virus enters cell, replicates itself, and causes the cell to burst
 Destroys the cells DNA, uses the cell to make viral proteins and viral DNA, then releases viral particles
 Lysogenic Infection
 Incorporation of the viruses DNA with the host cell DNA and replicates along with the host cell’s DNA
 Viral DNA is called a prophage which may lay dormant for an indefinite amount of time