Prokaryotes

Characteristics of Prokaryotes

1. Small

2. High metabolic rates

3. Diffusion is sufficient enough

4. Diverse shapes (Cocci = Round), (Bacilli = Rod), and spirals

5. Diverse colonial organization

6. DNA in the form of circular genomes

7. Lack membrane-bound organelles

Cell Wall (Prokaryotes)

1. Used for protection against changes in fluid pressure

2. Contains peptidoglycan, network of polysaccharide and peptides

3. Plasma membrane which is selectively permeable

Peptidoglycan - cross-linked structure of polysaccharides and peptides

Gram-positive Bacteria

Simple cell wall with thick layer of peptidoglycan which retains the crystal violet chemical stain
Appears purple due to stain being retained

Gram-negative Bacteria

Thin layer of peptidoglycan, additional layer of lipopolysaccharide, which disrupts the staining

Lipopolysaccharide often contains toxins contributing to symptoms such as fever
Appears pink due to the stain

Capsule

Sticky layer external to the cell wall, made up of polysaccharides and proteins. Helps with surface adhesion and evasion of immune cells by a lack of antigen that immune cells can detect

• Example; Dental plaque, a type of biofilm, made of cell communities and slimy matrix

Fimbriae

Short, hair-like structures, help prokaryotes adhere to surfaces

Flagella

Long, whip like structures. Provide ‘fast’ mobility to prokaryotes.

Pili

Similar appearance to fimbriae, sex pili transfer DNA in the form of plasmid between prokaryotes. Pili pull prokaryotes forward in a ‘twitching’ manner;
Pili extend → Pili contract → Cell moved

Endospores

Thick-coated, resilient cell produced by some bacteria during harsh conditions. It protects their genetic material from UV radiation, chemicals, head, salinity. Prokaryotes enter a ‘dormantt’ state. Environmental stressors trigger them

Prokaryotic DNA

Prokaryotes have a small genome, genetic information is organized as a single circular and condensed nucleoid. Some bacteria contain circular DNA called ‘plasmids’, found in the cytoplasm, contain helpful non-essential information.

Binary Fission

Single cell divides into two identical daughter cells without distinct phases. High rate of reproduction, environment can impact this rate. High rate of reproduction due to small genome and simplicity of the process.

Horizontal Gene Transfer

Exchange of genetic materials between species, complicates identification of ancestral traits

Three Mechanisms of Genetic Recombination (Prokaryotes)

1. Transformation

2. Transduction

3. Conjugation

Transformation

External DNA taken up from lysed cells and integrated into prokaryote cells.

Transduction

Phages (viruses) carry bacterial DNA from one bacterial cell to another

Conjugation

Direct transfer of DNA between cells that are temporarily joined with physical contact;

1. Donor cell attaches itself to the recipient with a pilus

2. Recipient pulled close

3. Material transferred unidirectionally

4. Recipient cell incorporates donor’s genetic material

Anabolism and Catabolism

Anabolism - Build molecules from smaller units

Catabolism - Break molecules into smaller units

Modes of Nutrition

Phototroph - Energy obtained from light

Chemotroph - Energy obtained from chemical

Autotroph - Simple, inorganic molecules as carbon sources for producing complex organic molecules

Heterotroph - Organic molecules as carbon source for growth and development

Types of Aerobes/Anaerobes

Obligate Aerobes - Biological processes rely on presence of oxygen to perform cellular respiration

Obligate Anaerobes - Biological process inhibited by presence of oxygen, rely on anaerobic respiration

Facultative Anaerobes - Biological processes can take place either in the presence or absence of Oxygen (E-coli for example)

Nitrogen Fixation

Prokaryotes that convert atmospheric nitrogen into ammonia through biological nitrogen fixation, helps reduce release of greenhouse gas but increases acidity of the soil

Domain Bacteria Groups

1. Proteobacteria

2. Chlamydia

3. Spirochetes

4. Cyanobacteria

5. Gram-positive Bacteria

Proteobacteria

Gram-negative bacteria, consists of alpha, beta, gamma, delta and epsilon.
Alpha proteobacteria - closely related to eukaryotic hosts, mitochondria in eukaryotes hypothesized to evolve from aerobic alpha-proteobacteria

Gamma proteobacteria: E-coli bacteria (causes food poisoning)

Epsilon proteobacteria: Pylori, causes stomach ulcers

Chlamydia

Gram negative, obligate intracellular parasites, exclusively on animal cells.

Cyanobacteria

Gram negative, first prokaryotes to generate oxygen. Chloroplasts hypothesized to evolve from cyanobacteria. Most are harmless, but several can cause toxins.

Gram-positive Bacteria

Essential decomposers, mostly harmless but some are dangerous (like the bacteria that causes anthrax). Lactobacillus is gram positive but can appear gram negative due to thin cell wall.

Methanogens

Archaea that inhabit anoxic environments, such as stomach of cattle. They produce methane as a waste product.

Extreme Halophiles

Archaea that inhabit salty environments. Often have diagnostic colors (pigments produced by the archaea).

Extreme Thermophiles

Archaea that inhabit high temperature environments. Many thermophiles are chemoautotrophs.

Ecological/Economic Function of Prokaryotes

1. Contributor of Oxygen

2. Fixation of nitrogen

3. play decomposition role in ecosystems

4. Used in biomediation, elimination of pollutant by organisms (used in water-treatment facilities)

5. Used in biomedical research, like using E-coli to manufacture insulin

Symbiosis Relationships

Symbiosis - long-term relationship between species, where at least one benefits

Mutualism - Symbiotic relationship in which both species benefit (ex; methanogens and cattle)

Commensalism - symbiotic relationship in which one species benefits and the other in unaffected

Parasitism - symbiotic relationship in which parasitic species benefits and the host suffers