Classification and Structure of Prokaryotic Cells Flashcards
Nucleoid region
Where the genetic material of prokaryotes is located: organized into a single circular molecule of DNA concentrated in this area of the cell
Prokaryotic Domains
Archaea and Bacteria
Archaea
Single-celled organisms that are visually similar to bacteria, but contain genes and several metabolic pathways that are more similar to eukaryotes than to bacteria.
What is a notable trait of Archaea
Their ability to use alternative sources of energy: some are photosynthetic, and many are chemosynthetic and can generate energy from inorganic compounds
Similarities between Archaea and eukaryotes
They start translation with methionine, contain similar RNA polymerases, and associate their DNA with histones.
Similarities between Archaea and prokaryotes
Contain a single circular chromosome, divide by binary fission or budding, and share a similar overall structure to bacteria.
Characteristics of bacteria
All bacteria contain a cell membrane and cytoplasm, and some have flagella or fimbriae (similar to cilia).
Mutualistic symbiotes
The relationship between the human body and some bacteria, where both humans and bacteria benefit from the relationship.
Cocci
Spherical bacteria, includes common pathogens such as streptococcus pyogenes
Bacilli
Rod-shaped bacteria, like Escherichia coli
Spirilli
Spiral-shaped bacteria, include such species as Treponema pallidum, which cause syphilis
Obligate aerobes
Bacteria that require oxygen for metabolism
Anaerobes
Bacteria that use fermentation, or some other form of cellular metabolism that does not require oxygen; there are different types.
Obligate anaerobes
Anaerobes that cannot survive in an oxygen-containing environment: the presence of oxygen leads to the production of reactive oxygen-containing radicals in these species, which leads to cell death
Facultative anaerobes
Bacteria that can toggle between metabolic processes, using oxygen for aerobic metabolism if it is present, and switching to anaerobic metabolism if it is not
Aerotolerant anaerobes
Unable to use oxygen for metabolism, but are not harmed by its presence in the environment
Physical characteristics of prokaryotic cells
They lack a nucleus and membrane-bound organelles, have a cell wall and cell membrane, and have flagella
Envelope
Consists of the cell wall and cell membrane together in a prokaryotic cell: cell membrane is composed of phospholipids, similar to eukaryote
What are the two main types of cell walls in bacteria
Gram positive and gram negative
How is the type of cell wall determined
The Gram staining process: a crystal violet stain, followed by a safranin counterstain. If the enveloped absorbs the crystal violet stain, it will appear deep purple –> said is said to gram-positive.
If the envelope absorbs the safranin counterstain instead, then the cell will appear pink-red and is called gram-negative
Physical properties of gram-positive cell walls
Consist of a thick layer of peptidoglycan, a polymeric substance made from amino acids and sugars –> structural and barrier functions, and may also aid a bacterial pathogen by providing protection from a host organism’s immune system.
Cell wall also contains lipoteichoic acid –> function not clear, but it may be activated by exposure to these chemicals
Physical properties of gram-negative cell walls
Very thin and also contain peptidoglycan, but in much smaller amounts than gram-positive cells. Peptidoglycan cell walls of these bacteria are adjacent to the cell membrane, and are separated from the membrane by the periplasmic space.
Cell walls also have outer membranes containing phospholipids and lipopolysaccharides –> latter is what triggers and immune response in human beings.
Chemotaxis
The ability of a cell to detect chemical stimuli and move forward or away from them
Components of a flagella
A filament, basal body, and a hook
