Prokaryotes Flashcards
How did early taxonomists classify species?
They classified all species as either plants or animals
What system has been adopted more recently for classifying species?
The three-domain system: Bacteria, Archaea, and Eukarya
What are the two domains of prokaryotes?
Bacteria and Archaea
What are the main three kingdoms included under the eukaryotic domain?
Fungi, Plantae and Animalia
What does the tree of life suggest about eukaryotes and archaea?
They are more closely related to each other than to bacteria
What is the tree of life based on?
It is largely based on rRNA, however, drawing the tree using genes other than rRNA reveals different relationships
Horizontal gene transfer
The movement of genes from one genome to another
How does horizontal gene transfer occur?
By exchanging of transposable elements and plasmids, viral infection, fusion of organisms, transformation
Can disparities in phylogenic trees be explained by the occurrence of horizontal gene transfer?
Yes some can - horizontal gene transfer has played a key role in the evolution of both prokaryotes and eukaryotes
What do some biologist argue about horizontal gene transfer and the tree of life?
They argue that horizontal gene transfer was so common that the early history of life should be represented as a tangled network of connected branches
Where can prokaryotes be found?
Wherever there there is life, they can thrive in habitats that are too cold, too hot, too salty, too acidic, or too alkaline for any eukaryote
Are prokaryotes important to our existence?
Yes - the vast majority of prokaryotes are essential for out existence
What kinds of materials do prokaryotes recycle?
They recycle carbon, nitrogen, and almost every chemical element, between organic mater and the soil, ocean, and atmosphere
Bacteria cells in/on the human body produce important vitamins, protect us from disease, and are integral to good health
How do Archaea differ from Bacteria?
In many key structural, biochemical, and physiological characteristics
Were mis-characterized as extremophiles since the first known archaea were found inhabiting extreme environments
Archaea dominate some of the largest habitats on Earth like ocean midwaters
Why are two prokaryotic domains recognized?
Because bacteria and archaea diverged so early in life and are so fundamentally different - both lack a membrane-bound nucleus but thats not a formal taxonomic classification, rather describes their appearance
Is the shared absence of a feature a good way to classify organisms together?
No - many microbiologists avoid and dislike the term “prokaryote” whose members share the absence of a nuclear membrane
What do most common prokaryotes look like?
Most are unicellular - some species may aggregate transiently - the most common shapes are spheres (cocci), rods (bacilli), and helices
What is an important feature of nearly all prokaryotic cells?
Their cell wall which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment (one with a low solute concentration)
What are bacteria cell walls made up of?
A modified sugar polymer called peptidoglycan
What do the walls of archaea lack?
Peptidoglycan
Gram stain
A valuable traditional tool for classifying many bacterial species into groups based on differences in their cell wall composition
Gram-positive bacteria
Have simpler cell walls, with large amounts of peptidoglycans - they are broadly a phylogenetic group although some members of the tree grouping do not stain Gram-positive
Gram-negative bacteria
Have more complex cell walls and less peptidoglycan
- an outer membrane on the cell wall contains lipopolysaccharides, carbohydrates boned to lipids
- gram-negative bacteria are phylogenetically diverse
- generally more pathogenic and antibiotic-resistant
- can evade defense systems because they are often coated with a sticky slime layer
What do may antibiotics inhibit?
The synthesis of cross-links in peptidoglycan, preventing the formation of a functional wall, particularly in gram-positive species
What is the cell wall of many gram-negative bacteria covered by?
A capsule/sheath/glycocalyx - a sticky layer of polysaccharide or protein
What is slime for?
- Capsules adhere the cells to their substratum
- They glue together the cells of those prokaryotes that live as colonies
What is another way for prokaryotes to adhere to one another or to the substratum?
Surface appendages called fimbriae or pili
- fimbriae or pili can fasten pathogenic bacteria to the mucous membranes of its host
- some are specialized for holding two prokaryote cels together long enough to transfer DNA during conjugation
What is the most common method of movement for prokaryotes?
The action of flagella, scattered over the entire surface or concentrate at one or both ends - the flagella of prokaryotes differ in structure and function from those of eukaryotes
What do bacterial flagellum look like?
They are chains of globular proteins wound in a tight spiral (like a corkscrew) from a filament which is attached to another protein (the hook) and the basal apparatus
What is rotation of the filaments driven by?
The entry of protons into the cell through the basal apparatus after the protons have been actively transported by proton pumps in the plasma membrane, the electrical potential from charge separation provides
How did flagella most likely evolve?
Flagella likely evolved as existing proteins were added to an ancestral secretory system
Exaptation
Where structures adapted for one function take on new functions through descent with modification
What is another way that cells move around?
By secreting a jet of slimy threads that anchor the cell to the substratum - the cell glides along at the growing end of threads
How do flagellated cells move around in relatively uniform evironments?
They may wander randomly
