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Name the basic characteristics of prokaryotes.
- most abundant organisms on earth
- mostly unicellular, although the cells of some species remain attached to each other after cell division
- smaller than eukaryotes, lack complex compartmentalization found in eukaryotes
- cell wall
What are the three most common shapes for prokaryotes?
1. Cocci – spherical prokaryotes
2. Bacilli – rod shaped prokaryotes
3. Spirilla/Spirochetes – spiral shaped prokaryotes
What happens to a prokaryotic cell in a hypertonic solution?
Lose water and shrink away from their wall (plasmolyze).
Compare the cell walls of Prokaryotes and Eukaryotes.
1. Eukaryote cell walls (plants and fungi have cell walls) are made of cellulose or chitin.
2. Prokaryote cell walls contain peptidoglycan, a polymer composed of modified sugars cross-linked by short polypeptides.
Describe the Gram Staining Process
Technique developed by Hans Christian Gram that is used to classify many bacterial species into two groups based on differences in cell wall makeup
Gram-positive bacteria: simpler walls with large amount of peptidoglycan
Gram-negative bacteria: less peptidoglycan, more complex, outer membrane contains lipopolysaccharides (carbohydrates bonded to lipids), outer membrane impeded entry of antibiotics and protect itself from immune system
The cell wall of many prokaryotes is surrounded by a sticky layer of polysaccharide or protein.
The layer is called a:
1. Capsule if it is well defined.
2. Slime Layer if it is less well organized.
Note: Some layers protect against dehydration and can stick to other prokaryotes or substrate.
Some prokaryotes stick to their substrate or to one another by means of hair like appendages called Fimbriae. Usually shorter and more numerous than pili: appendages that pull two cells together prior to DNA transfer from one cell to the other (example: sex pili).
About half of all prokaryotes are capable of taxis, a directed movement toward or away from a stimulus.
Chemotaxis: prokaryotes change their movement pattern in response to chemicals
1. Toward nutrients or oxygen – positive Chemotaxis
2. Away from toxic substance – negative Chemotaxis
What is the most common structure that enables prokaryotes to move?
Flagella: can be scattered, or concentrated at both ends, prokaryotic flagella thinner than eukaryotes
Note – Since the flagella of organisms in the three domains perform similar functions but probably are not related by common descent, it is likely that they are analogous.
What are the three main parts of a bacterial flagellum?
The motor, the hook, and the filament.
Note – Only half of the flagellum’s protein components (42 different kinds) appear to be necessary for function. Flagellum evolved as other proteins were added to an ancestral secretory system. This is an example of exaptation, the process in which existing structures take on new functions through descent with modification.
Describe the differences in cell walls between Aerobic and Photosynthetic Prokaryotes.
1. Infoldings of the plasma membrane, reminiscent of the cristae of mitochondria, function in cellular respiration in some basic prokaryotes.
2. Photosynthetic prokaryotes called cyanobacteria have thylakoid membranes, much like those in chloroplasts.
Describe the internal organization and DNA of prokaryotes.
- Prokaryote genome is structurally different from a eukaryotic genome and in most cases has considerably less DNA
- Circular chromosome with fewer proteins (vs. liner chromosomes in eukaryotes)
- Lack membrane bound nucleus
Where is the chromosome located in a prokaryotic cell?
In the Nucleoid – a region of cytoplasm that appears lighter than the surrounding cytoplasm in electron micrographs
Smaller rings of independently replicating DNA molecules found in prokaryotes, mostly carrying only a few genes.
(T/F) Prokaryotic Ribosomes are slightly smaller than eukaryotic ribosomes and differ in their protein and RNA content.
Process used in prokaryotes that allows them to reproduce quickly in favorable environments (multiplies by 2 each turn). However prokaryotic reproduction is limited by a shortage of nutrients, and excess of metabolic waste, or completion/consumption with/by other organisms.
Certain bacteria develop resistant cells called endospores when they lack an essential nutrient. The original cell produces a copy of its chromosome and surrounds it with a tough multilayered structure, forming the endospore.
What are the three factors that give rise to high levels of genetic diversity in Prokaryotes?
1. Rapid reproduction
3. Genetic recombination
Note – Prokaryotes do not reproduce sexually, their genetic diversity stems from rapid reproduction and mutation.
Discuss the role of spontaneous mutations in a given E. coli gene.
They average only one mutation every of 10 million cell divisions, but it quickly adds up (2000 mutations per day in human intestines).
Note – New mutations, though rare, can increase genetic diversity quickly in species with short generation times and large populations, resulting in rapid evolution.
(T/F) Meiosis and fertilization occurs in Eukaryotes but not in Prokaryotes.
Describe Horizontal Gene Transfer
Prokaryotes have three mechanisms that can bring together prokaryotic DNA from different individuals.
When the individuals are members of different species, this movement of genes from one organism to another is called Horizontal Gene Transfer.
In Transformation, the genotype and possibly phenotype of a prokaryotic cell are altered by the uptake of foreign DNA from its surrounding.
Example – a nonpathogenic cell takes up a piece of DNA carrying the allele for pathogenicity and replaces its own allele with the foreign allele, an exchange of homologous DNA segments. This produces a recombinant – chromosome contains DNA from two different cells
In Transduction, phages carry prokaryotic genes from one host cell to another, which results from accidents that occur during the phage replicative cycle.
In Conjugation, DNA is transferred between prokaryotic cells (same species) that are temporarily joined. In bacteria the transfer is always one way – one cell donates DNA the other receives (i.e. a pilus of the donor cell attaches to the recipient, formation of mating bridge).
(F for fertility) – The ability to form a pili and donate DNA during conjugation results from the presence of a particular piece of DNA called the F factor. The F factor can exist as a plasmid or as a segment of DNA within the bacterial chromosome.
F plasmid – The F factor in its plasmid form. Cells containing the F plasmid, designated F+ cells, function as DNA donors during conjugation while cells lacking the F factor, designated F-, function as DNA recipients.
A cell with the F factor built into its chromosome is called an Hfr cell (for high frequency of recombination) – they result in F+ cells.
Plasmids which carry resistance genes – genes that code for enzymes that specifically destroy or otherwise hinder the effectiveness of certain antibiotics (R for resistance).
Describe the three different categories when identifying prokaryotes by the way they get energy.
Phototrophs – obtain energy from light
Chemotrophs – obtain energy from chemicals
Autotrophs – organisms that need only CO2 in some form as a carbon source
Heterotrophs – require at least one organic nutrient, i.e. glucose, to make other organic compounds
What are the different classifications of prokaryotes with respect to oxygen.
Obligate Aerobes – must use O2 for cellular respiration and cant grow without it
Obligate Anaerobes – poisoned by O2, can live using either fermentation or by extracting chemical energy from anaerobic respiration – substances other than O2, such as nitrate ions (NO3-) or sulfate ions (SO4^2-), accept electrons at the downhill end of the ETC.
Facultative Anaerobes – use O2 if it is present but can also carry out fermentation or anaerobic respir.
Some cyanobacteria and some methanogens (Archaea) convert atmospheric nitrogen (N2) to ammonia (NH2), a process called Nitrogen Fixation.
(T/F) In terms of their nutrition, nitrogen-fixing cyanobacteria are some of the most self-sufficient organisms, since they need only light, CO2, N2, water, and some minerals to grow.
Found in the cyanobacterium Anabaena, they are specialized cells that carry out only nitrogen fixation, while most cells in a filament carry out only photosynthesis.
Metabolic cooperation between different prokaryotic species often occurs in surface-coating colonies known as biofilms. Cells in a biofilm secrete signaling molecules that recruit nearby cells, causing the colonies to grow.
(T/F) Archaea share certain traits with bacteria and other traits with eukaryotes. However, Archaea also has many unique characteristics.
What are Extremophiles and describe the two categories.
Extremophiles – The first prokaryotes assigned to the domain Archaea live in environments so extreme that few organisms can survive there (“lovers of extreme conditions”).
1. Extreme Halophiles – live in highly saline environments, proteins and cell wall of Halobacterium have unusual features that improve function in extremely salty environments
2. Extreme Thermophiles – thrive in very hot environments
Archaea that release methane as a byproduct of their own unique ways of obtaining energy. Many methanogens use CO2 to oxidize H2, a process that produces both energy and methane waste. Among the strictest of anaerobes, methanogens are poisoned by O2.
- inhabit gut of cattle and other herbivores
- important application as decomposers in sewage treatment facilities
What clade do many extreme halophiles and all known mathanogens take part of?
Chemoheterotrophic prokaryotes function as decomposers, breaking down dead organisms as well as waste products and thereby unlocking supplies of carbon, nitrogen, and other elements.
(T/F) Without the actions of prokaryotes and other decomposers such as fungi, all life would cease.
An ecological relationship in which two species live in close contact with each other.
1. Mutualism – an ecological interaction between two species where both benefit
2. Commensalism – an ecological relationship in which one species benefits and the other is unaffected
3. Parasitism – an ecological relationship in which a parasite eats the cell contents, tissues, or blood fluids of its host (parasites that cause disease are known as pathogens – usually prokaryotic)
(T/F) Bacteria cause about half of all human disease.
In the United States, the most widespread pest-carried disease is Lyme disease, which infects 15,000 to 20,000 people each year. Caused by a bacterium carried by ticks that live on deer and field mice, can result in arthritis, heart disease, nervous disorders, and death.
Pathogenic Prokaryotes usually cause illness by producing poisons, which are classified as _____ or _____.
Exotoxins – proteins secreted by certain bacteria (i.e. Cholera)
Endotoxins – lipopolysaccharide components of the outer membrane of gram-negative bacteria, released only when the bacteria die and their cell walls break down (unlike exotoxins)
List three applications of prokaryotes:
1. Bacteria that synthesize and store PHA, which can be extracted and used to make biodegradable plastic products
2. Spraying fertilizers on an oil soaked area stimulates growth of bacteria that metabolize oil
3. Research seeks to develop bacteria that produces Ethanol fuel
Another way to harness prokaryotes is in bioremediation, the use of organisms to remove pollutants from the soil, air, or water (i.e. decomposers of organic sewage matter by anaerobic bacteria and Archaea, oil cleanup, etc.)
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