Name the two prokaryotic domains.
Archaea and Bacteria
Decribe the appearance of the following bacterial types: bacilli, spirilla, and cocci.
Bacilli are long and rod-shaped, cocci are spherical, and spirilla are helical or “spiral-shaped.”
How would the shape of this bacterium be described?
This bacterium is a bacillus, meaning that it is rod-like in shape.
What is a plasmid?
A plasmid is a small piece of circular DNA present in a prokaryotic cell.
Plasmids are extragenomic, meaning that they exist and replicate separately from the main circular chromosome.
What polymer is the main component of bacterial cell walls?
Bacterial cell walls are composed of peptidoglycan.
Note that fungal cell walls are composed of chitin, while plant cell walls are composed of cellulose.
Name and describe the most common form of bacterial reproduction.
Bacteria generally produce offspring via binary fission, a form of asexual reproduction.
Name three methods of bacterial gene transfer.
Bacteria can transfer genes via transformation, transduction, and conjugation.
For the AP Biology exam, remember that binary fission is a mechanism of bacterial reproduction, not gene transfer. It results in an exact copy of the parent organism.
Describe how a bacterium might acquire new genetic material via transformation.
In transformation, a bacterium picks up genetic material from its surroundings and integrates that material into its genome.
Transformation can also be induced for research purposes. Generally, this involves the insertion of a specifically engineered plasmid, called a vector, into the cell.
Describe how a bacterium might acquire new genetic material via transduction.
In transduction, a virus (or bacteriophage) transfers DNA between bacteria during the process of infection.
Usually, a viral capsid will contain only viral DNA or RNA, but it can occasionally can take up host material as well. When a new bacterium is infected, the DNA from the previous host can be integrated into the new host’s genome.
Describe how a bacterium might acquire new genetic material via conjugation.
In conjugation, one bacterium transfers a piece of genetic material to another using a bridge, or sex pilus.
The most common example of conjugation involves a piece of material called the F plasmid. An F+ (plasmid-containing) cell will replicate its F plasmid, then extend a pilus to transfer it to an F- cell.
How do eukaryotic and prokaryotic cells differ in their processes of transcription and translation?
Eukaryotic transcription and translation occur separately, with the first process taking place in the nucleus and the second in the cytoplasm. In prokaryotes, both processes take place in the cytoplasm and can thus occur simultaneously.
Prokaryotic DNA does not contain introns, removing the need for the post-transcriptional splicing that occurs in eukaryotes.
What is a transposon, and where in a bacterial cell could it be found?
A transposon is a DNA sequence with the ability to excise itself from the genome and move to another location.
In both prokaryotes and eukaryotes, transposons are located in the chromosome(s).
The term “polycistronic” refers to a molecule of prokaryotic mRNA that can be translated into multiple proteins.
In contrast, eukaryotic mRNA is monocistronic, meaning that each mRNA molecule codes for a single protein.
What do streptomycin, tetracycline, and ampicillin have in common?
All three are examples of antibiotics.
Experiments described on the AP Biology exam may involve bacterial strains that are resistant to one or more of these chemicals.
What term describes bacteria that can produce their own nutrients from carbon dioxide?
Bacteria that can synthesize their own nutrients are called autotrophs.
This term is not limited to prokaryotes; for example, most plants and many species of algae are autotrophic.
Name the two main types of autotrophs.
Autotrophs can be divided into photoautotrophs and chemoautotrophs.
Photoautotrophs use sunlight to gain energy via photosynthesis, while chemoautotrophs use the oxidation of inorganic compounds. Both groups build macromolecules from carbon dioxide.
What term describes bacteria that need to obtain nutrients by consuming organic compounds?
Bacteria that must consume external organic compounds are called heterotrophs.
Like autotrophs, heterotrophs include more than simply bacteria. Humans, for example, are heterotrophic.
Name the two main types of heterotrophs.
Heterotrophs can be divided into photoheterotrophs and chemoheterotrophs.
Photoheterotrophs use sunlight to gain energy via photosynthesis, while chemoheterotrophs use the oxidation of inorganic compounds. However, both groups need to consume organic macromolecules to obtain carbon.
What group of bacteria cannot survive in the presence of oxygen?
Obligate anaerobes die in the presence of low to moderate oxygen concentrations. As such, they can only undergo anaerobic metabolism.
The term “obligate” means that a strain has to undergo a specific process. Obligate aerobes, then, can only use aerobic respiration.
What group of bacteria can survive in either oxygen-rich or oxygen-poor environments?
Facultative anaerobes can use either aerobic or anaerobic respiration, depending on the presence of oxygen.
E. coli sometimes uses the process of fermentation, and is able to survive outside the body for a significant period of time. What term best describes the metabolism of E. coli?
E. coli is facultatively anaerobic.
Fermentation, whether lactic acid or ethanol, is associated with anaerobic metabolism. However, if the strain can survive outside the body, it must not be killed by the presence of oxygen, as an obligate anaerobe would be.
What is the defining characteristic of a virus?
A virus can only replicate when inside a host cell. Viral replication, transcription, and translation all require use of the host cell’s machinery.
Since they are not composed of one or more cells, viruses are not classified as living organisms.
With regard to size, how does a viral particle compare to a bacterial or eukaryotic cell?
Viruses are significantly smaller than prokaryotes, which in turn are smaller than eukaryotic cells.
Though viruses vary in size, the largest are around 250 nanometers in diameter. In comparison, bacterial cells can be several micrometers in length.
Label the following parts of a virus on the diagram below: capsid, nucleic acid, tail sheath, tail fibers.
What macromolecule comprises the viral capsid?
The viral capsid is made from protein.
In some viruses, the capsid is encased within a lipid envelope.
A student concludes that a certain viral particle contains single-stranded DNA, ribosomes, a nuclear membrane, and enzymes. Assuming that the particle actually is a virus, about which of these structures must he be wrong?
The student must be wrong about ribosomes and the nuclear membrane. Viral particles do not contain a nucleus or any other organelles.
Viruses can contain either single- or double-stranded DNA or RNA, as well as enzymes like reverse transcriptase.
A certain virus contains a single-stranded RNA genome. Upon infection, it transcribes this material back into DNA. What name is given to this type of virus?
This virus is a retrovirus.
Retroviruses undergo the process of reverse transcriptase, in which they transform RNA into DNA to be integrated into a host genome. For this purpose, they contain the enzyme reverse transcriptase.
Name one common example of a retrovirus.
The most commonly mentioned retrovirus is the human immunodeficiency virus, or HIV.
HIV infects helper T cells, resulting in a damaged immune system.
A certain virus infects E. coli. How would this virus be classified?
The virus is a bacteriophage.
A bacteriophage is a virus that infects bacterial cells, such as E. coli. Experiment-based passages will sometimes shorten this to “phage.”
How does a bacteriophage infect a host cell?
Using its tail fibers, the phage attaches to the outside of the bacterial cell. Genetic material is then injected through the sheath and into the bacterium.
Note that the majority of the viral particle, including the capsid, never enters the host cell! New capsid proteins are assembled in the infected host cell.
How does an animal virus (such as those that infect humans) infect a host cell?
Viruses that infect eukaryotes enter the cell either by fusing with the cell membrane or via endocytosis.
Before infection can occur, the virus must identify the host cell using receptors on the cell surface.
Explain the difference between the lysogenic and lytic cycles.
In the lysogenic cycle, viral DNA is integrated into the genome of the host, remaining in a fairly harmless state. In the lytic cycle, the virus replicates and lyses, or kills, the host cell, releasing new viral particles.
Viruses in the lysogenic cycle, known as prophages, generally progress into the lytic cycle after certain events trigger this change.
A prophage is a virus that exists within the bacterial genome in a temporarily harmless state.
Prophages are found during the lysogenic cycle, in which viral genetic material integrates into the bacterial chromosome without immediately lysing the host cell.
What factors might cause a virus to move from the lysogenic to the lytic phase?
Damaging factors such as UV light and free radicals trigger progression into the lytic phase.
In other words, viruses often leave the lysogenic phase when outside events signify a stressful or unsafe environment.
If virally infected cells are dying, the virus must be in which phase?
The virus must be in the lytic phase.
The lytic phase is the state in which a virus lyses, or kills, the host cell.
Some species of the bacterial genus Legionella live in human cells, often causing a severe lung disease. What symbiotic relationship do these organisms display?
The relationship between Legionella and humans is an example of parasitism.
Unlike mutualism or commensalism, parasitism involves the harm of one species involved. Here, humans suffer while Legionella benefits.