Microbiology Flashcards
How do eukaryotic and prokaryotic cells differ with respect to organelles?
Eukaryoteshave a nucleus, whereas prokaryotes lack a nucleus, as well as all membrane-bound organelles.
Membrane-bound organelles include mitochondria, lysosomes, the ER, and the Golgi apparatus, but not ribosomes. Prokaryotes do contain ribosomes.
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.
How do eukaryotic and prokaryotic organisms differ in their cellular organisation?
Prokaryotes are always unicellular, while eukaryotes can be either unicellular or multicellular.
How do eukaryotic and prokaryotic organisms differ in the composition of their ribosomes?
Eukaryotic ribosomes are slightly larger, with 80S. Prokaryotic ribosomes have 70S.
Determine if an organism with the following traits is a prokaryote or a eukaryote:
composed of a single cell
linear DNA
has mitochondria
This organism is a eukaryote.
Only a eukaryote would possess mitochondria, since prokaryotes lack membrane-bound organelles. Eukaryotes also have linear, not circular, chromosomes. Note that both eukaryotes and prokaryotes can be unicellular.
Name the two prokaryotic domains.
Archaea
Bacteria
What polymer is the main component of bacterial cell walls?
peptidoglycan
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
transformation
transduction
conjugation
Describe how a bacterium might acquire new genetic material via 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.
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.
Define:
Plasmid
A small piece of circular DNA present in a prokaryotic cell.
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.
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 2 main types of heterotrophs
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.
Define:
chemotaxis
Chemotaxis is the movement of a cell toward a beneficial stimulus or away from a toxic one.
Both prokaryotes and eukaryotes exhibit chemotaxis. For example, human immune cells can move toward the site of an infection.
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.
What macromolecule comprises the viral capsid?
The viral capsid is made from protein.
In some viruses, the capsid is encased within a lipid envelope.
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.
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.
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.
