18 Questions
What is the main criteria for a microorganism to be considered 'pathogenic'?
Satisfying Koch's postulates
What drives key chemical cycles on Earth?
Beneficial bacteria
Are viruses considered 'alive'? Why or why not?
No, because they can only survive inside other living cells
Which classification method is NOT mentioned for viruses in the text?
Chemical activity
What distinguishes viruses from cellular organisms?
Their lack of cellular structure and independent metabolism
What did Robert Koch contribute to the understanding of diseases?
Proposing criteria to identify pathogenic bacteria
What factor makes it difficult to determine the phylogeny of viruses?
Rapid mutation rate and evolution
Which type of viruses may have evolved repeatedly from single-stranded RNA ancestors?
Negative-sense RNA viruses
What is a distinguishing characteristic of positive-sense single-stranded RNA viruses?
Production of cDNA from RNA genome
Which group of viruses is known for reproducing by reverse transcription?
Retroviruses
What distinguishes negative-sense RNA viruses in terms of RNA structure?
Single strand RNA is the complement of mRNA
Why does the tiny size of viral genomes restrict the analyses that can be done on viruses?
"Analysis tools cannot effectively interact with small viral genomes"
What is one key difference between the lytic and lysogenic cycles of a virus?
The lytic cycle involves immediate replication of the virus, while the lysogenic cycle can lay dormant within the host cell.
How do bacteriophages differ from other viruses?
Bacteriophages infect bacteria cells specifically, while animal viruses infect plant cells.
Why are some viruses considered non-cellular and not 'alive'?
Because they do not have a cellular structure or independent metabolism.
What is a characteristic feature of bacteriophages in terms of their infection specificity?
Bacteriophages can only infect specific types of bacteria cells.
How do bacteriophages enter host cells during the infection process?
By binding to specific receptor proteins on the host cell.
What distinguishes RNA viruses from DNA viruses in terms of their replication process?
RNA viruses translate their genes to produce viral proteins by the host, while DNA viruses incorporate their genome into host genome.
Study Notes
Pathogenicity of Microorganisms
- A microorganism is considered pathogenic if it causes disease in a host organism.
Chemical Cycles on Earth
- Key chemical cycles on Earth are driven by microorganisms.
Viruses and Life
- Viruses are not considered "alive" because they are unable to replicate or metabolize on their own.
- Viruses require host cells to replicate and complete their life cycle.
Classification of Viruses
- The following classification methods are used for viruses: morphology, genome type, and host range.
- The method not mentioned for virus classification is biological transmission.
Distinctions between Viruses and Cellular Organisms
- Viruses are distinguished from cellular organisms by their inability to replicate or metabolize on their own.
Contributions of Robert Koch
- Robert Koch contributed to the understanding of diseases by proposing the "gold standard" for determining the cause of an infectious disease.
Phylogeny of Viruses
- The phylogeny of viruses is difficult to determine due to their high mutation rates and high rates of genetic recombination.
Evolution of Viruses
- Single-stranded RNA viruses, such as picornaviruses, may have evolved repeatedly from single-stranded RNA ancestors.
Characteristics of RNA Viruses
- Positive-sense single-stranded RNA viruses have a genome that can be translated into protein directly.
- Negative-sense RNA viruses have a genome that must be transcribed into complementary RNA before it can be translated into protein.
- Retroviruses are a group of viruses that reproduce by reverse transcription.
Viral Genomes
- The tiny size of viral genomes restricts the types of analyses that can be done on viruses.
Lytic and Lysogenic Cycles
- The lytic cycle of a virus involves the production of new viral particles and the eventual lysis of the host cell.
- The lysogenic cycle involves the integration of the viral genome into the host genome, followed by the production of new viral particles without the lysis of the host cell.
Bacteriophages
- Bacteriophages are viruses that infect bacteria.
- Bacteriophages differ from other viruses in their specificity for bacterial hosts.
- Bacteriophages enter host cells during the infection process through specific interactions between the phage and the host cell surface.
- Bacteriophages have a high degree of specificity for their host cells.
Replication of RNA and DNA Viruses
- RNA viruses replicate their genomes through the synthesis of complementary RNA.
- DNA viruses replicate their genomes through the synthesis of complementary DNA.
Test your knowledge on bacteria, archaea, and viruses with this quiz. Learn about the classification of bacteria, Koch's postulates, the role of bacteria in Earth's chemical cycles, and an introduction to viruses.
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