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Gram-positive bacteria:
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2 steps5b)
Gram-positive bacteria:
- Have a thick peptidoglycan layer in their cell wall.
- Lack an outer membrane.
- Retain the crystal violet stain and appear purple after Gram staining.
- Examples: Staphylococcus aureus, Streptococcus pyogenes.
Gram-negative bacteria:
- Have a thin peptidoglycan layer in their cell wall.
- Possess an outer membrane containing lipopolysaccharides (LPS).
- Do not retain the crystal violet stain and appear pink or red after Gram staining.
- Examples: Escherichia coli, Salmonella typhi.
5c)
Koch's Postulates:
- The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.
- The microorganism must be isolated from a diseased organism and grown in pure culture.
- The cultured microorganism should cause disease when introduced into a healthy organism.
- The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.
5d)
Four examples of culture media:
- Nutrient Agar (general purpose)
- Blood Agar (enriched, differential)
- MacConkey Agar (selective, differential)
- Mannitol Salt Agar (selective, differential)
5e)
A bacterial growth curve illustrates the change in the number of viable bacterial cells in a population over time when grown in a batch culture. It typically consists of four phases:
- Lag phase: Bacteria adapt to the new environment; little to no cell division occurs.
- Log (exponential) phase: Cells divide rapidly at a constant rate, leading to exponential increase in population size.
- Stationary phase: The rate of cell division equals the rate of cell death due to nutrient depletion and waste accumulation, resulting in a plateau in population size.
- Death (decline) phase: The rate of cell death exceeds the rate of cell division, leading to a decrease in the number of viable cells.
6a)
Bacteriophages are viruses that infect and replicate within bacteria and archaea. They are composed of genetic material (DNA or RNA) enclosed in a protein shell called a capsid.
6b)
Determine the number of generations ().
The formula for bacterial growth is , where is the final number of cells, is the initial number of cells, and is the number of generations.
Given: cells, cells.Divide both sides by 1000:
To solve for , take the logarithm base 2 of both sides, or use common logarithms:
Calculate the generation time ().
Generation time is the time it takes for a population to double, calculated as , where is the total time.
Given: minutes.The generation time is approximately .
6c)
Four differences between lytic and lysogenic cycles:- Fate of Host Cell: In the lytic cycle, the host cell is lysed (destroyed) to release new virions. In the lysogenic cycle, the host cell is not immediately destroyed; the viral DNA integrates into the host genome.
- Viral DNA Integration: In the lytic cycle, the viral DNA remains separate from the host genome. In the lysogenic cycle, the viral DNA (prophage) integrates into the host bacterial chromosome.
- Replication: In the lytic cycle, the viral genome replicates independently and produces new viral particles. In the lysogenic cycle, the integrated prophage replicates along with the host chromosome during cell division.
- Prophage/Provirus State: The lytic cycle does not involve a prophage stage. The lysogenic cycle is characterized by the presence of a prophage, which can remain dormant for many generations.
6d)
One function for each:
i. Capsid: Protects the viral genetic material (DNA or RNA) and aids in the delivery of the viral genome into the host cell.
ii. Plasmid: Carries non-essential but often beneficial genes (e.g., antibiotic resistance, virulence factors) that can be transferred between bacteria.
iii. Ribosomes: Sites of protein synthesis (translation) in both prokaryotic and eukaryotic cells.
iv. Pili: Involved in bacterial conjugation (transfer of genetic material between bacteria) and attachment to surfaces.
v. Capsules: Provide protection against phagocytosis by host immune cells and aid in adhesion to surfaces.
vi. Flagella: Provide motility, allowing bacteria to move through liquid environments.
vii. Fimbriae: Short, hair-like appendages primarily involved in attachment to host cells and surfaces.
viii. Autoclave: Uses high-pressure steam to sterilize equipment and media, killing microorganisms including spores.
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