Microbiology Flashcards
What are the general characteristics of fungi?
Fungi are eukaryotic chemoheterotrophic organisms that absorb food and nutrients through chitinous cell walls. They can be either unicellular (yeast) or multicellular (mold, mushrooms) and may reproduce either sexually or asexually.
What are the functions of the mycelium of a fungi?
A mycelium absorbs nutrients, aids in decomposition of organic matter, and is involved in fungal growth and reproduction.
Describe what occurs during:
the asexual reproductive cycle of fungi
In many fungi, asexual reproduction occurs in the sporangium (n) found on the cellular walls of reproductive hyphae cells of the mycelium (n). Haploid spores (n) are formed in the sporangium by mitotic divisions and then released to germinate on a suitible substrate. Fungi may also undergo budding and fragmentation.
Describe what occurs during
the sexual life cycle of fungi
Viruses are considered non-living because they…
- Lack both organelles and a cytoplasm
- Do not respond to external stimuli
- Do not grow by increasing in size
- Are unable to independently undergo metabolic functions and instead replicate using the host’s metabolic machinery
Define
virion
a complete extracellular viral particle composed of a capsid-enclosed viral genome and in some cases a tail region and/or an envelope
The capsid region of a virus may contain either ____ or ____ but not both.
DNA; RNA
The image depicts a typical bacteriophage, with a capsid head region containing either single stranded or double stranded DNA or RNA and a protein tail region.
Compared to bacteria and animal cells, viruses are ____ in size and additionally lack both a ____ and ____.
smaller; cytoplasm; organelles
Define:
bacteriophage
a virus that infects bacteria, recognizable by its capsid head region (which encloses the viral genome) and its distinct protein “tail” region (which gets the genome through the bacterial cell wall)
Define:
capsid
protein coat surrounding viral genome that has a polyhedral or helical structure
Define:
<font><span>viral envelope</span></font>
a bilayer lipid membrane, made up of both viral and host proteins, which encloses the capsid and plays a major role in infection and pathogenisis
Viruses can be classified in 4 general categories, based on whether they have…
DNA:
- ssDNA (single stranded)
- dsDNA (double stranded)
RNA:
- ssRNA (single stranded)
- dsRNA (double stranded)
A virus cannot perform its own metabolic functions, therefore it must [insert phrase] in order to reproduce.
utilize the metabolic machinery of the host cell in order to reproduce.
The six basic stages in the lytic viral life cycle are:
- Adsorption
- Penetration
- Uncoating
- Protein Synthesis/Replication
- Maturation
- Release
Describe what occurs during:
the adsorption stage of the lytic viral life cycle.
During the adsorption stage the virus attaches itself to the membrane of a host cell. Viral attachment proteins recognize specific receptors on the outside of the cell, therefore only cells that have the appropriate receptors are susceptible to viral attack. For enveloped viruses adsorption may also occur through fusion or endocytosis.
Define:
endocytosis
a form of active transport in which substances enter the cell enclosed in vacuoles/vesicles formed from the cellular cytoplasmic membrane
Identify the process in the image below:
The image depicts the adsorption stage of the life cycle of an HIV virion. HIV is in the process of attaching to the CD4 receptor on the plasma membrane of a T-cell.
Describe what occurs during:
the penetration stage of the lytic viral life cycle.
During the penetration stage the virus infiltrates the host cell. Enveloped viruses may either fuse with the plasma membrane or enter using an endosome. Non-enveloped viruses may either cross the plasma membrane directly or be taken in by an endosome.
Describe what occurs during:
the uncoating stage of the lytic viral life cycle
During the uncoating stage, proteolytic enzymes remove the capsid from the nucleic acid of the virus. This stage always occurs in the cytoplasm of the host cell because this is where proteolytic enzymes are found.
The uncoating stage of the lytic viral life cycle occurs in the…
cytoplasm of the host cell
The eclipse period occurs between what two stages of the lytic viral life cycle?
uncoating and maturation stages
Define:
eclipse period
the period between the end of the uncoating and the beginning of the maturation stages in the viral life cycle in which no intact infectious virions are seen within the host cell
Describe what occurs during
the protein synthesis stage of the lytic viral life cycle
During the protein synthesis stage, viral nucleic acids and proteins are replicated and viral parts are synthesized using the metabolic machinery of host cell (ie. ribosomes, tRNA, mitochondria, golgi apparati, enzymes, etc). The virus is not infectious as this stage occurs during the eclipse period.
Where does the protein synthesis stage occur in most DNA viruses? How about RNA viruses?
DNA viruses: occurs mostly in the nucleus of the host cell
RNA viruses: occurs solely in the cytoplasm of the host cell
Describe what occurs during:
the maturation stage of the lytic viral life cycle
During the maturation stage, viral parts, such as the capsid, completed during the protein synthesis stage, are assembled around the replicated viral genome. The exact assembly process differs for enveloped and non-enveloped viruses.
For enveloped viruses, what happens during the maturation stage?
During the maturation stage, a capsid is formed around the viral genome and viral envelope glycoproteins are transported to and embedded in the plasma membrane of the host cell.
Compared to events occurring during the maturation stage of enveloped viruses, what DOES NOT happen during the maturation of non-enveloped viruses?
The maturation of non-enveloped viruses does not involve the transport of glycoproteins to the cytoplasmic membrane of the host cell, a process that occurs during the maturation of enveloped viruses.
For non-enveloped viruses, what happens during the maturation stage?
During the maturation stage, a capsid is formed around the viral genome.
Describe what occurs during:
the release stage of the lytic viral life cycle
During the release stage, the newly replicated assembled viruses exit the cell. Typically, non-enveloped viruses are released by lysis and enveloped viruses exit by budding from the cytoplasmic membrane of the host cell.
Compare the lytic and lysogenic viral life cycles.
Lytic cycle:
results in the immediate production of virulent (infectious) viruses; occurs in both eukaryotes and prokaryotes
Lysogenic cycle:
viruses lie latent within host cells and are passed on in subsequent cell divisions until the lytic cycle is triggered at a later time; occurs mostly in bacteria/prokaryotes
Define:
<font><span>lytic viral life cycle</span></font>
a six step replication pathway in which the virus rapidly multiplies within the cell and is released by cell lysis or budding
Define:
lysogenic viral life cycle
The lysogenic viral life cycle is a replication pathway in which the viral genome is incorporated with host cell DNA. This provirus lies latent and replicates during subsequent host cell divisions until an event triggers the lytic cycle releasing virions from a multitude of infected cells.
Define:
cell lysis
Cell lysis is degeneration of the cytoplasmic membrane of a cell often due to viral, enzemic or osmotic mechanisms. It can be thought of as “cell bursting”.
Define:
retrovirus
an enveloped RNA virus that contains two identical (+) ssRNA molecules and uses the enzyme reverse transcriptase to transcribe viral RNA into DNA