2.2Prokaryotic Cells And Viruses Flashcards
How are viruses classified
According to structure and type of nuclei acid
Name 3 types of virus and give examples
DNA virus eg lambda phage
RNA virus eg tobacco mosaic virus and Ebola
RNA retrovirus eg human
Immunodeficiency virus (HIV)
Describe the structure of a DNA virus
Nucleic acid: DNA (which can act directly as a template for mRNA transcription/ DNa replication)
Geometrical shape
Protein coat (capsid)
Viruses can have membranes- the surfaces have attachment proteins (viral antigens)which allow the virus to attach to the host cells
Compare and contrast the tobacco mosaic virus and Ebola
Both are RNA viruses
Tobacco mosaic virus contains ssRNA, which can be directly be translated into proteins by ribosomes
Ebola contains negative ssRNA, which needs to be transcribed to produce mRNA before translation
Describe the features of an RNA retrovirus
Single strand of RNA
Reverse transcriptase enzyme produces cDNA from RNA template
Double-stranded viral DNA integrates into host cell’s genome
Describe the lysogenic pathaway
1.Non-virulent viruses inject DNA into host cell DNA as provirus. Viral DNA replicates when host cell divides.
2. Virus produces repressor proteins to inhibit transcription.
3. Latent virus enters lytic pathway when host cell is damaged or immune system weakens.
Describe lyctic cycle
- virus attaches to host cell. Viral genetic information replicates immediately.
- Many virions assemble, causing cell lysis
Why are viruses classsified as non-living
They are acellular: no cytoplasm, no metabolism and cannot self-replicate
How do antivirals work?
Viruses have no metabolism = difficult to treat infection after initial contact. Antivirals inhibit viral replication by:
Targeting viral antigens to prevent entry into host
Targeting viral enzymes to prevent DNA replication and virion assembly
What is the focus of disease control for viral infections?
Prevent spread (especially when there is no effective vaccine).
Outline what happened during 2014 Ebola outbreak
Virus spread rapidly through areas of west Africa with poor hygiene. 4877 deaths. No effective vaccine, so disease control measures aimed to reduce spread
Outline common methods of controlling viral outbreaks
- Rapid indentification and testing the individuals contacts for disease
- reduce peer to personal contact with virus:
B) Quarantine
Sterilisation of equipment
Protective clothing
Suggest the ethical issue surrounding the use of untrialled drugs during epidemics
Severity of outbreak
How effective other avliable treatments are
Difficulty obtaining informed consent
Suggest arguments against the use of untrained drugs during epidemics
Unanticipated severe side effects
Difficult to decide which individuals to treat first
Drug may be falsely attributed as the cause of death
Severely ill patients cannot give informed consent
Structure and function of pili
Hair-like structures which attach to other bacterial cells and allow plasmids to move from cell to cell
Structure and function of flagellum
Tail like structures which attach to other bacterial cells and allow plasmids to move from cell to cell
What are 70s ribosomes composed of?
Composed of a large (50S) subunit and a small (30S) subunit. The site of protein synthesis
Structure and function of cell wall (bacterial)
The cell’s rigid outer covering made of peptidoglycan. Provides the cell with strength and support.
Since the contents of bacterial cells are usually hypertonic to the medium around them, water tends to move into the cells by osmosis.
Th cell wall prevents the the cell from swelling and bursting.
what is the nucleoid
irregularly-shaped region of cytoplasm where loop of bacterial DNA is located
What is a plasmid
1 or more rings of DNA found in some bacterial cells contains non-essential genes(not needed for the survival of bacteria) can be exchanged between bacterial cells via conjugation
describe the structure of a bacterial cell wall and slime capsule
peptidoglycan(murein) cell wall provides mechanical strength may be coated by slime layer to prevent desiccation(drying) ,adhere cells and provide nutrients
outline process of gram staining
- fixation-imobalises bacteria and makes it more permeable to dyes
- crystal violet dye-absorbed by peptidoglycan
- iodine solution forms crystals in violet dye
- decorization- alcohol gram positive will be clear as dyes will be washed out. gram negative will stay purple as peptidoglycan has more layers
- add red safranin to make negative appear red and examine under microscope
describe gram positive cell walls
have thicker layer of pepidoglycan (insoluble in alcohol) purple under microscope when stained
describe gram negative cell walls
thinner layer of petidoglycan with outer lipopolysaccharide membrane(surface membrane) (alcohol-soluble)
appear red under microscope when stained
