A2.3: Viruses Flashcards
List structural features common to all viruses.
- Nucleic acid as genetic material (RNA/DNA - either single or double stranded)
- Capsid made of protein
- NO Cytoplasm or Plasma Membrane
Explain why viruses are said to be nonliving
- They aren’t made of cells
- They can’t undergo self-replication
- They can’t perform independent metabolism
What is the genetic code said to be in cells and viruses?
- Universal; it is shared between viruses and living organisms
State an alternate name for viruses
Obligate intracellular parasites
Compare the size of viruses to bacterial cells and eukaryotic cells
Viruses are larger than bacterial cells and eukaryotic cells
What microscope can allow for viruses to be viewed
As they are too small to be seen by a light microscope, an electron microscope is used as it has a higher resolution and larger magnification
Outline the diversity of structure in viruses, including genetic material and the presence or absence of envelopes.
- Viruses can contain either RNA or DNA that is either single stranded or double-stranded
- Viral genomes can vary in the size as they have different number of genes
- Some viruses contain an extra layer of protection, outside the capsid called an envelope, of the viral genome and helps disguise the virus from the immune system of the host cell
Where is the envelope acquired from
-The host cell membrane when it is released
Characteristics of non-enveloped viruses?
- More resistant to extreme pH, heat, dryness etc
Characteristics of enveloped viruses?
- More sensitive to extreme pH, heat, dryness etc
Outline what positive-sense RNA is
-It is viral mRNA which can be directly translated into virus proteins
Outline what negative-sense RNA is
-RNA that must be transcribed first before being translated into virus proteins
Outline what Retroviruses are
- Retroviruses have RNA that is first reverse transcribed to make DNA which is transcribed and translated to make virus proteins
Outline what DNA Viruses are
- DNA Viruses are transcribed and translated to make virus proteins
Structure of bacteriophage lambda
- Icosahedral-shaped capsid head
- Double stranded DNA
- Short collar, tail and tail fibres to attach to the cell
- Virus contains enzymes (holin too which helps the bacteriophage to make holes in the cell wall of the bacterium)