A2.3 Flashcards
Viruses
Are viruses obligate parasites?
yes
What is an obligate parasite?
An organism that requires other living host cells to reproduce
What are the features all viruses have in common?
- extremely small with a fixed size range of 20-400nm in diameter
- have nucleic acid (DNA or RNA) as their genetic material
3.a capsid made of protein surrounds the nucleic acid
4.no cytoplasm - few or no enzymes
What is a virus?
a non-cellular parasite of animals, plants and bacteria that consists of nucleic acid surrounded by a protein coat (a capsid)
What is a bacteriophage?
a virus that infects bacteria
What is adenovirus?
a DNA virus that causes an eye disease
Where can the nucleic acid be replicated in RNA viruses?
either in the cytoplasm e.g. SARS-CoV-2 or in the nucleus e.g. influenza
What are some RNA viruses?
coronavirus or HIV
What is positive sense RNA?
Viral RNA that has the same base sequence as mRNA, this allows it to function as a template for protein synthesis during virus replication
What is a capsid?
the protein coat enclosing the viral genome. Comes in a variety of shapes such as helical, conical, and polyhedral
What is negative sense RNA?
viral RNA that is complementary to mRNA and so it cannot be directly encoded for potein synthesis but it must be converted to positive sense by RNA polymerase before translation
Is the nucleic acid single or double stranded in viruses?
some viruses have single stranded nucleic acid such as hepatitis E and some have double stranded nucleic acid such as HIV and SV-40
What is the viral envelope?
Some viruses can be classified as enveloped and others non-enveloped, the viral envelope encloses the nucleocapsids of many viruses that infect animals.
What is a capsomere?
one of the individual proteins that make up a capsid
What are the capsids of the bactereophages like?
they have elogenated icosahedral heads which are made of equilateral triangles fused together in a spherical shape forming a 20 sided structure
What is a nucleocapsid?
the capsid of a virus with an envelope
What is a virion?
an isolated but infectious virus particle found inside the host cell
What are the stages of viral reproduction?
attachment
entry
replication of viral genome
transcription of mRNA and protein synthesis using host cell ribosomes
maturation and assembly of viruses and release from host cell
Can viruses carry out life processes independently?
no they cannot, they rely on their host cell for energy supply, nutrition, protein synthesis and other life functions
What is the lytic life cycle?
a phage life cycle where it attaches to a host, injects its DNA which undergoes replication to form new virions which then lyse the cell
What does lysis mean?
breakdown, typically of cells
What is the lysogenic life cycle
a phage life cycle where it attaches to a host, injects its genome and becomes resident within the cell where it replicates alongside it
What is a prophage?
a bacteriophage in an inactive state in which the genome is typically integrated into the chromosome of the host
Do viruses have one common ancestor?
it is highly unlikely that viruses have a common ancestor
