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
What does polyphyletic mean?
means the virus has a few independent origins
What is the virus-first theory?
suggests that viruses evolved before or co-evolved with their current host cells
What is the escaped genes theory?
suggests that viruses arose from genetic elements that gained the ability to move between cells.
What is the regressive theory?
suggests that viruses are remnants of cellular organisms
Why do viruses evolve so fast?
due to mutations which are a natural by-product of viral replication
What does antigenic drift mean?
small changes caused by mutations in viral genes that can lead to changes in the surface proteins of a virus
What does antigenic shift mean?
an abrupt, major change in a virus maybe resulting in a new influenza A subtype
What is a retrovirus?
a virus that has RNA as its nucleic acid and uses the enzyme reverse transcriptase to copy its genome into the DNA of the host cells chromosome
What is reverse transcriptase?
an enzyme found in HIV and other retroviruses that is used to convert RNA into viral DNA in a process called reverse transcription
What is a provirus?
a virus that has integrated into a host’s genome and is replicated when the cell replicates its DNA
