Viruses Flashcards
Where does the word virus come from?
It comes from the latin word meaning poison
What kingdom to viruses belong to?
They don’t belong to any kingdom as they are not classified as living
What do viruses do that make them non living?
- they do not carry out their own metabolic functions
- they don’t eat
- they can’t reproduce by themselves
- it must be in a cell in order to reproduce
How big are viruses
range from 20 to 250 nm
Virus definition
Viruses are very small infectious particles consisting of nucleic acid enclosed in a protein coat or a capsid and in some cases and membranous envelope
Describe viral acid or genome
It can be either double or single-stranded DNA or double or single strand RNA
Viruses can be classified as either DNA or RNA viruses
What ‘protects’ the virus?
Capsids protect the genome. A capsid is a protein shell
Nucleocapsid or naked viruses
this is a virus that consists of only a capsid
How are viruses classified?
classified by shape based on the capsid - the capsid can have various structures.
Alternative name for a bacteriophage
Phage
Bacteriophage
a virus that infects bacteria
Which virus have the most complex capsid?
Bacteriophages
Which type of virus is most well studied?
Bacteriophages
Viruses infecting animals have these things that help them infect.
membranous envelopes that surround them
Where does viral envelope come from?
It comes from the host cell’s membrane.
What is the viral envelope made out of?
It is made up of both viral and host cell components.
What is the process that creates viral envelopes called?
Budding
Host Range
The types of cells a virus can infect.
For example:
- polio -> only human nerve and intestinal cells
- bacteriophages -> only infect bacteria
- rabies ->infect many mammalian species and even birds in the lab
Where can viruses reproduce?
Viruses can only reproduce within a host cell
Describe the process of viral reproduction
- Entry and uncaoting - The capsid is removed as the nucleic acid enters the cell
- Replication - copies of the nucleic acid are made
- Transcription and manufacture - viral proteins are made from the viral DNA
- Self-assembly - viral nucleic acid, and viral proteins make new viruses that exit from the host cell
Name the two possible reproductive cycles viruses use.
The lytic cycle and lysogenic cycle.
Give examples of viruses that use the Lytic cell.
Ebola, influenza
Describe the Lytic cycle.
The virus reproduces in the cell as more viruses are made it breaks open the host cell, resulting in the death of host cell.
What you call a virus that reproduces using the Lytic cycle.
Virulent
Give examples of viruses that use the lysogenic cycle
HIV, herpes, chicken pox.
Describe the Lysogenic cycle.
- copies the viral genome without destroying the host cell
- viral DNA incorporates into host cell’s chromosome
- the host cell passes the viral DNA to the daughter cell every time it divides
- an environmental signal can trigger the virus genome to exit the host’s chromosome and switch into lytic mode
provirus
the viral DNA that becomes part of the host cell’s chromosome
Temperate viruses
viruses that use both the lytic and lysogenic cycle.
retroviruses
RNA genome viruses
Glycoprotein
the thing sticking out of a virus
Describe the steps of the lytic cycle
- Attachment - a virus recognizes and attaches to a host cell when one of its proteins interlocks with a receptor on the host cell’s plasma membrane
- Entry of phage DNA and degradation of host DNA
- Synthesis of viral genomes and proteins. The host cell uses its own enzymes, raw materials and energy to make copies of viral genomes and viral proteins.
- Assembly - new virus particles are made
- Release - this can occur between 20-40 minutes after attachment and release 50 - 200 viruses
How do retroviruses work?
They use an enzyme called transcriptase to copy their RNA genome into DNA - the double stranded viral DNA is then taken into the host cell’s chromosome and becomes a provirus
