Chapter 20.1 Viruses Flashcards
What is a virus?
a non-living particle that can reproduce only by infecting living cells
What are viruses made up of?
proteins, nucleic acids (genetic material like DNA and/or RNA), and sometimes lipids (fats)
What is a capsid?
protein coat surrounding a virus (sometimes it can have different parts, like the head, tail sheath, and tail fibers)
- some viruses such as influenza have an
additional membrane that surrounds the capsid
What is a bacteriophage?
a type of virus that infects bacteria
What happens in a lytic infection?
inside a living host cell, viral DNA is copied and also translated into viral proteins, new viruses are assembled from these building blocks, and then the viruses “lyse” (destroy) the host cell and escape
What happens in a lysogenic infection?
inside a living host cell, viral DNA becomes part of the host cell DNA and is then called a “prophage”
the prophage may stay part of the host DNA for many host generations, getting copied every time the host cell reproduces
- this may cause disease!
How can a lysogenic infection convert to a lytic infection?
the viral DNA can sometimes come out of the host DNA (it will no longer be a prophage) and can begin the lytic cycle of infection, making new viruses that destroy the host cell
Are viruses alive or not?
NOT!
- not made up of one or more cells
- can only reproduce within a host cell
- do not grow and develop
- do not obtain and use matter & energy
- do not respond to environment
- do not maintain homeostasis
How does a virus enter a host cell?
most viruses have proteins on their surface membrane or capsid that bind to receptor proteins on the cell
- proteins “trick” the cell to take in the virus, or
sometimes, just the genetic material
How do viruses reproduce?
can only reproduce by infecting living cells
How did Wendell Stanley infer that viruses were not alive?
he isolated crystals of tobacco mosaic virus, and living organisms do not crystallize!
Who suggested that tiny particles in the juice can cause disease?
Martinus Beijerinck
“Virus” is the Latin word for what?
poison
Who named viruses “viruses”?
Martinus Beijerinck
What do viruses do once they’re in the cell?
the viral genes are eventually expressed and may destroy the cell
Do most viruses infect only a very specific kind of cell?
Yes!
What do plant viruses infect?
plant cells
What do most animal viruses infect?
only certain related species of animals
What do bacterial viruses infect?
only certain types of bacteria
What happens after a virus infects a cell?
Inside living cells, viruses use their genetic information to make multiple copies of themselves. Some replicate immediately, while others initially persist inactive state within the host.
The two patterns of viral infection are lytic infections and lysogenic infection.
What is a prophage?
bacteriophage DNA that becomes embedded in the bacterial host’s DNA (may remain part of DNA for generations)
Why are viruses parasites?
viruses and parasites depend entirely upon other living organisms for their existence, harming organisms in the process
What do viruses need to do in order to grow and reproduce?
they must infect living cells, taking advantage of the nutrients and cellular machinery of their hosts (this means that viruses are parasites!)
Did viruses develop before or after cells?
because viruses are dependent on living organisms, it seems more likely that viruses developed after living cells
What may the first viruses have been evolved from?
the genetic material of living cells
LYSOGENIC INFECTION
- virus injects DNA into a bacterium
- viral DNA inserts itself into the bacterial chromosome, where it is called a prophage
- prophage may replicate with the bacterium for many generations
- prophage can exit the bacterial chromosome and enter a lytic cycle
- bacterium makes new viral proteins and nucleic acids
- proteins and nucliec acids assemble into new viruses
- viral enzymes lyse the bacterium’s cell wall, new viruses escape and infect other bacterial cells
LYTIC INFECTION
- virus injects DNA into a bacterium
- viral genes are transcribed by the host cell
- bacterium makes new viral proteins and nucleic acids
- proteins and nucleic acids assemble into new viruses
- viral enzymes lyse the bacterium’s cell wall, new viruses escape and infect other bacterial cells
VIRUS
- structure
- reproduction
- genetic code
- growth and development
- obtain and use energy
- response to environment
- change over time
- structure: DNA or RNA in capsid, some with envelope
- reproduction: only within a host cell
- genetic code: DNA or RNA
- growth and development: no
- obtain and use energy: no
- response to environment: no
- change over time: yes
CELL
- structure
- reproduction
- genetic code
- growth and development
- obtain and use energy
- response to environment
- change over time
- structure: cell membrane, cytoplasm, eukaryotes also contain nucleus and many organelles
- reproduction: independent cell division, either asexually or sexually
- genetic code: DNA
- growth and development: yes, in multicellular organisms, cells increase in number and differentiate
- obtain and use energy: yes
- response to environment: yes
- change over time: yes
What is a retrovirus?
an RNA virus that contains RNA as its genetic information
*the genetic information of a retrovirus is copied from RNA to DNA instead of DNA to RNA
What happens when a retrovirus infects a cell?
it makes a DNA copy of its RNA which inserts into the DNA of the host cell
much like a prophage, the viral DNA may remain inactive for many cell cycles before making new virus particles and damaging the cells of the host’s immune system
once activated, it begins to destroy the very system of the body that would normally fight infection
(similar to lysogenic infections)
What happens when cold viruses attack?
a capsid settles on a cell, typically in the host’s nose, and is brought inside where a viral protein makes many new copies of the viral RNA
host cell’s ribosomes mistake the viral RNA for the host’s own mRNA and translate it into capsids and other viral proteins
new capsids assemble around the viral RNA copes and within 8 hours, the host cell releases hundreds of new virus particles to infect other cells
