Chapter 19 - genetics of viruses and bacteria Flashcards
1
Q
what is a virus
A
- a small infectious particle that consists of nucleic acid enclosed in a protein coat
- some have a viral envelope derived from the plasma membrane of the host cell
- viroids are more primitive than viruses
2
Q
what are some characteristics of viruses that can vary
A
- host range
- structure
- genome composition
3
Q
host range
A
- the number of species and cell types that can be infected
- viruses can’t live on their own so they take up various types of host cells
4
Q
Viral structure
A
- all viruses have a capsid
- capsid can vary in shape and complexity
- some have viral envelopes
- different spike glycoproteins define how it interacts with the host
5
Q
capsid
A
- protein coat enclosing a virus’s genome
6
Q
viral envelope
A
- structure enclosing a viral capsid that consists of a membrane derived from the plasma membrane of the host cell
- embedded with virally encoded spike glycoproteins
7
Q
Viral genomic differences
A
- can have DNA or RNA
- can be single stranded or double stranded
- linear vs circular
- nucleotide length varies significantly
8
Q
are viruses alive?
A
- NO
- they are not cells or composed of cells
- cannot carry out metabolism on theirownb
9
Q
6 basic steps of the viral reproductive cycle
A
- attachment
- entry
- integration
- synthesis of viral components
- viral assembly
- release
- looks different for different viruses
10
Q
Attachment in viral reproductive cycle
A
- first step of viral reproductive cycle
- usually specific to one kind of cell
- due to binding of specific molecules on the cell surface
11
Q
Entry in the viral reproductive cycle
A
- second step
- bacteriophage inject only the DNA into bacteria
- viruses like HIV fuse with the plasma membrane to enter
- one or several viral genes are expressed immediately
virus can either: - synthesize viral components
- integrate into host chromosome
12
Q
integrase
A
- enzyme coded for by some viruses that catalyzes the integration of the viral genome into a host-cell chromosome
13
Q
integration in viral reproductive cycle
A
- third step
- uses integrase to insert viral genome into chromosomal DNA
- RNA viruses (like HIV) use reverse transcriptase to make it DNA
14
Q
prophage
A
- the DNA of a phage that has become integrated into a bacterial chromosome
- occurs during integration step
15
Q
reverse transcriptase
A
- enzyme that catalyzes the synthesis of viral DNA starting with viral RNA as a template
- used to integrate it into the chromosomal DNA
18
Q
Synthesis of viral components in viral reproductive cycle
A
- 4th step
- host cell enzymes make copies of the phage DNA
- transcribes the genes in the DNA into mRNA
- in HIV, DNA isn’t excised, it’s transcribed in the nucleus
- makes many copies of viral RNA
- translated to make viral proteins
- serves as genome for new viral particles
19
Q
viral assembly in the viral reproductive cycle
A
- 5th step
- some viruses self-assemble
- some are too complicated to self-assemble
- require other proteins to either modify capsid proteins or serve as scaffolding to assemble the capsid
20
Q
release
A
- 6th step
- phages must lyse their host cell to escape
- enveloped viruses bud from the host cell
22
Q
lysogenic cycle
A
- integration, replication, and excision
- prophage DNA gets copied as the cells divide
23
Q
Lytic cycle
A
- Synthesis, assemble, and release
- new phages are synthesized in the cell
- causes the host cell to lyse, releasing the new phages and allowing them to bind to another cells
