Introduction to Viruses Flashcards
What are viruses?
Acellular microorganisms (biological) that cannot survive without a host: no metabolic abilities of their own “a borrowed life”
What do viruses rely on?
Completely on biosynthetic machinery of an infected cell to multiply
What is the most abundant biological entity on earth?
Viruses
What are viruses also?
Parasitic entities that hijack molecular resources of the host
What size is viruses?
10-400nm
What do viruses consist of?
2 parts and in some cases a third part
What are the 2 parts of the virus?
genetic material and capsid
What is the genetic material?
Made from either DNA or RNA
What is a capsid?
A protein coat that surrounds and protects the genetic material
What is the third part of a virus?
Envelope of lipids
What does the envelope of lipids do?
Surrounds the protein coat when they are outside the cell
What are capsids made of?
Multiple units of the same protein building block known as capsomers
What are capsomers?
Subunit of the capsid arranged in a precise and highly repetitive pattern around the nucleic acid
How many types of symmetry is there for capsids and capsomers?
3
What are the 3 types of symmetry?
Helical, icosahedral and complex
What is the helical arrangement?
Nucleic acid within helical structure of capsomers
What is the size of helical?
18x250nm
What is icosahedral?
20 face polyhedron- each face is an equilateral triangle-icosahedron
What is the size of icosahedral?
70-90nm diameter
What is complex?
The head has icosahedral symmetry and tail is helical
What is the size of complex?
80x225nm
What is the viral genome made up of?
Nucleic acid (DNA or RNA)
What could the viral genome be?
linear, circular or segmented
What can the sizes of the viral genome vary from?
4,000 to 1 million nucleotides (3 genes to 100-1000)
What possible forms of RNA and DNA are found in viruses?
Single stranded and double stranded RNA and DNA
What do viruses infect?
All cell types ad all forms of life
What is the host organism?
An organism a virus infects
What is the host cell?
A cell a virus multiplies in
What are bacteriophages?
Viruses that infect and replicate in bacteria
What were bacteriophages heralded as?
A potential treatment for diseases such as typhoid and cholers
What are the types of bacteriophage infections in bacteria?
Lytic infection (virulent) and Lysogenic infection
What happens in lytic infection?
Host cell dies
What is the first step of lytic infection?
Attachment
What happens after attachment?
Entry of phage DNA and degradation of host DNA
What happens after entry of phage DNA and degradation of host DNA?
Synthesis of viral genomes and proteins
What happens after synthesis of viral genomes and proteins?
Self assembly (complex and highly regulated)
What happens after self assembly?
Release
What is the burst size?
100-200 particles
What is the length of the lytic cycle?
20-30 minutes
What happens in lysogenic infection?
Host cell survives
What is the first step of lysogenic infection?
Phage DNA integrates into bacterial chromosome»_space; prophage
What happens after phage DNA integrates into bacterial chromosome?
Phage genome is silent- transcription of prophage genes is inhibited - does not kill the host
What happens after phage genome is silent- transcription of prophage genes is inhibited - does not kill the host?
Prophage is copied with bacterial chromosome
What happens after prophage is copied with bacterial chromosome?
Many cell divisions create many infected bacteria (daughter cell with prophage)
What happens after many cell divisions create many infected bacteria (daughter cell with prophage)?
Occasionally, a prophage exits the bacterial chromosome initiating a lytic cycle
What happens first in the HIV life cycle?
Entry and removal capsid proteins
What happens after entry and removal of capsid proteins?
Synthesis of a DNA strand complementary to the viral RNA
What happens after synthesis of a DNA strand complementary to the viral RNA?
Incorporation of double stranded DNA into the cells DNA
What happens after incorporation of double stranded DNA into the cells DNA?
Transcription of proviral genes and manufacture of viral proteins
What happens after transcription of proviral of double stranded DNA into the cells DNA?
Assembly of new virus particles
What happens after assembly of new virus particles?
Exit of new virus particles from the cell
