Viruses Flashcards
What is a virus?
A virus is a non-cellular particle that must infect a host cell to reproduce
Viruses
– are obligatory _________ __________
– that take over the _______ _______ ______ and direct the cell to produce more virus particles.
- obligatory intracellular parasites
– the infected cell’s machinery
A virus particle (______), consists of nucleus acid (___ or ___) contained within a protective coat called a _______
What do they not contain?
- Virion
-DNA or RNA
-capsid
-do not contain ribosomes or ATP generating machinery
What are the 6 general characteristics of viruses?
- Most viruses are very small
- Viruses contain nucleic acid (DNA or RNA)
- Nucleic acid is packaged in a protein coat (capsid)
- Some viruses are enclosed in an envelope
- Some viruses have spikes
- Each species of virus infects a particular group of host species, called the host range
What size is most viruses?
50-100 nm
Nucleic acid can be:
• DNA or RNA
• Single or double-stranded
• Circular or linear
The virus “genome” is usually very small and usually encodes only a few genes.
Name these 3 genes:
• Capsomere (capsid subunits)
• Envelope proteins (if enveloped virus)
• Polymerase (if special polymerase needed)
How many protein coding genes does Influenza A virus have?
11 coding genes
The nucleic acid is packaged in a protein coat called the _____
Capsid
Capsid is made of repeating protein subunits called _______. What do they do?
•capsomeres
• package and protect viral genome
Some viruses are enclosed in an envelope. What is an envelope?
bilayer that surrounding capsid, derived from the host cell membrane
What are enveloped viruses more sensitive to?
Heat or detergents
Virus have spikes. What are spikes? What are they involved in?
• The spikes are glycoproteins (carbohydrate-protein complexes) in the envelope.
• Spikes are involved in attachment to a host cell and escape from a host cell
Each species of virus infects a particular set of host’s. What can they infect?
• Bacteria
• Fungi
• Protozoa
• Plants
• Animals
Most viruses can only infect a specific type of cells within a single host species
What does the HIV virus infect?
HIV (virus) infects T cells (cell type) in humans (host species)
(Define)
- Host Range:
- Tissue tropism:
• Host range: set of species that a particular virus can infect
• Tissue tropism: tissue and/or cell type that virus can infect
Host range and tissue tropism are generally determined by what?
specific host attachment sites on the virus (spikes) and the presence of specific receptors on the host cell
There are 5 steps of Viral Replication (Viral Life Cycles)
What are the steps and give a small description of them:
- recognition/ attachment
• Viruses must contact and adhere to a host cell that can support replication of specific virus - entry
• The viral genome must enter the host cell and gain access to the host cell’s machinery for gene expression - Biosynthesis
• Includes synthesis of both viral genome and virus-specific proteins - Assembly of virions
• Components usually self-assemble spontaneously. - Exit and transmission
• Progeny virions must exit the host cell and reach new host cells and, if multicellular, new hosts to infect
Bacteriophage are viruses that infect bacteria. What kind of temperatures do they withstand? What shape do they have?
They are mostly mesophilic and mildly thermophilic.
Icosahedral head-filamentous tail shape
What are the 5 steps of the lytic cycle of a bacteriophage (Describe each briefly)
- Attachment: Phage attaches to host cell
- Penetration: Phage penetrates and inserts DNA into host cell
- Biosynthesis: Production of phage DNA and phage proteins by the infected cell
- Maturation: Self-assembly of phage particles; virus genome is packaged into capsid
- Release: Phage degrades infected host cell wall; host cell lyses (bursts); new phage particles are released
Define transduction
Transduction is the transfer of DNA from one bacterial cell to another bacterial cell by a bacteriophage
Generalized transduction involves the ______ life cycle of the phage and can move any _____
Lytic life cycle
Gene
(Define)
Virulent phage:
Temperate phage:
• Virulent phage: reproduce only through the lytic cycle, resulting in lysis of the host bacterial cell
– Ex: phage T4
• Temperate phage: can reproduce through the lytic cycle; can also undergo lysogeny, where the phage genome inserts into the host genome
– Ex: phage lambda
What are the 5 steps of the Lysogenic Cycle of a bacteriophage? (Give brief description of each)
- Attachment: Phage attaches to host cell
- Penetration: Phage inserts DNA into host cell
- Integration: Phage DNA integrates into bacterial chromosome by recombination; the integrated phage DNA is called a prophage
– expression of phage genes is repressed
– “lysogenic bacterium” divides normally; prophage is maintained in the
bacterial chromosome
-Phage may carry genes that give host cell an advantage - Excision: Prophage excises from chromosome (phage induction); excision can be stimulated by UV or chemical
- Lytic cycle: Excised phage enters lytic cycle
Specialized transduction involves the _______ life cycle. Moves only genes connected to site of _______ _______
Lysogenic cycle
Prophage insertion
What are The 6 steps of the General Life Cycle of Animal Viruses?
• Attachment:virus attaches to host cell membrane
2. Penetration: virus enters host cell by endocytosis or fusion
3. Uncoating:capsid removed by viral host enzymes
4. Biosynthesis: infected host cell produces viral nucleic acid and viral proteins → * may require viral enzymes* (IMPORTANT)
5. Maturation (or Assembly): viral nucleic acid and viral capsid proteins assemble into virus particle
6. Release: virus escapes host cell-by budding (enveloped viruses), exocytosis, or rupture (lysis)
What are the 3 primary factors determining the life cycle of an animal virus:
DNA viruses (uses host replication machinery)
RNA viruses causes an RNA dependent RNA polymerase to copy their RNA)
Retroviruses
Retroviruses use a _______ ________ to copy the RNA genome into DNA and an ______ to insert the DNA into the host chromosome
Reverse transcriptase
Integrase
All viruses required host cell for ________
Reproduction
What is HPV’s full name?
Human papillomavirus
HPV
Small _______ virus, envelope or no envelope?
Describe the genome:
How many coding genes?
Small icosahedral virus
No envelope
Genome: small, circular, d.s. DNA
- 8 kb, encoding 8 genes
(HPV disease)
Does it go away? Does it need treatment?
Infects _______ cells —-> causes _____ _____
HPV can also integrate into genome of host basal cells (“_____”, similar to Lysogeny) can cause cancers. But what kind?
Can go away on its own
Infects epithelial cells, causes general warts
“Latent” similar to lysoginy
Can cause cervical, penis, anus and throat cancer
HPV (Disease)
How is it transmitted?
How is it prevented?
How many adults are infected with HPV in the U.S?
Direct contact (sex)
Gardasil hpv vaccine, recommended for girls/boys at age 11-12
80% of adults
HPV
Papillomavirus: DNA genome
1. Virion attaches to host cell and is ______
2. Virion travels to ______
3. Viral genome is _______
4. Biosynthesis uses host enzymes. Viral DNA is _____ (nucleus) and translated (______) to produce _____ proteins
5. Assembly occurs in ______
6. Release, Virion are shed as ______ _______ slough off
- Endocytosed
- Nucleus
- Uncoated
- Transcribed (nucleus) and translated (cytoplasm) to produce (capsid) proteins
- Nucleus
- Epithelial cells
Viruses are responsible for ~____ - ____% of human cancers
-15-20%
What cancers do these viruses cause?
- Epstein-Barr virus
-Human papillomavirus (HPV; papilloma – wart)
- Hepatitis B
- Human Herpes Virus-8
• Epstein-Barr virus
-Burkitt’s lymphoma; Hodgkin’s disease
• Human papillomavirus (HPV; papilloma – wart)
-Cervical cancer, head and neck cancers; anogenital cancers
• Hepatitis B virus
-Liver (hepatocellular) cancer
• Human herpes virus-8
-Kaposi’s sarcoma
What are the RNA viruses that contribute to cancer?
Human t-cell leukemia virus
Hepatitis C virus - liver (hepatocellular) cancer
Influenza A virus
(-) or (+) strand RNA virus? _____ genome
______ virus with spikes
(-) negative strand RNA virus, segmented genome
Enveloped virus with spikes
Influenza A virus (disease)
What kind of infection?
Symptoms?
Who does it affect?
___% (36,000) of US population infected every year
How many deaths world wide each year?
Global pandemics, e.g. Flu of 1918 infected ~20% of the world
population, ____ - ______ million deaths worldwide
Upper respiratory infection
Sore throat, headache, resolves in <2 weeks
Affects elderly, very young, immune compromised people
-10%
50-100 million deaths per year
Influenza A virus (Disease)
Transmission?
Prevention?
Treatment?
Droplets ( sneezing, coughing)
Seasonal flu vaccine, hand washing
Tamiflu, Zanamivie (inhibits neuraminidase)
How many coding genes does Influenza A virus have?
-11 protein-coding genes on 8 separate RNA molecules
Influenza A viruses
How many “h” hemaggluttinin proteins does it have?
How many “N” Neuraminidase proteins dots it have?
– “H”: hemagglutinin protein (HA); 16 subtypes; lectin involved in attachment to host cell
– “N”: neuraminidase protein (NA); 9 subtypes; enzyme involved in release from host cell
What do these stand for?
• RdRP
• +ssRNA
• -ssRNA
RdRP= viral independent RNA polymerase
+rrRNA= positive (+) single strands
-ssRNA= negative (-) single strand RNA
What are antibodies?
Antibodies are proteins produced by the host(e.g. human) that bind to specific antigens (parts of the pathogen); antibody binding to an antigen stimulates many aspects of the immune response
RNA dependent RNA polymerase makes approx 1 mistake per _____nt
Influenza A virus genome ~ ______ nt
Every copy generally contains a ______
10,000 nt
14,000 nt
Mutation
What is an antigenic drift?
gradual change in surface molecules of virus (e.g. HA and NA spikes)
→ host antibodies may not recognize altered antigens ( IMPORTANT)
What are the 6 steps of influenza A virus replication cycle?
- Attachment
- Penetration
- Uncoating
- Biosynthesis
- Assembly
- Release
_____% virus particles are assembled correctly; moody new virus particles are defective
<1 %
A single infected cell can produce _______ virus particles
10,000
_______ of genome segments from different viral strains infecting the same host at the same time can generate new viral strains
Reassortment (mixing of 2 different viruses or more to create new virus)
Define antigenic shift
reassortment (mixing) of genome that occurs when two different viruses infect the same host at the same time – can result in fast, dramatic change in antigens (surface spike)
What is the full name of HIV
human immunodeficiency virus
HIV retrovirus (Disease)
Causes?
Infects _____ cells
Progressive loss of immune system leads to:
•Causes AIDS, immune deficiency syndrome
• HIV infects CD4+ T cells
• progressive loss of the immune
system leads to opportunistic infections and cancers
HIV retrovirus (Disease)
Causes?
Infects _____ cells
Progressive loss of immune system leads to:
•Causes AIDS, immune deficiency syndrome
• HIV infects CD4+ T cells
• progressive loss of the immune
system leads to opportunistic infections and cancers
HIV (disease)
____million people infected with HIV
___ million deaths per year
Is it equal between men and women?
33 million
3 million
Yes equal between men/women
HIV (disease)
Transmission?
Cure?
Contact with bodily fluids
Variety of treatments but no cure
Azidothymidine (AZT): nucleoside reverse transcriptase inhibitor (NRTI)
What are the 3 proteins in retrovirus HIV?
Matrix, nucleocapsid(bonds to RNA genome), capsid
What are the 3 enzymes in retrovirus HIV?
Protease, reverse transcriptase, integrase
Hiv-1 genome consists of:
1. Gag 2. Pol 3. Env
Describe each of these
- Gag-encodes capsid, nucleocapsid and matrix
- Pol- encodes reverse transcription (RT), integrase, protease (encodes enzymes)
- Encodes envelope (spike) proteins (envelope)
