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Questions and Answers
Which type of virus is responsible for chronic hepatitis, cirrhosis, and hepatocellular carcinoma?
Which type of virus is responsible for chronic hepatitis, cirrhosis, and hepatocellular carcinoma?
In which part of the host cell do most DNA viruses replicate?
In which part of the host cell do most DNA viruses replicate?
What is the key characteristic of viruses that allows them to replicate?
What is the key characteristic of viruses that allows them to replicate?
What is the function of the envelope in a virus?
What is the function of the envelope in a virus?
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Which type of cell is commonly used in the laboratory to grow viruses?
Which type of cell is commonly used in the laboratory to grow viruses?
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What is the characteristic of Hepatitis D virus (HDV)?
What is the characteristic of Hepatitis D virus (HDV)?
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What is the function of the enzyme RNA dependent RNA polymerase in the replication of RNA viruses?
What is the function of the enzyme RNA dependent RNA polymerase in the replication of RNA viruses?
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What is the result of a cell being infected with a virus that activates or introduces oncogenes?
What is the result of a cell being infected with a virus that activates or introduces oncogenes?
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In which part of the cell do RNA viruses normally undergo transcription, translation, and replication?
In which part of the cell do RNA viruses normally undergo transcription, translation, and replication?
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What is the function of the neuraminidase enzyme on the surface of the influenza virus?
What is the function of the neuraminidase enzyme on the surface of the influenza virus?
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What is the classification of HIV virus based on its genome?
What is the classification of HIV virus based on its genome?
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What is the target of the antiviral therapy, acyclovir, in the treatment of herpes viruses?
What is the target of the antiviral therapy, acyclovir, in the treatment of herpes viruses?
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What is the result of a mutation in the co-receptor of HIV virus?
What is the result of a mutation in the co-receptor of HIV virus?
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What is the purpose of the triple drug therapy in the treatment of HIV-1?
What is the purpose of the triple drug therapy in the treatment of HIV-1?
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What is the function of the GP120 protein in the replication of HIV virus?
What is the function of the GP120 protein in the replication of HIV virus?
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What is the location of the assembly of most DNA viruses?
What is the location of the assembly of most DNA viruses?
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Which of the following RNA viruses is a non-enveloped virus?
Which of the following RNA viruses is a non-enveloped virus?
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Which of the following viruses is responsible for causing infectious mononucleosis?
Which of the following viruses is responsible for causing infectious mononucleosis?
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What is the primary mode of transmission for Human Papilloma viruses?
What is the primary mode of transmission for Human Papilloma viruses?
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Which of the following diagnostic techniques is used to detect Hepatitis B?
Which of the following diagnostic techniques is used to detect Hepatitis B?
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Which of the following enzymes is essential for the replication of HIV?
Which of the following enzymes is essential for the replication of HIV?
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Which of the following cancers is associated with Human Papilloma viruses?
Which of the following cancers is associated with Human Papilloma viruses?
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What is the primary function of the envelope in a virus?
What is the primary function of the envelope in a virus?
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Which of the following steps is common to the replication of all viruses?
Which of the following steps is common to the replication of all viruses?
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Study Notes
Virus Classification
- Herpes virus: double-stranded DNA, enveloped
- Types: Herpes simplex (1 and 2), Varicella zoster virus, Cytomegalovirus, Epstein Barr virus
- RNA viruses:
- Influenza virus: single-stranded negative sense RNA, enveloped (RNA-dependent RNA polymerase)
- Coronaviruses: single-stranded RNA, enveloped (e.g., SARS-CoV-2)
- Polio: single-stranded RNA, non-enveloped
- Hepatitis C: single-stranded positive sense RNA, enveloped
- HIV: single-stranded RNA, enveloped (reverse transcriptase, integrase, and viral protease)
Virus Diagnosis
- Antigen detection: Hepatitis B
- PCR (Polymerase Chain Reaction): detect SARS-CoV-2 using primers that match a segment of the virus' genetic material
- Antibody test: HIV
Viruses and Cancer
- Human Papilloma viruses (HPV):
- Spread by contact (touch)
- More than 40 types can be passed on through sexual contact
- At least a dozen types are known to cause cancer (e.g., cervical, penis, anus, vagina, vulva, mouth, and throat)
- Vaccine widely used to prevent HPV infection in young adults
- Epstein Barr Virus (EBV):
- Causes infectious mononucleosis ("kissing disease")
- Passed from person to person by coughing, sneezing, or sharing drinks or eating utensils
- Infects and stays in B lymphocytes
- Can increase risk of developing nasopharyngeal cancer and certain lymphomas (e.g., Burkitt lymphoma)
- HIV:
- Causes acquired immune deficiency syndrome (AIDS)
- Increases the risk of cancer, especially those linked to other viruses (e.g., Kaposi's sarcoma - human herpesvirus 8 (HHV8))
Virus Replication
- Steps:
- Attachment to the appropriate cells
- Penetration of the virus into the cell (endocytosis or fusion of envelope with host cell membrane)
- Uncoating, leading to release of the genome and other materials into the host cell
- Production of virus-specific mRNA, resulting in the manufacture of virus components
- Assembly of components
- Release from target cells and further infection
Virus Structure
- Envelope: lipid bilayer - membrane acquired as the virus buds through the host cell membrane
- Capsid: protein coat for the viral genome and proteins
Virus Genome
- Types: DNA or RNA, double-stranded or single-stranded, positive or negative sense, circular or linear
- Most DNA viruses replicate in the nucleus
- Most RNA viruses replicate in the cytoplasm
DNA Viruses
- Adenoviruses: double-stranded DNA, non-enveloped
- Causes respiratory and gastrointestinal infections, conjunctivitis
- Hepatitis B virus: partially double-stranded DNA, enveloped
- Causes chronic hepatitis, cirrhosis, hepatocellular carcinoma
Effect on Host Cell
- Death: the cell is unable to function normally due to the virus taking over for its own multiplication
- Transformation: the cell can divide uncontrollably due to activation or introduction of oncogenes
- Latent infection: the virus remains dormant and does not cause symptoms until it is activated by some factor(s)
- Chronic infection: lasting over a period of time
RNA Virus Replication
- Occurs in the cytoplasm
- Positive sense single-stranded RNA can function as mRNA and get translated into proteins by the host ribosomes
- Negative sense RNA has to be changed to positive mRNA using the enzyme RNA-dependent RNA polymerase
DNA Virus Replication
- Occurs in the nucleus of infected cells
- Transcription and replication occur in the nucleus
- Most DNA viruses assemble in the nucleus
Antivirals
- Herpes viruses: acyclovir, famciclovir, and valacyclovir - stops viral DNA replication by inhibiting DNA polymerase
- Flu virus: Tamiflu - inhibits the neuraminidase enzyme on the surface of the virus, preventing the release of the virus
- HIV-1: triple drug therapy consisting of nucleoside reverse transcriptase inhibitors and either a non-nucleoside reverse transcriptase inhibitor, or a boosted protease inhibitor, or an integrase inhibitor
HIV Virus
- Single-stranded positive sense RNA
- Enveloped virus
- Family: retroviridae
- Genus: Lentivirus
HIV Replication
- GP120 binds to CD4 receptor and has to bind to a co-receptor
- CXCR4 on: T cells
- CCR5 on: T cells, macrophages, monocytes, and dendritic cells
- Mutation in co-receptor results in resistance to infection
Targets for HIV Therapy
- Post-attachment inhibitors
- Fusion inhibitors
- Reverse transcriptase inhibitors
- Integrase inhibitors
- Protease inhibitors
Retroviral Therapy
- Standard antiretroviral therapy (ART) consists of a combination of antiretroviral (ARV) drugs to maximally suppress the HIV virus and stop the progression of HIV disease.
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Description
Test your knowledge of different types of viruses, including herpes, influenza, coronaviruses, and more. Identify characteristics such as DNA/RNA, envelope, and strand type.
