Chapter 13/14: Viruses Flashcards
In its most simple form, a virus is composed of ____ ______ ______ __ _ ____ _____
Genomic material surrounded by a protein shell
Virus = “poison”
Virus particle also called virion
Virus size: 20 - 1000 nm
Genomic material
carries instructions for how to make more virus particles
Protein Shell
Protects the genomic material
Organized structure
A Virus Particle itself is inert
- Doesn’t reproduce, respire or divide by itself
- Does not have an energy source
- Does not have a way to make proteins
- or any building blocks to make more proteins or genomic material
Viruses are an ________ _______ __________
Obligate intracellular parasite
must get materials from a cell
Icosahedral
20 equal triangular faces
Naked and Enveloped Viruses
Naked - spike proteins attach to host cell receptors in a specific manner
capsomers are protein subunits
Enveloped - the envelope is a lipid bilayer with proteins (spikes embedded in lipid bilayer)
derived from eukaryotic cells
The eukaryotic cell is the ___ for animal viruses
Host
Animal Viruses
- Vary by size, shape, envelope/naked, type of genetic material (DNA/RNA), and by transmission routes
Steps of Virus Lifecycle
- Enter a cell
- Make more genomic material
- Make more protein
- Assemble protein and genomic material
- Exit a cell
Membrane Fusion (Enveloped)
Entry of enveloped animal viruses into host cells by membrane fusion - nucleic acid and capsid (protein coat) separate
Endocytosis (Naked and Enveloped)
naked and enveloped animal viruses can enter the host cell by endocytosis, process in which the host cell “engulfs” the virus
Protein coat and nucleic acid are separated in the host
The Viral Genome
- may be DNA or RNA, not both; single stranded or double stranded
- May be linear, circular or segmented
- may be positive(+) strand RNA, negative(-) strand RNA, double stranded RNA, double stranded DNA
- Life cycle is dependent on genome type
____ is required for translation
+mRNA
RNA animal viruses and their enzymes
- RNA —-> RNA (RNA replicase)
- RNA —-> ssDNA (Reverse Transcriptase)
- RNA —-> dsDNA (Reverse Transcriptase)
THESE ENZYMES DO NOT HAVE PROOFREADING ABILITY AND MAKE MANY MISTAKES = MUTATIONS
Retroviruses
Which structures on a virus mediate attachment to host cells?
Spike structures
Do these structures bind to specific receptors or to any receptor
Specific receptors
HIV - human immunodeficiency virus
enveloped
What is the genome of HIV composed of?
RNA
What enzymes are required for the lifecycle of HIV?
- Reverse transcriptase (RT)
- Integrase (IN)
- Protease (PR)
a RNA-dependent DNA polymerase; an enzyme that synthesizes a complementary DNA from an RNA template
Reverse Transcriptase
An enzyme produced by HIV that allows the integration of HIV DNA into the host cells DNA
Integrase
An enzyme that digests protein
Protease
Which cells are targeted by HIV?
Helper T cells and Macrophages
Surface Glycoprotein (SU) gp120
spike protein that binds to the CD4 receptor on helper T cells and macrophages
Which enzymes/proteins/processes in the HIV lifecycle do anti- HIV medications target?
- Targets the enzyme reverse transcriptase
- targets protease
- targets cell entry
- integrase inhibitors
Difference between HIV+ and AIDS
- HIV+ has the HIV virus
- AIDS must test positive for HIV virus and
- have a CD4 T cell count of less than 200/mm^3 of whole blood or less than 14% CD4 T cells/total lymphocytes
- CD4 T cell count of more than 200/mm3 and an opportunistic infection
- develops when HIV has caused serious damage to the immune system
Influenza Virus
I
What is the genome of influenza?
8 separate strands of RNA
_____ _____ is required for replication of the influenza genome
RNA replicase
is the reason for new influenza strains each year
Antigenic drift (point mutations)
can give rise to completely new H and N proteins, thus leading to potential epidemics
Antigenic shift (from reassortment)
Influenza Strains
- based on their hemagglutinin (H) protein and their neuraminidase (N) protein; the different numbers associated with the H and N indicate different H and N proteins
- antibodies are specific to specific flu strains
Exit a cell
Release of envelope viruses by budding
Types of Infections
- Carriers: persons with or without disease symptoms who shed the virus
Acute Infections
- self-limited diseases in which the virus often remains localized
- short duration
- mumps, measles, influenza, polio
Persistent infections
- Virus establishes infection that remains for years or even life, often without disease symptoms
-
Latent - symptom-less period followed by reactivation, can detect infection only during reactivation period
- ex. herpes, chickenpox (reactivates as shingles)
-
Chronic - infectious virus present at all times
- ex. hepatitis B virus is continually produced in carriers
-
Slow - infectious agent gradually increases in amount over a very long time; often there are no symptoms
- ex. HIV
Human Herpes Virus
- Herpesviridae family is very large with 100 different viruses
- double-strand DNA genome, enveloped with surface projections
- the shapeless tegument consists of viral enzymes
- latent infection
Hepatitis
- hepatitis - liver inflammation - symptoms are fatigue, fever, loss of appetite, nausea, right-side abdominal pain, dark urine, clay colored feces, jaudice
-
6 different viruses/diseases: Hepatitis A, B, C, D, E, G
- B virus: dsDNA genome
- C virus: ssRNA genome
Human Papilloma Virus (HPV)
most common sexually transmitted disease - 40 million Americans
diagnosed by looking for abnormal cells in pap smear
What is cancer
Uncontrolled cell growth and spread
relentlessly growing mass of abnormal cells, our cells
Tumor
- Benign Tumor : localized tumor
- Malignant Tumor : metastasized (spreading) tumor
HPV and cervical cancer
HPV is a major cause of cervical cancer
12,500 cases each year with 4,500 deaths
Antivirals
- antibiotics don’t work against them (no cell wall or ribosomes)
- most anti-virals are against a specific virus
- no anti-virals can eliminate latent viral infections
- Anti-virals typically work against virus-encoded enzymes
- often becomes resistant to drugs due to mutations
*
Differentiation of bacteria and viruses experimentally
- Filtration: viruses pass through .2 micron filters, but bacteria do not
- microscopy: bacteria are visible through light microscopes, but viruses are not; use electron microscope
- antibiotics: bacteria are susceptible to antibiotics, but viruses are not
- independent growth: bacteria are able to grow/reproduce on their own, but viruses need animal hosts and are thus cultured via tissues
