Lecture #9 Flashcards
Are viruses considered cells?
No because they have no internal cellular structures
What do viruses need in order to multiply?
Host cells as they are not free living
What do viruses do to a host cell?
Use host metabolic systems and usually disrupt normal host cell function
What does it mean for a virus to be an obligate intracellular parasite?
They do not reproduce outside, rather intracellular
What are viruses acellular?
They do not have a plasma membrane
What are viruses surrounded by?
A protein called a capsid
Do viruses contain DNA or RNA?
They contain a single type of nucleic acid. Can be RNA or DNA but never both
Do viruses have their own enzymes?
Very few, instead they take over the host enzymes
Do all viruses have a lipid envelope and or proteins?
No not all
What 5 things can viruses infect?
Animals, plants, fungi, bacteria and protozoa
Most viruses are specific for ______
A single host species
What must the virus recognize in order to infect a cell?
Particular features on the host cell surface
What does the HIV virus recognize in order to infect a human immune cell?
A specific receptors CO4
What microscope are you able to see viruses?
Electron
How long do viruses range in?
20-1000 nm
What type of genetic material is found in viruses?
Either RNA or DNA, not both
Can the genetic material in viruses be single or double stranded?
Both can be: dsDNA, ssDNA, dsRNA, or ssRNA
What 3 shapes can the nucleic acids of viruses be?
- Linear
- Circular (two ends connect)
- Segmented
What does it mean when a nucleic acid is segmented?
Arranged in many pieces
Why is segmented nucleic acids useful?
To make more of certain kinds of gene without having to make thousands of unnecessary genes ( don’t have to copy every single other gene not needed)
How many nucleic acids are there in a virus?
A few thousand- 250000 base pairs
How many base pairs does E.coli chromosome have?
4000000
What is the bare minimum thing you will find on a virus?
A capsid
What is a capsid?
A protein coat surrounding the nucleic acid
What is a capsomere?
Individual proteins that make up a capsid
What is a capsid made up of?
Capsomeres
What does a capsid do for a virus?
Provides the virus with its shape
How are capsomeres arranged on a virus?
As characteristic of a particular virus
What is a nucleocapsid? What is it in regards to a virus?
A nucleic acid and a capsid together
This is the minimal required structure for a virus
Are envelopes found on all viruses?
No
What is an envelope made up of? Where from?
A lipid bilayer (membrane) acquired from host cell
Where is the envelope located on a virus when present?
External coating around the nucleocapsid
What are spikes? Do all viruses have them?
Additional viral protein inserted into envelope
No
When a virus is enveloped, where is the spikes attached to? What about when it is naked?
Enveloped- attached to envelope
Naked- attached directly to capsid
What is the shape of a virus based on?
Capsid shape
What are the 3 shapes of viruses?
- Helical
- Polyhedral
- Enveloped
What does a helical virus look like? Describe
Long rod
Rigid and flexible
What does a icosahedral virus look like?
Icosahedral (20 triangular faces)
Other geometric shapes are possible
What shape are enveloped viruses? What dictates the shape?
Roughly spherical, dictated by lipid bilayer
What structure do complex viruses have?
Complicated structures
What may be attached to the capsid of a complex virus?
Additional protein structures
Complex viruses are most common in….?
Bacteriophages
Classification of viruses are based one what 3 things?
- Nucleic acid type
- Capsid structure
- Envelope presence
What 3 things are considered when classifying virus nucleic acid type?
- DNA or RNA
- Single or double stranded
- Segmented chromosome or single molecule
What are two types of capsid structures that are considered when classifying a virus?
- Polyhedral
2. Helical
If a virus ends with a viridae, what is it part of?
A family
If a virus ends with the suffix virus, it is part of a…?
Genus
If a virus is part of a species, how is the species specified?
The virus is given a descriptive name
Give examples of a virus genus, family and species
Family: Retroviridae
Genus: Lentivirus
Species: Human Immunodeficiency Virus (HIV)
What are the 6 steps of virus multiplication?
- Adsorption
- Penetration
- Uncoating
- Biosynthesis
- Maturation and Assembly
- Release
What occurs during adsorption?
Virus attaches to host cell at protein or glycoprotein attachment sites within the host membrane that the virus recognizes
What occurs during penetration?
Virus enters.
Naked viruses enter via endocytosis
Some enveloped enter via fusion of lipid bilayers
What occurs during uncoating?
Separation of viral nucleic acid from the capsid (opening the lid)
During biosynthesis, what occurs?
Viral nucleic acid is replicated
Where does DNA vs RNA replication occur during biosynthesis?
RNA- host cytoplasm
DNA- nucleus of host cell
Where are viral proteins synthesized during biosynthesis? What is constructed at the same time?
in the cytoplasm, capsomeres constructed
If an RNA virus is taking over a host cell, what needs to happen in order to make RNA from RNA?
an RNA enzyme needs to be brought into the host cell
What occurs during maturation and assembly of animal virus replication?
New virus particles are assembles from nucleic acids and capsomers forming nucleocapsids
What is the difference in release between enveloped and non enveloped cells?
Naked- burst from cell destroying it
Enveloped- bud out of the host cell causing steady release of mature enveloped viruses over time and host cell remains alive longer
What does the host defence do?
Protects against lethal infections
Do healthy humans carry both viruses and antibodies for viruses?
Yes
If a virus is transferred from the immune host to another individual, what can result?
In infection
What are 5 types of infections?
- Acute infections
- Acute infections with late complication
- Persistant viral infections
- Latent Viral Infections
- Chronic Viral Infection
How long do acute infections last?
Very short duration
The symptoms from acute infections can cause?
Tissue Damage
How does the host defence system eliminate the infection?
Gradually, from days to months
Does the host always develop long lasting immunity after an acute virus?
It can or cannot e.g.. measles or polio
How does a acute infection with late complications occur?
Following an acute infection, some particles still last which over time multiply and can cause a serious disease years later
What is an example of an acute infection with late complications?
Measles can turn into subacute sclerosing panencephalitis
What is a persistent viral infection?
An infection that is present at all times
With a persistent viral infection, is the disease always present?
NO
What is an example of a persistent viral infection?
Hepatitis B
How is Hepatitis B transmitted? What are acute symptoms? What are long term symptoms?
Transmitted sexually or via blood
Acute: Fever, nausea and jaundice
Longterm: cirrhosis or cancer of the liver
The infected host of a persistent viral infection serves as a…?
Reservoir
What are latent viral infections?
An acute infection followed by an asymptomatic (different symptoms) period
What does the virus do in a latent viral infection?
Virus inserts a copy of DNA into the host cell chromosome called a provirus (just sits there, doesn’t do anything)
Can a latent virus infection be reactivated years later?
Yes
What is an example of a latent virus infection? What family does it belong to?
Varicella Zoster Virus, belongs to herpes family
What is the varicella zoster virus present early on as? Later on?
Early: chicken pox in children
Later: Shingles
What is a chronic viral infection?
After an acute infection, infectious virus remains present at all times (may or may not have noticeable symptoms)
What is an example of a chronic viral infection?
Hepatitis B (serum hepatitis virus)
Viral DNA can transform normal animal cells into what?
malignant cancer cells
Do all viruses have the capability to transform cells into cancer cells?
No only some
What are photo-oncogenes?
Animal cells with normal genes
What are photo-oncogenes required for?
to stimulate normal cell growth
What do tutor suppressor cells do to cells?
Inhibit growth
When mutations occur in photo-oncogenes, what does it result in?
Uncontrolled cell growth which then leads to tumor formation and cancer
How can mutated genes form?
As a result of mutagens (carcinogens)
What are oncogenic viruses?
Carry oncogenes which interfere with cell control mechanisms
If oncogenes are present in viral DNA, what could be caused?
Proto-Oncogenes to be over expressed leading to increased transcription causing the proto-oncogne to become oncogene
What are 3 possible oncogenic viruses?
- Human Papilloma Virus
- Epstein- Barr Virus
- Hepatitis B Virus
How is the Human Papilloma Virus transmitted? What does it cause?
Sexually transmitted causing genital warts
Which oncogenic virus is thought to cause cervical cancer?
Human Papilloma Virus
How is the Epstein- Barr Virus transmitted?
Transmitted by sneezing
Can be caused by stress
What does the epstein- Barr virus cause?
Mononucleosis which may cause lymphoma and cancers in the nose and throat
Which virus is thought to cause almost all cases of liver cancer?
Hepatitis B and C
What is a virod?
A single piece of naked RNA with no protein coat
What does a virod result in?
Some plant diseases, not yet found in animals
What are prions?
Infectious protein particles (turned from good to bad)
Is there genetic material (DNA or RNA) present in prions?
No
What are prions linked to cause?
Several fatal human and animals diseases
- ex. Transmissible Spongiform Ecephalophathy
Why do prions cause FATAL human diseases? (what does it do)
Because it forms spongelike holes in brain tissue causing brain function to degenerate and neurons die
How are prions transmitted?
Most frequently by food?
How are prions transmitted to humans?
- Sheep is infected with prion (scrapie)
- Infected sheep eaten by cows and cow develops mad cow disease
- Cow is eaten by humans and develops Creutzfeldt- Jakob Disease
What are 4 reasons prions are so resistant?
- Not usually destroyed by high temps (only by autoclaving but then food is inedible
- Onset of disease occurs several years after infection
Does prions disease always kill you? Is there a cure?
Yes, no
How does a single protein become infectious?
A known protein (with an unknown function), gets converted into a prion protein shape. Eventually all np’s become pp and this results in disease
