Virus' Flashcards
Why are viruses defined as obligate intracellular parasites
Viruses are defined as obligate intracellular parasites because they are unable to live independently and require a host. They are completely inert (dormant) when outside living cells
What is the basic and complex chemical composition of viruses
Basic - nucleic acid and protein
complex - nucleic acid, protein, lipid and carbohydrate
What is a viral nucleocapsid
RNA of DNA nucleic acid (genome) and capsid (protein coat)
What is a viral envelope
Envelopes are lipid bilayers which form when i virus buds out of a cell or through an intracellular membrane. Not all viruses contain an envelope
How are viruses classified (which characteristics)
What kind of : DNA or RNA Symmetry Non/enveloped single or double stranded plus or minus sense (if RNA)
What are the benefits of classifying viruses
Because similar viruses have similar features and characteristics and a new unknown virus which is extremely similar as a known virus could be treated and removed the same way.
What is the acronym for the 7 stages of Virus replication
Adders attack people unless sensible and relaxed
Describe the first two stages of virus replication
Adsorption - random non specific binding to cell surface
Attachment - viral surface ligand binds specifically to host cell receptor molecule (key and lock)
Describe third and fourth stages of virus replication
Penetration - completed by receptor mediated endocytosis or direct fusion of virus with plasma membrane
Uncoating - release of nucleic acid from capsid and lysosomal enzymes are released into cytoplasmic vacuoles.
Describe the 5th, 6th and 7th stages of virus replication
Synthesis - of viral protein and nucleic acid
Assembly - usually self assembly
Release - by budding or cell lysis
Describe two ways in which viruses are grown for experimental, industrial and diagnostic purposes
Experimental animals are used in virus research to study viral pathogenesis and host immune responses
Cell Cultures are used for virus isolation/identification and production
What is the incubation period of a virus
The time that the virus enters the cell to being able to observe clinical signs and symptoms
What is the period of infectivity
The period of infectivity is the period during which the individual can affect other people or animals
Define viral latency and what is recrudescence of latent virus?
Viral latency is the ability of a virus to live dormant in the cell, meaning once the cell is infected, the cell will never not be infected.
Recrudescence of latent virus is the reactivation of a virus from latency, generally associated with stress
Define the word pandemic
A pandemic is when a virus/disease affects a whole country or the world.
Define antiginic drift
Antigenic drift is a point mutation in amino acid changes the loops surrounding the receptor binding site of H or the catalytic site of N
What is a viroid and how is it different to other ‘classical’ viruses
Virioid are infectious closed circle, single stranded RNA molecules with no protein that cause disease in plants
Explain the possible benefits and costs of viral infection on plants
Viral infection on crop is responsible for huge losses and cannot be directly controlled by chemical application, transgenic resistance has shown promise but people skeptical over GMOs
Explain the unique features of endogenous retroviruses
Endogenous retroviruses can become part of the ‘genetic dowry’ of the host. For example a cat becomes pregnant and the embyro is infected early, the virus remains dormant in genome. Kitten is born and thrives. The kitten then breeds and passes proviral DNA onto its offspring
Define structure of bacteriophages and how it defines its replication strategy
Bacteriophages contain heads, tails and other components. When they latch onto a cell surface with their legs, their tail drills a hole into the cell and the nucleic acid in their head is released into cell
Define the lytic cycle
The lytic cycle is where a phage enters a bacterium, takes over the bacterium to replicate lots of plaque and then kills the cell by making it explode (lyse)
Define the lysogenic cycle
The lysogenic cycle is where a phage enters a bacterium and inserts its DNA into the bacterial chromosme, allowing the phage DNA (prophage) to be copied and passed on along with cells own DNA
How can viruses be used as vectors in vaccine
Because viruses that attack an unfamiliar host will not infect it even if they are from the same family. Like how smallpox vaccine arised from cowpox.
Explain the first line of defence in providing protection from infection
The first line of defense is
- skin - different tissue/epidermis to protect
- mucous membrane (respiratory tract) coughing sneezing and blocked nose
Gastrointestinal tract - stomach acid, mucus production and peristalsis
Actions - fever (increase temp of body to kill)
