Mid sem exam review Flashcards
What are the main characteristics of a virus?
-smallest infectious agent (20-400nm)
-non living
-lack cellular organelles e.g. ribosomes so need to hijack host cells and use their machinery to produce progeny viruses
Viruses are particles
Describe the structure of a virus
it has either DNA or RNA
- enclosed with a protein coat or capsid
- can be further enclosed in a lipoprotein membrane called envelope
- contains simple enzymes
Describe the limitations of viruses
Dont contain all genes necessary for synthesis of a new virus or energy.
- they are obligate intracellular parasites
- heat 60 deg for 30 min
- envelope destroyed by detergent, chemically harder to kill than viruses.
How are viruses classified by nucleic acid.
describe the Baltimore classification
Class 1: DoubleStranded DNA--> mRNA Class 2: SSDNA >DSDNA > mRNA Class 3: DSRNA> mRNA Class 4: + SSRNA > -SSRNA >mRNA Class 5: -SSRNA > mRNA Class 6: + SSRNA > DNA/ RNA hybrid > DSDNA> mRNA
Reproduction of RNA and DNA viruses
- attachment
- Penetration
- Uncoating of virus and transport of genome to site of replication for
- early transcription (mRNA),
- Early translation and Early viral protein production
- Viral DNA and RNA synthesis
- Late transcription of further mRNA
- Late translation and synthesis of structural proteins
- Assembly
- Release
Structure of viruses
– Nucleic acid genome (either DNA OR RNA), enclosed in a protein coat or capsid, can be further enclosed in a lipoprotein membrane called an envelope.
– Contains simple enzymes
– Protein coat covering virus = viral Capsid (repeating protein units)- assists in attachgment and entry and protects nucleic acid from enzymes
– Viral envelope→ on some viruses. It’s a lipid bilayer made from membrane of host cell.
– Viruses lacking envelope = naked (more resistant)
Detection methods of viruses
- Signs and symptoms
- Immunoflorescence
- Nucleic acid analysis
- Reverse transcriptase PCR
- Branched DNA testing
- Nucleic acid sequence based amplification
- Real time PCR
What is PCR and how does it work?
A polymerase Chain reaction • Primers bind to unknown DNA • Amplify DNA • Sequenced • Compared with known sequences (genbank) Step 1: Denaturation Step 2: Annealing Step 3: extension Dean (denaturation) gave Anne (annealing) an Extension
Types of cell culture for growing viruses
- Primary Cell culture→ Embyonic tissue removed from embryo, tissue broken down to individual cells. Physically (chopped) and chemically (trypsin/ dtergents) cells are then placed into appropriate liquid medium. (in Primary school- you are just a little embryo and they physically chop and chemically separated cells then placed into a hot pan to cook you up and eat)
- Secondary Cell culture (cell strains)→ Cells derived by pre-trypsination and re-culture in fresh medium of successfully grown primary cells. These cell cultures have a finite lifespan and age and die. (they also have diploid cell chromosome number-same as the parent cells from which they are derived) (When you go to high school-
- Continuous cell culture (cell lines) → immortal→ originate from tumor and therefore are cancer cells. Easier to grow and maintain than primary cells but are limited in information gained. Eg CHO cells
Making vaccines- advantages and disadvantages of each method
Chicken eggs • Pro→ inexpensive and well established • Con→ need to source millions of eggs, not practical for pandemic and average time egg to injection is 6 months Incoorporating immortal cell line Advantages: • Scaled up quickly • No or fewer impurities • No albumin incase of allergy • Millions of cells stored in small containers appose to eggs • Established method for polio vaccine
Methods of inhibition and inactivation of viruses
Inhibition: 2 methods
1. Filtration→
• filters capable of filtering out viruses
• Uses nitrocellulose with pores less than 10nm diameter
2. Radiation
• Denatures DNA
• Uses Cobalt 60 source
• Radiation enters package so can be steralised after packaging
• Dangerous to use
Chemical Inactivation Detergents o Denature proteins o Alters lipoprotein envelope Alcohols o Best at 7-% as water reuired for denaturation. Not ideal Bleach o Not very effective o Requires more than bacteria
70% ethanol solution is more active than 100% (against viruses)
Halogens
o Iodine, chlorine, bromine and fluorine
o Can have effect on many viruses
o Used in operating theatres
Acids and alkalines
o Most viruses don’t like higher pH. Some can withstand low pH (GIT infections)
Formaldehyde
o Very effective against all viruses
o Can be toxic
o Balance between toxic and effective
Phenolics
o Carbolic acid (a phenol) was used by Lister in 1867.
o Used as a standard for comparison.
o Strong smell and irritant.
o More active against enveloped than non-enveloped viruses.
o A typical example includes dettol
Dettol is a phenol and acts against the non enveloped viruses (more resilient)
Chlorhexadine
o Studies by Dental Research suggest it is effective against a number of viruses
Physical inactivation
Heat
o Depends on contact time and temp
o >60 deg for 30 min
o Pasteurisation will not kill all viruses (contact time important)
o Best method involves heat, water and pressure (autoclave)
Sterilisation
o Removal; of living organisms
Autoclaving
o For sterilisation (121° C, 15 psi or 105 kPa for 15 min)
• Most effective method for sterilization
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What are the characteristics of a prion and what are they resistant to?
- causative agent of spongiform encephalopathies
- develop in most mammalian species
- transmitted or inherited
- abnormal protein
- no immunological activity
- protein alone can cause severe disease
- causes slow reduced function of the brain
- no vaccine available, no treatment available
- slow onset of disease (10-30 years)
Resistant to:
- chemical disinfectants
- heat(360 degrees, 1 hours)
- DNAse, RNAse, proteinases (enzymes that break down DNA and RNA into proteinases)
- UV light, ionizing radiation
- high temp autoclaving
- burying for 3 years
- formaldehyde fixation
- survive in pastures
What is innate immunity and who are the players?
Innate immunity is an inborn defence mechanism that is found in all classes of animals: -Innate immunity isn't specific for the pathogen innate defences include: -surface barriers -phagocytic cells -natural killer cells -inflammation -antimicrobial proteins -fever
Steps involved in inflammation (and don’t forget about who does what)
- Prescence of dead cells induces phagocytes
- Prescence of dead cells causes release of cytokines, liquid messengers and mediators of inflammation
- Causes recruitment of leukocytes
Step 1: Vascular responses to Inflammation
Step 2: Increased Blood flow
Step 3: Movement of proteins to tissue and into cells
Step 4: vascular events
Now extend on each of the steps in inflammation:
Step 1: Vascular responses
• Arterial dilation (opening of capillaries)
• Cause by histamine
• Increased blood flow
• Accumulation of protein rich extravascular fluid
• Vascular effects happens in seconds
Step 2: Increased Blood flow
• Increased hydrostatic pressure
Step 3: Movement of proteins from tissue into cells
• Increased osmotic pressure
• Increased cellular metabolism and vasodilation
• Oedema and loss of fluid from circulation
• This causes
o Redness, warmth, swelling (rubor, pallor, tumor)
Step 4: Vascular events:
• Blood becomes viscous
• Leukocytes adhere at site
• Chemical stimulation causes endothelial cells to contract forming gaps between cells
o Leukocytes can enter tissue between cells
o RBC can also enter trauma site
At trauma site neutrophils are first phagocytes to arrive (form pus) as they ingest debris and dead cells then die. Monocytes and macrophages are the next phagocytes to arrive (ingests debri and lasts longer than neutrophils)
