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Flashcards in Mid sem exam review Deck (25)
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1
Q

What are the main characteristics of a virus?

A

-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

2
Q

Describe the structure of a virus

A

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
3
Q

Describe the limitations of viruses

A

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.
4
Q

How are viruses classified by nucleic acid.

describe the Baltimore classification

A
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
5
Q

Reproduction of RNA and DNA viruses

A
  1. attachment
  2. Penetration
  3. Uncoating of virus and transport of genome to site of replication for
  4. early transcription (mRNA),
  5. Early translation and Early viral protein production
  6. Viral DNA and RNA synthesis
  7. Late transcription of further mRNA
  8. Late translation and synthesis of structural proteins
  9. Assembly
  10. Release
6
Q

Structure of viruses

A

– 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)

7
Q

Detection methods of viruses

A
  1. Signs and symptoms
  2. Immunoflorescence
  3. Nucleic acid analysis
  4. Reverse transcriptase PCR
  5. Branched DNA testing
  6. Nucleic acid sequence based amplification
  7. Real time PCR
8
Q

What is PCR and how does it work?

A
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
9
Q

Types of cell culture for growing viruses

A
  1. 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)
  2. 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-
  3. 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
10
Q

Making vaccines- advantages and disadvantages of each method

A
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
11
Q

Methods of inhibition and inactivation of viruses

A

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

12
Q

What are the characteristics of a prion and what are they resistant to?

A
  • 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
13
Q

What is innate immunity and who are the players?

A
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
14
Q

Steps involved in inflammation (and don’t forget about who does what)

A
  1. Prescence of dead cells induces phagocytes
  2. Prescence of dead cells causes release of cytokines, liquid messengers and mediators of inflammation
  3. 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

15
Q

Now extend on each of the steps in inflammation:

A

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)

16
Q

What is an antibody?

A
•	Protein 
•	Made by B-cells 
•	Also is a receptor of B cells 
•	Binds to antigens 
•	They are specific 
•	A member of a family of 5 
•	A product of the adaptive immune system 
•	The end product of humoral immunity 
Their primary function is to bind to the antigen
17
Q

What is acquired immunity?

A

Aquired immunity is the immunity that our body gains over time (specific)
• Special chemicals are generated also known as antibodies that neutralize the harmful toxins produced by the pathogen. Each specific type of pathogen requires a custom chemical to neutralize it. The major cells of acquired immunity are T cells and B cells (lymphocytes)
Characteristics of acquired immunity:
1. Specificity
2. Diversity
3. Discrimination between self and non-self
4. Memory

18
Q

What are the characteristics of all the immunoglobulins?

A

An antibody, also known as an immunoglobulin, is a large Y-shape protein produced by plasma cells that is used by the immune system to identify and neutralize foreign objects such as bacteria and viruses.
• Interaction between toxin and ‘operative components of serum’
Immunoglobulin G
* Half life 23 days
* predominate immunoglobulin in blood, lymph, CSF and peritoneal fluid
* MW 150,000 DA
* only Ig to pass through placenta
* activates complete system
* neutralization of viruses and toxin
Immunoglobulin M
* IgM for macroglobulin
* half life 5 days
* first antibody produced after immunization or infection
* high recent IgM values indicate recent infection
* MW 900,00 DA
* first antibody made by foetus
* IgM are isohaemagglutins
Immunoglobulin A:
* major antibody in external secretion
* saliva, mucous, tears, sweat, breast milk
* MW 400,00 DA
*does NOT bind complement
* active against gram negative bacteria only
Immunoglobulin D:
* present in low concentration
* CO-EXPRESSED with IgM in mature B cells
* marker of age in B cells
* J chain
Immunoglobulin E:
* MW 200,00DA
* Half life 2 days
* LOWEST SERUM concentration of all antibodies
* Active against parasites, mostly WORMS
Role in hypersensitivity reactions

19
Q

Whats the difference between primary response and a secondary response?

A

primary immune response refers to the first encounter of your immune system with a virus or bacteria. When this happens, naive T cells and B cells are activated and form memory cells. This process takes a week or so, which allows you to get sick and not feel well, but these cells eventually clear the pathogen from your body.

Secondary immune response refers to a re-encounter of the same virus/bacteria against which you have memory T cells and B cells. Since the memory cells have seen the bug before, they can respond very rapidly and robustly, preventing you from feeling sick.

20
Q

What is immunological memory?

A

Immunological memory is the ability of lymphocytes to respond faster and more strongly to reencounter of the same antigen. It is a central feature of the adaptive immunity and is the basis of vaccination.

21
Q

What is the variable region and crystallisable region?

A

Variable region of an antibody:
* The variable parts of an antibody are its V regions, and the constant part is its C region. The immunoglobulin Ig monomer is a “Y”-shaped molecule that consists of four polypeptide chains; two identical heavy chains and two identical light chains connected by disulfide bonds.

Crystallizable region of an antibody:
• The fragment crystallizable region (Fc region) is the tail region of an antibody that interacts with cell surface receptors called Fc receptors and some proteins of the complement system. This property allows antibodies to activate the immune system

22
Q

What is CD as in CD3?

A

CD antigen→ a group of cell surface molecules which act as markers on T lymphocytes
CD#–> found on T helper and T cytotoxic lymphocytes associated with signal transduction

23
Q

What are the 2 types of T cells?

A

refer to notes

24
Q

What are the co-receptors on T cells and what do they bind to?

A
Co receptors on T cells are either CD4 or CD8
•	CD4 binds to cells expressing MH C class 2 molecules eg dentritic cells, macrophages, B cells 
•	CD8 binds to cells expressing MHC class 1 molecules eg all nucleated cells
25
Q

What cells have MHC1, MHC2, CD3, CD4, CD8

A
  • MH class 1 cells are found in all nucleated cells
  • MH C class 2 cells are all antigen presenting cells (APC) including dentritic cells, macrophages, B cells and thymic epithelial cells
  • CD3→ only T cells express CD3 (used as a marker to distinguish T cells)
  • CD4→ CD4 (cluster of differentiation 4) is a glycoprotein found on the surface of immune cells such as T helper cells, monocytes, macrophages, and dendritic cells.
  • CD8→ binds to cells expressing MCH class 1 molecules (all nucleated cells)