16. Biological Knowledge and Society

Question 1

Epidemic

Answer 1

Outbreak of a contagious disease that spreads readily and extensively and effecting many individuals simultaneously in an area or a population

Question 2

Pandemic

Answer 2

An epidemic over a wide geographic area and affecting a large proportion of the population

Question 3

Conditions that support a pandemic

Answer 3

🔹 When a new pathogen or novel strain of an existing pathogen appears in geographic areas which humans have not come into contact with (little to no immunity)
🔹 Vaccine is unlikely to exist or the vaccine is available in limited amounts that are not sufficient to prevent the spread of the pathogen.
🔹 Pathogen causes serious illness in people and other species
🔹 Non human hosts act as reservoirs of the pathogen and pathogen moves from non human host to human host via suitable vector.
🔹 Pathogen easily transmitted from people by airborne particles or contact with blood or bodily fluids
🔹 Uncontrolled spread of pathogen occurs across wide geographic region, movement of infected individuals or migration of infected vectors that transmit pathogen from infected to non infected people.

Question 4

What is the structure of the influenza A virus?

Answer 4

🔹 Two kinds of protein embedded in the lipid bilharziasis membrane forming outer envelope of the virus
🔹 Hemagglutinin (HA) and neuraminidase (NA)
🔹 19 different Hemagglutinin types have been identified and 11 different subtypes of neuraminidase (NA)

Question 5

What is the size of the influenza virus?

Answer 5

Spherical particles with diameter in the range of 80-120 nm

Question 6

Genome of influenza virus

Answer 6

Single stranded RNA molecule organised into eight separate segments encoding 11 proteins.
Three of the segments encode sub unit of RNA polymerase, enzyme that is needed when infected host cell makes copies of the viral genome

Question 7

Role of Hemagglutinin (active at start of infection)

Answer 7

🔹 allows virus to attach to target cells
🔹 causes virus to fuse to cell membrane
🔹 allows viral genetic material to invade target cell where it will replicate

Question 8

Role of neuraminidase (active at end of infection)

Answer 8

🔹 allows virus to diffuse through protective mucus
🔹facilitates the exit of virus progeny from infected cells.
🔹 necessary for release of the next generation of virions for efficient spread of infection

Question 9

How do you name an influenza virus?

Answer 9

🔹 TYPE a b or c
🔹 STRAIN host, geographical origin and year of isolation
🔹 SUBTYPE applies to influenza only H1 to H15 and N1 to N9

Question 10

Antigenic drift (gradual small changes)

Answer 10

🔹 RNA of infected virus continually undergoes frequent mutations as it replicates, can have nucleotide change or point mutation on one of its genes
🔹 Initially mutated viruses closely related to one another and have similar antigenic properties
🔹 Under these circumstances the memory cells of a person’s immune system will recognise and respond to these viruses.
🔹 Over time accumulation of small changes means antigenic properties of mutated viruses altered to major degree. New subtype identified.
🔹 virus no longer recognised by immune system memory cells so infected person has symptoms.

Question 11

Antigenic shift (sudden BIG change)

Answer 11

🔹 Influenza A virus can undergo majors sudden change in HA and NA surface proteins
🔹 When one host is infected with 2 different kinds of influenza A virus a new combination of genetic material can be produced by reassortment and the virus cannot be identified by the immune system.
🔹 Influenza A genome not one long single stranded RNA chain but consists of 8 separate RNA segments that can be swapped.
🔹 Reassortment of viral genetic material commonly occurs when host becomes infected with two or more different influenza viruses at the same time. Can exchange genetic information so that the new influenza virus subtypes are formed.

Question 12

What is the effect of antigenic shift

Answer 12

No one in the population is likely to have immunity to the new viral subtype so that if people are exposed to this new subtype of virus they will contract influenza which can develop into an epidemic or even a pandemic

Question 13

Why is antigenic shift restricted to influenza A virus

Answer 13

They are the only influenza viruses that infected not only people but other species. As a result strains of influenza can become very different during their transmission within animal groups

Question 14

Steps of reassortment

Answer 14

🔹 Virus coat breaks down and RNA genes move to the cell nucleus to be copied and transcribed
🔹 Viral genes are copied and prepared for packaging into new virus particles
🔹 Repackaging of genes creates a virus that can transfer from human to human

Question 15

Define rational drug design

Answer 15

Construction of a drug to fit the active site of a molecule so that the natural action of the molecule cannot occur

Question 16

Why are scientists able to design a drug that’s effective against ALL influenza strains

Answer 16

🔹 Neurominidase is a surface antigen which is an enzyme responsible for allowing newly formed virions ot exit from an infected body cell.
🔹 Although there are many differ subtypes of Neurominidase with varying structures, all the subtypes have the SAME ACTIVE SITE

Question 17

What must scientists do when designing a drug against the influenza virus?

Answer 17

🔹 Work out shape and structure of active site
🔹 Identify the spatial arrangements of atoms surrounding active site
🔹 Note key amino acids that form the active site
🔹 Design inhibitor with complementary shape that could occupy the active site
🔹 Ensure the designed drug has charged groups on the molecule that would bind more tightly to the active site than the normal substrate

Question 18

How does relenza work?

Answer 18

🔹 Relenza = zanamivir
🔹 Relenza works by binding to the active site of Neurominidase so that the viruses are trapped on the surface of the cell.
🔹 With the active site blocked, the Neurominidase cannot cut the sialic acid attachment between cell and virus.
🔹 Therefore virus cannot be freed to invade other body cells so it reduces the number of viruses in the body, thus reduced symptoms

Question 19

What are physical methods of identifying VIRUSES

Answer 19

🔹 X Ray crystallography - determines the structure of viruses
🔹 Electron microscopy - images that distinguish various kinds of virus

Question 20

What is an immunological method of identifying viruses?

Answer 20

ELISA technique can be used to detect presence of specific viral antigen in a cell or sample of body fluid, serum. Or to detect presence of antibodies to a specific viral disease in body fluids

Question 21

How is ELISA used to detect for the presence of antigens?

Answer 21

🔹 A capture antibody bound to a solid surface, such as plastic, is used to identify the presence of a specific viral antigen through an antibody-antigen reaction
🔹 All unbound material is washed away.
🔹 A second antibody with an enzyme indicator is added, along with substrate for this enzyme that enables production of a coloured complex.
🔹 If colour appears the specific viral antigen is present, if no colour appears the specific antigen is absent

Question 22

How can ELISA be used to detect for the presence of antibodies?

Answer 22

🔹 To detect antibodies to viruses, viral protein is linked to the solid support and then the clinical specimen is added.
🔹 If antibodies against the virus are present in the specimen they will bind to the immobilised antigen.
🔹 The bound antibodies are then detected by using a second antibody that binds to the first antibody

Question 23

What are some molecular techniques for identifying viruses?

Answer 23

🔹 In situ hybridisation with DNA probes to detect and locate specific genetic sequences that are diagnostic of particular DNA viruses
🔹 Reverse transcriptase techniques can be used to identify RNA viruses
🔹 Restriction enzymes can be used to differentiate between different strains of the same DNA virus

Question 24

Phenotypic methods for identifying BACTERIA

Answer 24

🔹 Use of microscopy to differentiate bacteria on the basis of differences in cell wall, size and response to gram stain and physical features such as the presence or absence of a capsule.
🔹 Use of different media to differentiate bacteria on the basis of variation in growth patterns which can distinguish aerobic bacteria from facultative anaerobes
🔹 Use of range of biochemical tests eliciting different bacterial responses

Question 25

Shape

Answer 25

Spherical (coccus)
Rod like (bacillus)
Spiral (spirochaetae)

Question 26

Organisation

Answer 26

Single
In pairs
In chains (strepto)
Clustered (staphylo)

Question 27

Gelatinous external capsule

Answer 27

Present or absent

Question 28

Mobility

Answer 28

Motile (with flagella)

Immotile (no flagella)

Question 29

Gram positive

Answer 29

🔹 Thick peptidogylcan (disaccharide and amino acid) cross linked layers and teichoic acid (polysaccharide)
🔹 Turn violet when treated with gram stain
🔹 Effective antibiotics are penicillin and sulfonamide

Question 30

Gram negative

Answer 30

Thin peptidoglycan and lipid
When treated with gram stain remains pink
Effective antibiotics are streptomycin tetracycline
Phagocytosis by wbc difficult

Question 31

Immunological methods of identifying bacteria

Answer 31

Monoclonal antibodies
ELISA
Immunofluroescence

Question 32

Genotypes and molecular methods of identifying bacteria

Answer 32

Gene probes
Sequence analyses
Plasmid fingerprinting

Question 33

Antibiotics define

Answer 33

🔹 Class of antimicrobial drug used in the treatment and prevention of bacterial infections
🔹 Act by either killing pathogenic bacteria or by inhibiting their growth

Question 34

Antiviral drugs

Answer 34

Drugs only effective only when the viruses are located within cells and are undergoing replication
Antiviral drugs do not kill their target pathogen and instead inhibit their development
Different antiviral drugs target different stages of development in different viruses