Infection, Immunity and Forensics

Question 1

Describe introns.

Answer 1

Introgenic regions, non-coding blocks.

Within introns, there are series of repeated bases - short tandem repeats.

Question 2

Define exons.

Answer 2

Expressed, coding regions.

Question 3

Describe polymerase chain reaction.

Answer 3

A sample of tissue is added to DNA polymerase, DNA primers and nucleotides.
95°C the DNA separated into two strands.
55°C primers attach at the start of the short tandem repeat sequence.
70°C DNA polymerase attached, nucleotides are added. The STR and DNA sequence are replicated.
This is repeated to produce millions of STR fragments.

Question 4

Describe how to obtain a tissue sample.

Answer 4

Broken down in a buffer solution of salt and detergent, separated by centrifuging. Protease enzymes are incubated and cold ethanol is added. DNA is washed in a buffer solution. Treated with restriction endonucleases. Cut at specific basr sequences.

Question 5

Describe gel electrophoresis.

Answer 5

DNA is placed on gel agarose and submerged in buffer solution. Negatively charged fragments move through the gel. Smaller fragments travel faster.
Southern blotting transfers fragments to nylon/nitrocellulose. Incubated with excess DNA probes.

Question 6

Describe body temperature as part of forensic analysis.

Answer 6

Body cools due to lack of heat producing reactions. Only useful for 24 hours after death. Measured via rectum or abdominal stab.

Fever or hypothermia will affect body temperature at time of death.

Body size, position, clothing, air movement, humidity and temperature of surroundings will affect cooling of the body.

Question 7

Describe rigor mortis as part of forensic analysis.

Answer 7

Muscle cells are oxygen starved so oxygen dependent reactions stop. Respiration becomes anaerobic and cell pH falls due to production of lactic acid. Enzyme activity is inhibited. ATP is no longer produced. Bonds between muscle proteins become fixed. Proteins can no longer move over each other.

Question 8

Describe decomposition as part of forensic analysis.

Answer 8

Autolysis occurs when enzymes break down cells. Putrefaction is a green discoloration of the lower abdomen due to formation of sulfhaemoglobin. Darkens to red-green then to purple-black.
Gas or liquid blisters may appear.
The body bloats.

Question 9

What is forensic entomology?

Answer 9

Study of the succession of insects on the body after death.

Question 10

How do viruses work?

Answer 10

Virus attached to the host cell. Virus inserts nucleic acids which replicate. The protein coats synthesise. New viral particles are formed and then released due to cell lysis.

Question 11

What is the difference between specific and non-specific immune responses.

Answer 11

Non-specific are instant and immediate responses whereas specific are carried out over time.

Question 12

Describe the activity of B cells.

Answer 12

Produced in the bone marrow. Have a specific antigen receptor. When an antigen binds it becomes activated and produces immunoglobulin which binds to the antigen and acts as a label.

These bind with active T helper cells and releases cytokinesis, stimulating the division of B cells.

Question 13

Describe the activity of B memory cells.

Answer 13

Produced by clonal selection (mitosis) of B cells.

These cells are longer lived and allow an individual to respond to antigens in the future.

Question 14

Describe the activity of B effector cells.

Answer 14

Produced in the clonal selection of B cells.

Differentiate to produce plasma cells which release blood and lymph and are short-lived.

Question 15

Describe the activity of T helper cells.

Answer 15

Produced in the bone marrow but mature in the thymus gland.

Move to lymph nodes and spleen. They are specific antigen receptors that enhance the activity of phagocytes.
When an antigen binds to CD4 receptors, the T helper cell is activated and divides into active T helper cells and T memory cells.

Question 16

Describe the activity of T helper cells.

Answer 16

Longer-lasting, can respond more quickly to antigens.

Question 17

Describe the activity of T killer cells.

Answer 17

Bind to antigen presenting cells with the complementary CD4 receptors. Divide to produce an active clone, stimulated by cytokines.
Produce enzymes creating pores in the membrane of the infected cell, which lyses. The pathogens are released and labelled by B cells.

Question 18

Describe the activity of neutrophils.

Answer 18

Leave capillaries through cells in the walls. They are short-lived and ingest and destroy bacteria.

Question 19

Describe the activity of macrophages.

Answer 19

Begin as monocytes. Exit via walls of capillaries.
Become macrophages and engulf bacteria, foreign matter and cell debris. Ingested material is enclosed in a vacuole. Lysosomes fuse with the cell, releasing enzymes to destroy the bacteria.

Longer-lived.

Question 20

Describe the activity of lysozyme.

Answer 20

Tears and mucal secretions contain the enzyme that kills bacteria by breaking down cell walls.

Question 21

Describe inflammation.

Answer 21

Damaged white blood cells release histamines causing arterioles to dilate. Plasma fluid, white blood cells and antibodies lead to oedema.

Question 22

Describe lymph and interferon.

Answer 22

Lymph activates lymphocytes to destroy antigens.

Interferon inhibits microbial protein synthesis.

Question 23

Describe physical barriers.

Answer 23

Skin, containing keratin.
Skin flora, providing competitive bacteria.
Mucus.
Cilia.
Stomach acid.
Gut flora.

Question 24

Define mutualistic.

Answer 24

A beneficial relationship for both participants.

Question 25

Describe tuberculosis.

Answer 25

Mycobacterium tuberculosis is carried in mucus and saliva and passed on through droplet infection.
Primary infection is asymptomatic. An anaerobic granuloma forms. There is an inflammatory response.
Active TB is symptomatic. Reduced immune system.

Question 26

How is tuberculosis diagnosed?

Answer 26

Through skin and blood tests.

Positive skin tests are confirmed with a sputum sample or a chest x-ray.

Question 27

Describe HIV.

Answer 27

Passed on in body fluids. Gp120 binds to CD4 receptors. Viral RNA enters the cell. Uses reverse transcriptase and integrase to integrate into the host DNA.

The acute phase is few symptoms, the release of HIV antibodies and the loss of T helper cells.
The chronic phase is asymptomatic, the virus rapidly reproduces and dormant diseases reappear.
The disease phase is when opportunistic infections occur.

Question 28

How is HIV treated?

Answer 28

Reverse transcriptase inhibitors.
Protease inhibitors.

Suggested to use integrase inhibitors or fusion inhibitors.

Question 29

What is a type of each: active artificial immunity, active natural immunity, passive artificial immunity, passive natural immunity.

Answer 29

Active artificial immunity - vaccination
Active natural immunity - memory cells
Passive artificial immunity - injection of antibodies
Passive natural immunity - maternal antibodies.

Question 30

What is a vaccine?

Answer 30

Weakened viruses, killed bacteria, altered toxin or antigen-bearing fragment.

Question 31

Define a bactericidal antibiotic.

Answer 31

Destroys bacteria.

Question 32

Define a bacteriostatic antibiotic.

Answer 32

Prevents bacterial multiplication.

Question 33

How do antibiotics work?

Answer 33

Inhibit cell wall, nucleic acid, protein synthesis, disrupt cell membrane, inhibit specific enzymes.

Question 34

How can you avoid antibiotic resistance?

Answer 34

Antibiotics should only be used when needed.
Complete the course of antibiotics.
Infection control in hospitals.

Question 35

How do bacteria spread genes?

Answer 35

Conjugation, via cell-to-cell contact.