topic 6

Question 1

what happens when an active B cell encounters an antigen?

Answer 1

1) produces antibodies
2) antibodies label antigen
3) labelled antigen binds to the antibody receptor on a macrophage
4) macrophage engulfs antibodies & bacterium
5) lysosomes fuse with vacuole & release digestive enzymes which destroy the bacterium

Question 2

what does an antibody look like?

Question 3

how are macrophages involved in the activation of T helper cells?

Answer 3

1) bacterium engulfed by macrophage
2) macrophage becomes an APC
3) APC binds to a T helper with a complementary CD4 receptor -the T helper is activated & divided
4) produces clone of T memory& active T helpers

Question 4

What happens when a B (w/ complementary receptors) cell binds to a bacterium with antigens on its surface?

Answer 4

1) bacterium with antigens on surface binds to a B cell with a completely receptor -becomes APC
2) APC binds to an activated T helper & produces cytokines (which stimulate B cell)
3) B cell divides to produce B memory clones & B effector clones
4) B effectors differentiate into plasma cells (which secrete antibodies)

Question 5

what do B effector cells do?

Answer 5

• differentiate to produce plasma cells, which release antibodies into the blood and lymph
• short lived, last a few days

Question 6

what do B memory cells do?

Answer 6

-remain in body for months/years, enable an individual to respond more quickly to the same antigen in the future

Question 7

how do T killer cells work?

Answer 7

1) bacterium infects cell of host
2) cell presents antigens & becomes APC
3) T killer with a complementary receptor binds to APC
4) cytokines stimulate differentiation into active T killers & memory T killers
5) active T killer binds to APC
6) T killer releases chemicals that cause pores to form in the infected cell - infected cell dies

Question 8

what does the secondary immune response involve?

Answer 8

memory cells (only takes 2-7days)

• > B memory cells can differentiate immediately to produce plasma cells
• > invading pathogens are destroyed so quickly that the person is often unaware of symptoms ( said to be immune )

Question 9

why can we distinguish between our own cells & of foreign invaders?

Answer 9

some of the membrane proteins on the surface of our cells & mark the body as ‘self’

Question 10

what happens for lymphocytes for ‘self’ membrane proteins?

Answer 10

• destroyed by apoptosis (programmed cell death)

- only lymphocytes with receptors for ‘non-self’ antigens remain

Question 11

why does the body sometimes attack itself?

Answer 11

particular cells may alter in some ways so they appear ‘foreign’ and get destroyed by the immune system (ie. rheumatoid)

Question 12

what causes TB?

Answer 12

Mycobacterium tuberculosis

Question 13

what are the most common forms of TB?

Answer 13

respiratory or pulmonary

Question 14

how many people closely exposed to TB get infected & how many of those develop symptoms?

Answer 14

30%

5-10%

Question 15

what is the first phase of TB?

Answer 15

primary infection ( several months & may have no symptoms )

Question 16

what happens in TB primary infection?

Answer 16

M.tuberculosis causes an inflammatory response:

• macrophage engulfs bacteria
• granuloma (mass of tissue) forms -in TB these are anaerobic & have dead bacteria and macrophages in the centre
• called tubercules
• after 3-8 weeks, the infection is controlled & infected region heals

Question 17

where can M.Tuberculosis survive?

Answer 17

inside macrophages

• > they have very waxy & thick cell walls which make them very hard to break down
• > they can lie dormant for years

Question 18

what can TB do to T cells?

Answer 18

suppress them

->reduces antibody production & attacks by T killer cells

Question 19

what is the 2nd phase of TB?

Answer 19

active TB

• > occurs if the patient’s immune system cannot contain the disease when it first arrives in the lungs
• > the no. of bacteria is too great OR an old infection may break out

Question 20

why may the activity of the immune system be reduced?

Answer 20

• old age
• young
• malnutrition
• poor living conditions
• AIDS

Question 21

what does active TB do in the lungs?

Answer 21

multiply rapidly & destroy the lung tissue , creating holes.
-> eventually kill the patient

Question 22

what are symptoms of active TB?

Answer 22

• coughing
• shortness of breath
• loss of appetite
• weight loss
• fever
• extreme fatigue

Question 23

what happens with fever?

Answer 23

• fever-causing substances released from neutrophils/macrophages
• affect hypothalamus- raises core body temp (40.5º)
• raised temp enhances immune function &phagocytosis
• bacteria &viruses may reproduce more slowly at higher temps

Question 24

what is the main symptom of glandular TB

Answer 24

-enlarged lymph glands (neck/armpits)

Question 25

what happens in skin tests?

Answer 25

-a small amount of the bacterium is injected under the skin of the forearm

positive result= inflamed area if skin around test site (antigens already present)

Question 26

why don’t skin tests always work?

Answer 26

• can give a negative result if the have latent TB
• can give a false positive if the person had an anti-TB vaccination
• > has led to the development of blood tests specifically for T cells that are specific to TB antigens

Question 27

how is a skin test confirmed?

Answer 27

a sample of sputum coughed up by the patient is taken to be cultured to see which bacteria are present

Question 28

why are chest X-rays used?

Answer 28

to see the extent of damage

Question 29

what are introns

Answer 29

non coding sections of DNA

Question 30

what are exons?

Answer 30

expressed/coding parts of DNA

Question 31

what are STRs?

Answer 31

short tandem repeats (sequences of repeated bases)

Question 32

where do STRs occur?

Answer 32

at the same locus on both chromosomes of a homologous pair

BUT the no. of times they are repeated on each chromosome may be different.

Question 33

what makes it highly likely that 2 people would have the same combo of STRs?

Answer 33

• each person has a large number of introns

- large amount of variation as to the no. of repeats at each locus

Question 34

how is a DNA sample prepared?

Answer 34

1) broken down in a buffer solution (salt & detergent) to disrupt the cell membranes
2) small, suspended particles (inc. DNA) are separated from the rest of the cell debris through centrifuging
3) proteases incubated w/ the suspension to remove proteins
4) cold ethanol added to precipitate out the DNA
5) wash in buffer solution

Question 35

what are restriction enzymes?

Answer 35

restriction endonucleases

Question 36

what do restriction endonucleases do?

Answer 36

only cut DNA at specific base sequences

Question 37

why are bacteria’s own DNA nit affected by their own restriction enzymes?

Answer 37

their DNA does not contain the sequences that are targeted by their own restriction enzymes

Question 38

what is put into the PCR reaction tube?

Answer 38

• a sample (treated w/ detergent to break open cells and release the DNA)
• DNA polymerase
• DNA primers (w/ fluorescent markers)
• nucleotides

Question 39

what is the 1st PCR temp & what happens?

Answer 39

95°

-> DNA separates into 2 strands

Question 40

what is the 2nd PCR temp?

Answer 40

55°

-> primers attach at the start of the STR

Question 41

what is the 3rd PCR temp?

Answer 41

70°

• > DNA polymerases attach
• > nucleotides are added, extending the DNA from the primer
• > the STR and adjacent DNA is replicated