topic 6 Flashcards
what happens when an active B cell encounters an antigen?
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
what does an antibody look like?
how are macrophages involved in the activation of T helper cells?
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
What happens when a B (w/ complementary receptors) cell binds to a bacterium with antigens on its surface?
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)
what do B effector cells do?
- differentiate to produce plasma cells, which release antibodies into the blood and lymph
- short lived, last a few days
what do B memory cells do?
-remain in body for months/years, enable an individual to respond more quickly to the same antigen in the future
how do T killer cells work?
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
what does the secondary immune response involve?
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 )
why can we distinguish between our own cells & of foreign invaders?
some of the membrane proteins on the surface of our cells & mark the body as ‘self’
what happens for lymphocytes for ‘self’ membrane proteins?
- destroyed by apoptosis (programmed cell death)
- only lymphocytes with receptors for ‘non-self’ antigens remain
why does the body sometimes attack itself?
particular cells may alter in some ways so they appear ‘foreign’ and get destroyed by the immune system (ie. rheumatoid)
what causes TB?
Mycobacterium tuberculosis
what are the most common forms of TB?
respiratory or pulmonary
how many people closely exposed to TB get infected & how many of those develop symptoms?
30%
5-10%
what is the first phase of TB?
primary infection ( several months & may have no symptoms )
what happens in TB primary infection?
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
where can M.Tuberculosis survive?
inside macrophages
- > they have very waxy & thick cell walls which make them very hard to break down
- > they can lie dormant for years
what can TB do to T cells?
suppress them
->reduces antibody production & attacks by T killer cells
what is the 2nd phase of TB?
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
why may the activity of the immune system be reduced?
- old age
- young
- malnutrition
- poor living conditions
- AIDS
what does active TB do in the lungs?
multiply rapidly & destroy the lung tissue , creating holes.
-> eventually kill the patient
what are symptoms of active TB?
- coughing
- shortness of breath
- loss of appetite
- weight loss
- fever
- extreme fatigue
what happens with fever?
- 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
what is the main symptom of glandular TB
-enlarged lymph glands (neck/armpits)
what happens in skin tests?
-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)
why don’t skin tests always work?
- 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
how is a skin test confirmed?
a sample of sputum coughed up by the patient is taken to be cultured to see which bacteria are present
why are chest X-rays used?
to see the extent of damage
what are introns
non coding sections of DNA
what are exons?
expressed/coding parts of DNA
what are STRs?
short tandem repeats (sequences of repeated bases)
where do STRs occur?
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.
what makes it highly likely that 2 people would have the same combo of STRs?
- each person has a large number of introns
- large amount of variation as to the no. of repeats at each locus
how is a DNA sample prepared?
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
what are restriction enzymes?
restriction endonucleases
what do restriction endonucleases do?
only cut DNA at specific base sequences
why are bacteria’s own DNA nit affected by their own restriction enzymes?
their DNA does not contain the sequences that are targeted by their own restriction enzymes
what is put into the PCR reaction tube?
- a sample (treated w/ detergent to break open cells and release the DNA)
- DNA polymerase
- DNA primers (w/ fluorescent markers)
- nucleotides
what is the 1st PCR temp & what happens?
95°
-> DNA separates into 2 strands
what is the 2nd PCR temp?
55°
-> primers attach at the start of the STR
what is the 3rd PCR temp?
70°
- > DNA polymerases attach
- > nucleotides are added, extending the DNA from the primer
- > the STR and adjacent DNA is replicated
