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CMB 2004 BIOLOGY OF THE IMMUNE SYSTEM EXAM QUESTIONS AND CORRECT ANSWERS
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CMB 2004 BIOLOGY OF THE IMMUNE SYSTEM EXAM QUESTIONS AND CORRECT ANSWERS..
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CMB 2004 BIOLOGY OF THE IMMUNE SYSTEM EXAMQUESTIONS AND CORRECT ANSWERS
What is a pathogen? - ANSWER A microorganism that causes disease e.g. bacteria,
fungi, viruses, parasite
For an effective immune response, the immune system must... - ANSWER - be able
to recognise and respond to any invading organism
- not overreact to benign or self
- be able to direct different effector mechanisms against different pathogens
What is specific/adaptive immunity? - ANSWER - it is induced by exposure to a
particular infection
- shows a high degree of specificity
- exhibits memory
What is the clonal selection theory? - ANSWER 1. Removal of potentially
self-reactive immature lymphocytes by clonal selection
2. Pool of mature naive lymphocytes
3. Proliferation and differentiation of activated specific lymphocytes to form a
clone of effector cells
What are BCRs and what do they do? - ANSWER B cell receptor expressed by B
lymphocytes is subsequently secreted when a B cell is activated now known as an
antibody
What is the structure of an antibody? - ANSWER
What is the function of a T cell receptor? - ANSWER - Unlike antibodies, it doesn't
bind free antigen
- Binds/recognises processed antigen
,- Presented in the cleft/binding groove of MHC class I or class II molecules
What are MHC molecules? - ANSWER major histocompatibility complex
molecules, also called HLA (human leukocyte antigens)
a collection of cell surface markers that identify the cells as self
Rearrangement of Ig genes - ANSWER - Genes rearrange during B cell
development to form a functional gene
- Production of functional immunoglobulin genes involves recombination to bring
gene segments together
- After DNA breaks, a single V and a single J gene segment are joined together to
encode the V region of the light chain
- Similarly, a single V, D and J gene segment are joined together in a single B cell
to encode the V region
Types of segments in heavy and light chains - ANSWER V - variable
D - Diversity
J - joining
C - constant
Hierarchy of rearrangements - ANSWER - greater variability in heavy chains as V,
D and J
- first heavy chain genes (D-J then V-D)
- then light chains genes; kappa first (V-J)
- if kappa rearrangement is unsuccessful then lama genes rearrange
What are recombination signal sequences? - ANSWER Conserved sequences of
non coding DNA that are recognised by the RAG1/RAG2 enzyme complex during
V(D)J recombination in immature B and T cells
5 mechanisms for the generation of antibody diversity - ANSWER 1) Multiple
gremlins genes - multiple VH, Vkappa, Vlambda
, 2) Combinational diversity - different V, D and J segments to recombine to produce
different sequences
3) Junctional diversity - imprecise joining, N regions
4) Combinations of heavy and light chains
5) Somatic hypermutation - mutation frequency in antibody Vhgenes orders of
magnitude higher than normal spontaneous mutation rate, occurs in germinal
centres as B cells recognised Ag and proliferates, involves the enzyme AID which
acts on DNA to de-animate cytosine to uracil , which is then recognises by error
prone DNA repair pathways leading to mutations
Generation of TCR diversity - ANSWER The diversity of TCR repertoires is
generated by the combinatorial associations of V, D, and J gene segments and
junctional diversity generated by the addition or removal of random nucleotides at
the site of recombination. These mechanisms generate the most diversity at the
junctions of the segments that form the third hypervariable regions of both antibody
and TCR polypeptides.
What are the 3 MHC Class I molecules that humans synthesize? - ANSWER
HLA-A
HLA-B
HLA-C
What is the reason for high levels of MHC polymorphism? - ANSWER - allows the
binding of a vast range of peptides that can be presented to T cells, provides a clear
evolutionary advantage to the population
- however, downside with highly polymorphic MHC: increases risk of many
immune mediated diseases and makes selection of suitable donor organs for
transplantation very complex and inefficient
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