immunology quiz 4

Ig structure

IgM

main antibody of primary response

B-cell receptor

immune system memory

compliment system

PENTAMERIC

IgG

binds to phagocytes

main blood antibody for secondary response

crosses placenta

MONOMER (one Y)

IgD

B-cell receptor

stimulates release of IgM

not soluble in blood

MONOMER

IgE

binds to mast cells —> release granulocytes and histamines

allergies and antiparasitic activity

MONOMER

IgA

mucosal membrane, saliva, tears

tags pathogens for destruction

DIMER

Dreyer and Bennett somatic recombination

wanted to know how polypeptide sequences can have stable constant regions AND have so much diversity in variable regions

proposed that DNA encoding heavy or light chain is divided into constant and variable segments. there are few constant segments and LOTS of variable. mixing and matching these creates diversity in the Ag binding region while keeping the rest of the molecule intact

somatic variation theory

have few Ig genes but in each B cell the Ig genes undergo rearrangement at the DNA level in a way that creates new sequences and thus diversity

good theory! probably true!

Tonegawas experiment

supported dreyer and bennett theory

hypothesized that gene rearrangement of Ig occurs and may be linked to B cell development

used mice embryonic and myeloma cells from different stages of B cell development

isolated DNA from these cells and ran a digest with BamHI

ran gel and it showed that germ cell DNA (embryonic) had several smaller segments compared to developed cells (myelomic)

conclusions: a segment specifying the V region and a segment specifying the C region became joined during B cell development

kappa light chain

chromosome 2

30 V segments, 5 J segments, and 1 C segment

VJ recombination

lambda light chain

chromosome 22

30 V segments, 4 J segments, and 4 C segments

VJ recombination

somatic recombination

happens to B cells

occurs in BONE MARROW

heavy chain

chromosome 14

40 V segments, 23 D segments, 6 J segments, and 9 C segments

VDJ recombination

D and J join first

leader signal peptide

address label for the light chain peptide to the ER where it’ll get modified and assembled with heavy chain

cleaved prior to final assembly of heavy and light chain

basically just a postage stamp for light chain stuff

recombination process

• germline config: V(D)J regions line up

• somatic recombination: happens to DNA, RAG pulls up and binds to recombinement signal sequence (RSS). RAG then pulls the sequences together which makes that little loop guy

• RAG cleaves unwanted piece of DNA

• remaining segments joined by lipase

RSS sequences

recombinement signal sequence

where RAG binds on DNA during recombination

TWO KINDS

• one turn (12 bp)

• two turn (23 bp)

one turn binds with two turn, OPPOSITES ATTRACT

RAG complex and junctional diversity

• generation of junctional diversity: a one turn and two turn segment line up

• RAG cleaves the heptamer RSS from these segments which yields DNA hairpins

• RAG opens up these hairpins, creating palindromic P-nucleotides

• TdT (terminal deoxynucleotidyl transferase) adds random nucleotides to these segments

• not all the nucleotides line up and match, so some are removed via exonuclease

• DNA ligase fills in gaps in chain with matching nucleotides —> coding joint formed

• junctional diversity complete great job team now the D and J segments can join together with even more diversity woooooo

flow cytometry

analyzes cells by identifying the types of cels present

lymph nodes

lymphocytes introduced to pathogens and activated

spleen

this is where T cells get activated and T cells activate B cells which make antibodies so this is kinda a big deal