chapter 7 Flashcards
(49 cards)
Glycoproteins expressed on all nucleated cells: interact with Tc (CD8+ T ) cells
Class I MHC genes
Glycoproteins expressed APC cells: interact with TH (CD4+ T) cells.
Class II MHC genes
Secreted protein: complement and tumor necrosis factor (TNF)
Class III MHC genes
-Member of the Ig superfamily
-Larger 45 kDa glycoprotein α chain
-Smaller 12 kDa β2-microglobulin protein
-peptide binding groove between α1 and α2 domains
Class I molecules
-Member of the Ig superfamily
-Heterodimeric: 33 kDa α chain & 28 kDa β chain
-Both chains pass through the plasma membrane
-A peptide-binding cleft is formed by the pairing of the
α1 and β1 domains
class 2 molecules
occurs when two or more clearly different phenotypes
exist in the same population of a species
Polymorphism
Where do class I and class II molecules exhibit polymorphism?
in the peptide-binding region
How many class I and class II molecules can be expressed per person?
up to 6 class I and 12 class II
How does the limited group of molecules (class I & 2) present the vast diverse array of possible antigen peptide fragments?
A given MHC molecule can bind numerous different peptides, and some peptides can bind to several different MHC molecules
Describe the Class I MHC-peptide interactions:
-present peptides to CD8+ T cells
-some amino acids anchor the peptide into the groove
-other amino acids are available to interact with a TCR
Describe the Class II MHC-peptide interactions:
-present antigen peptides to CD4+ T cells
-some amino acids anchor the peptide into the groove
-other amino acids are available to interact with a TCR
What is the difference between class I and II regarding the nature of the peptide-binding groove?
MHC I is closed at both ends
MHC II is open at both ends
What is the size difference between class I and class II molecules?
class I is 8-10 amino acids
class II is 13-18 amino acids
describe the peptide motifs involved in binding to the MHC molecule for class I:
-anchor residues at both ends of peptide
-generally hydrophobic carboxyl-terminal anchor
describe the peptide motifs involved in binding to the MHC molecule for class II:
conserved residues distributed along the length of the peptide
describe the nature of bound peptide for class I:
extended structure in which both ends interact with MHC groove but middle arches up away from MHC molecule
describe the nature of bound peptide for class II:
extended structure that is held at a constant elevation above the floor of the MHC groove
describe the gene sequence of class I:
-5’ leader exon for signal peptide followed by 5–6 exons
encoding α chain
–Signal peptide is eventually removed
one of a number of alternative forms of the same gene or
same genetic locus (a group of genes)
allele
what is a haplotype?
each set of allele
what is the definition of inbreeding?
-reproduction from the mating of parents who are closely
related genetically
______________________ of mice has allowed for more standardized MHC genotypes to control variability
Inbreeding
Why are MHC alleles codominantly expressed?
-this gives the best chance for an organism to have some capability of presenting all the possible antigen peptides it encounters
Why does codominant expression of MHC alleles make transplantation somewhat dificult?
humans are heterozygous at each locus
