BIOLOGY 2F03 Chapter Notes - Chapter 3: Hbb, Yolk Sac, Hemoglobin

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3.1 GLOBIN GENES: STRUCTURE AND FUNCTION
1. Importance of globin genes
encode for proteins which make up haemoglobin essential physiologically
prevalent monogenic disorders commonly affect globin genes
their evolution are paradigms for other vertebrate genes
2. Structure of Haemoglobin & types of globin chains
Haemoglobin
65.4kDa protein that constitutes 90% of RBC protein
o CA is next biggest protein constituent
made of 2a-like and 2b-like globin chains, which are roughly 50% similar
each globin chain is associated with a porphyrin ring, with a haem group and Fe atom in its
centre
o The porphyrin ring binds to histidine residues on the E7 and F8 domains of globin
o oxygen lies between the E7 histidine and iron atom
oxygen binding subtly changes the conformation of haemoglobin from a tight protein (T) to a
relaxed one (R)
o binding one O2 makes binding another easier. the same for losing one O2
Types of Globin & types of Haemoglobin
A-like
b-like
Hb name
description
alpha2
beta2
HbA
Adult; 97%
alpha2
delta2
HbA2
Adult; 1-3%
alpha2
gamma2
HbF
Fetal; also <1% of total adult Hb
zeta2
gamm2
Hb Portland
Embryonic
zeta2
epsilon2
Hb Gower1
alpha2
epsilon2
HbGower2
3. Globin gene & temporal relationship to haemoglobin subtypes
The alpha-like cluster lies on chromosome 16
o there are two alpha genes downstream of the embryonic zeta gene
The beta-like cluster lies on chromosome 11
o there are 2 gamma genes and one each of epsilon, delta and beta
transcription of the genes changes temporally in relation to their distance fro the 5’ ed
o except for delta, whih lies 5’ to eta ut is proaly trasried later i life
embryonic transcription occurs in the yolk sac
fetal transcription occurs in the liver and spleen; adult transcription occurs in the BM
all genes are highly conserved 3 exons and 2 introns
4. brief evolution of globin genes
universal monogenic globin gene underwent duplication and mutation both alpha and beta on
the same chromosome
o this occurs in meiosis due to unequal recominbation
transposition led to separation of the genes
alpha and beta then gave rise to other variants and pseudogenes (relics)
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