BIOLOGY 2F03 Chapter Notes - Chapter 3: Hbb, Yolk Sac, Hemoglobin
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’ ed
o except for delta, whih lies 5’ to eta ut is proaly trasried 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)
find more resources at oneclass.com
find more resources at oneclass.com