HAEMOGLOBIN SYNTHESIS, FUNCTION AND BREAKDOWN

Comprehensive flashcards covering haemoglobin structure, variants across developmental stages, biochemical synthesis of haem and globin chains, functional oxygen-binding properties, and the physiological breakdown process.

Haemoglobin Molecular Weight

$$68,000$$

Haemoglobin A (Hb A)

The principal haemoglobin of adults, consisting of a pair each of alpha ($\alpha$) and beta ($\beta$) polypeptide chains designated as $\alpha_2\beta_2$.

Haemoglobin F (Hb F)

The predominant haemoglobin in foetal life, containing a pair of alpha ($\alpha$) and a pair of gamma ($\gamma$) chains ($\alpha_2\gamma_2$).

Haemoglobin A2 (Hb A2)

A minor adult haemoglobin variant consisting of a pair of alpha ($\alpha$) and a pair of delta ($\delta$) chains ($\alpha_2\delta_2$).

Haem

An iron-containing pigment consisting of a protoporphyrin IX ring with iron in the ferrous ($Fe^{2+}$) form at its center.

Globin

The protein component of haemoglobin formed by polypeptide chains.

Protoporphyrin IX

A tetrapyrrole structure formed by four pyrrole rings that combines with iron to form the haem molecule.

Hb Gower I

An embryonic haemoglobin variant with the polypeptide structure $\xi_2\epsilon_2$.

Hb Portland

An embryonic haemoglobin variant with the polypeptide structure $\xi_2\gamma_2$.

Hb Gower II

An embryonic haemoglobin variant with the polypeptide structure $\alpha_2\epsilon_2$.

Chromosome 16

The location of the $\alpha$-cluster genes ($\alpha$ and $\zeta$ globin genes) on its short arm.

Chromosome 11

The location of the $\beta$-cluster genes ($\beta$, $\gamma$, $\delta$, and $\epsilon$ globin genes) on its short arm.

$\delta$ - aminolevulinic acid (ALA) synthase

The key rate-limiting enzyme in haem synthesis that condenses two molecules of Succinyl CoA with two molecules of glycine.

Pyridoxal phosphate (vitamin B6)

The coenzyme required for the ALA synthase reaction during haem synthesis.

ALA dehydratase

A zinc-requiring enzyme (also known as porphobilinogen synthase) that condenses two molecules of ALA to produce the pyrrole ring compound porphobilinogen (PBG).

Ferrochelatase

The enzyme that facilitates the combination of Protoporphyrin IX with ferrous iron ($Fe^{2+}$) to form haem in the mitochondria.

Transcription

The process of synthesizing a single strand of RNA (mRNA) from a DNA template using the enzyme RNA polymerase.

Poly-A tail

A sequence of about $150$ adenylic acid residues added to the $3'$ end of mRNA to ensure transcript stability and transport.

Translation

The process occurring on ribosomes in the cytoplasm where a polypeptide chain is synthesized according to the mRNA template directions.

$$P_{50}$$

The partial pressure of $O_2$ at which haemoglobin is half-saturated, which is $26.6\,mmHg$ for normal blood.

2,3-diphosphoglycerate (2,3-DPG)

An intraerythrocyte factor that affects oxygen affinity; high levels reduce affinity and shift the dissociation curve to the right.

Haem oxygenase

The enzyme responsible for breaking down haem into iron and the green pigment biliverdin.

Biliverdin

A green pigment produced during haem breakdown that is subsequently converted to the orange pigment bilirubin.

Conjugated Bilirubin

Water-soluble bilirubin that has been joined with glucuronic acid in the liver to be excreted in bile.

Urobilinogen

A substance formed from bilirubin in the intestine; it can be reabsorbed and excreted in urine as yellow urobilin or oxidized in stool to brown stercobilin.

Stercobilin

The brown pigment excreted in stool, formed by the oxidation of urobilinogen by intestinal bacteria.