In first step of haem synthesis, which amino acid is required ?
**Core Concept:**
The question is asking about the initial step of heme synthesis, a process that produces heme, a porphyrin group containing molecule. Heme is a crucial component of hemoglobin, myoglobin, and cytochromes, which are involved in oxygen transport, storage, and electron transport in cells, respectively. The correct amino acid is part of heme's porphyrin ring structure.
**Why the Correct Answer is Right:**
Heme synthesis occurs in the mitochondria of red blood cells and liver cells. The first step is catalyzed by aminolevulinic acid synthase (ALAS), which uses five amino acids as substrates. These amino acids are:
1. Glu (Glutamic acid)
2. Ser (Serine)
3. Gly (Glycine)
4. His (Histidine)
5. Pro (Proline)
**Why Each Wrong Option is Incorrect:**
A. **Glu (Glutamic acid):**
- While Glu is part of the porphyrin ring structure, it is not the correct first substrate for ALAS, as it is only one of the five amino acids required for heme synthesis.
B. **Ser (Serine):**
- Ser is also part of the porphyrin ring structure, but it is not the first amino acid utilized in heme synthesis.
C. **Gly (Glycine):**
- Gly is another component of the porphyrin ring, but it is not the first amino acid utilized in heme synthesis.
D. **His (Histidine):**
- Histidine is present in the porphyrin ring but is not the initial amino acid involved in heme synthesis.
E. **Pro (Proline):**
- Pro is part of the porphyrin ring, but it is not the first amino acid used in heme synthesis.
**Clinical Pearls:**
1. Understanding the correct sequence of amino acids in heme synthesis is crucial for diagnosing porphyria, a group of genetic disorders caused by impaired heme synthesis.
2. Aminolevulinic acid and its subsequent conversion to porphobilinogen are vital in the diagnosis of porphyria cutanea tarda, a liver disease-induced condition.
Remember, porphyrias are characterized by the accumulation of porphyrins, which are precursors to heme, leading to skin lesions (porphyria cutanea tarda, for example, is caused by impaired heme synthesis in the liver).