Lecture 4. Steroid hormone Synthesis

Question 1

Synthesis pathway for dopamine and catecholimines

also what are the cofactors for each enzyme?

SOM.1ai.BPM2.1.ER.2.BCHM.EC.0402 Analyze
the cofactors that are needed during the
biosynthesis of hormones that are derived from
amino acids.

Identify hormones formed from tyrosine and explain the biosynthetis of catecholamines.

Answer 1

Question 2

Degradation of Dopamine yields

Answer 2

Homovanillic Acid (HVA)

Question 3

Degradation of Norepinephrine and Epinephrine yields?

Describe VMA, metanephrine and homovanillic acid as the degradation products of the
catecholamines

Answer 3

NE>>normetanephrine>>Vanillylmandelic Acid (VMA)

Epi>>metanephrine>> VMA

Question 4

Synthesis Pathway of serotonin

Indicate the steps in the formation of serotonin (5-hydroxy tryptamine; 5-HT).
• Explain the formation of 5-HIAA formation (Role of MAO) and analyze its clinical significance
• Indicate the precursor molecule of melatonin and identify its significance in the pineal gland

Answer 4

Question 5

What are the characteristic symptoms of Carcinoid Syndrome and what is the unique clinical finding to confirm this diagnosis?

Answer 5

This syndrome arises from a tumor of serotonin producing cells in GIT called APUD cells.

symptoms: cutaneous flushing, GI hypermobility (diarrhea)

In this syndrome, there will be INCREASED 5-HIAA excretion in urine

Question 6

Name the enzymes that require Tetrahydrobiopterin (BH4) as its coenzyme?

Answer 6

Question 7

Deficiency of dihydrobiopterin synthesis OR dihydrobiopterin reductase leads to?

Answer 7

Hyperphenylalaninemia AND decreased synthesis of neurotransmitters (catecholamines and serotonin)

Question 8

How is Thyroid hormone made in the Thyroid? What are the steps?

Answer 8

It’s formed on the thyroglobulin protein in the thyroid gland; also tyrosine is IODINATED here (substituted on the ring).

Steps: 1. Trapping iodine in the thyroid cell

2. Iodination of the thyroglobulin protein
3. Coupling of the iodinated tyrosine side chains
4. Release of Throid hormone
5. De-iodination of T4 to the ACTIVE T3

Question 9

What are the functions of throperoxidase (TPO)?

Answer 9

1. Fixes iodine to thyroglobulin on specific Tyrosine side chains.
2. Acts as a peroxidase to link two iodo-tyrosine side chains together.

Question 10

Pheochromocytoma: what is it? Defining symptoms? What lab finding indicates this condition?

Answer 10

It is a tumor in the adrenal medulla that overproduces epinephrine. Defining features are: hypertension, headache, sweating, tachycardia.

The unique lab finding would be high urinary VMA and catecholamines

Question 11

How is iodine taken up into the thyroid gland? (Transport mechanism)

Answer 11

Secondary Active Transport; SYMPORT