Thyroid Hormone

[G1SG2]

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TPR classifies thyroid hormone as a "peptide hormone." I know T3 and T4 are tyrosine based; however, from my understanding (and what I remember from EK), they act as steroids and act at the level of transcription. Could it be possible that TPR was referring to calcitonin? This is from the "MCAT Science Review Questions and Solutions" booklet from the hyperlearning course, btw.

 

[wanderer]

TPR classifies thyroid hormone as a "peptide hormone." I know T3 and T4 are tyrosine based; however, from my understanding (and what I remember from EK), they act as steroids and act at the level of transcription. Could it be possible that TPR was referring to calcitonin? This is from the "MCAT Science Review Questions and Solutions" booklet from the hyperlearning course, btw.

Thyroid hormones are lipid-soluble amino acid (not peptide) hormones (unlike the catecholamines which are hydrophillic). This is a mistake.

http://en.wikipedia.org/wiki/Thyroxine

 

[G1SG2]

Thyroid hormones are lipid-soluble amino acid (not peptide) hormones (unlike the catecholamines which are hydrophillic). This is not a mistake.

http://en.wikipedia.org/wiki/Thyroxine

Don't you mean it is? They said it is a peptide hormone. Isn't that a mistake?

 

[wanderer]

Don't you mean it is? They said it is a peptide hormone. Isn't that a mistake?

lol, yea it's a mistake.

 

[G1SG2]

lol, yea it's a mistake.

Haha, okay, just making sure. Thanks.

 

[sv3]

it is a peptide hormone (fine, technicially an amino acid derivative) but acts like a steroid. Hence that's why it's called the exception.

 

[stockraider]

from our friend the wikipedia:

T3 and T4 cross the cell membrane easily as they are lipophilic molecules, and function via a well-studied set of nuclear receptors in the nucleus of the cell, the thyroid hormone receptors.

 

[dougkaye]

it is a peptide hormone (fine, technicially an amino acid derivative) but acts like a steroid. Hence that's why it's called the exception.

They're not the same thing. It's important in keeping the correct classification for hormones and neurotransmitters:

1. peptides
2. amino acid derivative/biogenic amines
3. steroid

amino acid derivatives are much smaller and have a different synthetic pathway because they're not transcribed/translated but built from the amino acid building block. this is a huge difference in terms of synthesis and control mechanisms.

 

[dougkaye]

they act LIKE steroids not AS steroids since they're not steroids and you pointed out 😉 LIKE steroids in the sense that they pass through membranes and bind to intranuclear receptors and affect transcription.