Hormones in the Biomolecules chapter: how to sort steroid vs polypeptide vs amino-acid-derived ones without just cramming?

I like to understand things before I memorise them, and hormones in the Biomolecules chapter are testing that. NCERT classifies hormones by chemical nature into steroid hormones, polypeptide hormones and amino acid derivatives, and then lists examples that all start to blur together for me: insulin, glucagon, thyroxine, adrenaline, cortisol, testosterone, oxytocin.

What I have so far is that insulin is a polypeptide and lowers blood glucose, and that lack of iodine causes goitre because of thyroxine. But I couldn't tell you why thyroxine belongs in the "amino acid derivative" group while cortisol is in the steroid group, other than the textbook said so. Also is adrenaline related to thyroxine somehow, since both are in the same category?

I did a PYQ-style question yesterday, "which of the following is NOT a steroid hormone", and I second-guessed myself into a wrong answer. A way to sort these with logic instead of rote would really help. And what is each one actually doing in the body? A one-line role for each would be great.

7 answers & replies

[+]Kavya NaikDropperSample· 11d ago

Sort by what they are built from.

Steroid hormones are made from cholesterol and share the four-ring steroid skeleton: sex hormones (testosterone, estradiol, progesterone), cortisol (a glucocorticoid), aldosterone (a mineralocorticoid).

Polypeptide hormones are chains of amino acids: insulin, glucagon, oxytocin, vasopressin, ACTH, growth hormone.

Amino acid derivatives are small modified amino acids: thyroxine, adrenaline (epinephrine), noradrenaline. They are made from tyrosine, which is why thyroxine and adrenaline sit together even though they do totally different jobs. Different jobs, same raw material.

[+]Farhan ShaikhDropperSample· 11d ago

I always thought thyroxine was a steroid since it controls metabolism and burns fat, so lipid kind of thing? That's how I memorised it 😅

[+][–]Siddharth RaoDropperSample· 11d ago
Farhan, no, controlling metabolism doesn't make it a steroid. Thyroxine is an iodinated derivative of tyrosine, the amino acid. That's also why iodine in the diet matters: no iodine means the gland can't make enough thyroxine, and the gland enlarges, which is goitre.

Quick filter for the "not a steroid" MCQ: if the option has iodine, or is a chain of amino acids, it's not a steroid.

[+]Mehak AroraDropperSample· 10d ago

Roles, one by one, the way I revise them:

Insulin: lowers blood glucose. It's a polypeptide of 51 amino acids in two chains (A with 21, B with 30) joined by disulphide bonds. Not enough insulin is diabetes mellitus.
Glucagon: raises blood glucose by breaking down glycogen. Opposite of insulin.
Thyroxine: controls basal metabolic rate.
Adrenaline: "fight or flight", raises heart rate and blood pressure.
Cortisol: glucocorticoid, regulates carbohydrate metabolism and stress response.
Aldosterone: mineralocorticoid, regulates sodium and water balance.
Testosterone / estradiol / progesterone: development of male / female characters and reproduction.
Oxytocin: uterine contractions in childbirth, and milk ejection.

[+]Rahul DubeyDropperSample· 10d ago

One more way to think about it, which helped me on elimination questions: steroid hormones are lipid-soluble, so they pass through the cell membrane and act inside the cell. Peptide hormones are water-soluble and can't cross the membrane, so they bind to receptors on the surface. Amino acid derivatives vary (adrenaline works through surface receptors, thyroxine goes inside).

I wouldn't go deep into this for NEET, but it helps when you see the word "steroid" in a different chapter, say reproduction in bio, and want it to make sense.

[+]Ishita GoyalDropperSample· 10d ago

Template I use, three columns:

Type	Built from	Examples
Steroid	cholesterol	cortisol, aldosterone, testosterone, estradiol, progesterone
Polypeptide	amino acids in a chain	insulin, glucagon, oxytocin, vasopressin
Amino acid derivative	tyrosine	thyroxine, adrenaline, noradrenaline

Revise the table once and the "odd one out" question is easy.

[+][–]Zoya Khan12thSample· 10d agoAuthor
this is exactly what I needed. A logic first, mugging later. thank you all, and farhan, no stress, I had the same instinct at first 🙂

In the lac operon how does the inducer actually switch it on? Plus is DNA fingerprinting based on VNTRs?

Revising the last part of Molecular Basis of Inheritance and I want to make sure I actually understand the lac operon instead of just memorising the diagram. My understanding: the i gene makes a repressor. When lactose i

🧬 NEET Biology❓ Question1 min read👏 8💬 7

Zoya Khan12thSample· 17d ago

Electrostatic precipitator vs scrubber vs catalytic converter: what exactly does each remove, and why does a converter need unleaded petrol?

I've been reading the air pollution section slowly because I find the three devices easy to blur. What I have so far: - Electrostatic precipitator thermal power plants : removes particulate matter. NCERT says it can remo

🧬 NEET Biology❓ Question1 min read👏 6💬 7

Zoya Khan12thSample· 21d ago

CoCl3·5NH3 with AgNO3, how do I decide how many moles of AgCl form using Werner's primary and secondary valence?

I have been going through Werner's postulates for a few days and I can recite them, but I get stuck the moment a question asks me to apply them. The series I am looking at is the classic one in NCERT: CoCl3·6NH3, CoCl3·5

🧪 NEET Chemistry❓ Question1 min read👏 7💬 7

Keep reading

Kavya NaikDropperSample· 3d ago

Arrhenius: my Ea for 'rate doubles per 10 K' is 53.6 kJ but the book says 52.9. Who is right?

Also what does the factor P actually do and what does a catalyst change?

🧪 NEET Chemistry❓ Question1 min read👏 6💬 6

Nisha Verma12thSample· 4d ago

Benzaldehyde gives Tollens' test but not Fehling's, and which compounds give the iodoform test?

Revision month, chemistry, distinction tests. Every board and NEET paper has at least one "which reagent distinguishes X from Y" question, so I need this airtight. The thing I got wrong in a mock: "Benzaldehyde and propa

🧪 NEET Chemistry❓ Question1 min read👏 7💬 7

Kavya NaikDropperSample· 5d ago

Green chemistry examples in NCERT: which process replaced which (dry cleaning, bleaching, ethanal)? Mixing up the chemicals

Amma says I study chemistry like I'm doing a quiz show, fast but with mistakes 😅. Soil pollution and green chemistry is one of the "easy" last pages that I still get wrong in tests because the examples blur. What I know:

🧪 NEET Chemistry❓ Question1 min read👏 7💬 6