Among all the biological molecules, only proteins serve as catalysts in cellular reactions and hormones. Why is it that other class of molecules, say lipids, cannot act as catalysts or hormones?
I think maybe you have to think of it in a different way. It is not ONLY proteins that are hormones or catalysts. As has been stated above there are other molecules able to catalyze chemical reactions. However, proteins are extremely overrepressented as catalysts. This is likely due to the large chemical flexibility of proteins. With their 20 amino acids with varying chamical properties, proteins easily outperform ribozymes which has much less chemical flexibility. So evolution has come to rely on proteins for catalysis.
Regarding hormones, there are many examples of hormones that are not proteins. In plants for example gibberilin, jasmonate and ethylene are alle important hormones, but none of them are proteins. But you are right, there are a lot protein hormones. The advantage of using proteins as hormones, I guess, lies in the specificity of the binding site. Much along the lines I stated above, protein chemical diversity enables for some pretty specific binding interfaces - which is a good idea if you want to minimize hormonal confusion.
I hope it answered your question.
Cheers.
Enzymes (Proteins) have an active site with several amino acid side chains involved, which a fatty acid can not have. I suggest to consult a basic biochemistry textbook. Hormones are no catalysts.
Don't forget that other classes of biomolecules have catalytic properties : ribozymes are a good example !
Even some carbohydrates such as Cyclodextrins are acting as catalytic molecule. Beta-Cyclodextrin shows hydrolytic activity on the b-lactam ring of penicillins and thereby inactivate the antibiotic under alkaline conditions.
I think maybe you have to think of it in a different way. It is not ONLY proteins that are hormones or catalysts. As has been stated above there are other molecules able to catalyze chemical reactions. However, proteins are extremely overrepressented as catalysts. This is likely due to the large chemical flexibility of proteins. With their 20 amino acids with varying chamical properties, proteins easily outperform ribozymes which has much less chemical flexibility. So evolution has come to rely on proteins for catalysis.
Regarding hormones, there are many examples of hormones that are not proteins. In plants for example gibberilin, jasmonate and ethylene are alle important hormones, but none of them are proteins. But you are right, there are a lot protein hormones. The advantage of using proteins as hormones, I guess, lies in the specificity of the binding site. Much along the lines I stated above, protein chemical diversity enables for some pretty specific binding interfaces - which is a good idea if you want to minimize hormonal confusion.
I hope it answered your question.
Cheers.
According to me the most probable reason proteins are hormones(in most cases) is that they can be regulated at the gene level. for eg if you are in stress condition then adrenaline will be secreted so at that time only the gene coding for adrenaline synthesis will be regulated and adrenaline protein will be synthesized which is not possible for other biomolecules.this is also true for catalyst and apart from this conformation change and specific active site is possible for proteins only.
I agree with the contributions above. I believe proteins have the greatest structural versatility arising from the fact that they are generally composed of 20 different monomers. The monomers (amino acids) also have the advantage of being made of moieties that can ionize, produce charges, form H-bonding, the aromatic ones can also participate in hydrophobic interactions etc. These are some of the factors involved in chemical reactions. It is therefore easy for the protein molecule , through its amino acid composition, to provide the milieu that is conducive for several types of chemical reactions. The conformational changes necessary in some catalytic activities also give proteins an edge over other biomolecules. This is coupled with the issue of control. To achieve the synergy, harmony or homeostasis required by the living system, catalytic or enzymatic activities must be subject to accurate, near perfect control system. Again, proteins have an advantage over other biomolecules because they can be more easily induced, repressed, regulated through the gene.
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