enzymes - (Oct/30/2005 )

hi
why do proteins alone act as enzymes?

thanks in advance

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What do you mean by alone proteins?

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hi Minnie Mouse

i am really sorry i typed it in a hurry , i have now retyped it correctly.

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There are RNA enzymes (ribozymes)...

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hi HomeBrew

i know there are RNA enzymes too.but most of the enzymes are proteins-why is it like that?why cant it be carbohydrate , lipids or nucleic acids

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The structure of a molecule dictates its function. If you were to consider NAs, for example, they wouldn't be good enzymes since you only have a limited number of NA types as well as conformation. Which part of the NA would a reactant bind to? Same questions for CHOs and lipids. The way proteins are structured, you have so many conformations (recall 4 levels of structure) possible depending on composition. Variability in conformation among different protein molecules is important since conformation is critical in being able to bind with the reactants to enable catalysis of a reaction.

This is a very simplified explanation. You can also look at what exactly, within each active site, is interacting with any particular reactant.

A parallel question to your question is, why can't proteins be the MAIN component of cell membranes? Why do they have to be lipids? Why not carbohydrates or NAs?

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The RNA-world-hypothesis suggests that, even thought that's the case now, possibly in early life RNA was "used" both for storage and enzymatic funktion. For example in the ribosome still the RNA seems to be the enzymatic part. But the variability is quite small for nucleic acids compared to aminoacids (as stated by maru), so evolution brought up a system that comprizes of more possible building blocks

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hi maru

because lipid is insoluble in water whereas proteins,nucleic acids and carbohydrates r soluble in water.lipids also have the ability to act as signaling molecules and can also form bilayers.they dont have many conformations as protein,nucleic acids and carbohydrates do .the main thing is that lipid dont act as enzymes.

anyway thanks alot for answering to my question and 4 clearing my doubt.

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They mostly have a polar head, tht's why they form micelles or the like. If insoluble they should precipitate



bilayers or micelles will change on temperature change

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hi Kersten

yes they do have polar head and micelle is formed due to increase of water,temperature etc but the polar head jus forms hydrogen bond with the surrounding water and the lipid bilayer doesnt get dissolved into the water.i.e it is insoluble.

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