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Author Topic:   Definition of Life
Wounded King
Member (Idle past 2957 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 41 of 77 (337150)
08-01-2006 6:31 AM
Reply to: Message 40 by inkorrekt
07-31-2006 10:44 PM


Optical isomer issues
I like the last part of your post that "we do not know". The soup of D-and L-forms of amino acids will be biologically useless as the D-forms act as biological poisons.

Could you be more specific? How do D-forms act as biological poisons? How do you know that that mode of action would be relevant in a pre or proto biological environment? If a mechanism such as RAZD posits could locally skew the proportions of the enantiomers could this overcome whatever inhibitory effects the D-amino acids might have?

I'm not saying that D-amino acids can't act as posions on living things, I just don't think that the extent to which they do so supports your contention that this is a significant problem for abiogenesis.

TTFN,

WK


This message is a reply to:
 Message 40 by inkorrekt, posted 07-31-2006 10:44 PM inkorrekt has responded

Replies to this message:
 Message 42 by inkorrekt, posted 08-01-2006 11:23 PM Wounded King has responded

  
Wounded King
Member (Idle past 2957 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 43 of 77 (337341)
08-02-2006 3:05 AM
Reply to: Message 42 by inkorrekt
08-01-2006 11:23 PM


Re: Optical isomer issues
Enzyme must have a substrate(Substrate is a substance which is acted upon by the enzyme to give the product) L-forms are natural substrates.

Surely L-forms are only natural substrates for enzymes whose reactions act on amino acids and possibly on L-form amino acids specifically, it really depends on the specific enzyme. The substrate of an enzyme can be any one of a huge number of molecules indeed there are enzymes that convert L-amino acids into D-amino acids.

As an explanation this has pretty much no value. Do you have any evidence to support your contention that D-amino acids are general inhibitors of enzyme activity?

TTFN,

WK


This message is a reply to:
 Message 42 by inkorrekt, posted 08-01-2006 11:23 PM inkorrekt has responded

Replies to this message:
 Message 44 by RAZD, posted 08-02-2006 7:27 AM Wounded King has responded
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 Message 50 by inkorrekt, posted 08-02-2006 9:39 PM Wounded King has responded

  
Wounded King
Member (Idle past 2957 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 45 of 77 (337360)
08-02-2006 8:52 AM
Reply to: Message 44 by RAZD
08-02-2006 7:27 AM


Re: Optical isomer issues
There are enzymes which convert some D to L amino acids, though not neccessarily in a one step process. There doesn't seem to be as extensive a literature on this as on the L to D converting enzymes. I'm not sure that these would be neccessary for your concentration to occur, I'd have thought some material with a chirally selective adsorption would be more likely.

TTFN,

WK


This message is a reply to:
 Message 44 by RAZD, posted 08-02-2006 7:27 AM RAZD has responded

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Wounded King
Member (Idle past 2957 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 51 of 77 (337587)
08-03-2006 2:54 AM
Reply to: Message 50 by inkorrekt
08-02-2006 9:39 PM


Re: Optical isomer issues
But, in nature, this is not the case.

What do you mean 'in nature', are you claiming that racemases are synthetic? these enzymes occur in nature, but I have no problem agreeing that they would not have been present when life first arose, if that is what you were getting at.

Threre are specific control mechanisms modulating cellular activity. What happens if there is no control? This is when we develop some diseases known as Metabolic disorders. For example, if Phenyl alanine is not metabolized, then it accumulates. The clinical condition is known as Phenylketonuria.

I don't see what this has to do with chirality.

Random chemical reactions cannot and should not occur. If they did, then there will be chaos and severe metabolic disorders.

Well actually they occur a lot, and there are a number of systems in the cell to cope with them when they do. The entire point of many enzymes is to catalyse reactions which might otherwise occur randomly but only rarely.

In the brain, Phenylalanine is converted into hydroxy phenylalanine by the enzyme phenyl alanine hydroxylase. L-Phenylalanine is the substrate. But, D-Phenylalanine is an inhibitor of this enzyme.

Which is interesting but one D-amino acid acting as an inhibitor of a specific enzyme is by no means clear evidence that D-amino acids are general inhibitors of enzyme activity.

TTFN,

WK


This message is a reply to:
 Message 50 by inkorrekt, posted 08-02-2006 9:39 PM inkorrekt has responded

Replies to this message:
 Message 52 by inkorrekt, posted 08-04-2006 4:43 PM Wounded King has responded

  
Wounded King
Member (Idle past 2957 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 53 of 77 (338058)
08-05-2006 2:46 AM
Reply to: Message 52 by inkorrekt
08-04-2006 4:43 PM


Re: Optical isomer issues
I can't find anything saying that in Stryer.

Why not try and back your claims up for once and provide an actual reference, even from a textbook, which supports your claim.

TTFN,

WK


This message is a reply to:
 Message 52 by inkorrekt, posted 08-04-2006 4:43 PM inkorrekt has responded

Replies to this message:
 Message 54 by inkorrekt, posted 08-13-2006 8:56 PM Wounded King has responded

  
Wounded King
Member (Idle past 2957 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 56 of 77 (339922)
08-14-2006 3:15 AM
Reply to: Message 54 by inkorrekt
08-13-2006 8:56 PM


Re: Optical isomer issues
Stryer is pretty much one of the standard university level Biochemistry textbooks, it says nothing in line with your claims. You claimed that I would find something supporting your claims in...

any basic text book in biochemistry.

Since this claim seems to be false why not try to show that your prior claim was not also false. The full text of Stryer is available in a searchable format online so you don't even need to go to the library to show me where I'm wrong. Just find the evidence in this standard biochem texbook, which I have apparently missed, supporting your claim.

I am not your teacher.

You're right, you aren't. I am the one teaching you, because I am the one who has a clue what they are talking about. You just seem to grab hold of some plausible sounding argument and keep repeating it regardless of whether there is actually any truth in it or any evidence suggesting it is a valid argument. As Iname has suggested this is going against the forum guidelines and is also very much debating in bad faith.

TTFN,

WK


This message is a reply to:
 Message 54 by inkorrekt, posted 08-13-2006 8:56 PM inkorrekt has not yet responded

  
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