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Author Topic:   Cell membrane and Proteins
Kingdom_of_God
Inactive Member


Message 1 of 7 (78066)
01-12-2004 4:33 PM


I am not a biologist or anything, but today in school I was taught that through a mixture of gasses and a spark amino acids are formed, and then they linked together to form protein. But in my Moms college book it states that the cell needs to be LIVING in order to link together properly. So how did the amino acids form to make proteins which help make cells if the cell ALREADY needs to be LIVING to link them?
Also: Cell membranes are a 2 layer membrane of lipids, BUT lipids only form from LIVING cells.

Replies to this message:
 Message 2 by Loudmouth, posted 01-12-2004 5:15 PM Kingdom_of_God has not replied

  
Loudmouth
Inactive Member


Message 2 of 7 (78071)
01-12-2004 5:15 PM
Reply to: Message 1 by Kingdom_of_God
01-12-2004 4:33 PM


Welcome to the forum!
I think you are referencing the Miller-Urey experiment that showed the formation of amino acids from simpler compounds. I don't remember if they claimed that these amino acids polymerized into a peptide (short protein) or not. Anyway, proteins are polymers whose subunits are amino acids, that is amino acids are the pearls of a pearl necklace, so to speak. Here is a general diagram:
(added in Edit: The R and H are supposed to line up with the middle Carbon (C). For some reason the darn thing won't let me slide them over.)
* R
* |
* (-)COOH----C----NH4(+)
* |
* H
The R represents the different R groups that exist in amino acids (alanine has a simple methyl group as an R group for example). The negative and positive charges on the right and left allow the amino acids to bond to each other like opposing poles on a magnet. This process results in peptide bonds (the COOH- from one amino acid binds to the NH4+ from another). This is important in that it is simple chemistry. Because of this, peptides (short proteins) can be made outside of the cell using chemistry and special lab equipment. So, no, proteins do not require some "living energy" in order to form, but it is difficult to build long chains outside of the cell. The same can be said for lipids as well, not all sources of lipid are biological.
Just a general comment. The theory of abiogenesis (the process of getting life from non-life) is still in it's infancy. Also, it is not tied to the theory of evolution. Evolution starts with the first replicating organism and describes how species were formed after life started. The two theories are not necessarily the same theory. Anyway, hope this helps.
[This message has been edited by Loudmouth, 01-12-2004]
[This message has been edited by Loudmouth, 01-12-2004]
[This message has been edited by Loudmouth, 01-12-2004]

This message is a reply to:
 Message 1 by Kingdom_of_God, posted 01-12-2004 4:33 PM Kingdom_of_God has not replied

Replies to this message:
 Message 4 by DNAunion, posted 01-14-2004 9:33 PM Loudmouth has replied

  
Adminnemooseus
Administrator
Posts: 3974
Joined: 09-26-2002


Message 3 of 7 (78477)
01-14-2004 5:40 PM


Thread moved here from the Human Origins forum.

  
DNAunion
Inactive Member


Message 4 of 7 (78516)
01-14-2004 9:33 PM
Reply to: Message 2 by Loudmouth
01-12-2004 5:15 PM


quote:
I think you are referencing the Miller-Urey experiment that showed the formation of amino acids from simpler compounds. I don't remember if they claimed that these amino acids polymerized into a peptide (short protein) or not.
Just so we are all on the same page, no proteins, polypeptides, or even proteinoids were created in the Miller electric-discharge experiments.
quote:
"The negative and positive charges on the right and left allow the amino acids to bond to each other like opposing poles on a magnet. This process results in peptide bonds (the COOH- from one amino acid binds to the NH4+ from another). This is important in that it is simple chemistry.
I realize you are trying not to be too technical, but the above statements make it sound like if someone took some amino acids and just threw them in a solution they'd simply stick together and form proteins.
Under biological and most natural settings, forming a peptide bond is thermodynamically unfavorable: it's uphill (or more technically, endergonic). That's why OOL researchers - and cells - activate the amino acids somehow: to provide energy to drive the reaction uphill, against its thermodynamic tendency.
But you are correct overall, in the sense that getting amino acids to bond together does not require cells (note I didn't say you could get proteins without a cell - that's debatable).
[This message has been edited by DNAunion, 01-14-2004]

This message is a reply to:
 Message 2 by Loudmouth, posted 01-12-2004 5:15 PM Loudmouth has replied

Replies to this message:
 Message 5 by Loudmouth, posted 01-15-2004 12:03 PM DNAunion has replied

  
Loudmouth
Inactive Member


Message 5 of 7 (78657)
01-15-2004 12:03 PM
Reply to: Message 4 by DNAunion
01-14-2004 9:33 PM


quote:
I realize you are trying not to be too technical, but the above statements make it sound like if someone took some amino acids and just threw them in a solution they'd simply stick together and form proteins.
Under biological and most natural settings, forming a peptide bond is thermodynamically unfavorable: it's uphill (or more technically, endergonic). That's why OOL researchers - and cells - activate the amino acids somehow: to provide energy to drive the reaction uphill, against its thermodynamic tendency.
Good point. In the cell it requires one ATP per peptide bond because the reaction is uphill thermodynamically. I was trying to make it simple in that the positive and negative sides of the molecule allow specificity for peptide elongation (carboxy to amino). Correct me if I am wrong, but once the peptide bond is made there is no backwards reaction within the same mechanism, which I think is important with respect to OOL research. There can be inorganic proteolytic reactions, but those are usually unrelated to peptide elongation reactions. In other words, peptide elongation/peptide breakdown is not a function of equilibrium between the two states.
quote:
But you are correct overall, in the sense that getting amino acids to bond together does not require cells (note I didn't say you could get proteins without a cell - that's debatable).
Just as a note, there are cell free systems that produce proteins. However, the system does use E. coli lysates so maybe "cell-free" is a bit misleading.

This message is a reply to:
 Message 4 by DNAunion, posted 01-14-2004 9:33 PM DNAunion has replied

Replies to this message:
 Message 6 by DNAunion, posted 01-15-2004 1:03 PM Loudmouth has not replied
 Message 7 by DNAunion, posted 01-15-2004 1:16 PM Loudmouth has not replied

  
DNAunion
Inactive Member


Message 6 of 7 (78667)
01-15-2004 1:03 PM
Reply to: Message 5 by Loudmouth
01-15-2004 12:03 PM


quote:
But you are correct overall, in the sense that getting amino acids to bond together does not require cells (note I didn't say you could get proteins without a cell - that's debatable).
quote:
Just as a note, there are cell free systems that produce proteins. However, the system does use E. coli lysates so maybe "cell-free" is a bit misleading.
Touche

This message is a reply to:
 Message 5 by Loudmouth, posted 01-15-2004 12:03 PM Loudmouth has not replied

  
DNAunion
Inactive Member


Message 7 of 7 (78671)
01-15-2004 1:16 PM
Reply to: Message 5 by Loudmouth
01-15-2004 12:03 PM


quote:
Correct me if I am wrong, but once the peptide bond is made there is no backwards reaction within the same mechanism, which I think is important with respect to OOL research. There can be inorganic proteolytic reactions, but those are usually unrelated to peptide elongation reactions. In other words, peptide elongation/peptide breakdown is not a function of equilibrium between the two states.
Hydrolysis of peptides bonds is thermodynamically spontaneous: it's an allowed, downhill reaction that releases energy (i.e., is exergonic).
That doesn't mean it will happen instantaneously, but that the tendency is there and it will occur any chance it gets, even if at an impercetible rate (for example, the reaction between oxygen and paper is thermodynamically spontaneous, as can be seen by putting a lit match to just one corner: the whole sheet of paper burns. Without the lit match, oxygen still reacts with the paper but at such a slow rate that it is imperceptible). In a non-enzymatic setting, the conditions - temperature, pH, and so on - determine the rate of hydrolysis of peptides.
[This message has been edited by DNAunion, 01-15-2004]

This message is a reply to:
 Message 5 by Loudmouth, posted 01-15-2004 12:03 PM Loudmouth has not replied

  
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