It is usually said that C, H, N, O, P, S are the essential elements of life “as we know it”: that is, life based on amino acids and DNA/RNA.

C, H, N, O, P are required for DNA/RNA: S is used in only a small number of amino acids, and different life forms use different sets of amino acids.

Question 1/
Are there any living things that do not use any of the S-bearing amino acids?

Question 2/
Are there any living things that only require CHNOPS to function?

dv said:

Question 1/
Are there any living things that do not use any of the S-bearing amino acids?

It is highly unlikely because a key reaction in metabolism is the incorporation of acetate into the citric acid cycle which involves activation of the carboxyl group with coenzyme A as a thioester.

dv said:

Question 2/
Are there any living things that only require CHNOPS to function?

Transition metals have a crucial role in the function of many enzymes..

“It is highly unlikely because a key reaction in metabolism is the incorporation of acetate into the citric acid cycle which involves activation of the carboxyl group with coenzyme A as a thioester.”

Then I guess we can cross out all aerobic life forms.

“Transition metals have a crucial role in the function of many enzymes..”

Mmm.

dv said:

“It is highly unlikely because a key reaction in metabolism is the incorporation of acetate into the citric acid cycle which involves activation of the carboxyl group with coenzyme A as a thioester.”

Then I guess we can cross out all aerobic life forms.

Pretty much any life form that has an oxidative metabolism, even if the oxidant isn’t oxygen. However, the biosynthesis of fatty acids from acetate also involves activation of acetate as the acetyl-CoA thioester.

> Are there any living things that only require CHNOPS to function?

No. All cells in all creatures contain salt water. Salt is normally sodium chloride, there may be some that can get away with some other salt such as magnesium chloride, but I doubt it.

dv said:

“Transition metals have a crucial role in the function of many enzymes..”

Mmm.

For example, the dual oxidation states of Fe and Cu make them important in electron transport mechanisms.

For example, the dual oxidation states of Fe and Cu make them important in electron transport mechanisms.
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Yeah I know … but are there exceptions?

Have to admit that so far in my reading I haven’t found any examples of organisms without any use of metals.

ATPase requires Na and K. Ca is a second messenger. All animals require the former. All plants and animals and (?many ?all) protists require the latter. Then we have eukaryotes using various heavy metals for oxygen transport proteins and other molecules with coordination chemistry.

And I think plants have the same ATP synthase but different proteins downstream.

How about Archaea?

Ditto yeast etc.

I’m a doktar, not an Archaeologist.

Are we including viruses in this?

LMGTFY…

http://textbookofbacteriology.net/environment.html

Have a read. I’m busy reading a book for fun.

Are we including viruses in this?
—
Let’s say no. Fully replicative RNA/DNA/peptide according-to-Hoyle life.

http://textbookofbacteriology.net/environment.html

I would need a ruling … is a Bacteriologist going to gaf about Archaea?

dv said:

Yeah I know … but are there exceptions?

Have to admit that so far in my reading I haven’t found any examples of organisms without any use of metals.

Zn(II) is an efficient Lewis acid and is found in many enzymes. According to Wikipedia, it is the only metal found in all enzyme classes.

The point is that living processes need to catalyse particular types of reactions, and the enzymes that perform the catalysis need to be able to “activate” the reactants in a specific manner, thus requiring a specific type of chemistry at the active sites of the enzymes, limiting the possible ways in which this can be done.

KJW said:

dv said:

Yeah I know … but are there exceptions?

Have to admit that so far in my reading I haven’t found any examples of organisms without any use of metals.

Zn(II) is an efficient Lewis acid and is found in many enzymes. According to Wikipedia, it is the only metal found in all enzyme classes.

The point is that living processes need to catalyse particular types of reactions, and the enzymes that perform the catalysis need to be able to “activate” the reactants in a specific manner, thus requiring a specific type of chemistry at the active sites of the enzymes, limiting the possible ways in which this can be done.

All hail the Zinc Finger.

dv said:

Question 1/
Are there any living things that do not use any of the S-bearing amino acids?

I seriously doubt it. Before oxygen, sulfur was king, and many (if not all ?) anaerobes still use sulfur.

Two of the amino acids which are directly encoded by the universal genetic code contain sulfur: methionine and cysteine. So even if an organism doesn’t normally use S-bearing amino acids it’d only take a single point mutation to change that, assuming that the mutation is non-lethal & the organism has the sulfur available to synthesize the amino acid. IANAB, but I assume that if a particular amino acid can’t be found when building a peptide chain the peptide will be terminated at that point.

Furthermore, the codon for methionine acts as a start codon.
From Wikipedia
Wikipedia said:

Methionine is one of only two amino acids encoded by a single codon (AUG) in the standard genetic code (tryptophan, encoded by UGG, is the other). The codon AUG is also the most common eukaryote “Start” message for a ribosome that signals the initiation of protein translation from mRNA when the AUG codon is in a Kozak consensus sequence. As a consequence, methionine is often incorporated into the N-terminal position of proteins in eukaryotes and archaea during translation, although it can be removed by post-translational modification. In bacteria, the derivative N-formylmethionine is used as the initial amino acid.

…

And then there’s the weird one, selenocysteine , which contains selenium. It’s codon is UGA, which is normally a stop codon; organisms that use selenocysteine have a sequence called the SECIS element (about 60 nucleotides long) soon after the UGA codon which essentially modifies the interpretation of the UGA sequence.

Sure, selenocysteine’s not that common, but it’s got a venerable history.

From Biosynthesis of Selenocysteine

Although UGA is normally a termination codon that dictates the cessation of protein synthesis, it is also used as a Sec codon by numerous organisms in each of the 3 domains of life: eubacteria, archaea, and eukaryotes. Of the >500 genomes sequenced in eubacteria, only ∼20% encode the machinery for inserting Sec into protein, and in archaea, ∼10% have this machinery (4, 5). In eukaryotes, the Sec insertion machinery has been found in a number of lower organisms such as green algae, kinetoplastida, and slime molds and it is widespread in animals but absent in fungi and higher plants (4, 5).

PM 2Ring said:

I assume that if a particular amino acid can’t be found when building a peptide chain the peptide will be terminated at that point.

I believe that the peptide chain will remain bound to the ribosome (perhaps it will slowly hydrolyse from the ribosome by uncatalysed reaction with water) because it is a specific STOP code that terminates the peptide.

Thanks all.

PM2, I did find out that there are life forms that do not require selenoproteins.

dv said:

PM2, I did find out that there are life forms that do not require selenoproteins.

Ok. FWIW, I wasn’t implying that all life forms use selenoproteins, I was just mentioning it because Sec is one of the amino acids that DNA can encode, albeit in a rather hackish fashion.