AlphaArgonian
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Ok so I'll give any people who haven't studied A-level (or equivalent) biology some context:
Amino acids are biological molecules that make up proteins, there are 20 (known) of them. some examples are glycine, valine and tryptophan.
Proteins form from unique combinations of these amino acids...

Now, textbooks say there are 8000 (20^3) combinations...

My teacher and I argue that there are 20! combinations...

Help?
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username1793709
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Because amino acids can be arranged in many different combinations, it's possible for your body to make thousands of different kinds of proteins from just the same 21 amino acids. You may see books that say there are only 20 amino acids.

Hope this explains it
There's 20 amino acids, but thousands of proteins (I think)
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Serine Soul
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Pretty sure it's 20! different combinations :mmm:

But I guess there's a fewer amount in nature....

Interesting questions
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Arbolus
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The answer is infinite, for all intents and purposes, because there's no theoretical limit on how long a peptide chain can be. In general, if you have a chain of n objects, each of which can be one of 20 different options, and there is no limit on how many times each option can be used, the number of possible combinations is 20n.

20! is the number of ways of arranging 20 different amino acids in a chain if each acid can only be used once.
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Serine Soul
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(Original post by Arbolus)
The answer is infinite, for all intents and purposes, because there's no theoretical limit on how long a peptide chain can be. In general, if you have a chain of n objects, each of which can be one of 20 different options, and there is no limit on how many times each option can be used, the number of possible combinations is 20n.

20! is the number of ways of arranging 20 different amino acids in a chain if each acid can only be used once.
Great point
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AlphaArgonian
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Ah, thanks everyone, this really helps
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AlphaArgonian
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(Original post by Porcupayne)
Because amino acids can be arranged in many different combinations, it's possible for your body to make thousands of different kinds of proteins from just the same 21 amino acids. You may see books that say there are only 20 amino acids.

Hope this explains it
There's 20 amino acids, but thousands of proteins (I think)
There's 21?

Damnit, this better not be one of those "a student at this education stage would not understand it" situations...
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username1793709
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(Original post by AlphaArgonian)
There's 21?

Damnit, this better not be one of those "a student at this education stage would not understand it" situations...
Haha!! There's 20 common amino acids, but selenocysteine (the 21st) is found in a very small number of proteins in humans as well!!

It's a topic for debate whether it should be included aha
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AlphaArgonian
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(Original post by Porcupayne)
Haha!! There's 20 common amino acids, but selenocysteine (the 21st) is found in a very small number of proteins in humans as well!!

It's a topic for debate whether it should be included aha
Oh thank Darwin! I honestly thought the 21st would be some kind of unique molecular complex in comparison to the others
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nexttime
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(Original post by AlphaArgonian)
... some kind of unique molecular complex...
Well a protein is a huge chain of amino acids folded upon and bonded to itself in a way that is dependent on the number of water and hydrogen molecules which bond with it, sometimes is used to carry a rare transition metal seemingly out of nowhere. 'Some kind of unique molecular complex' is surely just every protein :p:

I'd like context for that textbook as it just seems bizarre that you'd only have your protein 3 acids long. Were they talking about an example chain of 3 amino acids in the context of a longer protein? In which case the specific order is important and it would indeed be 20^3 (for that tiny subsection).
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futureDOCTOR2k15
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There can be more than 20! combinations of different amino acids.
And there are over 200 amino acids tbh....just that 20-22 (some sources say 20..21 or 22) are used for protein synthesis....rest are used for different purposes such as neurotransmitters as acetylcholine(Studying this in A2 bio right now )
* for a levels tho I always use 20 amino acids as it is the "safe" no. to use
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Aubrey_79
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(Original post by AlphaArgonian)
Ok so I'll give any people who haven't studied A-level (or equivalent) biology some context:
Amino acids are biological molecules that make up proteins, there are 20 (known) of them. some examples are glycine, valine and tryptophan.
Proteins form from unique combinations of these amino acids...

Now, textbooks say there are 8000 (20^3) combinations...

My teacher and I argue that there are 20! combinations...

Help?
64 COMBINATION of bases.
20 amino acids
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AlphaArgonian
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(Original post by Aubrey_79)
64 COMBINATION of bases.
20 amino acids
Dude that sounds waaaaaayyyyyyyyyy too small.
That basically implies each amino acid only has one triplet code assigned to it. But we know plenty of amino acids have a degenerate code.
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Aubrey_79
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(Original post by AlphaArgonian)
Dude that sounds waaaaaayyyyyyyyyy too small.
That basically implies each amino acid only has one triplet code assigned to it. But we know plenty of amino acids have a degenerate code.
43 = 64

4=base
3=triplet
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morgan8002
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(Original post by AlphaArgonian)
Ok so I'll give any people who haven't studied A-level (or equivalent) biology some context:
Amino acids are biological molecules that make up proteins, there are 20 (known) of them. some examples are glycine, valine and tryptophan.
Proteins form from unique combinations of these amino acids...

Now, textbooks say there are 8000 (20^3) combinations...

My teacher and I argue that there are 20! combinations...

Help?
There are 21 possible amino acids, but one of them(I can't remember the name) can only come at the end of a chain.
Therefore the number of combinations is 21^2(20)^{n-2}, where n is the number of amino acids in the chain. Trivially, if n=1, then the number of combinations is 21.
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morgan8002
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(Original post by futureDOCTOR2k15)
There can be more than 20! combinations of different amino acids.
And there are over 200 amino acids tbh....just that 20-22 (some sources say 20..21 or 22) are used for protein synthesis....rest are used for different purposes such as neurotransmitters as acetylcholine(Studying this in A2 bio right now )
* for a levels tho I always use 20 amino acids as it is the "safe" no. to use
Maybe say 20 \alpha amino acids produced biologically.
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Ambitious1999
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There are around 21 common amino acids.

Each amino acid is chosen from the genes by a code consisting of 3 base pairs. The arrangement of this code determines what Amino acids make up the polypeptide chain.

An infinite number of combinations is possible especially considering gene mutations. Cancer cells for example produce proteins and peptides that are unknown of.
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rajboy3
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(Original post by Arbolus)
The answer is infinite, for all intents and purposes, because there's no theoretical limit on how long a peptide chain can be. In general, if you have a chain of n objects, each of which can be one of 20 different options, and there is no limit on how many times each option can be used, the number of possible combinations is 20n.

20! is the number of ways of arranging 20 different amino acids in a chain if each acid can only be used once.
But there is a limit, isn't there? You can't have a protein to large to fit in a cell for example. So there must be a definite limit to the size of the protein but maybe we just haven't figured out what that limit is yet? In school we were taught the the number of combinations was 20(to the power of)n, so I agree on that. Interesting topic to look into though, .
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QuentinM
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Definitely infinite, depends on the following factors:

*Whether amino acids repeat in a sequence (they do frequently)
*How long the sequence is....a small peptide (e.g. insulin)? or a larger protein (e.g. actin/ATPase)
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bobby147
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(Original post by QuentinM)
Definitely infinite, depends on the following factors:

*Whether amino acids repeat in a sequence (they do frequently)
*How long the sequence is....a small peptide (e.g. insulin)? or a larger protein (e.g. actin/ATPase)
Hw would you answer the post above you ?
Is it that cells have different shapes and sizes ?
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