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Where did amino acids get their one-letter codes?

Tryptophan For instance, is there a reason 'W' specifically was chosen for tryptophan (other than the fact that 'T' was taken)? Once you have assigned the other 19 amino acids, there are only 7 ...
orthocresol's user avatar
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22 votes
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Etymology of alanine

In the original German paper [1] Adolf Strecker used Aldehyd-Ammoniak or aldehyde-ammonia as a precursor, that's where the name derives from: Vor einigen Jahren habe ich gezeigt, daſs Aldehyd-...
andselisk's user avatar
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20 votes

How do I calculate the isoelectric point of amino acids, each of which has more than two values of pKa?

Since the $\mathrm{pI}$ is the $\mathrm{pH}$ at which the amino acid has no overall net charge, you need to average the $\mathrm pK_\mathrm a$ values relevant to the protonation/deprotonation of the ...
orthocresol's user avatar
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18 votes

Where did amino acids get their one-letter codes?

Some single letter codes that aren’t the amino acid’s starting letter actually make sense when viewed from certain angles. Here’s the list starting with the bloomin’ obvious: G — Glycine A — Alanine ...
Jan's user avatar
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15 votes

How can I draw alpha helices in ChemDraw?

I use ChemDraw Professional 19.1.1.32. If you follow File>Open Templates>Advanced BioDraw, you will find the black helix that I have reoriented from horizontal to vertical. The red helix was ...
user55119's user avatar
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14 votes
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Why does tryptophan absorb UV light?

Any molecule can absorb UV light. What the question is probably going for is why those three molecules absorb at longer wavelengths than other amino acids. This has to do with the conjugated pi bonds ...
Blaise's user avatar
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13 votes
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How can I properly calculate the isoelectric point (pI) of amino acids?

Isoelectric point of an amino acid is the $\mathrm{pH}$ at which the molecule carries no net charge[1]. It can be calculated by the average of the relevant $\mathrm pK_\mathrm a$ values as you have ...
trinitrotoluene's user avatar
13 votes

How can I draw alpha helices in ChemDraw?

This illustration may be a combination of two images, or simply a program I don't know about. However, there are many (3D) protein visualisation programs that can show alpha-helices such as PyMol, VMD ...
CuriousTree's user avatar
12 votes
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Why are amino acids least soluble at isoelectric point?

In order for molecules to precipitate out of solution, they need to aggregate together. Amino acids that have zero net charge can aggregate together much more easily than those that are charged. ...
Andrew's user avatar
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11 votes
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Why is arginine's positive side chain classified as basic and not acidic?

Your textbook is imprecise. We consider whether a sidechain is acidic or basic based on the action of the sidechain when it is neutral. Because arginine's sidechain is basic, it preferentially picks ...
a-cyclohexane-molecule's user avatar
11 votes

Where did amino acids get their one-letter codes?

See IUPAC-IUB Commission on Biochemical Nomenclature A One-Letter Notation for Amino Acid Sequences The Journal of Biological Chemistry Vol. 243, No. 13, pp. 3557-3559, 10 July 1968. : The ...
DavePhD's user avatar
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10 votes

Where did amino acids get their one-letter codes?

The three-letter designation came before the single letter code. The three-letter codes themselves went several refinements and revision finally accepted by IUPAC and International Union of ...
ankit7540's user avatar
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9 votes
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Is selenocysteine C3H6NO2Se or C3H7NO2Se?

Selenocysteine can be either of the following: $\ce{C3H8NO2Se+, C3H7NO2Se, C3H6NO2Se-}$ or $\ce{C3H5NO2Se^2-}$. This is because the neutral form of selenocysteine is both a base and a diprotic acid: ...
Jan's user avatar
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9 votes

How can I draw alpha helices in ChemDraw?

This answer is for ChemDoodle, but I think you can import SVG files into ChemDraw as well. Just take an SVG image of an alpha helix and copy and paste it into ChemDoodle. Or go to File -> Insert ...
user137's user avatar
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8 votes
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Why do Asn-Ser and Gln-Thr have different H bonding patterns?

I don't have the textbook you've gotten this from, but unless there's a statement to the contrary, I suspect these are intended as examples of hydrogen bonding, rather than an exhaustive list of the ...
R.M.'s user avatar
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8 votes
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Can =NH2+ in Arginine's side chain form hydrogen bonding at physiological pH?

Yes, the arginine side chain is an excellent hydrogen bond donor. Charged N-H groups are even better hydrogen bond donors than the corresponding neutral N-H groups. Here is an article that gives ...
Karsten's user avatar
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8 votes
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IUPAC name for dicarboxylic acid with aldehyde and amine groups

The preferred name of the parent structure is butanedioic acid. The name ‘succinic acid’ is retained for general nomenclature with functionalization but no substitution is allowed (see Rule P-65.1.1.2....
Loong's user avatar
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8 votes
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Experimental evidence for zwitterions

That is a very difficult problem worth a PhD project in physical chemistry. Intially, I thought one could try capillary electrophoresis at different pHs and if the analyte travels with the ...
AChem's user avatar
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7 votes
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Ionization of amino acids

The two forms of amino acids that your question asks about are called zwitterions (technically IUPAC says they should be called dipolar ions but the term zwitteron is pervasive). Since amino acids ...
NotEvans.'s user avatar
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7 votes

ʟ-Glutamine solubility in hot water

Glutamine in aqueous solutions degrades slowly when stored in room temperature. Therefore, we can expect that rate of degradation is faster at higher temperatures. It is evident that the hydrolysis ...
Mathew Mahindaratne's user avatar
7 votes
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Amino Acid Derivative Naming Conventions

As you're aware, biochemists typically do not use systematic naming for most compounds, preferring instead to use common names and modifying them as needed for related compounds. In the case of amino ...
Andrew's user avatar
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6 votes
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Reaction to form amino acid

The starting compound is an organic compound known as acrolein. $\ce{CH2=CH-CH=O}$ Now your first reaction would be: $$\ce{CH2=CH-CH=O ->[CH3SH][1,4 addition]CH3-S-CH2-CH=CH-OH} $$ Now, this ...
Safdar Faisal's user avatar
6 votes
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Why are Tyrosine and Tryptophan considered hydrophobic?

Unlike that in organic chemistry, polar and non-polar compounds determination is done differently in biochemistry, probably because most biochemical reactions are done in aqueous medium. Therefore, ...
Mathew Mahindaratne's user avatar
6 votes

How to determine the charge of amino acid at certain pH?

Behaviour of amino acids in water solution Amino acids exist in the solution in the form of zwitterions (molecules that contain an equal number of positively and negatively charged functional groups). ...
Exeplone's user avatar
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5 votes

Is the molecule in the attached image technically an amino acid?

No it is not, as there is no carboxylic acid functionality present. An amino acid is defined in this Wikipedia article as follows: Amino acids are organic compounds containing amine ($\ce{-NH2}$) ...
airhuff's user avatar
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5 votes

Etymology of alanine

User364914 may be confused by the "odd" formulas in Strecker's 1854 paper. At that time there was no universal agreement on the masses of atoms. Was carbon 6 or 12? Was oxygen 8 or 16? Strecker used 6 ...
user55119's user avatar
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5 votes
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Why do α-amino acids have a C-H bond at the α-carbon?

In the most general sense, the term α-amino acid does encompass doubly substituted structures like those you mention. After all, the name doesn't specify any particular substitution, or lack thereof, ...
orthocresol's user avatar
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5 votes
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What does "sine" mean?

According to Textbook of metabolism and metabolic disorders (1964): The ribosides derived from purines have the suffix -osine; those from pyrimidines, the suffix -idine. The corresponding ...
DavePhD's user avatar
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5 votes
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Why is N-acetyl alanine methyl amide considered a dipeptide?

The nomenclature here is based on counting the number of backbone peptide bonds rather than the number of aminoacids. This does not apply the usual naming convention. If you look at the wikipedia page ...
Buck Thorn's user avatar
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5 votes

Histidine vs Lysine

As their name imply, each amino acid has at least one amine and one acid functional group, but in most amino acids, the basicity of the amine is offset by the carboxylic acid group at physiological $\...
Mathew Mahindaratne's user avatar

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