All amino acids (in VCE, at least. inb4 someone who actually knows biochem knocks me back) are zwitterions, not all zwitterions are amino acids. A zwitterion is a type of ion that shows a positive and negative charge at the same time, an amino acid is just a type of zwitterion (hence the name "amino acid" being kinda stupid)
This is true -a zwitterion is a type of molecule. It's a molecule with positive and negative charges, that balance out to be overall positive.
(Worth pointing out that molecules that aren't amino acids can be zwitterionic.)
The ionic state of an amino acid depends on a the pH. At neutral/near neutral pH (depends on the pKa of the carboxyl/amino groups in the amino acid,) the amino acid will be zwitterionic. As you expect, when you lower the pH (more protons,) you portent the carboxyl group (now -COOH,) so the amino acid is now negative. The opposite if you raise the pH (deprotenate the amino group - now NH2).
By putting that amino acid into solution.
Technically incorrect (the best kind of incorrect.) Amino acids are zwitterionic in the solid phase (even in the gas phase apparently.)
Regarding the bonds of proteins and their structures, how can you describe the secondary structure, and what bonds are responsible for the alpha helices and b pleated sheets to form?
Usually, through covalent bonds, di-sulfide bridges and other intermolecular forces.
Secondary structure is
just formed by backbone hydrogen bonding.
Tertiary structure is a consequence of several interactions - disulphide bonds (although these are actually quite rare), electrostatic interactions between amino acids, hydrogen bonding, hydrophobic interactions etc (actually mainly the latter - although I can't remember if they are mentioned in VCE.)
explain the use of a reference sample, TMS,
i'm not sure what they mean by reference sample, is that a sample with no sample in it, so we can work out any absorbency by impurities
TMS simply accounts for the fact that not all spectrometers are the same - in a 100 MHz spectrometer the protons will resonate around 100 MHz, in an 800 MHz spectrometer, they will resonate at around 800 MHz. How can you compare data between spectrometers when the data from each spectrometer will be different? You use a reference compound (tetramethyl silane, TMS) and decide (entirely arbitrary!) that it's protons will resonate at 0 ppm. You can use this to convert a measurement in MHz to a measurement in PPM - which can be compared between spectrometers.
NMR can't usually deal with impurities (unless you knew what the impurities were and could subtract them from the spectrum.) Usually a sample which is subjected to NMR is highly pure.
Home
Help
Search
Login
