Flashcards

amino acids

megan trent A level Chemistry English 28 cards

Cards in this deck (28)

1Amino acids have the general formula:-
2They are called α-amino acids becausethe amino (–NH2) and carboxylic acid (–COOH) groups are both attached to the second or α-carbon atom.
3Physical properties- Amino acids contain both acidic -COOH and basic -NH2 groups.
The -COOH of one molecule will protonate the -NH2 group of an adjacent molecule forming a zwitterion.
4zwitterion structure
5when will the -COOH of one molecule protonate the -NH2 group ?This can occur both in solution at about pH 7 or in the solid state. Thus amino acids show important physical properties typical of ionic compounds:-
-they are white solids which melt or decompose at relatively high temperatures, around 300ºC
-they are soluble in water, but mostly insoluble in organic solvents.
6The ions formed by an amino acid depend onthe pH of the solution
7Low pH =[H+] high
8High pH =[H+] low
9The ions formed by an amino acid depend on the pH of the solution:- At a low pH :
10The ions formed by an amino acid depend on the pH of the solution:- At a high pH :
11All amino acids form zwitterions, however their isoelectric points may differ due tothe different character of the R side chain.
12At what pH can an amino acid act as an acid?at the isoelectric point the -NH3+ group can donate a proton; at lower pH values the -COOH group can also donate a proton
13At what pH can an amino acid act as a nucleophile?A nucleophile has a lone pair on the N. This only occurs at higher pH values
14Amino acids exhibit ................. behaviours .and solutions can act as buffers.amphoteric
15All natural amino acids, except glycine are?optically active
16StereoisomerismOne isomer rotates the plane of plane polarised light in one direction, the other isomer rotates it in an equal but opposite direction.
All naturally occurring amino acids have the same absolute configuration as L-alanine.
17Why does glycine not form optical isomers?Two H atoms on the central carbon mean that is is not a chiral centre and does not form two non-superimposable mirror images.
18Acidity and basicity reaction results? add a few drops of indicator to HCl and add NaOH in small portions repeat using glycine instead of HClDoes the pH change gradually or sharply?
- Addition of HCl + NaOH ---> rapid change in pH
-NaOH to glycine -----> gradual change (little to no change) in pH
What type of acid–base behaviour is occurring?
-Glycine solution acts as a buffer removing added H+ or OH- so minimising the change in pH
19form amino acids to peptides and proteinsamino acids can be joined together to make a peptide then join together in even longer chains to form polypeptide and proteins.
link between amino acids is called amide link and is formed in a condensation reaction forming water
20Hydrolysis of the peptide bonds-Heat under reflux with 6M HCl for up to 24hr (or 5-35 min in a microwave!)
-Followed by addition of water.
21CONDENSATION POLYMERSA condensation polymer is formed by making a amide or ester link and eliminating a small molecule, usually water or HCl. There are two types, polyester with ester links between monomers and polyamides with amide links between monomers
22POLYESTERSPolyesters are formed from the reaction between a dicarboxylic acid and a diol or a diacyl chloride and a diol or even a molecule which has an alcohol group on one side and a carboxylic acid/acid chloride group on the other. A molecule of water is produced
23reactions between dicarboxylic acids and diamines make polymers
24proteins are condensation polymers of amino acid s
25dicarboxylic acids and diols
26brea the amide link or ester link to find the monomer of a condensation polymer
27join the monomer functional groups to find a condensation polymers
28paper chromatography used to identify unknown amino acids