4.7 Amino Acids Flashcards
Draw an alpha amino acid
Are amino acids optical isomers?
- all optical isomers other than aminoethanoic acids
- have one or more chiral centres, one of which is the alpha carbon
What makes amino acids amphoteric?
- zwitterion nature
- gain a proton in acidic, and lose one in basic
Describe a zwitterion
- H+ lost by CoOOH group and gained by NH2 group
- only exist as zwitterion at a certain pH called the isoelectric point
—> pH below isoelectric point: acts as base
—> pH higher than isoelectric point: acts as acid
Describe the melting points of amino acids
- exist as solids in room temp
- due to zwitterion nature
- ionic nature means they can form strong ionic bonds to give higher than expected melting points
Describe solubility of amino acids
- soluble in water because strong ionic attractions form between zwitterion and polar molecules
- insoluble in non-polar solvents due to lack of attraction
How do dipeptides form?
Condensation reactions
What happens when different amino acids are joined?
2 different dipeptides can be formed - isomers
Describe acid hydrolysis
- H2O and 2H+
+NH3 on each end of the amino acids
Describe alkaline hydrolysis
- add NaOH
- O-Na+ on ends instead of OH
Describe primary structure of proteins
- single polypeptide chain of amino acids joined together with peptide bonds
Describe secondary structure of proteins
- hydrogen bonding
- alpha helix spiral or beta pleated sheet
Describe tertiary structure of proteins
- extra bonds forming between different parts of polypeptide chains
—> ionic, hydrogen, disulphide
What is meant by the term zwitterion?
Molecule/ion with +ve and -ve charges
State reagents and conditions for breakdown of protein into amino acids
- water
- reflux
- HCl
Draw breakdown of glutamic acid in acidic and basic hydrolysis
Suggest why aminoethanoic acid is insoluble in methanol
- zwitterions
- ionic compounds are not generally soluble in covalent solutions
Explain why an aqueous solution of aminoethanoic acid does not affect the plane of polarised light
No chiral centre
Wavelength equation
f = c/y
