Amino Acids, Proteins and DNA
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What are the two functional groups in an amino acid?
Amine group - basic Carboxylic acid group - acidic
How many naturally occurring amino acids are there?
20
What do almost all naturally occurring amino acids exist as?
The negative enantiomer since they have a chiral carbon.
Describe the carboxylic acid group.
Has a tendency to lose a proton. (act as an acid)
Describe the amine group.
Has a tendency to accept a proton. (act as a base)
What are compounds with two functional groups called?
Bifunctional compounds
In what form do amino acids exist as in solids? What consequences does this have?
Zwitterions (ionic lattice)
Why do amino acids have a high melting point?
They’re ionic.
What is a zwitterion?
An ion with a permanent positive charge and a permanent negative charge but the overall compound is neutral.
Do zwitterions dissolve in water? Non-polar solvents? Why?
Yes but not in non-polar solvents. This is due to the ionic nature and the polar bonds.
What colour/state are zwitterions at room temperature?
White solid
What does a zwitterion act similarly to?
An ionic salt
What happens to amino acids in strongly acidic conditions?
The lone pair of the amine group accepts a proton to form the positive ion. When a proton is gained, the amino group is said to be protonated.
What happens to amino acids in strongly alkaline conditions?
The -OH group loses a proton to form a negative ion. The carboxylic acid group has lost a proton and so is deprotonated.
What do amino acids link to form?
Peptides
What are molecules containing up to 50 amino acids called?
Polypeptides.
What are molecules containing more than 50 amino acids called?
Proteins
What functional group does an amide have?
CONH2
How does an amide linkage form?
The amine group of one amino acid reacts with the carboxylic acid group of another to form an amide linkage.
What is a peptide with two amino acids called?
Dipeptide
Why are proteins biodegradable?
They can be hydrolysed
What kind of polymer is a polypeptide/protein?
Condensation polymers
How is a protein hydrolysed?
Boil with hydrochloric acid (6 moldm^-3) for 24 hours under reflux. It breaks down to a mixture of all the amino acids that made up the original protein or peptide. The acid hydrolyses all the peptide linkages.
What holds proteins together?
Hydrogen bonds and IMF as well as disulfide bridges.