Biological Chemistry - Amino Acids (9.1) Flashcards
Why are amino acids important in life?
They are central to many chemical processes within the human body
What are alpha amino acids?
They are amino acids that have -NH2 group & -COOH group attached to the same carbon
What are essential amino acids?
They are amino acids that the body cannot synthesise itself - so they have to be obtained from food
Name at least 3 properties of amino acids
- Are amphoteric
- Form zwitterions in the solid state
- Have high m.p & b.p
- Generally soluble in water
- Have an isoelectric point
- Usually contain at least 1 chiral centre
What does it mean when a molecule is ‘amphoteric’?
An amphoteric molecule can act as both an acid and a base
Why are amino acids amphoteric?
They contain acidic & basic functional groups
Describe what happens when you add an alkaline solution to amino acids
- The carboxylic acid group can act as an amino acid
- The -COOH group donates H+ ions to form the carboxylate ion -COO^-
Describe what happens when you add an acidic solution to amino acids
- The amine group can act as a base
- The lone pair on the N can accept a H+ ion
What is the effect of amophoteric properties on amino acids? (What does this allow to happen?)
- In the solid state, amino acid molecules react in acid-base reactions w/ neighbouring molecules
- One amino acid donates H+ to form -COO^- group & the other amino acid can accept it to form -NH3+
(One acts as an acid, one acts as a base)
What do amino acids form in the solid state?
Zwitterions
What is a zwitterion?
An ion that contains a region of positive & negative charge in the same molecule (overall neutral)
Explain why amino acids have high melting & boiling points
- There are strong electrostatic forces of attraction between molecules (zwitterions)
- These intermolecular forces require a large amount of energy to be broken
What is meant by the ‘isoelectric point’?
The pH at which the amino acid exists only as species w/ zero net charge
What does an amino acid at the isoelectric point look like?
A zwitterion
In what conditions are amino acids below the isoelectric point? What happens to the zwitterion (amino acid)?
- In acidic conditions
- The H+ protonates -COO^- to -COOH
In what conditions are amino acids above the isoelectric point? What happens to the zwitterion (amino acid)?
- In alkaline conditions
- H+ is taken away from -NH3+ to form -NH2
Why are amino acids generally soluble in water?
- They form zwitterions in solution & can form strong ion-dipole bonds w/ water molecules
What affects the degree of solubility of amino acids?
- The identity/type of side chain
- Properties of the side chains
What types of group decrease the solubility of an amino acid?
- Uncharged groups
- Non-polar side chains
Wha types of group increase the solubility of an amino acid?
- Polar side chains
- Charged side chains
What makes an amino acid more soluble? A polar side chain or a charged side chain?
A charged side chain - can form stronger intermolecular forces with oppositely charged groups
How does the length of the amino acid affect its solubility?
If two amino acids were exactly the same in terms of the types of side chains but one was longer, the longer amino acid would be less soluble
Why are longer, non-polar amino acids less soluble?
It is energetically unfavourable for water molecules to form London forces w/ non-polar parts of the molecule (more energetically favourable for water molecules to form H bonds with one another)
