Amino Acids & Chirality Flashcards
What is the general formula of an amino acid?
RCH(NH2)COOH
What are alpha - amino acids?
Amino group and carboxylic acid group are attached to the same carbon atom.
Amino acids are BIFUNCTIONAL. Explain what this means.
They have two functional groups present:
- NH2 (base)
- COOH (acid)
What is an acid?
A proton donor (gives a H+ ion)
What is a base?
A proton acceptor.
What is a zwitterion?
An ‘internal’ salt of an amino acid, in which the -COOH group donates a proton to the -NH2 group forming NH3+ & COO-.
What effect does a zwitterion have on the properties of an amino acid?
Ionic charges increase the attractive forces between the amino acid in the solid, so raising the melting point significantly.
What is formed when amino acids react with acids or bases?
A salt.
At a low pH, what is the charge of a zwitterion?
Positive.
At a high pH, what is the charge of a zwitterion?
Negative.
What is the definition of an isoelectric point?
When the solution of an amino acid has the maximum concentration of zwitterions.
How are peptide bonds formed?
Via condensation reactions (condensation polymerisation).
How an you represent a peptide link?
-CONH- or -NHCO-
-C=O -N-H
| |
N-H- -C=O
What happens if you repeat condensation reactions many times?
You get polypeptides or proteins.
What is hydrolysis?
The process of breaking the peptide link by a reaction with water.
What is the catalyst for hydrolysis (living and lab)?
They are catalysed by enzymes in living organisms.
In the lab, they are catalysed by acids or alkalis.
What does an a-amino acid and an excess alkali react to form?
Carboxylate salts e.g. In case of Sodium, on COOH group COO-Na+ formed.
What is stereoisomerism?
When atoms have the same order of bonds and atoms but a different spatial arrangement of atoms.
What is the difference between E and Z isomerism?
E - opposite sides
Z - same side
What are optical isomers?
Molecules that are non-superimposable mirror images of each other.
What is a chiral centre?
A (carbon) atom in a molecule attached to 4 different groups.
How many optical isomers are formed and what are the differences between them?
2:
• 1 rotates plane polarised light to left
• the 2nd rotates plane polarised light to right
What is a equal split of enantiomers called?
A racemic mixture.
What can’t a racemic mixture do?
Deflect polarised light.
How do drugs work?
Drugs work by binding to enzymes active sites or cell surface receptors causing a chemical reaction.
Drugs must have the correct shape to fit into binding site - only one enantiomer will do.
The other enantiomer may bind to another active site and have no effect, or cause a harmful side effect.
Why would pharmaceutical companies make drugs with only one optical isomer?
- smaller doses can be used (only 1/2 amount)
- fewer side effects
- drug is more efficient and effective
- reduces risk of litigation
- this increases costs as optical isomers are difficult and expensive to seperate
What methods can you use to produce single enantiomers?
- using natural enzymes or bacteria
- using naturally occurring single optical isomers compounds as the starting material
- using chemical chiral synthesis
- using chiral catalysts - reusable but $$$
Describe the properties of proteins.
- polypeptides with high molecular mass
- chains can be lined up with each other
- the C=O and N-H bonds are polar due to difference in electronegativity
- hydrogen bonding exists between chains
What are the reagents and conditions for a hydrolysis reaction?
Reagents: aqueous acid (H2SO4)/ alkali (NaOH)
Conditions: warm/hot, reflux
When you are given a chemical with chloride and you’re asked for a reagent that would make it turn to an amino acid, what is this reagent?
(ethanolic) ammonia
