4.2.1- Amino Acids And Chirality

Question 0

What is an alpha amino acid

Answer 0

Where both NH2 and COOH are attached to the same carbon. They are amphoteric, having both acidic and basic qualities

Question 1

What is the general formula for an alpha amino acid

Answer 1

RCH(NH2)COOH

Question 2

What is the isoelectric point

Answer 2

The pH at which an amino acid exists as a zwitterion (thus there is no net charge)

Question 3

What can cause differences in the isoelectric point, and give examples

Answer 3

Different R groups. For example, extra amine group within R results in HIGHER isoelectric point, extra carboxylic acid group gives a LOWER isoelectric point.

Question 4

What is a peptide

Answer 4

A compound containing amino acids linked by peptide bonds (also called amide linkage)

Question 5

What is a polypeptide

Answer 5

A polypeptide or protein is a long chain of amino acids joined together by peptide linkages

Question 6

What are the conditions for the acid hydrolysis of polypeptides

Answer 6

Heat under reflux for 24 hours, 6 moldm^-3 HCl.

Question 7

What is extra reagents in acid hydrolysis of polypeptides

Answer 7

H2O and 2H+ (as the reaction forms protonated amino acids due to the acidic conditions.

Question 8

Give the conditions for the alkaline hydrolysis of polypeptides

Answer 8

NaOH (aq) and > 100°C

Question 9

Define stereoisomers

Answer 9

Molecules with the same structural formula but different arrangement of atoms in space

Question 10

What are the two types of sterioisomerism

Answer 10

Optical isomerism and E/Z isomerism

Question 11

Define optical isomers

Answer 11

Non-superimposable mirror images about a chiral centre

Question 12

Define a chiral centre

Answer 12

For different groups attached to a carbon atom.

Question 13

Name a way you can distinguish between optical isomers

Answer 13

Optical isomers retaliate plane polarised light differently one will rotate it clockwise and the other anticlockwise. Therefore if a mixture contains equal amounts of each isomer, it will have no effect on plane polarised light.

Question 14

Give three disadvantages of having multiple optical isomers in pharmaceutical synthesis

Answer 14

1. Increased costs of production due to difficulty separating them (if you do need just one isomer)
2. One of the isomers may have harmful side-effects
3. A larger dosage will be required as only one stereoisomer is pharmacologically active

Question 15

Give three modern techniques for chiral synthesis

Answer 15

1. Using enzymes/enzyme containing bacteria which promote stereoselectivity (molecules of the same compound produced naturally by enzymes in living systems often create one optical isomer only. Therefore manufacturers use these enzymes/bacteria to bio-catalyse any reaction step that produces a chiral carbon).
2. Chemical chiral synthesis/chiral catalysts
3. Natural chiral molecules as starting materials (e.g. natural alpha amino acid and sugars)