Organic 2 Section 3 - Unit 30: Amino acids, Proteins & DNA Flashcards
Explain how hydrogen bonding occurs between proteins (4 marks)
- Nitrogen and oxygen are very electronegative
- Therefore, C=O and N–H are polar
- Which results in the formation of a hydrogen bond between O and H
- In which a lone pair of electrons on an oxygen atom is strongly attracted to the δ+H
Outline the steps needed to locate the positions of the amino acids on the TLC plate and to determine their Rf values (4 marks)
- Spray with developing agent or use UV
- Measure distances from initial pencil line to the spots (x)
- Measure distance from initial pencil line to solvent front line (y)
- Rf value = x / y
Explain why different amino acids have different Rf values (2 marks)
- Amino acids have different polarities
- Therefore, have different retention on the stationary phase or different solubility in the developing solvent
In terms of the intermolecular forces between the polymer chains, explain why polyamides can be made into fibres suitable for use in sewing and weaving, whereas polyalkenes usually produce fibres that are too weak for this purpose (3 marks)
- In polyamides - H bonding
- In polyalkenes - van der Waals forces
- Stronger forces (of attraction) in polyamides
Outline briefly why chromatography is able to separate a mixture of compounds. Practical details are not required (3 marks)
- Phase or solvent is mobile
- Stationary phase
- Separation depends on balance between solubility or affinity in each phase
State how you could hydrolyse dipeptides (1 mark)
- Heat
- With concentrated HCl or concentrated strong alkalis
Define zwitterion (1 mark)
- A molecule which has separate positively and negatively charged groups
Explain why amino acids have high melting points and dissolve in water (1 mark)
- They are ionic
State the meaning of the term complementary when it is used to refer to DNA strands (1 mark)
The two strands must have base sequences that match A to T and C to G
