O-Chem Module 4

Question 1

what does co-enzyme A do?

Answer 1

helps enzymes catalyse reactions

Question 2

redox reactions in body systems are typically done by…

Answer 2

enzymes

Question 3

what is a thiol?

Answer 3

R-SH

Question 4

what is a disulfide?

Answer 4

R-S-S-R

Question 5

what is a hemiacetal?

Answer 5

R-O-C-OH

Question 6

what is an acetal?

Answer 6

R-O-C-OR

Question 7

what is an ether?

Answer 7

R-O-R

Question 8

what is an imine?

Answer 8

C=N-R

Question 9

what is the chemistry behind vision?

Answer 9

• retinol oxidised to retinal
• The aldehyde of retinal reacts with an amine of the protein (the opsin)
• The comparatively small 11-cis-retinal ‘fits well’ and is ‘recognised’ by the much larger protein
• Different opsins are optimized for different colours, which gives colour vision.

Question 10

what are the rules for fischer projections?

Answer 10

• Chiral carbon represented as a cross piece
• For aldoses, drawn with the aldehyde at the top and CH2OH at the bottom
• longest carbon chain runs top-to-bottom on the page

Question 11

the D isomer means that…

Answer 11

the non-hydrogen atom is pointing to the right

Question 12

the L isomer means that…

Answer 12

the non-hydrogen atom is pointing to the left

Question 13

in a cyclic hemiacetal, the alpha anomer means that…

Answer 13

the OH is the opposite side to CH2OH, is down

Question 14

in a cyclic hemiacetal, the beta anomer means that…

Answer 14

the OH is the same side to CH2OH, is up

Question 15

the reactivity for Nucleophilic acyl substitution is determined by what 3 factors

Answer 15

• The electronegativity of the carbonyl carbon
• The stability of the leaving group
• The nucleophilicity of the nucleophile

Question 16

what is the reactivity for Nucleophilic acyl substitution groups ordered? (most reactive to least)

Answer 16

1. acid chloride
2. acid anhydride
3. ester
4. carboxylic acid
5. amide

Question 17

to be a reducing sugar, the molecule must contain a…

Answer 17

hemiacetal

Question 18

furanose contains how many carbons?

Answer 18

4

Question 19

pyranose contains how many carbons?

Answer 19

5

Question 20

how does the carboxypeptidase A mechanism work?

Answer 20

• glutamic acid side chain reacts with H2O that is coordinated to zinc ion
• hydroxide nucleophile can now attack carbonyl carbon of amide bond to be cleaved, possible as zinc ion polarises carbonyl bond
• forms tetrahedral intermediate. carbonyl then reformed, regenerates carboxylate
• C-terminal amino acid now cleaved from rest of peptide, diffuses out
• zinc, glutamic acid, carboxylate and water ready to do to another peptide

Question 21

what does zinc do to pKa?

Answer 21

lowers it

Question 22

what is the slow step for carboxypeptidase A?

Answer 22

attack of nucleophile

Question 23

what makes a molecule aromatic?

Answer 23

rings of atoms which are joined via alternating double and single
bonds