Carboxyl groups

Question 1

Tell me about ester hydrolysis and why they are important in metabolism?

Answer 1

• Triglycerides are converted to glycerol and fatty acids by lipases
• As with proteases, these reactions occur under remarkable mild conditions: 37˚c, near to neutral pH
• Lipases are extremely versatile and are often used in synthetic chemistry

Question 2

Draw the different carboxyl functional groups?

Answer 2

Question 3

Tell me about the characteristics of the carbonyl and the carboxyl group

Answer 3

Question 4

Why is amide hydrolysis really important in the HIV life cycle?

Answer 4

• HIV protease chops up long polypeptide chains produced by translation into functional proteins
• HIV protease inhibitors are attractive targets for anti-HIV drugs

Question 5

Compare amide hydrolysis in biological and chemical processes (acidic and basic)

Answer 5

Question 6

What type of media can carboxyl substitution occur in?

Answer 6

basic or acidic

Question 7

Draw the mechanism for carboxyl substitution in basic conditions ?

Answer 7

Question 8

The general mechanism (addition-elimination): under basic conditions

Answer 8

Question 9

Draw the general mechanism for carboxyl substitution under acidic conditions?

How many steps are there to this mechanism?

Answer 9

Question 10

Whats the first part of the mechanism of carboxyl substitution under acidic conditions?

Answer 10

Question 11

Whats the second part of the mechanism of carboxyl substitution under acidic conditions?

Answer 11

Question 12

Is the mechanism really addition-elimination?

Answer 12

Question 13

Draw the mechanism of acid-catalysed ester hydrolysis to carboxylic acids

Answer 13

Question 14

Learn this mechanism pathway and how they link and what conditions are required

Answer 14

Question 15

Why can’t esters be formed from carboxylic acids under basic conditions?

Answer 15

Question 16

Drae the mechanism for basic amide hydrolysis

Answer 16

Question 17

Whats Chymotrypsin and what family does it belong to?

Answer 17

It is a digestive enzyme and is a member of the serine protease family

Question 18

In Chymotrypsin, what in its active site is critical to its catalytic activity?

What does it catalyse?

Answer 18

The serine residue in the active site is critical to its catalytic activity

It catalyses hydrolysis of proteins in the small intestine

Question 19

Whats the catalytic triad and draw it?

Answer 19

• The three amino acids in the catalytic triad are Asp-102, His-57 and Ser-195
• They are central to the enzyme’s catalytic activity

Question 20

Whats the catalytic mechanism?

Answer 20

Question 21

In the catalytic mechanism, how is the intermediate stabilised?

Answer 21

• charge stabilised by an ‘oxyanion hole’
• Two backbone amide protons form a hydrogen bond

Question 22

This shows the entire catalytic mechanism

Answer 22

Question 23

What is substrate specificity determined by?

Answer 23

The properties and spatial arrangement of the amino acids forming the active site

Question 24

How do small changes in the amino acid residues affect substrate specificity?

Answer 24

Small changes in the amino acid residues forming the active site will have a large effect on the substrate specificity of an enzyme.

Question 25

Carboxyl groups can undergo substitution under what conditions?

Answer 25

Acidic or basic

but not all possible substitutions occur

Question 26

What mechanism do all substituton reactions occur by?

Answer 26

via an addition-elimination mechanism with a tetrahedral intermediate

its crucial the intermediate is drawn in the mechanism

Question 27

What do you need to consider with carboxyl substitution reactions?

Answer 27

• Is ‘Y’ a good enough nucleophile
• is the starting material sufficiently reactive
• which is the better leaving group ‘X’ or ‘Y’
• Is the product more or less reactive than the starting material

Question 28

Are carboxyl substitution reactions reversible?

Answer 28

yes

Question 29

Name 2 carboxyl substitution reactions which are important in nature

Answer 29

• ester hydrolysis in lipases
• amide hydrolysis in proteases