Carbohydrates

Question 1

What are the main classes of carbohydrates

Answer 1

Monosaccharides, Ogliosacharides and Polysaccharides.

Question 2

What are the two classes of monosaccharides

Answer 2

Aldose and Ketose - in reference to the placement of the double bonded O group. Most in nature are aldose sugars.

Question 3

What is the difference between L and D molecules

Answer 3

The placement of the hydroxyl group on the chiral carbon furtherest away from the carbonyl at the top of the molecule.
L means that it is ‘on the left’ or not on the same side as the O
D means it is on the right or on the same side as the O

Question 4

How are diffent monosaccharides with the same chain length differentiated

Answer 4

By using their stereoisomerism between the interim carbons
I.e if it was a pentose sugar, the stereoisomerism on carbons 2-4
(Positioning of H and OH molecules)

Question 5

What is an epimer

Answer 5

Monosaccharides that differ on in the configuration around one carbon atom
Eg D-mannose and D-glucose, only differ in their placement of the OH on carbon 2

Question 6

How is the cyclical structure of a carb formed eg glucose or ribose

Answer 6

The carbonyl group (CHO) reacts with a hydroxyl group further down the chain eg carbon 4 or 5.
Pentose and Hexoses are usually cyclic in aqueous solution.

Question 7

What is formed by the reaction of the carbonyl group and the hydroxyl group.
And how does this different between it being a ketone or an aldehyde

Answer 7

An aldehyde and an alcohol make a hemiacetal - RCOHORH
A ketone and an alcohol make a hemiketal, same structure

They both also form a new chiral centre

Question 8

What is an anomer and how is it formed

Answer 8

As the sugar is initially planar, the hydroxyl group can react with the carbonyl group from above or below forming two different structures of the final ring product

Anomers are Alpha ( Hydroxyl group on the bottom)
Or beta ( Hydroxyl group on the top)

Question 9

What are pentose and hexose anomers called

Answer 9

Pentose - furanose
Hexose - pyranose

Question 10

How are cyclic monosaccharides represented by the Haworth perpective

Answer 10

Bonds on the side of the O (right side) in a planar sugar will face on the underside of the ring.

Therefore, D enantiomers with have C6 above the ring where are L enantiomers will have C6 inside the ring

Question 11

What is mutarotation

Answer 11

The ability of the hydroxyl group to spontaneously flip positons on C1
It is important for some pathogens to enable them to pass through the cytoplasm of a cell and enter the central metabolism