Carbohydrates after Midterm

Question 1

How is an aldonic acid formed?

Answer 1

when the aldehyde group on a sugar is oxidized to a carboxylic acid
can be done using: Br2 dissolved in water, Tollen’s reagent (Ag(NH3)2)+, or Benedict’s/Fehling’s reagent (Cu2+ in citrate or tartrate)

Question 2

When using Benedict’s/Fehling’s reagents what indicates the oxidation of an aldehyde?

Answer 2

Cu2O formation (red solid)

Question 3

How is an aldaric acid formed?

Answer 3

using nitric acid (HNO3) to oxidize the aldehyde and primary alcohol of a sugar (i.e. there is now a COOH on each end)

Question 4

How is a uronic acid formed?

Answer 4

oxidize only the primary alcohol of a sugar NOT the aldehyde (i.e. COOH on one end)
need to use a protecting group if you’re doing it in the lab
there are enzymes in the liver that can do it

Question 5

How is an alditol formed? Is a new stereocentre formed?

Answer 5

aldehyde or ketone carbonyl is reduced to an alcohol
uses H2/metal, NaBH4 or LiAl4
If a ketose is reduced, a new stereocentre may be formed

Question 6

What three sugars if placed in a basic solution will always form the same equilibrium mixture?

Answer 6

D-glucose
D-mannose
D-fructose

Question 7

What is are epimers?

Answer 7

Diastereomers that differ in the configuration of only ONE stereocentre

Question 8

Name two disaccharides of D-glucose

Answer 8

maltose and cellobiose

Question 9

What kind of linkage does maltose have?

Answer 9

alpha (1,4) glycoside bond

has a hemiacetal, can mutarotate

Question 10

What kind of linkage does cellobiose have?

Answer 10

beta (1,4) glycoside bond

Question 11

What makes up lactose? How is it linked?

Answer 11

D-galactose linked beta (1,4) to D-glucose

Question 12

What makes up sucrose? How is it linked?

Answer 12

D-glucose and D-fructose
BOTH anomeric carbons 
alpha (1,2) at glucose 
beta (2,1) at fructose 
does NOT mutarotate

Question 13

What is invert sugar?

Answer 13

a mixture of D-glucose and D-fructose

called invert sugar because after hydrolysis from sucrose the optical spin goes the other way

Question 14

What are the two types of starch? What are they polymers of?

Answer 14

amylose and amylopectin

D-glucose

Question 15

Describe the structure of amylose

Answer 15

continuous, unbranched chains of up to several thousand D-glucose joined by alpha (1,4) glycoside linkages
forms a hollow, helical structure

Question 16

Describe the structure of amylopectin

Answer 16

branched polymer of D-glucose 
has alpha (1,4) glycoside linkages
and alpha (1,6) glycoside branches every 24-30 units

Question 17

Describe the structure of glycogen

Answer 17

branched polymer of D-glucose 
has alpha (1,4) and alpha (1,6) glycoside linkages (much more branched than amylopectin)

Question 18

Describe the structure of cellulose

Answer 18

linear polymer of D-glucose linked beta (1,4)
every second unit is rotated to allow extra H-bonding to occur
very insoluble in water because multiple chains H-bond together tightly
forms a supramolecuar structure i.e. microfibrils, fibrils, fibres

Question 19

What is a ylide?

Answer 19

overall neutral compound that has adjacent positive and negative charges

Question 20

What is a good marker for liver damage?

Answer 20

increased levels of aminotransferase in the blood

Question 21

What is pyroxidoxal phosphate (PLP)?

Answer 21

coenzyme that functions as an amino-group carrier