Lecute 4

Question 1

What does the small amount of molecules with a free aldehyde mean in reactions

Answer 1

Easily oxidised
In too far

Question 2

In the absence of H+ acetals are…

Answer 2

Stable

Because -OR is a poor leaving group

Question 3

Reaction of D-glucose and methanol to make acetal formation - what is produced

Answer 3

• substitution reaction is reversible
• nucleophille can attach from either side of carbocation intermediate
• both a and b glycosides (acetals) are formed

Question 4

a and b glycosides are…

Answer 4

Acetals

Question 5

The pure glycosides dissolved in H20 in absence of strong acid are:

Answer 5

• stable
• no open chain form possible
• no reaction with Ag+
• NON REDUCING SUGARS

Question 6

OH group used is glycoside formation can also be from

Answer 6

• another sugar
• larger carbohydrates contain glucose or other sugar units links together by glycosidic bonds

Question 7

How can glycoside hydrolysis be acheived (glycoside hydrolysis)

Answer 7

• enzymatically
• H30+

Question 8

Maltose is

Answer 8

A diasscaride with two glucoses linked together

Question 9

Gylcosidic linkage in maltose is…

Answer 9

The glycosidic bond from c-1 (anomeric carbon) is pointing down while the CH2OH is up, thus an a-1,4-glycosidic linkage

Question 10

Is maltose a reducing sugar?

Answer 10

• RH sugar contains a hemiacetal
• this is an equilibrium with the open chain aldehyde form of the right hand sugar
• thus maltose is a REDUCING sugar
• reducing sugar will work with tollens

Question 11

What is cellobiose

Answer 11

• two glucose units linked though the same positions with a B-linkage (equatorial bond) produces a flatter structure

Question 12

What is sucrose made up of and what forms

Answer 12

• made up of D-glucose and D-fructose linked together
• the D-glucose is in a phyranose form
• the D-fructose is in a furanose form
• non reducing - no hemiactely

Question 13

Amylose - what kinds of bonds

Answer 13

• component of starch, polysaccharide of glucose units
• 4000 units joined together by a-1,4 glycosidic bonds in maltose

Question 14

Structure of amylose and what happens in digestion

Answer 14

• helical 3D structure
• in digestion, a-amylose hydrolysed by enzyme (a-amylase) —-> glucose

Question 15

Cellulose (polysaccride) type of bonds

Answer 15

• polymer of glucose with B-1,4 glycosidic bonds

Wood = 50% cellulose
Cotton = 100% cellulose

Question 16

Geometry of cellulose B-1,4 glycosidic bonds

Answer 16

• geometry of these linkages leads to straight molecular rods established by a network of hydrogen bonds - useful for structural material

Question 17

Digestion of cellulose

Answer 17

• mammals without a rumen cannot digest cellulose
• digestive enzymes have reactive sites which are the right shape for a-1,4’-glycosidic linkages
• B-1,4’-glycosidic links do not fit - CANNOT DIGEST CELLULOSE

Question 18

Carbohydrates and molecular recognisiton

Answer 18

• large scope for variability
• many combinations that can give unique patterns on cell surfaces
  Monosaccharides can differ in:
• number of carbons
  Strerochemistly
  Functional groups
  Ring sizes - furanose and pyranose
  Orientation of groups - a and b