Introduction to carbohydrate structure:

Question 1

Describe the classification of carbohydrates:

Answer 1

Monosaccharides - single monomers, glucose, simplest sugar molecules, can’t be split into simpler by hydrolysis
Disaccharides - 2 monosaccharides linked by glycosidic bond, lactose & maltose
Oligosaccharides - short chain of monosaccharides linked by glycosidic bonds
Polysaccharides - long chain of monosaccharides, glycogen & starch

Question 2

What are stereoisomers?

Answer 2

2 or more molecules with the same molecular formula and the same sequence of bonded atoms but differ in the 3D arrangement of their atoms

Question 3

What is the difference between an enantiomer and a diastereoisomer?

Answer 3

Enantiomer - chiral molecules which are non superimposable mirror images of each other
Diastereoisomer - molecules with multiple chiral centres which are non-superimposable but also not mirror images

Question 4

What is starch?

Answer 4

Starch is the storage polysaccharide of plants and exists in 2 forms
Amylose - hydrophobic inner surface, 200-2500 glucose units
Amylopectin - up to 6000 glucose units, highly branched and dense molecule

Question 5

What is glycogen?

Answer 5

Storage polysaccharides of animals
Similar to amylopectin but more frequent branch points
Metabolised via glycolysis
Accessible storage of glucose

Question 6

How are disaccharides formed?

Answer 6

Monosaccharides joined together by condensation reaction forming glycosidic bond
Glycosidic bond joining the 2 monosaccharides can be alpha or beta
If glycosidic bond is down then alpha, up is beta

Question 7

What are anomers?

Answer 7

2 possible orientations chemical groups attached to carbon 1 from functional aldehyde group - anomeric carbon
Anomers classified as either alpha (below plane of ring) or beta (above plane of ring) depending on the orientation of the hydroxyl group attached to the anomeric carbon

Question 8

What is mutarotation?

Answer 8

Interconversion between alpha and beta pyranose rings is termed mutarotation and this process passes through a straight chain intermediate conformation

Question 9

What are pyranose rings?

Answer 9

Pyranose aren’t planar and rather adopt 2 conformations called the chair and the boat
The chair is preferred as there is less steric hinderance

Question 10

What is the general formula of carbohydrates?

Answer 10

Cx(H2O)y.

Question 11

What is the function of carbohydrates?

Answer 11

Energy stores
Structural elements in cell walls of plants and bacteria
Mediators of cell-cell interactions by attaching to proteins