Carbohydrates

Question 1

What is an anomeric carbon and where is it formed?

Answer 1

Anomeric carbon is a carbon that is bonded to TWO oxygen atoms. They are formed in the ring structures of monomers.

Question 2

Structure of α-glucose and β-glucose.

Answer 2

α-glucose linked by:
- α(1,4) glycosidic bond formed between carbon atom 1 of one glucose and carbon atom 4 of the other
- α(1,6) glycosidic bond formed between carbon atom 1 of one glucose and carbon atom 6 of the other

β-glucose linked by:
- β(1,4) glycosidic bond formed between carbon atom 1 of one glucose and carbon atom 6 of another alternate inverted β-glucose unit

Question 3

Define condensation reaction.

Answer 3

A reaction where small molecules are combined to form larger molecules with the formation of water molecule.

Question 4

Define hydrolysis.

Answer 4

A reaction where large molecules are broken into smaller molecules with the addition of water.

Question 5

What is starch?

Answer 5

• Starch is formed from excess glucose synthesized via photosynthesis (commonly found in plant tissues)
• Serves as a carbon source (ONLY consists of α-glucose monomers: unbranched amylose w α(1,4) glycosidic bonds (10-30%), branched amylopectin w α(1,6) glycosidic bonds & α(1,4) glycosidic bonds (70-90%))
• Stored in plant cells as starch grains within chloroplasts/amyloplasts (specialized plastids for starch storage)

Question 6

What are reducing sugars?

Answer 6

• RS can reduce other compounds and are oxidized in the process of reduction. (RS contain free aldehyde or ketone groups. They can transfer H ions to other compounds and cause reduction of other compounds.)
• All monosaccharides (glucose, fructose, galactose) and some disaccharides (maltose, lactose) are RS.
• NRS (sucrose) have no free carbonyl group (both carbonyl groups are linked in a glycosidic bond) and cannot participate in the redox reactions characteristic of reducing sugars.

Question 7

What is the structure of amylose?

Answer 7

• Unbranched chain that consists of hundreds-thousands of α-glucose residues joined by α(1,4) glycosidic bonds
• Forms compact helical structure
• 6 glucose units per turn in the helix
• Bulky thus poorly soluble in water, does not exert osmotic influence in the cell

Question 8

What is the structure of amylopectin?

Answer 8

• More complex form of starch consisting of α-glucose residues
• Contains α(1,4) glycosidic bonds & α(1,6) glycosidic bonds (making it branched)
• Branch points occur at every 12-30 residues
• Average branch length is between 24-30 residues
• Easily hydrolysed (many branch ends allow a larger number of enzymes to act on it at any one time)
• Highly compact due to extensive branching (can contain up to twice as many α-glucose residues as amylose)