2.1.2e and f- Carbohydrates

Question 1

List 3 exmaples of monosaccharides, disaccharides and polysaccharides

Answer 1

MONOSACCHARIDES: glucose, fructose, galactose
DISACCHARIDES: sucrose, lactose, maltose
POLYSACCHARIDES: glycogen, starch, cellulose

Question 2

The fundamentals of polysaccharides

Answer 2

• can be composed of hundreds to thousands of monosaccharides combined together
• monosaccharides are joined together through many condensation reactions
• polysaccharides have several functions including structural support and storage- they are insoluble so have no osmotic effect

Question 3

How does the water potential of cells affect carbohydrate storage?

Answer 3

• if lots of glucose molecules dissolved in cytoplasm, water potential would decrease and water would be drawn into cell from surrounding areas by osmosis
• this could disrupt normal functioning of the cell, so polysaccharides are used to store monosaccharides as they are insoluble and have no effect on the function of a cell

Question 4

Features of starch

Answer 4

• main storage polysaccharide in plants
• pure starch is white, tasteless and odourless, and insoluble in cold water or alcohol
• starch is formed when α-glucose monomers are joined together by glycosidic bonds during condensation reactions
• 20-30% of starch made up of long unbranched chains called amylose where α-glucose monomers are held together by 1 – 4 glycosidic bonds

Question 5

Features of amylopectin and amylose

Answer 5

• key structural feature of amylose and amylopectin is their ability to coil into a spiral shape where hydrogen bonds hold the spiral in place
• in amylose, the -OH groups on carbon 2 are situated on the inside of the coil, making molecule less soluble and this allows hydrogen bonds to form to maintain the coil’s structure

Question 6

Features of cellulose

Answer 6

• main structural constituent of plant cell walls

- the microfibrils are strong and so are structurally important in plant cell walls

Question 7

Joining more than one beta glucose molecule

Answer 7

• after the 1st 1-4 glycosidic bond, all the other 1-4 glycosidic bonds after this will rotate 180 degrees
• so the first bond- you have O at the top and then O at the bottom and then O at the top….
• as well as the rotated glycosidic bonds additional bonds will form on the same cellulose chains

Question 8

Features of glycogen

Answer 8

• glycogen occurs in dense granules in liver cells where it may form up to 7% of the mass of this organ
• main storage polysaccharide in animals and fungi
• the number and length of the branches means that it is extremely compact and very fast hydrolysis

Question 9

What are the different types of glycosidic bonds

Answer 9

In glycogen, a 1 - 4 glycosidic bond is formed between the 1st of one monosaccharide and the 4th carbon of the adjacent monosaccharide but branches are also formed by glycosidic bonds between the 1st carbon and 6th carbon