Biological molecules: carbohydrates

Question 1

what are carbohydrates?

Answer 1

molecules that only contain carbon, hydrogen and oxygen. Carbohydrates literally mean hydrated carbon (carbon and water). Carbohydrates are also known as saccharides.

Question 2

sugars with six carbon atoms are called…

Answer 2

hexose sugars

Question 3

What is a monosaccharide and name the four examples?

Answer 3

It is a single sugar unit. Examples: glucose, galactose, fructose and ribose.

Question 4

why are monosaccharides polar and soluble?

Answer 4

because the OH group forms hydrogen bonds with the water molecules. This allows glucose to be dissolved in the cytosol.

Question 5

what are pentose monosaccharides and name the example?

Answer 5

monosaccharides which contain 5 carbon atoms e.g ribose

Question 6

what are the differences between the isomers of glucose?

Answer 6

the isomers of glucose is alpha glucose and beta glucose. If the carbon 1 hydroxyl points below the ring it is alpha glucose. If above, beta glucose.

Question 7

how is the disaccharide, maltose made?

Answer 7

formed by two alpha glucose molecules

Question 8

what is made when a disaccharide is formed from two monosaccharides?

Answer 8

water is made from a hydrogen from one of the monosaccharides and a hydroxyl group from the other. This is a condensation reaction.

Question 9

what is the new chemical bond formed when monosaccharides join and what type of bond is it?

Answer 9

glycosidic bonds which is a covalent bond

Question 10

How do you break glycosidic bonds?

Answer 10

by adding water, this is called hydrolysis.

Question 11

How is the disaccharide, sucrose formed?

Answer 11

formed from monosaccharides, glucose and fructose

Question 12

How is the disaccharide, lactose formed?

Answer 12

formed from monosaccharides, glucose and galactose

Question 13

plant cells store glucose as… and what two molecules does it consist of?

Answer 13

starch. Starch consists of two molecules, amylose and amylopectin.

Question 14

Describe the structure of amylose polysaccharide and what bonds occur?

Answer 14

• polymer of alpha glucose molecules joined by 1-4 glycosidic bonds.
• twists into a complex, compact helix with hydrogen bonds forming in between glucose molecules along the chain which stabilises the structure and is ideal for storage. This makes starch insoluble.
• unbranched

Question 15

Describe the structure of amylopectin polysaccharide

Answer 15

• polymer of alpha glucose molecules joined by 1-4 glycosidic bonds
• have branches every 25-30 glucose molecules
• the branches are held by 1-6 glycosidic bond

Question 16

As amylose and amylopectin are polysaccharides, they are too big to pass through the cell membrane therefore…

Answer 16

enzymes are used to break the glycosidic bonds which is a hydrolysis reaction. The enzymes act at the end of the molecules

Question 17

animals store glucose as… and describe the structure

Answer 17

glycogen, which has the same structure as amylopectin but forms more branches than amylopectin. Major stores of glycogen is in the liver and muscle cells.

Question 18

why can enzymes convert glycogen and amylopectin quickly into glucose?

Answer 18

Because as they have many branches, they have many ends which increases the rate as enzymes only work on the ends. Glycogen is quicker at converting as it has more branches, this is important as animals have a high rate of respiration.

Question 19

what is the plant cell wall made of?

Answer 19

cellulose

Question 20

what are the polysaccharides of alpha glucose?

Answer 20

amylose, amylopectin and glycogen

Question 21

describe the structure of cellulose

Answer 21

• polymer of beta glucose molecules joined by 1-4 glycosidic bonds
• every second beta glucose is flipped upside down as hydroxyl groups are now close enough to react and form the glycosidic bond.
• unbranched

Question 22

why is cellulose strong?

Answer 22

-as it is a straight chain, it allows the cellulose molecules to get close together. Therefore lots of hydrogen bonds form between neighbouring chain, making it strong and insoluble.

Question 23

how does a microfibril develop into a fibre?

Answer 23

microfibrils join to make a macrofibril and macrofibrils join to make a fibre

Question 24

why does cellulose need to be strong?

Answer 24

so they cell doesn’t burst.

Question 25

how is glycogen adapted for food storage?

Answer 25

it is insoluble and it is compact so more can be stored in a less space

Question 26

why is it important for a storage molecule to be insoluble and compact?

Answer 26

compact meaning more can be stored in a small area. Insoluble meaning it doesnt affect water potential

Question 27

how does beta glucose differ from alpha glucose? (2marks)

Answer 27

OH and H are reversed (1) on the right carbon (1)