Biological Molecules - Carbohydrates and Lipids

Question 1

Define monomer

Answer 1

Monomers are the smaller molecules from which polymers are made

Question 2

Define polymers

Answer 2

Polymers ae molecules made from a large number of monomers joined together

Question 3

Name 3 types of monosaccharides

Answer 3

Glucose, Fructose, Galactose

Question 4

Name three types of disaccharides

Answer 4

Maltose, Lactose, Sucrose

Question 5

Name 3 types of polysaccharides

Answer 5

Starch, Glycogen, Cellulose

Question 6

How are disaccharides maltose, sucrose and lactose formed?

Answer 6

glucose + glucose —> maltose

glucose + fructose —> sucrose

glucose + galactose —> lactose

Question 7

What is the name given to the bond between 2 alpha glucose molecules?

Answer 7

A glycosidic bond

Question 8

Describe and explain how the structure of starch relates to its function

Answer 8

• Insoluble - Does not lower the water potential of the cell so does not affect osmosis
• Large and insoluble - Does not diffuse across the cell membrane and out of the cell
• Coiled into a helix - Compact
• Branched - Provides more ends / larger surface area for faster hydrolysis

Question 9

Describe and explain how the structure for glycogen relates to its function

Answer 9

• Coiled into a helix - Compact so that a lot can fit into a small space
• Insoluble - Does not lower the water potential of the cell so does not affect osmosis
• Large and insoluble - Does not diffuse across the cell membrane and out of cells
• Very highly branched - Provides many ends/ larger surface area for faster hydrolysis by enzymes to form alpha glucose for use in respiration

Question 10

Describe and explain how the structure of cellulose relates to its function

Answer 10

• Long straight + unbranched chains of beta glucose linked together by many hydrogen bonds to form microfibrils and cellulose fibres - Provides strength to the cell wall

Question 11

Describe the biochemical test for starch including the outcome of a positive test

Answer 11

• Add iodine solution to the sample
• For positive test result: a colour change from orange to blue-black

Question 12

Describe the biochemical test for a reducing sugar including the outcome of a positive test

Answer 12

• Add benedict’s solution to the sample and heat to 95 degrees C
• For positive test result : a colour change from blue to red precipitate

Question 13

Describe the biochemical test for a non-reducing sugar including the outcome of a positive test

Answer 13

• Add benedict’s solution to the sample and heat to 95 degrees C
• If there is no change then boil a fresh sample with dilute hydrochloric acid for a few minutes
• Neutralise by adding solid sodium hydrogen carbonate
• Then add the Benedict’s solution and heat to 95 degrees C
• For positive test result: a red precipitate will form and a colour change from blue to red

Question 14

Name the reducing and non-reducing sugars

Answer 14

• Reducing sugars - Glucose, galactose, lactose, maltose and fructose
• Non-reducing sugars - Sucrose

Question 15

Define condensation

Answer 15

A reaction which joins two glucose molecules together by a chemical bond and involves the elimination of a molecule of water

Question 16

Define hydrolysis

Answer 16

Breaking a achemical bond between 2 molecules and involves the use of a water molecule

Question 17

Describe the structure of triglycerides

Answer 17

Triglycerides are made up of one glycerol molecule and three fatty acid molecules

Question 18

Relate the structure of triglycerides to their function

Answer 18

• Long hydrocarbon fatty acid chains - Contains lots of stored chemical energy which is why triglycerides are used as an energy storage molecule
• Hydrophobic fatty acid tails - Insoluble in water therefore it does not affect the water potential of a cell

Question 19

Describe how triglycerides form

Answer 19

Triglycerides are formed by the condensation of one glycerol and three fatty acid molecules forming three ester bonds and three water molecules produced

Question 20

Describe the stages of the emulsion test including what a positive result will be

Answer 20

• Add ethanol to the sample and shake
• Then add water drop wise
• If a lipid id present, a white emulsion will be visible

Question 21

Describe the structure of phospholipids

Answer 21

Phospholipids are made of one glycerol molecule, two fatty acid molecules and a phosphate group

Question 22

Relate the structure of phospholipids to their function

Answer 22

• Hydrophobic fatty acid tails and hydrophilic phosphate heads - Will form a bilayer in water. This forms cell membranes and the fatty acid centre means that water soluble molecules cannot easily pass across the membrane

Question 23

Describe and explain how phospholipids arrange themselves in cell membranes

Answer 23

• Phosphate head is hydrophillic wheras the fatty acid tails are hydrophibic
• This allows the phospholipids to form a bilayer in water
• Hydrophobic fatty acid tails are pointing inwards away from the water while the hydrophilic phosphate heads are pointed outwards facing the water

Question 24

Compare and contrast the structure of triglycerides and phospholipids

Answer 24

• Tryglycerides have three fatty acid tails and phospholipids have two fatty acid tails
• Phospholipids have a phosphate group and triglycerides do not
• Phospholipids are polar and triglycerides are non-polar

Question 25

Define saturated fatty acid

Answer 25

No carbon to carbon double bonds are in the hydrocarbon chain

Question 26

Define unsaturated fatty acid

Answer 26

Contains carbon to carbon double bonds in the hydrocarbon chain

Question 27

What is a monosaccharide

Answer 27

The monomers from which larger carbohydrates are made

Question 28

What are the two isomers of glucose

Answer 28

Alpha glucose and Beta glucose

Question 29

What are the differences between the structures of starch and glycogen

Answer 29

• Glycogen has shorter chains than starch
• Glycogen is more highly branched than starch
• Glycogen has a larger surface area than starch