1: BIOLOGICAL MOLECULES - MONOSACCHARIDES AND POLYSACCHARIDES

Question 1

What are monosaccharides?

Answer 1

monomers that form polysaccharides (carbohydrates) (eg: glucose)

Question 2

What are the 2 types of glucose?

Answer 2

• alpha glucose
• beta glucose

Question 3

What are isomers?

Answer 3

molecules with the same molecular formula but with the atoms connected in different ways

Question 4

What is the difference between alpha glucose and beta glucose?

Answer 4

• they are isomers
• the 2 types of glucose have the last groups reversed

Question 5

How are disaccharides formed?

Answer 5

a disaccharide is formed when 2 monosaccharides are joined together by a condensation reaction

Question 6

What type of bond is formed between monosaccharides as H2O is released in a condensation reaction?

Answer 6

a glycosidic bond

Question 7

What is maltose?

Answer 7

a disaccharide formed from a condensation reaction between 2 alpha glucose molecules

Question 8

What is sucrose?

Answer 8

a disaccharide formed from a condensation reaction between a glucose molecule and a fructose molecule

Question 9

What is lactose?

Answer 9

a disaccharide formed from a condensation reaction between a glucose molecule and a galactose molecule

Question 10

What do reducing sugars include?

Answer 10

all monosaccharides and some disaccharides (eg: maltose and lactose)

Question 11

How do you test for reducing sugars?

Answer 11

• add benedict’s reagent to a sample and heat in a water bath
• if the test is +ve it will form a coloured precipitate (green/yellow/orange/brick red depending on the conc. of sugar)

Question 12

How do you test for non-reducing sugars (eg: sucrose)?

Answer 12

• add dilute HCL and gently heat to break the sample down into monosaccharides
• neutralise the solution by adding sodium hydrogencarbonate
• add benedict’s reagent and heat in a water bath
• if the test is +ve it will form a coloured precipitate (green/yellow/orange/brick red depending on the conc. of sugar)

Question 13

What are polysaccharides?

Answer 13

carbohydrates

Question 14

How are polysaccharides formed?

Answer 14

polysaccharides are formed when 3+ monosaccharides are joined together by condensation reactions

Question 15

What are 3 examples of polysaccharides?

Answer 15

• starch
• glycogen
• cellulose

Question 16

What is starch used for?

Answer 16

• plants store excess glucose as starch
• when a plant needs more glucose for energy, it breaks down starch to release the glucose

Question 17

What is starch made up of?

Answer 17

• 2 polysaccharides of alpha glucose:
  
  • amylose
  • amylopectin

Question 18

What is the structure of amylose and how does it relate to its function?

Answer 18

• long, unbranched chain of alpha glucose
• angles of glycosidic bonds give it a coiled structure which makes it more compact for storage

Question 19

What is the structure of amylopectin and how does it relate to its function?

Answer 19

• long, branched chain of alpha glucose
• side branches allow enzymes that break down the starch to reach the glycosidic bonds easily so the glucose can be released easily

Question 20

Is starch soluble/insoluble and how does that relate to its function?

Answer 20

• starch is insoluble and has no effect on water potential
• therefore it doesn’t cause water to enter the cell which would make the cell swell
• this makes it good for storage

Question 21

What is glycogen used for?

Answer 21

• animals store excess glucose as glycogen
• when more glucose is required for energy, glycogen is broken down to release the glucose

Question 22

What is the structure of glycogen and how does it relate to its function?

Answer 22

• long, branched chain of alpha glucose
• many side branches allow enzymes that break down the starch to reach the glycosidic bonds easily so the glucose can be released easily
• compact which makes it good for storage

Question 23

What is the structure of cellulose and how does it relate to its function?

Answer 23

• long, unbranched chain of beta glucose
• cellulose chains linked together by hydrogen bonds to form microfibrils (strong fibres) which allow cellulose to provide structural support (eg: in cell walls)

Question 24

How do you test for starch?

Answer 24

-add iodine dissolved in potassium iodide
-if the test is +ve the colour of the solution would change from orange/brown to blue black