Unit 2 - Carbohydrates

Question 1

A single sugar unit is known as a…

Answer 1

Monosaccharide (a monomer of sugar)

Question 2

What is the chemical composition of a carbohydrate?

Answer 2

Carbon, oxygen, & hydrogen

Question 3

When two or more monosaccharides are linked they form…

Answer 3

A polymer called a polysaccharide.

Question 4

Glucose is a monosacharride composed of six carbons and is therefore a…

Answer 4

Hexose monosaccaride

Question 5

Name the two structural variation of the glucose molecule

Answer 5

1. Alpha (α) glucose
2. Beta (β) glucose

Question 6

How does alpha glucose differ from beta glucose?

Answer 6

The hydroxyl group (OH) on carbon 1 is in opposite positions

This affects the structure and properties of the polysaccarides when it bonds

Question 7

How is a disaccharide formed?

Answer 7

• A condensation reaction
• 2 monosaccharides join together in a condensation reaction.
• The two hydroxyl groups interact - bonds are broken in the OH group and a new glycosidic bond is formed
• Water is released

Question 8

Name this dissacharide…

Answer 8

Glucose + galactose = Lactose

Question 9

Name this dissacharide…

Answer 9

Glucose + glucose = Maltose

Question 10

Name this dissacharide…

Answer 10

Glucose + fructose = Sucrose

Question 11

What is a pentose sugar?

Answer 11

Sugars that contain five carbon atoms

Question 12

Which two pentose sugars are important components of biological molecules?

Answer 12

Ribose (sugar found in RNA) and Dexoyribose (sugar found in DNA)

Question 13

What are the properties of starch?

Answer 13

• Compact
• Chemical energy store
• Easily digestible
• Made of amylose (mainly, 1-4 glycosidic bonds) and amylopectin (1-4 and some 1-6 glycosidic bonds)
• Insoluble does not create a water potential gradient (doesn’t cause water to enter cells by osmosis which would make them swell up)

Question 14

Describe the properties and structure of amylose.

Answer 14

• Long chains of alpha glucose (unbranched)
• Joined by 1-4 glycosidic bonds
• Insoluble (does not create water potential gradient)
• Metabolically inactive
• Long chain of glucose that twists into a helix (compact for storage)
• Helix held together by hydrogen bonds

Question 15

Describe the properties and structure of amylopectin.

Answer 15

• Long, branched chains of alpha glucose
• Joined by 1-4 glycosidic bonds (chains) and 1-6 glycosidic bonds (branches)
• 1-6 branching points occur approximately one in every 25 glucose subunits.
• Compact and idealy for storage
• Insoluable (do not affect water potential)
• Branches gives ‘free ends’ so glucose can be added or released quickly

Question 16

Describe the properties and structure of glycogen

Answer 16

• Short, branched chains of alpha glucose
• Joined by 1-4 glycosidic bonds (chains) and 1-6 glycosidic bonds (branches)
• Compact and insoluble so good for storage
• Branching means many ‘free ends so glucose can be released (or stored) quickly

Question 17

What is the function of glycogen?

Answer 17

• Main energy store in animals
• Stores soluble glucose that affects water potential as insoluble polysaccharide until needed

Question 18

Describe the structure and properties of cellulose.

Answer 18

• Long, unbranched chain of beta (β) glucose
• Contains 1-4 glcyosidic bonds
• Beta (β) glucose molecules bond forming straight cellulose chains
• Every other glucose molecule is orientated at 180 degrees - e.g alternate beta (β) glucose are turned upside down.
• Chains are linked by hydrogen bonds forming strong fibres called microfibrils (compact)
• Microfibrils join to make macrofibrils, which combine to make fibres

Question 19

Describe the function of cellulose?

Answer 19

• Cellulose is an important part of our diet as it is very hard to breakdown so if the fibre necessary for a healthy digestive system
• Cellulose provides structural support for cells

Question 20

How is a disaccharide broken down?

Answer 20

• Hydolysis reaction
• Addition of water to hydrolyse the disaccharide into (useable) monomers
• Reactions are catalysed by enzymes
• These are the opposite of condensation reactions that form glycosidic bonds.