Carbohydrates and Lipids

Question 1

What are carbohydrates?

Answer 1

Biological molecules containing carbon, hydrogen and oxygen atoms and they are fundamental cellular components vital for cellular functions

Question 2

What is a ‘saccharide’?

Answer 2

A termed name for a carbohydrate

Question 3

What are 3 functions of carbohydrates?

Answer 3

1. Provide a rapid and regular supply of energy for cellular reactions
2. Form part of important molecules in the cell
3. Form markers on the cell surface which aid cell recognition

Question 4

What is a disaccharide?

Answer 4

Two monosaccharides linked together (a dimer)

Question 5

What is an oligosaccharide?

Answer 5

A polymer of 3-20 monosaccharides

Question 6

What is a polysaccharide?

Answer 6

A polymer of monosaccharide units linked together

Question 7

What are 3 examples of monosaccharides?

Answer 7

Glucose, ribose and fructose

Question 8

What is a monosaccharide?

Answer 8

Single sugar molecules providing instant energy

Question 9

What is a ‘Fischer projection’?

Answer 9

A two-dimensional representation of a three-dimensional organic molecule by projection

Question 10

Give the 3 examples of aldohexose sugars with the same chemical formula

Answer 10

Glucose, galactose and mannose

Question 11

What is a stereoisomer?

Answer 11

Molecules with the same chemical formula and the same order and type of bonds. However, they are non-overlapping mirror images of each other and thus have different spatial arrangements and different biological functions.

Question 12

What does stereoisomerism require?

Answer 12

A chiral carbon centre

Question 13

What is a chiral carbon?

Answer 13

A carbon that has 4 different groups attached to it

Question 14

How does cyclization occur?

Answer 14

The OH group on the second to last carbon reacts with carbonyl group

Question 15

What is the resulting product for the cyclization of an aldose?

Answer 15

A hemiacetal

Question 16

What is the resulting product for the cyclization of a ketose?

Answer 16

A hemiketal

Question 17

Why are only small amounts of straight chain monosaccharides present in mixtures?

Answer 17

Monosaccharides cyclize spontaneously under normal conditions

Question 18

Describe the cyclization of D-glucose

Answer 18

• The cyclic form of D-glucose is D-glucopyranose
• The OH group can attack the planar C=O group from either side
• Thus there are two possible hemiacetal products: the alpha and beta anomers of D-glucopyranose

Question 19

Describe the structure and function of glucose

Answer 19

• 7 energy rich C-H bonds which are broken down during cellular respiration
• Released energy is stored as ATP for use by the cell
• Primary source for life

Question 20

Describe the structure and function of fructose

Answer 20

• 7 energy rich C-H bonds
• Forms a furan-based ring structure despite being a hexose
• An important source of energy
• Found in fruits, honey, berries and melons

Question 21

What is a furanose?

Answer 21

A five membered cyclization product

Question 22

Giver 3 examples of disaccharides

Answer 22

Sucrose, maltose and lactose

Question 23

How are disaccharides formed?

Answer 23

By dehydration synthesis (condensation reaction) with the loss of a water molecule and this reaction is aided by biological catalysts (enzymes)

Question 24

How are disaccharide molecules bonded together?

Answer 24

Joined at -OH groups by glycosidic links/ bonds

Question 25

What is the primary function of disaccharides?

Answer 25

Nutritional source of monosaccharides

Question 26

Describe the structure of maltose

Answer 26

Two glucose molecules joined at carbons 1 and 4 via an alpha -1,4 glycosidic link

Question 27

How can maltose be generated?

Answer 27

The breakdown of starch

Question 28

How is maltose converted into individual glucose monosaccharides

Answer 28

Digested by maltase

Question 29

Where is maltase present?

Answer 29

Germinating seeds and grain

Question 30

What is maltase metabolised by?

Answer 30

Yeast

Question 31

What does maltase metabolism yield?

Answer 31

Ethanol and carbon dioxide

Question 32

How is maltase formed?

Answer 32

• Condensation reaction

- 2 glucose molecules combine to form maltose and a water molecule

Question 33

Describe the structure of lactose

Answer 33

Glucose and galactose molecules are joined at carbons 1 and 4 via an beta -1,4 glycosidic link

Question 34

Where is lactose produced?

Answer 34

Lactating mammals as an energy source for their young

Question 35

How is lactose converted to its constituent monosaccharides?

Answer 35

Digested by the enzyme lactase

Question 36

Describe the structure of sucrose

Answer 36

Glucose and fructose molecules are joined at carbons 1 and 2 via an alpha -1,2 glycosidic link

Question 37

Where is sucrose abundant?

Answer 37

In plants/ sap (especially sugar cane and beet) and plentiful in a Western diet

Question 38

How is sucrose digested into it constituent monosaccharides?

Answer 38

Digested by the enzyme sucrase

Question 39

Write the general disaccharide hydrolysis equation

Answer 39

Disaccharide (+ water molecule) —-> Monosaccharides

Digested by an enzyme

Question 40

Write the 3 disaccharide hydrolysis equations (including enzymes involved)

Answer 40

Maltose –Maltase–> glucose + glucose

Lactose –Lactase–> glucose + galactose

Sucrose –Sucrase–> glucose + fructose