Biological molecules - CARBOHYDRATES

Question 1

How does a condensation reaction between two monosaccharides form a glycosidic bond?

Answer 1

A water molecule is released and a covalent bond between one O and a carbon (4) is formed

Question 2

What are monomers?

Answer 2

Monomers are the smaller units from which polymers are made

Question 3

What are polymers?

Answer 3

Polymers are (often chains) made up of many monomers

Question 4

Name examples of monomers

Answer 4

Monosaccharides, amino acids and nucleotides

Question 5

What are some common disaccharides?

Answer 5

Sucrose, lactose and maltose

Question 6

How are common disaccharides formed?

Answer 6

By the condensation of two monosaccharides

Question 7

How is maltose formed?

Answer 7

By the condensation of two α-glucose molecules

Question 8

How is sucrose formed?

Answer 8

By the condensation of a glucose molecule and a fructose molecule

Question 9

How is lactose formed?

Answer 9

By the condensation of a glucose molecule and a galactose molecule

Question 10

How are glycogen and starch formed?

Answer 10

By the condensation of α-glucose (alpha glucose)

Question 11

How is cellulose formed?

Answer 11

By the condensation of β-glucose (beta glucose)

Question 12

How can we test for reducing sugars and non reducing sugars?

Answer 12

Benedict’s solution: heat in a water bath at 80-85 degrees celsius for 5 minutes; (REDUCING SUGARS) colour change from blue - brick red, yellow, green/(NON_REDUCING SUGARS) add HCl + heat, then add sodium hydrogencarbonate to neutralise, then Benedict’s solution and heat - colour change to brick red

Question 13

How can we test for starch?

Answer 13

Iodine solution: colour change from orange/brown - blue/black

Question 14

What is the molecular formula for carbohydrates?

Answer 14

Cn(H2O)n

Question 15

Molecular formula of general name ‘triose’?

Answer 15

C3H6O3

Question 16

Molecular formula of general name ‘pentose’ and example?

Answer 16

C5H10O5 - ribose

Question 17

Molecular formula of general name ‘hexose’ and examples?

Answer 17

C6H12O6 - glucose (α & β), fructose, galactose

Question 18

What is an isomer?

Answer 18

Same molecular formula but different displayed/structural formula

Question 19

What does ABBA stand for and how can we use it?

Answer 19

‘Alpha below’ and ‘Beta above’
In an α-glucose, the OH is below the 1st carbon.
In a β-glucose, the OH is above the 1st carbon.

Question 20

Key characteristics of condensation and hydrolysis reactions? (In terms of: water, covalent bonds and size)

Answer 20

CONDENSATION
water - released
covalent bond - form glycosidic bonds
size - larger

HYDROLYSIS
water - used
covalent bond - broken
size - smaller but more of them

Question 21

Why are sugars soluble?

Answer 21

They have the ability to form hydrogen bonds between the solute (glucose) and water (solvent)

Question 22

What polymers of alpha glucose can be formed?

Answer 22

Animals & funghi: GLYCOGEN
Plants: STARCH (amylose and amylopectin)

Question 23

Describe Amylose

Answer 23

Monomer: α-glucose
Covalent bonds: α 1,4 glycosidic
Structure : Spiral, coiled, α-helix
Function: Stores glucose for use in respiration

Question 24

Describe Amylopectin

Answer 24

Monomer: α-glucose
Covalent bonds: α 1-4 AND 1-6 glycosidic bonds
Structure: relatively few 1-6 bonds, branched, crystalline
Function: Stores glucose for use in respiration

Question 25

Describe Glycogen

Answer 25

Monomer: α-glucose Covalent bonds: α 1-4 AND 1-6 glycosidic bonds Structure: More branches than amylopectin, spherical Function: Stores glucose for use in respiration

Question 26

Structure to function of amylose, amylopectin and glycogen?

Answer 26

1) Insoluble - doesn't affect the water potential and cause water to move by osmosis 2) Large molecules - cannot diffuse across cell membrane and be lost from cell 3) Branched or coiled - more compact, so more can fit in the cell 4) Polymer of α-glucose - respiratory substrate 5) Highly branched - allows rapid hydrolysis to provide glucose for respiration (ONLY GLYCOGEN)

Question 27

Describe Cellulose

Answer 27

Monomer: β-glucose Covalent bonds: β 1-4 glycosidic bonds Structure: Straight, unbranched chain that form fibrils Function: Cell wall

Question 28

Structure to function of cellulose?

Answer 28

1) H bonds - Produce high tensile strength, so cell walls are flexible 2) Straight chains - form fibrils, which are stronger 3) Offset ends of chains - strengthens the fibre to prevent breaking

Question 29

BENEDICT'S TEST - Why do you repeat the test for a reducing sugar using distilled water?

Answer 29

To provide us with a control experiment - so we can compare and check that the heat is not causing the reagent to change colour

Question 30

BENEDICT'S TEST - Why did you initally test sucrose without the treatment with hydrochloric acid and sodium hydrogencarbonate?

Answer 30

To test and see if sucrose is a reducing sugar (it is not!)

Question 31

BENEDICT'S TEST - Why did you heat the sucrose with hydrochloric acid at the start of the test for non-reducing sugars? Explain the reactions occurring during this part of the experiment

Answer 31

HCl and heat hydrolyses the sucrose without an enzyme, breaking the glycosidic bonds

Question 32

BENEDICT'S TEST - Why is sodium hydrogencarbonate added to the tube before testing with Benedict’s solution?

Answer 32

The sodium hydrogencarbonate neutralises the acidic solution so the Benedict's can react

Question 33

BENEDICTS'S TEST - How could you modify the procedure to determine the amount of glucose in a solution?

Answer 33

Use a colorimeter

Question 34

BENEDICT'S TEST - How could you improve the validity of the experiment?

Answer 34

1) Filter twice - the remaining Cu2O will affect absorbance 2) Cuvette volume - affect absorbance - measure volume 3) Volume measurement - air bubbles/meniscus ; smallest syringe for the volume 4) Reaction didn't stop at 5 minutes - delays in filtering as it was still hot; put in ice bucket

Question 35

Where would you identify maltose?

Answer 35

Germinating seeds as it is the intermediate stage of polysaccharide digestion starch -> maltose + glucose

Question 36

Where would you identify lactose

Answer 36

Milk sugar - produced in lactation in mammals

Question 37

Where would you identify sucrose?

Answer 37

Transport in the phloem - allows for specialist transport proteins