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AQA a-level biology 🧬🔬 > Biological molecules - CARBOHYDRATES > Flashcards

Biological molecules - CARBOHYDRATES Flashcards

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1
Q

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

A

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

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2
Q

What are monomers?

A

Monomers are the smaller units from which polymers are made

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3
Q

What are polymers?

A

Polymers are (often chains) made up of many monomers

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4
Q

Name examples of monomers

A

Monosaccharides, amino acids and nucleotides

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5
Q

What are some common disaccharides?

A

Sucrose, lactose and maltose

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6
Q

How are common disaccharides formed?

A

By the condensation of two monosaccharides

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7
Q

How is maltose formed?

A

By the condensation of two α-glucose molecules

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8
Q

How is sucrose formed?

A

By the condensation of a glucose molecule and a fructose molecule

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9
Q

How is lactose formed?

A

By the condensation of a glucose molecule and a galactose molecule

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10
Q

How are glycogen and starch formed?

A

By the condensation of α-glucose (alpha glucose)

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11
Q

How is cellulose formed?

A

By the condensation of β-glucose (beta glucose)

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12
Q

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

A

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

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13
Q

How can we test for starch?

A

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

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14
Q

What is the molecular formula for carbohydrates?

A

Cn(H2O)n

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15
Q

Molecular formula of general name ‘triose’?

A

C3H6O3

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16
Q

Molecular formula of general name ‘pentose’ and example?

A

C5H10O5 - ribose

17
Q

Molecular formula of general name ‘hexose’ and examples?

A

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

18
Q

What is an isomer?

A

Same molecular formula but different displayed/structural formula

19
Q

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

A

‘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.

20
Q

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

A

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

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

21
Q

Why are sugars soluble?

A

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

22
Q

What polymers of alpha glucose can be formed?

A

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

23
Q

Describe Amylose

A

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

24
Q

Describe Amylopectin

A

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

25
Q

Describe Glycogen

A

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

26
Q

Structure to function of amylose, amylopectin and glycogen?

A

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)

27
Q

Describe Cellulose

A

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

28
Q

Structure to function of cellulose?

A

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

29
Q

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

A

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

30
Q

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

A

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

31
Q

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

A

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

32
Q

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

A

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

33
Q

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

A

Use a colorimeter

34
Q

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

A

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

35
Q

Where would you identify maltose?

A

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

36
Q

Where would you identify lactose

A

Milk sugar - produced in lactation in mammals

37
Q

Where would you identify sucrose?

A

Transport in the phloem - allows for specialist transport proteins

AQA a-level biology 🧬🔬 (32 decks)

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