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Biology Module 2 > Carbohydrates > Flashcards

Carbohydrates Flashcards

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1
Q

What is a condensation reaction?

A

A reaction in which two molecules join together by a chemical bond with the release of a water molecule.

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2
Q

What is a hydrolysis reaction?

A

A reaction whereby water is added to break a chemical bond between molecules.

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3
Q

What are bonds between carbohydrates known as?

A

Glycosidic bonds

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4
Q

What is a single monomer in a carbohydrate?

A

A monosaccharide

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5
Q

What is a pair of monomers in a carbohydrate called?

A

A disaccharide

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6
Q

What is a long chain of monomers in a carbohydrate called?

A

A polysaccharide

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7
Q

What are the two key monosaccharides?

A
  • Glucose
  • Ribose
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8
Q

What is glucose?

A

Glucose is a “hexose monosaccharide”, meaning it consists of a hexagon of 6 carbon atoms.

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9
Q

What is ribose?

A

Ribose is a “pentose monosaccharide”, meaning it consists of a pentagon of 5 carbon atoms.

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10
Q

What is an isomer?

A

An isomer is a compound with the same chemical formula as another, but with a different arrangement of atoms.

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11
Q

What are the two isomers of glucose?

A
  • Alpha glucose
  • Beta glucose
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12
Q

What is the difference between alpha and beta glucose?

A

The orientation of the hydroxyl group (OH) is different in alpha and beta glucose.

In alpha glucose, the hydroxyl group is situated below the carbon ring, but in beta glucose it is above it.

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13
Q

How can a disaccharide be formed?

A

Two monosaccharides can join together by a glycosidic bond in a condensation reaction, forming a disaccharide.

In this reaction, a molecule of water is produced.

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14
Q

What is maltose?

A

A disaccharide formed by condensation of two glucose molecules.

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15
Q

What is sucrose?

A

A disaccharide formed by condensation of glucose and fructose.

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16
Q

What is lactose?

A

A disaccharide formed by condensation of glucose and galactose.

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17
Q

What are polysaccharides?

A

They are macromolecules that have been formed by many monosaccharides which have joined together by glycosidic bonds in a condensation reaction to form chains.

They are not sugars and are insoluble in water.

18
Q

What three polysaccharides do we need to know?

A
  • Glycogen
  • Starch
  • Cellulose
19
Q

How are glycogen and starch formed?

A

By the condensation of alpha glucose molecules.

20
Q

How is cellulose formed?

A

By the condensation of beta glucose molecules.

21
Q

How can polysaccharide chains be set out?

A
  • They can be branched or unbranched
  • They can be folded (makes them more compact - ideal for storage
  • They can be straight - making the molecule to construct cellular structures - or straight
22
Q

Where is glycogen and starch stored?

A
  • Glycogen - muscles and the liver
  • Starch - in the stroma of plants’ chloroplasts
23
Q

What is the function of glycogen?

A

It is the main energy storage molecule in animals.

24
Q

How is glycogen bonded?

A

Glycogen molecules are bonded by carbon molecules 1 and 4, AND by molecules 1 and 6.

25
Q

Why is important that glycogen molecules have many side branches?

A

This is important as it means that many enzymes simultaneously on these branches, allowing a faster release of energy.

26
Q

How is glycogen used to regulate blood sugar levels?

A

The body’s muscles and liver hydrolyse the glycogen stored within them, breaking it down into glucose molecules which can be used in respiration.

27
Q

What is the size of glycogen?

A

It is a relatively large but compact molecule - this maximises the amount of energy it can store, making it optimal for energy storage.

28
Q

Why is it important that glycogen is insoluble?

A

This is important as it means it will not affect the water potential of cells and it cannot diffuse out of other cells.

29
Q

What is the orientation of glucose in glycogen?

A

All glucose units are in the same orientation (alpha).

30
Q

What is starch?

A

Starch is a mixture of two polysaccharides called amylose and amylopectin. Both of these polysaccharides are long chain alpha glucose polymers.

31
Q

What is the structure of amylose?

A
  • Long, unbranching chains
  • Carbon 1,4 glycosidic bonds
  • Chains coil into a helical shape

Amylose makes up 10-30% of starch

32
Q

What is the structure of amylopectin?

A
  • Shorter, branched chains
  • Carbon 1,4 and 1,6 bonds
  • Branches out (C1 bonds to C6)

Amylopectin makes up 70-90% of starch

33
Q

What is cellulose?

A

A polysaccharide found in plants which consists of long chains of beta glucose joined together by 1,4 glycosidic bonds.

In order to form these bonds, alternating beta glucose molecules must be rotated 180°.

34
Q

How is cellulose structured?

A

It consists of unbranched, linear chains of around 10,000 beta glucose molecules in a long, unbranched chain called a microfibril.

35
Q

What are microfibrils?

A

Strong threads made from long cellulose chains which run parallel to each other. They are formed by hydrogen bonds, forming strong cross linkages.

This gives cellulose high stability.

36
Q

Why is cellulose important?

A

It is key in preventing the plant from bursting under osmotic pressure. This is because it exerts inward pressure to stop the influx of water - allowing the cell to stay turgid and rigid, maximising it’s surface area.

37
Q

What is the test for starch and what is the colour change?

A

Iodine Test - brown / yellow –> blue / black

38
Q

What is the test for sugar and what is the colour change?

A

Benedict’s test - Benedict’s solution is an alkaline copper (II) sulphate which is blue and changes colour in the presence of sugar.

Turns from blue to green, yellow or red. Green = low concentration, red = high concentration.

39
Q

What are reducing sugars?

A

Reducing sugars are able to give electrons to other molecules. The reducing sugar becomes oxidised and the other molecule becomes reduced.

40
Q

How do reducing sugars change the colour of Benedict’s solution?

A

Electrons are transferred from the sugar to the Cu 2+ ions in the Benedict’s - reducing them to Cu+.

This forms copper (I) oxide (Cu2O) which forms an orange-red solid suspended in the reaction mixture as a precipitate.

41
Q

Which sugars are reducing and which are non-reducing?

A

All monosaccharides, maltose and lactose are reducing sugars.

Sucrose and polysaccharides are non-reducing sugars.

42
Q

What happens when testing for sucrose?

A

When testing for a non-reducing sugar, in this case, sucrose, the glycosidic bond in the sugar is hydrolysed by hydrochloric acid and neutralised by sodium hydrogen carbonate, freeing up the reducing sugars. For sucrose, these are alpha glucose and fructose.

Biology Module 2 (11 decks)

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