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A Level Biology - Chapter 3 - Biological Molecules > 3.3 and 3.4 - Carbohydrates > Flashcards

3.3 and 3.4 - Carbohydrates Flashcards

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1
Q

What elements do carbohydrates contain?

A

Carbohydrates are molecules that contain only the elements carbon, hydrogen and oxygen.

The literal meaning ‘hydrated carbon’.

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2
Q

What are carbohydrates also known as?

A

Saccharides or sugars.

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3
Q

What is a single sugar unit called?

A

A monosaccharide.

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4
Q

Give three examples of monosaccharides.

A

Glucose, fructose and ribose.

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5
Q

How are two monosaccharides that are joined together called?

A

A disaccharide.

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6
Q

Give two examples of disaccharides.

A

Lactose and sucrose.

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7
Q

When two or more monosaccharides are joined together, what is that molecule called?

A

A polysaccharide.

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8
Q

Give three examples of polysaccharides.

A

Glycogen, cellulose and starch.

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9
Q

What is the chemical formula for glucose?

A

C6H12O6

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10
Q

What does it mean if a molecule, for example glucose, is called a hexose monosaccharide?

A

It means that it contains 6 carbon atoms.

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11
Q

What is the difference between alpha glucose and beta glucose?

A

The difference between the two is the positioning of the hydroxyl - OH - group. It is in opposite positions on carbon 1.

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12
Q

How are the carbons numbered in molecular structure diagrams?

A

They are numbered in a clockwise direction, with carbon 1 starting from the right, going to the left.

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13
Q

How are the glucose molecules soluble in water and polar?

A

It is due to the hydrogen bonding between the hydroxyl groups and water molecules.

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14
Q

Why is it important that glucose is soluble in water?

A

The solubility in water is important as it means that glucose can be dissolved in the cytosol of the cell.

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15
Q

What reaction takes place between two alpha molecules and how?

What is the bonding that takes place called?

A

A condensation reaction takes place between the two alpha glucose molecules when they are side by side.

The two hydroxyl groups interact, one on carbon 1 and one on carbon 4, and a covalent bond called a glyosidic bond is formed.

When this happens bonds are broken and new bonds are reformed in different places producing new molecules.

As it is a condensation reaction, a water molecule is produced as a result of this interaction.

Two hydrogen molecules are removed along with one oxygen molecule.

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16
Q

Name two pentose monosaccharides.

A

Ribose in RNA, and deoxyribose in DNA.

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17
Q

How is glucose made in plant cells?

A

Through photosynthesis.

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18
Q

What kind of energy store is glucose?

A

Chemical energy store.

19
Q

What are the two polysaccharides found in starch, and what is the difference in their bonding?

A

Amylose and amylopectin

Amylose is bonded only by 1,4 glycosidic bonds.

WHEREAS,

Amylopectin is bonded by 1,4 glycosidic bonds, BUT, amylopectin has a branched structure occurring every 25 glucose subunits causing 1,6 glycosidic bonding.

20
Q

What is the structure and properties relating to the structure of amylose?

A

Amylose is joined by 1,4 glycosidic bonds, and the angle of the bonding means that this long chain of glucose twists to form a helix.

This makes the polysaccharide more compact and much less soluble than the glucose used to make it.

21
Q

What is the structure and properties relating to the structure of amylopectin?

A

Amylopectin also has 1,4 glycosidic bonding, but some glycosidic bonds are formed between carbon 1 and 6.

This occurs approximately every 25 glucose subunits.

This means amylopectin has a branched structure.

22
Q

What is the functionally equivalent energy storage to starch used in animals and fungi called?

A

Glycogen

23
Q

What is the energy store in plants called?

A

Starch

24
Q

What is the structure of glycogen and how does it relate to its function?

A

Glycogen forms more branches than amylopectin, therefore making it more compact and much less space is needed for it to be stored.

The branching also means that there are a lot of free ends where glucose molecules can be added or removed.

25
Q

What are the key properties of amylopectin and glucose?

A

They are insoluble, branched, compact.

26
Q

How do animals and plants release glucose as energy?

A

They undergo hydrolysis reactions, which requires the addition of water molecules.

Hydrolysis is the reverse of a condensation reaction.

27
Q

What is the reverse of a condensation reaction?

A

A hydrolysis reaction

28
Q

What is the reverse of a hydrolysis reaction?

A

A condensation reaction?

29
Q

Why are beta glucose molecules not able to join together in the way that alpha glucose molecules can?

A

Because the hydroxyl groups are too far to interact with each other.

30
Q

How do beta glucose molecules get around the problem of the hydroxyl groups being too far to interact with each other?

A

Alternate beta glucose molecules are turned upside down.

Check page 49 of the kerboodle book for diagrams.

31
Q

What is subsequently caused due to the turning of the beta glucose molecule?

A

When a polysaccharide is formed in this way it is unable to coil or form any branches.

A straight chain molecule called cellulose is formed.

Check page 49 of kerboodle for diagrams.

32
Q

What bonds do cellulose molecules make between each other?

A

Hydrogen bonds

33
Q

When cellulose molecules join together with hydrogen bonds, what do they form?

A

Microfibrils

34
Q

When microfibrils join together, they form ________?

A

Macrofibrils

35
Q

Macrofibrils join into what?

A

Fibres

36
Q

What are the properties and uses of fibres?

A

Strong and insoluble

Used to make cell walls

37
Q

Why is cellulose important in our diet?

A

Because it is very hard to break cellulose down to its monomers and forms the ‘roughage’ necessary for a healthy digestive system.

38
Q

What is the food test for carbohydrates?

A

The Benedict’s test

39
Q

What is the food test for starch?

A

The Iodine Test

40
Q

What is the positive result for the iodine test for starch?

A

The solution goes for yellow-orange to blue-black.

41
Q

What is the positive result for reducing sugars test?

A

A brick red precipitate is formed

42
Q

What is the positive result for non-reducing sugars?

A

The solution stays blue after warming.

43
Q

What is the process for the Benedict’s Test for carbohydrates?

A
  1. Sample in boiling tube
  2. Add equal part Benedict’s reagent solution
  3. Heat the mixture gently in a boiling water bath for 5 minutes

If the solution turns brick red, then the test for reducing sugars is positive, and if the solution stays blue, therefore it is positive for a non-reducing sugars test.

44
Q

What is the process for the iodine test for starch?

A

Add a few drops of iodine solution dissolved in iodine potassium iodide solution and mix with the sample.

If the solution changes colour from yellow-brown to purple-black, then starch is present.

A Level Biology - Chapter 3 - Biological Molecules (3 decks)

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