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A-Level Biology > Carbohydrates > Flashcards

Carbohydrates Flashcards

Monday 9th Spetember 2019

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1
Q

What elements do carbohydrates contain?

A

Carbon, hydrogen and oxygen (CHO)

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2
Q

What are monosaccharides?

A

The monomers of carbohydrates - glucose, fructose and galactose. Used for energy (respiration) & building larger sugars (polysaccharides and disaccharides)

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3
Q

Name some carbohydrate based:

a) Monomers
b) Dimers
c) Polysaccharides

A

a) Monosacharides glucose, fructose and galactose
b) Disaccharides sucrose, maltose and lactose
c) Polysaccharides starch, cellulose and glycogen

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4
Q

(CH2O)n is the formula for what?

A

Monosaccharides - where n is a number from 3-7. If n is 6, it is a hexose sugar

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5
Q

Define isomerism

A

The same ingredients forming a different shape. For example, alpha & beta glucose

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6
Q

What are hexose sugars?

A

A sugar with 6 carbons forming a ring for example glucose

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7
Q

What is the main difference between alpha glucose and beta glucose

A

From the right, alpha glucose has the hydrogen group on the top and the hydroxide group below. This is the opposite in beta glucose - the hydroxide group has swapped to the top

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8
Q

Give the test for reducing sugars. Is it quantitative or qualitative?

A

Benedict’s solution (semi-quantitative)
Heat the mixture in a water bath. No sugar –> lots of sugar
blue, green, orange, brick red
REVERSE RAINBOW

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9
Q

What is a reducing sugar?

A

Any sugar capable of reducing another molecule (as it has another free aldehyde group or free kethone group)

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10
Q

Benedict’s solution is the test for reducing sugars, and a water bath must be used in the experiment. True or false?

A

True. It is semi-quantative (reverse rainbow)

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11
Q

How is a disaccharide formed?

A

When 2 monosaccharides join by a glycosidic bond (C-O-C). It is a condensation reaction as a molecule of water is formed

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12
Q

What does a 1-4 glycosidic bond look like?

A

Straight chains (1 on a hexose sugar is the Carbon point the furthest to the right)

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13
Q

What is the bond between 2 monosaccharides called?

A

A glycosidic bond

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14
Q

Is the monosaccharide to dimer reaction reversible? Why?

A

Yes - because it is a condensation reaction (2 molecules joining up and producing a molecule of water), it is reversible through hydrolysis - adding water to split it up

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15
Q

What monosaccharides are in these disaccharides?

a) Maltose (malt sugar)
b) Sucrose (table sugar)
c) Lactose (milk)

A

a) Glucose - glucose
b) Glucose - fructose
c) Galactose - fructose

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16
Q

What disaccharides are made from these monosaccharides?

a) Glucose - fructose
b) Galactose - glucose
c) Glucose - glucose

A

a) Sucrose
b) Lactose
c) Maltose

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17
Q

What enzyme digests these disaccharides? What are the products?

a) Lactose
b) Maltose
c) Sucrose

A

a) Lactase. Forms galactose and glucose
b) Maltase. Forms glucose and glucose
c) Sucrase. Forms glucose and fructose

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18
Q

What are polysaccharides?

A

Polymers formed from man monosaccharides

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19
Q

Name some polysaccharides

A

Starch (amylose, amylopectin), glycogen, cellulose

20
Q

What is cellulose?

A

A polysaccharide found in the cell wall of plant cells.

21
Q

What is starch?

A

Naturally occuring polysaccharide (rice, bread, potatoes) that has 2 forms. Amylose (important in plant storage), amylopectin (aids in energy supply for plants)

22
Q

What is glycogen?

A

A polysaccharide used as a storage molecule for animals, found as small granules in the liver and muscles.

23
Q

Name the monosaccharides in each of these polysaccarides:

a) Starch
b) Glycogen
c) Cellulose

A

a) Alpha glucose only
b) Alpha glucose only
c) Beta glucose only

24
Q

Which polysaccharide is the only one to contain beta glucose?

A

Cellulose - it only has beta glucose, no alpha glucose at all

25
Q

What is amylose?

A

A type of starch important for plant storage. It is less readily digested, and insoluble

26
Q

What is amylopectin?

A

A type of starch important for aiding energy supply for plants

27
Q

What is the formula for starch?

A

(C6 H10 O5)n - only alpha glucose remember

28
Q

Talk about the structure of the starch amylose

A

Only alpha glucose. 1-4 glycosidic bonds which form straight chains, but have a spiralled structure. Compact too, which helps it in plant storage.

29
Q

Talk about the strucure of the starch amylopectin

A

Only alpha glucose. Branches occur with 1-4 AND 1-6 (so the branch goes off at right angles to the main chain) glycosidic bonds every 24-30 glucose units. It is compact. Because it is branched out, it has a larger surface area with more exposed points, so hydrolysis can occur easier and it can be broken down into its products (glucose)

30
Q

What is the difference between the 2 types of starches - amylose and amylopectin?

A

Amylose has only 1-4 glycosidic bonds, so the chains are very straight. Amylopectin has 1-4 and 1-6 glycosidic bonds every 24-30 glucose units, so it has a much more branched out structure. Because it is branched out, it has a larger surface area with more exposed points, so hydrolysis can occur easier and it can be broken down into its products (glucose)

31
Q

Give the test for starch. Is it quantitative or qualitative?

A

Iodine (qualitative)

Remains yellow/ brown if starch isn’t present. Turns blue black if starch is present.

32
Q

What do these chemicals test for?

a) Benedict’s solution
b) Iodine

A

a) Reducing sugars

b) Starch

33
Q

How is starch perfect for its role?

A

IF IT WAS SOLUBLE: water would move into the cells as starch lowers the water potential inside the cell, so more osmosis would occur into the cell & it would expand too much, which is bad as it could burst
COMPACT: so its tight coils make it easier to store
WON’T EASILY DIFFUSE OUT OF CELLS: If it did, cells would struggle using it as it would disappear
EASILY HYDROLYSED: to give off glucose for respiration

34
Q

If starch was soluble, why would that be an issue?

A

Water would move into the cells as starch lowers the water potential inside the cell, so more osmosis would occur into the cell & it would expand too much, which is bad as it could burst

35
Q

Talk about the structure of glycogen

A

Only alpha glucose. 1-4 and 1-6 glycosidic bonds. Similar to starch, but has shorter chains and more branches (so it is hydrolysed easier with a larger SA/ more exposed points, so it breaks down into glucose faster)

36
Q

Talk about the structure of cellulose

A

Only beta glucose. 1-4 glycosidic bonds - unbranched alternating chains & straight chains. Hydrogen bonds link adjacent long chains, which are weak but there are LOADS of them which is why cellulose is so strong.

37
Q

How do beta glucose chains form?

A

PROBLEM - because the hydroxide group is flipped on the right so it’s at the top, and the next beta glucose molecule has its hydroxide group on the bottom of the left side, it can’t join for a condensation reaction to produce water.
SO - the adjacent beta glucose molecule flips, so that it hydroxide group on the left is now at the bottom, so a condensation reaction can occur.
AS A RESULT - Beta glucose produces alternating, unbranched chains, seen only in cellulose

38
Q

Why can’t humans digest tree bark?

A

Becasue it is mainly cellulose. We don’t have the enzyme cellulase, so we can’t digest it. When we eat plants, it leaves (ha unintentional pun there) fibre as the leftover cellulose.

39
Q

How is cellulose so strong?

A

Because of the huge amounts of hydrogen bonds linking the unbranched, alternating 1-4 beta glucose chains.

40
Q

What are microfibrils?

A

Cellulose wound and plaited together in parallel groups called fibres, so it is strong.

41
Q

What form cellulose fibres?

A

Macrofibrils, which is wound up microfibrils, which is wound up cellulose.
They make the plant’s cell walls ridiculously difficult to burst as it’s so string. And it keeps the cell turgid - full of water - which helps the structure stay strong under the pressure

42
Q

What are macrofibrils?

A

Microfibrils wounded up and plaited together (which is just wound up cellulose)

43
Q

What are cellulose fibres?

A

Macrofibrils wound up together. They make the plant’s cell walls ridiculously difficult to burst as it’s so string. And it keeps the cell turgid - full of water - which helps the structure stay strong under the pressure

44
Q

What does turgid mean?

A

Full of water. Cellulose fibres help plant cells do this

45
Q

Each –> means “is wound up and plaited to form”

Cellulose –> macrofibrils –> microfibrils —> cellulose fibres. True or false?

A

False -

Cellulose –> microfibrils –> macrofibrils –> cellulose fibres

A-Level Biology (18 decks)

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