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Biological Molecules > 3.1.2 Carbohydrates > Flashcards

3.1.2 Carbohydrates Flashcards

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Organic Chemistry 101 flashcards
1
Q

How are disaccharides formed? Explain using the examples: maltose, sucrose and lactose.

A
  • Disaccharides are formed by the condensation of 2 monosaccharides.
  • E.g. maltose, sucrose and lactose
  • Glucose + glucose = maltose
  • Glucose + fructose = sucrose
  • Glucose + galactose = lactose
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2
Q

Define the term isomer

A

When molecules have the same molecular formula but the atoms are arranged differently.

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3
Q

How many isomers does glucose have?

A

Glucose has 2 isomers, alpha-glucose and beta-glucose.

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4
Q

What are the differences between the 2 isomers of glucose?

A

. Alpha-glucose: OH groups below C1 and below C4.
* Beta-glucose: OH groups above C1 and below C4 i.e. position of OH on C1 is reversed compared to alpha glucose.

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5
Q

What is the function of glycogen?:

A

Energy store in animal cells.

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6
Q

What is the structure of glycogen?

A
  • Polysaccharide of alpha-glucose.
  • C1-C4 and C1-C6 glycosidic bonds so branched.
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7
Q

How is the structure of glycogen related to its function?

A
  • Branched; can be rapidly hydrolysed to release
    glucose for respiration to provide energy.
  • Large polysaccharide molecule; can’t leave cell.
  • Insoluble in water; water potential of cell not affected i.e. no osmotic effect.
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8
Q

What is the function of starch?

A

Energy store in plant cells.

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9
Q

What makes up starch?

A
  • Polysaccharide of alpha-glucose.
  • Made of amylose and amylopectin.
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10
Q

What is the structure of amylose?

A

1,4 glycosidic bonds and unbranched

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11
Q

What is the structure of amylopectin?

A

1,4 and 1,6 glycosidic bonds branched.

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12
Q

How does the structure of amylose related to its function?

A
  • Helical; compact for storage in cell.
  • Large polysaccharide molecule; can’t leave cell.
  • Insoluble in water; water potential of cell not affected i.e. no osmotic effect.
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13
Q

How does the structure of amylopectin relate to its structure?

A
  • Branched; can be rapidly hydrolysed to release glucose for respiration to provide energy and compact to fit more molecules
  • Large polysaccharide molecule; can’t leave cell.
  • Insoluble in water; water potential of cell not affected i.e. no osmotic effect.
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14
Q

What is the function of cellulose?

A

Provides strength and structural support to plant/algae cell walls.

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15
Q

What is the structure of cellulose?

A
  1. Polysaccharide of beta glucose
  2. 1,4 glycosidic bond
  3. Straight and unbranched chains
  4. Chains are linked in parallel by hydrogen bonds forming microfibrils.
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16
Q

How does the structure of cellulose relate to its function?

A
  1. Every other beta glucose chain is inverted in a long, straight chain, unbranched chain.
  2. Many hydrogen bonds link parallel strands to form microfibrils (strong fibres)
  3. Hydrogen bonds are strong in high numbers, so it provides strength.
17
Q

What are reducing sugars?

A
  1. All monosaccharides
  2. Some disaccharides e.g. maltose/lactose
18
Q

What are non-reducing sugars?

A
  1. No monosaccharides
  2. Some disaccharides e.g. sucrose
19
Q
A
20
Q

Describe how to carry out the Benedict’s test for reducing sugars

A
  1. Add benedict’s reagent (blue) to food sample.
  2. Heat in a boiling water bath.
  3. Positive = green / yellow / orange / red precipitate (reducing sugar present).
    * If negative result (Benedicts reagent doesn’t change colour) then test for non-reducing sugar.
21
Q

Describe how to carry out the Benedict’s test for non-reducing sugars

A
  1. Add an equal volume of sample and dilute hydrochloric acid to hydrolyse the sugar.
  2. Heat in a boiling water bath.
  3. Neutralise with sodium bicarbonate.
  4. Carry out normal benedict’s test.
  5. Non-reducing sugar present = green / yellow / orange / red precipitate.
22
Q

Suggest a method to measure the quantity of sugar in a solution:

A
  1. Carry out Benedict’s test then filter AND dry.
  2. Find mass/weight
23
Q

Explain how the concentration of glucose in a sample can be determined.

A
  1. Produce a dilution series of glucose solutions of known concentrations.
  2. Perform a Benedict’s test on each sample (use same amount of solution for each test) and remove any precipitate (e.g. by centrifuging).
  3. Using a colorimeter, measure the absorbance of each sample to establish a calibration curve.
  4. Repeat with unknown sample and compare the absorbance to the calibration curve to determine glucose concentration.
24
Q

Describe the test for starch

A
  1. Add iodine dissolved in potassium iodide to solution and shake/stir.
  2. Blue-black colour = starch present.

Biological Molecules (6 decks)

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