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A-Level Biology > 1.2-1.4 Monosaccharides + Polysaccharides > Flashcards

1.2-1.4 Monosaccharides + Polysaccharides Flashcards

1
Q

Define monosaccharide

A

The monomers from which larger carbohydrates are made
Single sugar unit

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2
Q

Give 3 examples of monosaccharides

A

Glucose, fructose and galactose

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3
Q

What does a condensation reaction between two monosaccharides form? Draw it

A

A glycosidic bond between carbon 1 and carbon 4

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4
Q

How does maltose form? Draw it

A

Condensation of two alpha glucose molecules

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5
Q

How does sucrose form? Draw it

A

Condensation of a glucose molecule and a fructose molecule

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6
Q

How does lactose form? Draw it

A

Formed by the condensation of a glucose molecule and a galactose molecule

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7
Q

Define disaccharides

A

Pair of monosaccharides

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8
Q

Define polysaccharide

A

Formed by the condensation of many glucose units/ monosaccharide molecules

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9
Q

Give 3 examples of disaccharides

A

Maltose, sucrose and lactose

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10
Q

How is the glycosidic bond broken?

A

Hydrolysis

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11
Q

Where is starch found and what does it do?

A

Found in many parts of a plant in the form of small grains
Important component of food and major energy source in most diets
Never found in animal cells
Made of two different polysaccharides, amylose and amylopectin

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12
Q

What are some characteristics of polyaccharides?

A

Large molecules so are insoluble so can be stored
When hydrolysed break down into disaccharides/monosaccharide

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13
Q

How are glycogen and starch formed?

A

The condensation of alpha glucose

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14
Q

How is cellulose formed?

A

Condensation of beta glucose

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15
Q

How is amylose (sub-unit of starch) formed? Define amylose

A
  • Each glycosidic bond forms a small bond in the polymer
  • Collectively, these give a spiral/helix shape
  • Amylose is a long unbranched chain of glucose units
    Alpha 1-4 glycosidic bond
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16
Q

Define amylopectin

A

Highly branched polymer of glucose units
Alpha 1-6 glycosidic bond

17
Q

What is the role of starch?

A
  • Found in plants as small grains
  • Seeds and storage organs
  • Important components of good and major energy source in most diets
  • Never found in animal cells
  • Made of two different polysaccharides, amylose and amylopectin
18
Q

What are the 5 main structures and functions of starch and how does it help with energy storage?

A
  • Helices are compact so lots can be stored in a small space
  • (Can be branched or unbranched) Branching chains have many ends so lots of ends for enzymes to hydrolyse starch quickly and release glucose which is easily transported and used in respiration
  • Relatively long chains with few branches so is compact
  • Insoluble so doesn’t affect water potential of cell
  • Too big to pass through membranes so does not diffuse out of cells
19
Q

What is different about glycogen’s structure?

A

Same overall structure as amylopectin but significantly more branching (more 1-6 glycosidic bonds)
Made of alpha glucose only

20
Q

In what organisms and where is glycogen found?

A

Stored in liver and muscles of animals as small granules
Fungi cells also stores their carbohydrates as glycogen
Animals have a higher metabolic rate than plants
Found in animals and bacteria but never in plant cells

21
Q

Compare starch structure to glycogen

A
  • Glycogen has shorter chains and is more highly branched
  • Glycogen has more ends for the enzymes to hydrolyse to release glucose molecules at a faster rate
22
Q

What are the 3 main structure features of glycogen and their functions?

A
  • Insoluble so does not tend to draw water into the cells by osmosis and does not diffuse out of cells
  • Compact so lots stored in a small space
  • More highly branched than starch so more ends that can be more rapidly broken down to form glucose (respiration)
  • Important to animals –> higher metabolic and therefore respiratory rate than plants because they are more active
23
Q

How is cellulose formed?

A

Beta glucose where each glucose molecule is inverted with respect to its neighbour

24
Q

What is it called when lots of beta glucoses bond together?

A

Produces a long, straight, unbranching chain
This places many hydroxyl (OH)

25
Q

What is formed when chains of beta glucose crosslink?

A

Hundred of these chains are tightly cross-linked to form microfibrils, whilst microfibrils are bound into fibres
Hydrogen bonds hold the celluloid chains together

26
Q

What do cellulose fibres do?

A

Maintain turgidity in plant cells, preventing bursting

27
Q

What is the role of cellulose?

A
  • Major component of plant cell walls and provides rigidity to the plant cell
  • Cell walls prevents bursting as water enters
  • Turgid so provide max surface area for photosynthesis
28
Q

What are the 3 structures of cellulose?

A
  • Made up of beta glucose: form long straight, unbranched chains (not coiled like starch)
  • Cellulose molecular chains run parallel and cross-linked by hydrogen bonds (collectively strong)
    Chains —> microfibrils –>fibres: Give cellulose even more strength
29
Q

Describe a test for non-reducing sugar

A
  • Add Benedict’s solution and the food sample
  • Heat in a hot water bath
  • Result is negative (blue colour)
  • Boil with hydrochloric acid to hydrolyse the glycosidic bond
  • Add alkali to neutralise the solution and test with pH paper and repeat the Benedict’s test
    Positive results = brick red –> non-reducing sugar present
    Negative result = not non-reducing sugar present
30
Q

How many carbons does glucose have and therefore what is it called?

A

6
Hexose

31
Q

What is the test for starch?

A

Change the colour of the iodine in potassium iodide solution
- Place 2cm3 of the sample being tested into a test tube
- Add two drops of iodine solution and shake or stir
- The presence of starch is indicated by a blue-black coloration

A-Level Biology (19 decks)

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