Carbohydrates Flashcards

1
Q

What do all polysaccharides have in common?

A

They contain many (more than 10) monosaccharides linked by glycosidic bonds.

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2
Q

Most carbohydrates found in nature occur as?

A

polysaccharides, polymers of medium to high molecular weight (Mr >20,000).

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3
Q

Polysaccharides, also called ……….?

A

Glycans

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4
Q

How do polysaccharides differ from each other in the identity of their recurring monosaccharide units?

A
  • The lengths of their chains,
  • Types of bonds linking the monosaccharide units,
  • The degree of branching.
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5
Q

Polysaccharides are classified into?

A

Homopolysaccharides and Heteropolysaccharides

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6
Q

Differentiate between the classes of polysaccharides

A

Homopolysaccharides are formed by the same kind of monosaccharides; eg’s starch, glycogen and cellulose. Each of them are formed by hundreds of molecules of glucose linked by glycosidic bonds.
On the other hand, the polysaccharide molecules of heteropolysaccharides are formed by different kinds of monosaccharides.

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7
Q

Examples of heteropolysaccharides

A
  • Hyaluronic acid
  • Chondroitin sulfate
  • Heparin
  • Keratan sulfate
  • Dermatan sulfate.
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8
Q

What is hyaluronic acid formed from?

A

It is formed by thousands of alternating units of N-acetyl glucosamine and glucuronic acid.

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9
Q

What are inulins?

A

Inulins are polymers composed mainly of fructose units, and typically have a terminal glucose.

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10
Q

Why is inulin not digested by enzymes in the human GIT?

A

Because of the β(2,1) linkages

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11
Q

List features of inulin

A

Inulins are polymers composed mainly of fructose units, and typically have a terminal glucose.

They are linked by β(2,1) glycosidic bonds.

Standard inulin is slightly sweet

It is soluble in water.

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12
Q

What is the application of inulin in Renals?

A

Used to determine glomerular filtration rate (kidney fxn)

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13
Q

Classify polysaccharides on the basis of structure/linkages of the monosaccharides

A

i) Branched polysaccharides

ii) Unbranched/Linear polysaccharides

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14
Q

Amylose and cellulose and cellulose are examples of ………?

A

Unbranched/Linear polysaccharides

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15
Q

Examples of branched polysaccharides are?

A

Starch and glycogen

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16
Q

Non digestible polysaccharides include:

A

Fibres; Soluble fibre and Insoluble fiber

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17
Q

Digestible polysaccharides include

A

Starch (Amylose, Amylopectin)
Glycogen

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18
Q

Characteristics of starch

A
  • 3000 monosaccharides
  • Contain alpha bonds
  • High Glycemic Index
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19
Q

Differentiate between amylose and amylopectin

A

Amylose
- Consistsof long unbranched polysaccharide chains (straight chain)
- More resistant to digestion

Amylopectin
- Consists of branched polysaccharide chains.
- Easier to digest

20
Q

Plants store glucose in chains of ……..

A

Starch

21
Q

Possible benefits of amylose include;

A
  • May improve health of digestive tract
  • May improve glucose tolerance
  • May stimulate growth of beneficial intestinal bacteria
22
Q

List 7 features of amylose

A
  • It is a linear homopolysaccharide
  • It is made up of D-glucose units linked by α 1,4- glycosidic bonds
  • Insoluble in water
  • Gives blue colour with iodine
  • Forms the outer layer of the starch granule
  • Composes about 30% of the granule
  • Hydrolysis by α-amylase
23
Q

List 8 features of Amylopectin

A
  • It is a branched homopolysaccharide (see structure)
  • It is made up of D-glucose units linked by α- 1,4- glycosidic bonds at the linear chains and α- 1,6-glycosidic bonds at the branches
  • Insoluble in water.
  • Gives red-violet colour with iodine
  • Forms the inner layer of the starch granule
  • Composes about 70% of the granule
  • Linear chains hydrolysed as in amylose but α-1,6-bonds are hydrolyzed by by α-1,6-glucosidase
  • Amylopectin shows a branch at each 24-30 units of glucose.
24
Q

What are fibres?

A

Non-digestible polysaccharides that provide no energy

25
Q

What’s the difference between soluble and insoluble fibres?

A

Soluble fibres are easily fermented by intestinal bacteria, while Insoluble fibres are not easily fermented.

26
Q

Examples of insoluble polysaccharides include;

A

Cellulose, lignin, some hemicelluloses

27
Q

Examples of soluble polysaccharides include;

A

Pectins, beta-glucan, some gums, mucilage

28
Q

What are the health benefits of soluble fibres?

A
  • Slow gastric emptying and may delay absorption of some nutrients
  • Helps reduce serum cholesterol
  • Improve appetite control
  • Normalize blood glucose levels
  • May help protect against colon cancer
29
Q

What is the health benefit of insoluble fibres?

A

Relieves constipation

30
Q

Why is cellulose am insoluble fibre?

A

Because we lack the cellulase enzyme to hydrolyze the β(1→4) glycosidic bond.

31
Q

Cellulose can be hydrolyzed by ………..

A

the intestinal bacteria in cattle and other ruminants which have the enzyme cellulase (β-glucosidase).

32
Q

7 features of cellulose include:

A

This glycosidic bond configuration changes the three-dimensional shape of cellulose compared with that of amylose.

The chain of glucose units is straight. This allows chains to align next to each other to form a strong rigid structure.

Cellulose is a linear homopolysaccharide of D-glucose units found in the cell wall of plants (structural fxn)

It constitutes the strength and framework of plants

Glucose units are linked by β-1,4- glycosidic bonds

Bonds are resistant to acid hydrolysis and glucosidases in the GIT (not digestible) in humans and other higher animals.

Can be hydrolyzed by the intestinal bacteria in cattle and other ruminants which have the enzyme cellulase (β-glucosidase).

33
Q

What is a good source of cellulose?

A

Whole grains.

34
Q

Why is cellulose important in our diet?

A

Cellulose is important in our diet because it assists with digestive movement in the small and large intestine.

35
Q

Partial hydrolysis of cellulose with strong mineral acids yields ……..?

A

Cellobiose.

36
Q

………… is an important source of “bulk” in the diet

A

Cellulose

37
Q

Chitin is made up of a modified β-D-glucose called ………..

A

N-acetylglucosamine with β(1→4) glycosidic bonds.

38
Q

What is the function of chitin in wound healing?

A

As a surgical thread that biodegrades as a wound heals.

39
Q

How is chitin utilised in cosmetics?

A

When ground, chitin becomes a powder that holds in moisture, and it can be added to cosmetics and lotions.

40
Q

What is the function of chitin in insects’ exoskeletons?

A

serves to protect them from water. Because of this property, chitin can be used to waterproof paper.

41
Q

Describe glycogen in 3 sentences

A

It is a storage glucose in animal tissues (mainly found in the liver (400 kcal) and muscles (1400 kcal)

Glycogen is a branched homopolysaccharide composed of D-glucose units linked by α- 1,4- glycosidic bonds at the linear chains and α- 1,6- glycosidic bonds at branches.

Its structure is similar to amylopectin but with more complex branching

Hydrolyzed by α- amylase and α-1,6-glucosidase to yield maltose and glucose.

Glycogen shows a branch at each 8-10 units of glucose

42
Q

Glycogen shows a branch at each ……. units of glucose?

A

8 -10

43
Q

Glycogen is hydrolysed by ………….. to yield ……………

A

Glycogen is hydrolysed by α- amylase and α-1,6-glucosidase to yield maltose and glucose.

44
Q

What organs is glycogen stored in?

A

liver and muscle

45
Q

……… is a storage form of glucose in animals?

A

Glycogen

46
Q

How does liver glycogen response to blood glucose (BG) levels

A

Low BG leads to glycogen breakdown, which in turn increases blood glucose.