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Chemistry S2 > Test 3: Carbohydrates > Flashcards

Test 3: Carbohydrates Flashcards

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1
Q

What are carbohydrates? What are they composed of? What are they also called?

A
  • major energy source
  • composed of: C, H, and O
  • called “saccharides” meaning sugar
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2
Q

Explain the formation and distruction of carbohydrates.

A

formation: photosynthesis
- eg. glucose in plants from CO2, H2O and ATP (sun).

destruction: respiration (oxidation)
- produces CO2, H2O and energy

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3
Q

Give a precise definition of carbohydrates.

A
  • polyhydroxyaldegydes,
  • polyhydroxyketones
  • substances that give such compounds on hydrolysis.
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4
Q

What are the different types of carbohydrates? What do they form when water is added?

A

monosaccharides:
- simplest carbohydrates
- + H2O –> no hydrolysis
- cannot be hydrolysed

disaccharides:
- two monosaccharides
- + H2O –> two monosaccharide units

olgosaccharides:
- 2+ monosaccharides

polysaccharides:
- 100-1000 monosaccharides
- + many H2O –> many monosaccharide units

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5
Q

How are monosaccharides classified?

A
  • number of carbon atoms (3-6 usually)
  • the carbonyl group: aldehyde or ketone
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6
Q

What is the colour of monosaccharides? Are they soluble? What taste do they have?

A
  • colourless
  • crystalline solids
  • soluble in water
  • insoluble in nonpolar solvents
  • sweet taste
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7
Q

State the two major types of monosaccharides.

A
  • ketoses
  • aldoses
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8
Q

What are aldoses?

A

monosaccharides with:
- aldehyde group (H-C=O)
- many hydroxyl groups

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9
Q

What are ketoses?

A

monosaccharides with:
- ketone group (C=O)
- many hydroxyl groups

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10
Q

What structure is used to represent carbohydrates? What are the two types? How to tell them apart?

A

fisher projection:
- L-isomer: OH- is on the left of the chiral carbon
- D-isomer: -OH is on the right of the chiral carbon

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11
Q

What are the principal rules of the fisher projection?

A
  • most oxidised group on top
  • chiral carbon shown at the intersection of vertical and horizontal lines
  • -OH of chiral carbon determines L-/D- isomer
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12
Q

What is D-glucose?

A
  • aldohexose
  • C6H12O6
  • blood sugar
  • monosaccharide of starch, cellulose, and glycogen
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13
Q

What is the normal level of glucose in the blood?

A

4-6mmol/L

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14
Q

What is D-fructose?

A
  • ketohexose
  • C6H12O6
  • sweetest carbohydrate
  • converts to glucose in the body
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15
Q

What is D-galactose?

A
  • aldohexose
  • C6H12O6
  • not found free in nature
  • obtained from lactose
  • essential for the formation of certain glycoproteins and cerbrosides
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16
Q

What are the most important pentoses?

A

D-ribose and D-deoxyribose

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17
Q

What is the function of ribose?

A
  • coenzyme A
  • ATP
  • cyclic AMP
  • monomeric units of RNR
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18
Q

What is teh name of the other structure of carbohydrates (not fisher)?

A

W. Haworth projection

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19
Q

Explain cyclic structures. When do they form? What are they?

A
  • two forms of monosaccharides with 5 or 6 atoms

form when the hydroxyl group on C-5 reacts with the aldehyde/ketone group

20
Q

How are stable cyclic hemiacetals formed?

A
  • C=O group of ketone or aldehyde group
  • -OH group of C’5

cyclic structure of D-isomer has CH2OH above the ring.

21
Q

How to draw a W. Haworth projection?

A
  • turn chain clockwise (90 * )
  • bend chain to make hexagon
  • ## draw new -OH on C1
22
Q

What is the difference between alpha and beta glucose?

A
  • alpha and beta glucose have identical configurations except at C-1
    alpha glucose: -OH on bottom
    beta glucose: -OH on top
23
Q

What is a reducing sugar?

A
  • monosaccharide
  • carbonyl group which oxidises to form carboxylic acid
  • undergo fehlings reaction, benedicts reagent
  • eg. glucose, galactose and fructose
24
Q

What reactions do reducing sugars undergo?

A
  • with Fehling’s reagent (Cu2+ complexed with tartrate ion) –> deep blue colour achieved
  • with Benedict’s reagent (Cu2+ complexed with citrate ion
25
Q

State monosaccharide examples of reducing sugars.

A
  • glucose
  • galactose
  • fructose
26
Q

When do ketoses qualify as reducing sugars?

A

if they can isomerate to aldoses

27
Q

What do monosaccharides form when they react with alcohols?

A

acetals
- called: glycosides
- with glycosidic bonds

28
Q

What is a disaccharide?

A
  • two monosaccarides
  • glycosidic bond (between anomeric carbon and hydroxyl group)
29
Q

What are the three important disaccharides?

A
  • maltose
  • lactose
  • sucrose
30
Q

What is maltose?

A
  • malt sugar
  • 2 D-glucose molecules
  • hydrolysis of starch
  • alpha-1,4-glycosidic bonds:
    alpha-OH on C’1 & -OH C’4 of
31
Q

In what forms is maltose found in?

A

both alpha and beta

32
Q

Why is maltose a reducing sugar?

A

it closes and opens

33
Q

What bond does maltose have? Between what molecules?

A

2 alpha glucoses
- alpha-1,4-glycosidic bond

34
Q

What is lactose? What bonds does it contain? What monosaccharides is it formed from? Is it a reducing sugar? Why?

A

beta-D-galactose and alpha/beta-D-glucose
- beta-1,4-glycosidic bond
- reducing sugar: opens and closes

35
Q

What is sucrose? What bonds does it contain? What monosaccharides is it formed from? Is it a reducing sugar? Why?

A
  • sugar cane and sugar beets
  • alpha-D-glucose + beta-D-fructose
  • alpha,beta-1,2-glycosidic bond
  • NOT a reducing sugar
  • easily hydrolysed
36
Q

What does the hydrolysis of sucrose form?

A

alpha-glucose and beta-fructose

37
Q

What are polysaccharides?

A
  • polymers of** D-glucose**
  • amylose, amylopectin, starch, glycogen made of alpha-D-glucose
  • cellulose made of beta-D-glucose
38
Q

What is starch? How can it be seperated?

A
  • energy storing carbohydrate
  • plants (glucose storage)
  • seperated into 2 fractions: amylose and amylopectin
39
Q

What is amylose? What bonds are present? What does it form?

A
  • polymer of alpha-D-glucose units
  • alpha-1,4-glycosidic bonds
  • continuous unbranched chain (forms coils ‘amyl”O”se’)
40
Q

What is amylopectin? What bonds are present? What does it form?

A
  • polymer of glucose units
  • branched polysaccharide chain
  • alpha-1,4-glycosidic bonds (in horizontal lines)
  • alpha-1,6-glycosidic bonds (between branches)
41
Q

Explain the function of the starch iodine test.

A

starch: deep blue colour complex with iodine
- iodine + amylose helix = large complex

(other polysaccharides give other colours (ie. glycogen- red))

42
Q

What is glycogen? What is it composed of? What is its function?

A
  • energy storing carbohydrate
  • made of 1,4- and 1,6- linked glucose units
  • helps maintain glucose balance in the body
  • removes and stored excess glucose
  • branched!
43
Q

What is cellulose? What is it composed of? What is its function?

A
  • polysaccharide of glucose
  • unbranched chains
  • beta-1,4-glycosidic bonds
  • cannot be digested by humans
44
Q

Why can cellulose not be digested by humans?

A

Humans cannot break down beta-1,4-glycosidic bonds.

45
Q

What are the two types of starch?

A
  • amylose
  • amylopectin
46
Q

What are chitins?

A
  • nitrogen containing polysaccharides
  • forms crustaceans shells + insect exoskeletons
47
Q

What are pectins?

A

polysaccharides
- used for jellies
- monomer: galacturonic acid

Chemistry S2 (5 decks)

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