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1) Biochemistry I > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

How are carbohydrates produced?

A

Produced from CO2 and H2O via photosynthesis in plants

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2
Q

What do carbohydrate functions include?

A
  • energy source and energy storage
  • structural component of cell walls and exoskeletons
  • informational molecules in cell-cell signaling – The “Sugar Code”
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3
Q

Carbohydrates covalently linked to proteins form what?

A

glycoproteins and proteoglycans

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4
Q

Carbohydrates covalently linked to lipids to form what?

A

Glycolipids

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5
Q

What are the chemical classifications of carbohydrates?

A

Poly-hydroxyl aldehydes or ketones

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6
Q

Name the 4 classes of carbohydrates.

A

1) Monosaccharides
2) Disaccharides
3) Oligosaccharides
4) Polysaccharides

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7
Q

How many monosaccharides are contained in oligosaccharides? What are they linked onto?

A
  • 3-10 monosaccharides

- linked onto lipids & proteins

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8
Q

How many monosaccharides are contained in polysaccharides? Name examples.

A
  • > 10 monosaccharides
  • Cellulose and amylose
  • Can be 1000s or millions of monosaccharides
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9
Q

What is the empirical formula of monosaccharides? What can n be?

A

(CH2O)n
Equal and greater than 3
Equal and lower than 7

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10
Q

What is the Glycome?

A
  • One of the most complex “omics” (because there’s no template for it, organisms can do whatever they want, change with the environment)
  • Describes total sugars produced in a cell or an organism
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11
Q

What is an aldehyde? How is it formed?

A

organic compound containing the group —CHO, formed by the oxidation of alcohols

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12
Q

What is a ketone? How is it formed?

A

organic compound containing a carbonyl group =C=O bonded to two hydrocarbon groups, made by oxidizing secondary alcohols

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13
Q

Polymers of monosaccharides are linked by what bonds?

A

O glycosidic bond by a condensation reaction

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14
Q

Based on the empirical formula, what are the names when n=3 to n=7?

A 
N= 3 	Triose
N=4		Tetrose
N=5		Pentose
N=6		Hexose
N=7		Heptose
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15
Q

The names from the empirical formula can exist in what forms? What are the prefixes?

A

Aldehydes or ketones

  • Aldo-
  • Keto-
    ex: aldotriose, ketotriose
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16
Q

How many chiral centers does glyceraldehyde have? How many configurations? How many isomeric forms? How many mirror images?

A
  • One Chiral Center
  • 2 different Configurations
  • 2 Isomeric forms
  • 2 mirror images
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17
Q

What are two mirror image isomers referred to?

A

Enantiomers

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18
Q

What are enantiomers?

A

is one of two stereoisomers that are mirror images of each other that are non-superposable

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19
Q

What is the difference in diastereoisomers?

A

more than one chiral carbon and more than one stereoisomer

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20
Q

How many Chiral carbons in ketotriose or dihydroxyacetone?

A

None (0)

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21
Q

What is the right configuration? Left?

A 
Right = Detro (D)
Left = Levo (L)
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22
Q

What defines the configuration in glyceraldehyde? What should you ALWAYS draw on the top?

A

Position of hydroxyl

Aldehyde/Ketone

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23
Q

What are the two formulas to represent isomers?

A
  • Fisher Projection

- Perspective Formulas

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24
Q

How do you determine the D/L configuration of aldehydes?

A

1) Aldehyde on the top
2) Hydroxyl on the right = D
3) Hydroxyl on the left = L

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25
Q

Is the D/L configuration the same as the R/S?

A

NOT the same

R/S = priority of atomic number across the chiral carbon

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26
Q

What is the number of stereoisomers in a monosaccharides is equal to?

A

2^n

where n = number of chiral carbons

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27
Q

Define epimers. How do you name them?

A
  • two monosaccharides that have the same absolute configuration but differ only in the configuration around ONE carbon atom
  • Ex: epimer at C-2, epimer at C-4
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28
Q

How do you determine the number of epimers for an absolute configuration?

A

Count the amount of chiral carbons and subtract ONE

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29
Q

In what configuration do monosaccharides tend to be in solution?

A

Closed configuration

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30
Q

How does a monosaccharide go from the open to closed configuration?

A

hydroxyl group of carbon 5 doing a nucleophilic attack on carbon 1 from that same molecule, forms a hydroxyl and you’ve successfully closed this ring

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31
Q

According to the Haworth projection, what does the hydroxyl group on carbon one pointing up mean? Down? Which structure is most stable?

A

Up: beta
Down: alpha
- Beta is more stable since you don’t have repulsion from the other OH group

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32
Q

Why are Hemiacetal and Hemiketal compounds interesting? How do they form?

A
  • They are reversible, so they can open the ring
  • Aldehyde + Alcohol -> Hemiacetal
  • Ketone + Alcohol -> Hemiketal
33
Q

What happens when Hemiacetal and Hemiketal compounds close again?

A
  • If the next closure is from the bottom, you’ll end up with an alpha
  • If the next closure is from the top, you’ll end up with a beta
  • Gives you a chance to go to a different configuration
34
Q

What does the anomeric carbon result from? Is A or B more common?

A

The closure of the linear structure to a closed structure

- B more common since more stable

35
Q

What is the anomeric carbon also known as? Why?

A
  • Reducing end
  • It is not easily oxidized in the closed configuration, but it can open up and we can oxidize the aldehyde to a carboxylic group
  • Once you oxidize, the closed configuration will think that you have “lost” the linear configuration, so it will keep converting some of itself to the linear configuration –> uses up your closed configuration
36
Q

How can you know which carbon is the reducing end/anomeric carbon?

A

Carbon linked to an oxygen, they are always drawn on the right side by convention

37
Q

What is a five-membered ring called? Six-membered ring?

A
  • Furan Ring : 5

- Pyran Ring : 6

38
Q

Name the 3 structural representations of monosaccharides.

A

1) Fischer Projection
2) Haworth Projection
3) Chair Conformation (not configuration, not breaking bond)

39
Q

In a chair configuration, in what direction is the OH pointing in depending on whether it is alpha or beta?

A

Alpha: OH pointing down
Beta: OH pointing to the right

40
Q

How do you quantify reducing sugars? What is this used to determine?

A
  • To determine glucose levels in blood or urine samples
  • If you through cupric oxide which will give you a blue colour will precipitate as a red mixture indicating that you can oxidize this aldehyde
  • If somebody is diabetic, you will have more glucose, more oxidizing aldehyde, colour will go from blue to red
  • If it stays blue, then you know that you don’t have glucose in there, or if you don’t a reducing end, you won’t have an aldehyde that will oxidize
41
Q

What compounds are able to oxidize?

A
  • ***- If it is able to open up, then it will be able to oxidize
  • If you have a hydroxyl, then you can open up the structure
42
Q

If you add an R group to the anomeric carbon what happens?

A

You form an acetal, way more stable than hemiacetal, no more reducing end

43
Q

What happens when a condensation reaction forms between two anomeric hydroxyls?

A

You lose the reducing end since the hemiacetal becomes an acetal

44
Q

Are acetal carbons anomeric?

A

Yes, still anomeric but they lose their reducing end

45
Q

Which carbons are linked in a O-glycosidic bond?

A

Carbon 1 and Carbon 4

46
Q

What is particular to sucrose condensation?

A

Linking both anomeric groups = losing BOTH reducing ends

47
Q

How are natural carbohydrates usually found?

48
Q

Name the 2 polysaccharides.

A
  • Homopolysaccharides (same monosaccharides)

- Heteropolysaccharides (two or more monosaccharides)

49
Q

What are the 2 roles of homopolysaccharides?

A

Energy storage function and structural function

50
Q

What are the 2 roles of heteropolysaccharides?

A

Structural function and cellular function

51
Q

What is the main storage homopolysaccharide?

52
Q

What is starch made up of?

A

Two homopolysaccharides of glucose

  • Amylose
  • Amylopectin
  • D-glucose
53
Q

What is amylose?

A

unbranched polymer of (alpha-1 to 4) linked residues

54
Q

What is amylopectin?

A

branched; a polymer of (alpha-1 to 4) linked residues BUT the branch-points with (alpha-1 to 6) linkers occur every 24-30 residues

55
Q

What is the branch point for amylopectin?

A

Alpha 1-6 branch point

56
Q

What is the branching frequency in starch?

A

24-30 residues

57
Q

Where can amylase digest from?

A

From the NON-reduced end only

58
Q

What is the conformation of amylose and amylopectin?

A

Helical conformation

59
Q

Compare amylopectin, glycogen and amylose.

A

Both Amylopectin and Glycogen have the same basic structure as Amylose but with branches (α1→6)

60
Q

Name the 2 storage homopolysaccharides. Where are they found?

A
  1. Amylopectin (plants)

2. Glycogen (animals)

61
Q

What is the ONLY big difference between amylopectin and glycogen? What does that cause?

A
  • The branching frequency
  • Amyopectin: every 24-30 glucose residues
  • Glycogen: every 8-12 glucose residues
  • Glycogen has higher frequency, so more nonreducing end (since each of these branches has a non-reducing end)
  • More frequent branching = more D-glucose per unit time (enzyme) ex: 2-3 glucose vs 1 glucose compared to amylopectin
62
Q

What is a structural homopolysaccharide?

63
Q

3 test tubes containing colorless 2% maltose, 2% sucrose, and 2% lactose. The addition of Benedict’s reagent to each of the three disaccharides could cause a Fehling’s reaction to occur. What disaccharide is in the test tube that is colored blue?
A) Sucrose
B) Maltose
C) Lactose

64
Q

Name the 5 chemical modifications of monosaccharides.

A
  • Phosphorylation
  • Amidation
  • Acetylation
  • Oxidation
  • Methylation
65
Q

What is the difference between amylose and cellulose?

A

Cellulose: B1 –> 4
Amylose: A1 –> 4

66
Q

What gives cellulose its strength?

A

The 2 monosaccharides with beta linkages are basically at 180o of each other –> hydrogen bonds are perfectly aligned, which makes them much stronger

67
Q

What is the most abundant polysaccharide in nature?

68
Q

What is the natural configuration of amino acids?

69
Q

What is the natural configuration for carbohydrates?

70
Q

What are the roles of monosaccharides and oligosaccharides added onto proteins? (3)

A
  1. Cell-cell interactions, through special receptor proteins
  2. Stabilize proteins against degradation (most surface proteins)
  3. Role in proper folding of protein
71
Q

Name the 2 types of carbohydrates linked onto proteins.

A

1) N-linked oligosaccharides

2) O-linked oligosaccharides

72
Q

In which proteins are N-linked oligosaccharides added onto?

A

Proteins that have this consensus sequence:

Asn-XXX-Ser or Asn-XXX-Thr

73
Q

How are N-linked oligosaccharides added onto proteins?

A

As pre-assembled oligosaccharide units

74
Q

Where are N-linked oligosaccharides added?

A

Proteins that are destined to the extracellular side

75
Q

In which proteins are O-linked oligosaccharides added onto?

A

Onto either Thr or Ser amino acids (no consensus sequence)

76
Q

How are O-linked oligosaccharides added onto proteins?

A

Onto proteins one monosaccharide at a time

77
Q

Where are O-linked oligosaccharides added?

A

Proteins that are destined to intracellular and extracellular side

78
Q

What is a more specific test to measure glucose levels than the Fehling reaction?

A
  • Enzyme (glucose oxidase) treated with D-Glucose to obtain hydrogen peroxide (H2O2)
  • Measure the amount of H2O2 // dye changes colour when catalyzed with H2O2
79
Q

What is mutarotation?

A

Converting between alpha and beta

1) Biochemistry I (12 decks)

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