Carbohydrates Flashcards
(79 cards)
1
Q
How are carbohydrates produced?
A
Produced from CO2 and H2O via photosynthesis in plants
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”
3
Q
Carbohydrates covalently linked to proteins form what?
A
glycoproteins and proteoglycans
4
Q
Carbohydrates covalently linked to lipids to form what?
A
Glycolipids
5
Q
What are the chemical classifications of carbohydrates?
A
Poly-hydroxyl aldehydes or ketones
6
Q
Name the 4 classes of carbohydrates.
A
1) Monosaccharides
2) Disaccharides
3) Oligosaccharides
4) Polysaccharides
7
Q
How many monosaccharides are contained in oligosaccharides? What are they linked onto?
A
- 3-10 monosaccharides
- linked onto lipids & proteins
8
Q
How many monosaccharides are contained in polysaccharides? Name examples.
A
- > 10 monosaccharides
- Cellulose and amylose
- Can be 1000s or millions of monosaccharides
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
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
11
Q
What is an aldehyde? How is it formed?
A
organic compound containing the group —CHO, formed by the oxidation of alcohols
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
13
Q
Polymers of monosaccharides are linked by what bonds?
A
O glycosidic bond by a condensation reaction
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
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
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
17
Q
What are two mirror image isomers referred to?
A
Enantiomers
18
Q
What are enantiomers?
A
is one of two stereoisomers that are mirror images of each other that are non-superposable
19
Q
What is the difference in diastereoisomers?
A
more than one chiral carbon and more than one stereoisomer
20
Q
How many Chiral carbons in ketotriose or dihydroxyacetone?
A
None (0)
21
Q
What is the right configuration? Left?
A
Right = Detro (D) Left = Levo (L)
22
Q
What defines the configuration in glyceraldehyde? What should you ALWAYS draw on the top?
A
Position of hydroxyl
Aldehyde/Ketone
23
Q
What are the two formulas to represent isomers?
A
- Fisher Projection
- Perspective Formulas
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
25
Is the D/L configuration the same as the R/S?
NOT the same
R/S = priority of atomic number across the chiral carbon
26
What is the number of stereoisomers in a monosaccharides is equal to?
2^n
| where n = number of chiral carbons
27
Define epimers. How do you name them?
- 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
28
How do you determine the number of epimers for an absolute configuration?
Count the amount of chiral carbons and subtract ONE
29
In what configuration do monosaccharides tend to be in solution?
Closed configuration
30
How does a monosaccharide go from the open to closed configuration?
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
31
According to the Haworth projection, what does the hydroxyl group on carbon one pointing up mean? Down? Which structure is most stable?
Up: beta
Down: alpha
- Beta is more stable since you don't have repulsion from the other OH group
32
Why are Hemiacetal and Hemiketal compounds interesting? How do they form?
- They are reversible, so they can open the ring
- Aldehyde + Alcohol -> Hemiacetal
- Ketone + Alcohol -> Hemiketal
33
What happens when Hemiacetal and Hemiketal compounds close again?
- 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
What does the anomeric carbon result from? Is A or B more common?
The closure of the linear structure to a closed structure
| - B more common since more stable
35
What is the anomeric carbon also known as? Why?
- 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
How can you know which carbon is the reducing end/anomeric carbon?
Carbon linked to an oxygen, they are always drawn on the right side by convention
37
What is a five-membered ring called? Six-membered ring?
- Furan Ring : 5
| - Pyran Ring : 6
38
Name the 3 structural representations of monosaccharides.
1) Fischer Projection
2) Haworth Projection
3) Chair Conformation (not configuration, not breaking bond)
39
In a chair configuration, in what direction is the OH pointing in depending on whether it is alpha or beta?
Alpha: OH pointing down
Beta: OH pointing to the right
40
How do you quantify reducing sugars? What is this used to determine?
- 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
What compounds are able to oxidize?
* *******- 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
If you add an R group to the anomeric carbon what happens?
You form an acetal, way more stable than hemiacetal, no more reducing end
43
What happens when a condensation reaction forms between two anomeric hydroxyls?
You lose the reducing end since the hemiacetal becomes an acetal
44
Are acetal carbons anomeric?
Yes, still anomeric but they lose their reducing end
45
Which carbons are linked in a O-glycosidic bond?
Carbon 1 and Carbon 4
46
What is particular to sucrose condensation?
Linking both anomeric groups = losing BOTH reducing ends
47
How are natural carbohydrates usually found?
Polymers
48
Name the 2 polysaccharides.
- Homopolysaccharides (same monosaccharides)
| - Heteropolysaccharides (two or more monosaccharides)
49
What are the 2 roles of homopolysaccharides?
Energy storage function and structural function
50
What are the 2 roles of heteropolysaccharides?
Structural function and cellular function
51
What is the main storage homopolysaccharide?
Starch
52
What is starch made up of?
Two homopolysaccharides of glucose
- Amylose
- Amylopectin
* D-glucose
53
What is amylose?
unbranched polymer of (alpha-1 to 4) linked residues
54
What is amylopectin?
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
What is the branch point for amylopectin?
Alpha 1-6 branch point
56
What is the branching frequency in starch?
24-30 residues
57
Where can amylase digest from?
From the NON-reduced end only
58
What is the conformation of amylose and amylopectin?
Helical conformation
59
Compare amylopectin, glycogen and amylose.
Both Amylopectin and Glycogen have the same basic structure as Amylose but with branches (α1→6)
60
Name the 2 storage homopolysaccharides. Where are they found?
1. Amylopectin (plants)
| 2. Glycogen (animals)
61
What is the ONLY big difference between amylopectin and glycogen? What does that cause?
- 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
What is a structural homopolysaccharide?
Cellulose
63
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
Sucrose
64
Name the 5 chemical modifications of monosaccharides.
- Phosphorylation
- Amidation
- Acetylation
- Oxidation
- Methylation
65
What is the difference between amylose and cellulose?
Cellulose: B1 --> 4
Amylose: A1 --> 4
66
What gives cellulose its strength?
The 2 monosaccharides with beta linkages are basically at 180o of each other --> hydrogen bonds are perfectly aligned, which makes them much stronger
67
What is the most abundant polysaccharide in nature?
Cellulose
68
What is the natural configuration of amino acids?
L
69
What is the natural configuration for carbohydrates?
D
70
What are the roles of monosaccharides and oligosaccharides added onto proteins? (3)
1. Cell-cell interactions, through special receptor proteins
2. Stabilize proteins against degradation (most surface proteins)
3. Role in proper folding of protein
71
Name the 2 types of carbohydrates linked onto proteins.
1) N-linked oligosaccharides
| 2) O-linked oligosaccharides
72
In which proteins are N-linked oligosaccharides added onto?
Proteins that have this consensus sequence:
Asn-XXX-Ser or Asn-XXX-Thr
73
How are N-linked oligosaccharides added onto proteins?
As pre-assembled oligosaccharide units
74
Where are N-linked oligosaccharides added?
Proteins that are destined to the extracellular side
75
In which proteins are O-linked oligosaccharides added onto?
Onto either Thr or Ser amino acids (no consensus sequence)
76
How are O-linked oligosaccharides added onto proteins?
Onto proteins one monosaccharide at a time
77
Where are O-linked oligosaccharides added?
Proteins that are destined to intracellular and extracellular side
78
What is a more specific test to measure glucose levels than the Fehling reaction?
- 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
What is mutarotation?
Converting between alpha and beta
