note: We reviewed all of these structures in discussion, plus they are readily available to you in the compendium,
so you'll only see comments where structures need to be drawn.
I. Monosaccharides
1) All biological sugars are D enantiomers. This means that humans have enzymes that process D sugars (i.e. glucose),
and our planet Earth generally has presented us with D-sugars for our consumption. If you somehow got ahold of a potato
from some other planet in the universe that produces L sugars and had the nerve to take a bite, you'd probably get
pretty sick with indigestion, having all those L-glucoses in your stomach.
2) Glucose-remember that right-left-right transfers to down-up-down when you go from the straight chain, Fischer
projection to the ring, Haworth form.
3) Mannose is a C2 epimer of glucose.
Galactose is a C4 epimer of glucose.
Fructose looks like glucose, sorta.
4) "oside" means that the anomeric carbon is an acetal.
"ose" means that the anomeric carbon is a hemiacetal.
II. Disaccharides
1) A glycosidic bond originates from an anomeric carbon and is bonded to the oxygen of the hydroxyl group on something
else, which can be another monosaccharide (ie glucose, fructose, etc), or a serine in a polypeptide (resulting in a
glycoprotein), or an alcohol (like methanol), or glycerol (resulting in a glycolipid). It's a C to O bond, not an area,
but one bond.
2) The reducing end refers to a Tollen's test result, which is experimentally derived, but can be predicted based on the
configuration of the anomeric carbon. A sugar solution is reacted with Tollen's reagent, which contains silver nitrate,
an oxidizing agent. Sugars with free anomeric carbon atoms are reasonably good at reducing oxidizing agents. So, if
the anomeric carbon is free, that is called the reducing end (RE) of the sugar. If not (ie engaged in a covalent
glycosidic bond), it is called non-reducing (NRE). One caveat is that this test was based on amount of reduced Tollen's
reagent per weight, so very high MW polysaccharides that do have one RE and many many NRE's are considered
non-reducing.
3) Maltose: glucose-a(1-4)-glucose
Cellobiose: glucose-b(1-4)-glucose
Lactose: glucose-b(1-4)-galactose
Sucrose: glucose-a(1-2)-fructose or fructose-b(2-1)-glucose
III. Polysaccharides
1) Beta linkages usually result in linear structures. Thus beta-linked polysaccharides are ideal for a structural
function. Alpha linkages usually result in open, globular structures. So, alpha-linked polysaccharides are ideal for a
storage function.
2) Cellulose is composed of glucoses, linked b(1-4), resulting in a linear structures that stack up nicely to give us
the major component of wood.
Amylose is composed of glucoses, linked a(1-4). The geometry of these linkages gives rise to a natural helix. Each
turn has 5-6 glucoses, so these turns and thus this helix is a lot larger than the alpha-helices that form from amino
acids in proteins. The overall structure is globular, which is perfect for storage of energy. Amylose comprises 10-30%
of starch, the form of energy storage in plants.
Amylopectin is composed of glucoses, linked a(1-4). Unlinke amylopectin, there is branching, on an average of 1 of
every 25 residue (4%). The overall structure is open and globular, like a tree branched out, also perfect for energy
storage. Amylopectin comprises the remaining 70-90% of starch in plants.
Glycogen, the form of short-term energy storage in animals, has the same linkages as amylopectin: a(1-4) and a(1-6) for
branching. The branching is 1 of every 10 residues, on average (10%). The overall structure is thus open and globular.
However, using the tree analogy, this tree has even more branches (and thus more NRE's) and no amyloses wedged into the
branches as starch does. So the glucoses stored in animals in the form of glycogen are more spatially accessible and
there are more NRE's available.
Hyaluronic acid you should be able to recognize. It's a protective polysaccharide, in the same class as structural
polysaccharides. The linkages are beta, 1-3 within the dimer and 1-4 between dimers. The dimer is composed of
glucuronic acid, which is glucose with the CH2OH group at C6 replaced with a carboxyl (COO), and N-acetylglucosamine,
which is glucose with an N-acetyl group at the C2 position.
Questions to Consider:
1) Lactose is composed of glucose linked b(1-4) to galactose. Humans can break down glucose and galactose, the
individual monomers. That must mean that there's a problem breaking the bond. It's a beta linkage. Garrett and
Grisham says that adult humans produce a lot less lactase than infant humans. So, lactase is the enzyme that breaks
that b(1-4) bond.
2) Humans can break down glucose, the monosaccharides that compose maltose. Given this information that maltose in beer
doesn't give anyone digestive problems, we can safely assume that humans can break that a(1-4) bond that connects the
two glucoses of this disaccharide. This is, in fact, a great disaccharide to have around, because it makes malted
milkshakes so smooth.
3) Forgive me for not flipping the ring substituents on that second glucose.
The systematic name for trehalose is a-D-glucopyranosyl-a(1-1)-b-D glucopyranoside.
(I am being somewhat redundat putting the alpha both places, but why not be sure to cover all bases.)
Both anomeric carbons are occupied in the glycosidic bond, so this disaccharide is neither mutarotatory or capable of
being a reducing agent.
4) This polysaccharide is amylopectin or glycogen, depending on the branching.
Each sugar residue has an NRE, which can be liberated to give us or plants energy in the form of glucose.
The function of this polysaccharide is thus for energy storage.
The structural characteristics that give rise to the function are alpha linkages (open, globular structure) and many
NRE's due to branching.
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153A VOH page
1) All biological sugars are D enantiomers. This means that humans have enzymes that process D sugars (i.e. glucose), and our planet Earth generally has presented us with D-sugars for our consumption. If you somehow got ahold of a potato from some other planet in the universe that produces L sugars and had the nerve to take a bite, you'd probably get pretty sick with indigestion, having all those L-glucoses in your stomach.
2) Glucose-remember that right-left-right transfers to down-up-down when you go from the straight chain, Fischer projection to the ring, Haworth form.
3) Mannose is a C2 epimer of glucose.
Galactose is a C4 epimer of glucose.
Fructose looks like glucose, sorta.
4) "oside" means that the anomeric carbon is an acetal.
"ose" means that the anomeric carbon is a hemiacetal.
1) A glycosidic bond originates from an anomeric carbon and is bonded to the oxygen of the hydroxyl group on something else, which can be another monosaccharide (ie glucose, fructose, etc), or a serine in a polypeptide (resulting in a glycoprotein), or an alcohol (like methanol), or glycerol (resulting in a glycolipid). It's a C to O bond, not an area, but one bond.
2) The reducing end refers to a Tollen's test result, which is experimentally derived, but can be predicted based on the configuration of the anomeric carbon. A sugar solution is reacted with Tollen's reagent, which contains silver nitrate, an oxidizing agent. Sugars with free anomeric carbon atoms are reasonably good at reducing oxidizing agents. So, if the anomeric carbon is free, that is called the reducing end (RE) of the sugar. If not (ie engaged in a covalent glycosidic bond), it is called non-reducing (NRE). One caveat is that this test was based on amount of reduced Tollen's reagent per weight, so very high MW polysaccharides that do have one RE and many many NRE's are considered non-reducing.
3) Maltose: glucose-a(1-4)-glucose
Cellobiose: glucose-b(1-4)-glucose
Lactose: glucose-b(1-4)-galactose
Sucrose: glucose-a(1-2)-fructose or fructose-b(2-1)-glucose
1) Beta linkages usually result in linear structures. Thus beta-linked polysaccharides are ideal for a structural function. Alpha linkages usually result in open, globular structures. So, alpha-linked polysaccharides are ideal for a storage function.
2) Cellulose is composed of glucoses, linked b(1-4), resulting in a linear structures that stack up nicely to give us the major component of wood.
Amylose is composed of glucoses, linked a(1-4). The geometry of these linkages gives rise to a natural helix. Each turn has 5-6 glucoses, so these turns and thus this helix is a lot larger than the alpha-helices that form from amino acids in proteins. The overall structure is globular, which is perfect for storage of energy. Amylose comprises 10-30% of starch, the form of energy storage in plants.
Amylopectin is composed of glucoses, linked a(1-4). Unlinke amylopectin, there is branching, on an average of 1 of every 25 residue (4%). The overall structure is open and globular, like a tree branched out, also perfect for energy storage. Amylopectin comprises the remaining 70-90% of starch in plants.
Glycogen, the form of short-term energy storage in animals, has the same linkages as amylopectin: a(1-4) and a(1-6) for branching. The branching is 1 of every 10 residues, on average (10%). The overall structure is thus open and globular. However, using the tree analogy, this tree has even more branches (and thus more NRE's) and no amyloses wedged into the branches as starch does. So the glucoses stored in animals in the form of glycogen are more spatially accessible and there are more NRE's available.
Hyaluronic acid you should be able to recognize. It's a protective polysaccharide, in the same class as structural polysaccharides. The linkages are beta, 1-3 within the dimer and 1-4 between dimers. The dimer is composed of glucuronic acid, which is glucose with the CH2OH group at C6 replaced with a carboxyl (COO), and N-acetylglucosamine, which is glucose with an N-acetyl group at the C2 position.
1) Lactose is composed of glucose linked b(1-4) to galactose. Humans can break down glucose and galactose, the individual monomers. That must mean that there's a problem breaking the bond. It's a beta linkage. Garrett and Grisham says that adult humans produce a lot less lactase than infant humans. So, lactase is the enzyme that breaks that b(1-4) bond.
2) Humans can break down glucose, the monosaccharides that compose maltose. Given this information that maltose in beer doesn't give anyone digestive problems, we can safely assume that humans can break that a(1-4) bond that connects the two glucoses of this disaccharide. This is, in fact, a great disaccharide to have around, because it makes malted milkshakes so smooth.
3) Forgive me for not flipping the ring substituents on that second glucose.
The systematic name for trehalose is a-D-glucopyranosyl-a(1-1)-b-D glucopyranoside.
(I am being somewhat redundat putting the alpha both places, but why not be sure to cover all bases.)
Both anomeric carbons are occupied in the glycosidic bond, so this disaccharide is neither mutarotatory or capable of being a reducing agent.
4) This polysaccharide is amylopectin or glycogen, depending on the branching.
Each sugar residue has an NRE, which can be liberated to give us or plants energy in the form of glucose.
The function of this polysaccharide is thus for energy storage.
The structural characteristics that give rise to the function are alpha linkages (open, globular structure) and many NRE's due to branching.
Back to Handouts or goto 153A VOH page