Chapter 7: Carbohydrates

Question 1

1) What are Monosaccharides, what are they composed of?
2) What are Oligosaccharides, what are they composed of?

Answer 1

1) - One sugar unit.
- Aldehydes or ketones with two or more hydroxyl groups.
- Carbons onto which these are attached are chiral centers.
- D-glucose (dextrose) is the most common. Names end with ‘ose’
2) - Short chains of sugars joined with glycosidic linkages
- Disaccharides are the most abundant.
- Sucrose is common = D-glucose + D-fructose, names end in ‘ose’

Question 2

What are Polysaccharides?

Answer 2

• > 20 linked monosaccharides. Up to thousands.
• Some chains are linear and some are branched.
• Starch and cellulose differ greatly in function.
• Bonds→Structure→Function (How the polysaccharides are put together is the most important aspect)

Question 3

1. What are the two families of monosaccharides?
2. What is more important in biology open-chain structures or cyclic structure?
3. What do open forms contain?
4. What are some examples?
5. What is a Triose?

Answer 3

1. Backbones of most are unbranched carbon chains with single bonds.
2. Can be open-chain or cyclic (most important in biology)
3. Open forms have a carbonyl carbon.

1) Aldose: carbonyl carbon is at one end
2) Ketose: carbonyl carbon is anywhere but an end.
4. Named for the position of the carbonyl carbon and the number of carbon atoms in their backbones.
5. Triose = 3 carbons

Question 4

1. What kind of centers do monosaccharides have?
2. What are chiral carbon atoms?
3. How many chiral centers does Glyceraldehyde have?
4. What chiral carbon do we look at?
5. Where do we begin numbering carbons?
6. What are epimers?

Answer 4

1. Have asymmetic centers
2. Chiral carbon atoms = rotate the plane of polarized light.
3. Glyceraldehyde has one chiral center and thus two enantiomers (D and L)
4. Based on the configuration of the chiral center most distant from the carbonyl carbon. D hydroxyl on the right, L on the left.
5. Beginning at the carbonyl carbon end. ‘ul’ in the name = ketose
6. Epimers are isomers that differ only in rotation about a single carbon.

Question 5

1. Monosaccharides with 5 or more carbons are what?
2. What is the carbonyl carbon bonded to?
3. What type of additional carbon do this structures contain?
4. How can we tell alpha from beta isomers?
5. What are 5-membered rings called? What are 6-membered rings called? Which is less common and which is less stable?

Answer 5

1. They are cyclic in nature.
2. Bonded to a hydroxyl group.
3. Conatins an additional asymmetric carbon, so they have stereoisomers.
4. alpha (hydroxyl group is opposite of oxygen), beta (hydroxyl group is on the same side as the oxygen).
5. 5-membered rings are furanoses, 6-membered rings are pyranoses. Furanoses are much less stable and less common.

Question 6

1. Can monosaccharides be reducing agents?
2. What is the end of the sugar that is able to reduce other molecules called?

Answer 6

1. Yes, monosaccharides can reduce cupric ion or other molecules. Called reducing sugars.
2. The end of the sugar that undergoes the oxidation-reduction is called the reducing end.

Question 7

1. What does the oxidation of carbonyl carbon result in?
2. What does the oxidation of the carbon farthest from the carbonyl result in?

Answer 7

1. Aldonic Acid
2. Uronic Acid

Question 8

1. What are disaccharides?
2. What is a product of these reactions?
3. What is the reducing end?
4. What are anomers?
5. What are the non-reducing ends?
6. What are the joined positions?

Answer 8

1. Monosaccharides joined by O-glycosidic bonds. Hydroxyl on one sugar plus anomeric carbon of the other sugar.
2. Water is another product.
3. The end with free anomeric carbon.
4. Differ only in their rotation about hemiacetal or hemiketal carbon. Hemiacetal or carbonyl carbons are Anomerica carbons.
5. Glycosides
6. Anomeric Carbons

Question 9

1. What are polysaccharides (Glycans)?
2. What are homopolysaccharides?
3. What are heteropolysaccharides?

Answer 9

1. Have varying degrees of chain length, branching, and types of bonds.
2. Structural elements and fuels.
3. Extracellular support in all kindoms.

Question 10

1. What are the two stored fuels?
2. What are they polymers of?
3. Where do they occur?

Answer 10

1. Starch and Glycogen
2. Glucose polymers
3. Occur in nature as large aggregates.

Question 11

1. What is amylose? Describe it
2. What is amylpectin? Describe it
3. What is their molecular weight?
4. What structure is most stable, why?

Answer 11

1. amylose is a glucose polymer (starch). Long, unbranched glucose chain with (α1→4) linkages.
2. amylpectin is a glucose polymer (starch). Highly branched with (α1→6) linkages.
3. 10³ to >10⁶ units.
4. Most stable structure is a coil. Most stable structure with an (α1→4) linkage is also a coil, because of hydrogen bonding.

Question 12

1. What is glycogen? What type of linkages do they contain?
2. How often do do branches occur?
3. What does each branch end with? Where are sugars added or removed?

Answer 12

1. A glucose polymer with (α1→4) linkages and (α1→6) branches.
2. Contains many branches: one per 8-12 residues.
3. Each branch ends with a non-reducing sugar (no free anomeric carbon). Sugars are removed or added as needed from the non-reducing ends.

Question 13

1. What type of polysaccharide is cellulose?
2. What are it’s properties?
3. What type of h-bonds does it contain?

Answer 13

1. Homopolysaccharide
2. Fiberious, water insoluble, linear unbranched homosaccharides with 10,000-15,000 monomers per molecule.
   
   1. Straight, stable supermolecular structure with high tensile strength and low water content.
3. Many intrachain and interchain covalent bonds.
   
   1. Weak interactions, no interchain covalent bonds.

Question 14

1. What kind of polysaccharide is chitin? What kind of linkages does it have?
2. How is different from cellulose?
3. Describe its structure
4. What does it form in arthropods?
5. What type of chitin do arthropods have? What type of chitin do crustaceons have?

Answer 14

1. Linear homopolysaccharide of N-acetylglucosamine with β linkages.
2. Acetylated amino at C-2 instead of hydroxyl.
3. Forms long, fibrous chains like cellulose.
4. Forms the hard, water-tight exoskeletons pf arthropods.
5. Beta Chitin (weak H-bonds, parallel sheets). Alpha chitin (strong H-bonds, antiparallel sheets).

Question 15

1. What type of polysaccharide is Sephadex?
2. What type of branches does it have?
3. What dicates chromatography?

Answer 15

1. Homopolysaccharide.
2. Branched homopolysaccharide of D-glucose.
   
   1. Mostly (α1→6)
   2. Some (α1→2), (α1→3), (α1→4) branches.
   3. Dextrans, degree of crosslinking dictates chromatography = Sephadex

Question 16

1. Where can heteropolymers be located?
2. What type of linkages do they have?
3. Describe their properties.
4. What is similar and what is different about the cell wall of gram-negative and gram-positive bacteria?
5. How does penicillin treat bacterial infections?

Answer 16

1. Bacterial cell wall PTG
2. Alternating N-acetylglucosamine and N-acetylmuramic acid in (β1→4) linkage.
3. Linear polymers side-by-side. Cross-linked by short peptides (species specific). Very strong!
4. Same PTG, different cross-linking.
   
   1. Gram-Positive contain a pentaglycine bridge glycosidic bond.
   2. Gram-Negative contain Ala-Gly direct cross-link peptide bond.
5. By preventing the synthesis of peptide cross-links, leads to osmotic lysis of bacteria.

Question 17

1. What is the Extracellular Matrix? What is it composed of?
2. What are Glycosaminoglycans? Describe them
3. Where do they attach?
4. What are some Glycosaminoglycans? What makes them different from each other?

Answer 17

1. Gel like substance filling the space between cells and tissues. Composed of fibrous proteins, heteropolysaccharides called glycosaminoglycans.
2. Heteropolysaccharides.
   
   1. Linear repeating polymers of disaccharides.
   2. One is always N-acetylglucosamine or N-acetylgalactosamine (The other is most often a uronic acid)
   3. Linkages often incorporate a sulfer-containing group (Position of sulfur identifies the molecule).
3. Attach to extracellular proteins to form Proteoglycans.
4. Hyaluronic Acid, Chondroitin Sulfate, Dermatan Sulfate, Keratan Sulfate, Heparin. Bonds, number of sulfur groups, and the placement of those sulfur groups, determines the molecule.

Question 18

1. What are the functions of glycoconjugates?
2. What are their structure?
3. What are the 3 classes?

Answer 18

1. Carry information and signal
2. Carbohydrate coupled to a protein or lipid.
3. Proteoglycan Aggregates, Glycoproteins, Glycolipids and Lipopolysaccharides

Question 19

1. What do proteoglycan aggregates consist of?
2. How many core proteins do they have?
3. Do they have multiple binding sites?
4. What does the binding event direct?

Answer 19

1. Supermolcular complexes that consist of Aggrecan+Chondrotin sulfate+Kerratan sulfate.
2. This the core protein ( 1,000,000 daltons), 100+ core proteins are attached to Hyaluronate, for a total molecular weight of >2 x 10⁸ d
3. Yes, many proteoglycans have multiple binding sites for multiple extracellular matrix proteins. Matrix binds to Integrins.
4. Directs cell migration, cell-cell adhesion, and signaling.

Question 20

1. What are glycoproteins?
2. Where are they found?
3. What are their linkages?

Answer 20

1. 1 or more carbohydrate moieties on a protein core.
2. Found on the extracellular face of cells (plasma membrane). Found on the luminal side (Golgi, ER, and lysosomes)
3. Carbohydrate attached to the core. Two linkages: N and O

Question 21

1. What are glycolipids and lipopolysaccharides?
2. What are gangliosides?
3. What do lipopolysaccharides consist of?

Answer 21

1. Membrane lipids with carbohydrate as the polar head group.
2. Eukaryotic membran lipids.
   
   1. contain polar head group that is a complex carbohydrate containing sialic acids,
   2. A.K.A. Neuraminic acid, N-acetyl-neuraminic acid
   3. Virtually always on the outside of the plasma membrane.
3. Lipid + large carbohydrate chains
   
   1. Major component of the outer membrane of gram negative bacteria.

Question 22

1. What are lectins?
2. Are they specific?
3. What are their functions?

Answer 22

1. Carbohydrate-binding proteins with high specificity and affinity.
2. Specificity: ability to discriminate amoung similar structures. Lectins discriminate using certain hydrogen-bonding domains.
3. Functions
   
   1. Cell recognition, cell adhesion, and signaling
   2. Used as a lab tool for labeling and carbohydrate detection.