Chem 212Quiz 10 (SU04)p.1

NAME______

Carbohydrates 20 pts + 10 pts x.c.!

The following table may be useful for some of the questions below:

  1. (10 pts) Below each of the following structures, write all of the appropriate terms from the list: triose, tetrose, pentose, hexose, aldose, ketose, pyranose, furanose, “”, “”, amino sugar, deoxy sugar, alditol, aldonic acid, uronic acid, phosphate ester

#C’s:pentosehexosehexosehexosetetrose

Funct grp:aldoseketoseuronic acidketosealdonic acid

Ring size:furanosepyranosefuranose

Stereocenter:

Deriv.s2-deoxy3-amino

5-phosphate

  1. (10 pts) The carbohydrate structure shown below, called Lewis X, is expressed on the surface of certain cancer cells. Antibodies developed against it might be used a treatment for cancer.
  2. Circle and identify the individual sugar groups in Lewis X.
  3. Point an arrow to each glycosidic bond and identify its type (i.e. “1,2” etc.)

  1. (3 pts) Match the carbohydrate with its role in biochemistry (not all letters are used)

_h_ Energy storage in plantsa. Cellulose

_g_ Energy storage in muscle tissueb. Glucose

_a_ Structural material in plantsc. Glucouronic acid

_i_ Non-nutritive sweeteners (gum, tooth paste)d. Oligosaccharides

_d_ Determines ABO blood typee. Aldonic acids

_c_ Makes certain metabolites water solublef. Sucrose

g. Glycogen

h. Starch

i. Alditols

  1. (3 pts) Both starch and cellulose are made from long chains of glucose molecules linked by a 1,4-glucosidic bond, yet humans can digest starch but not cellulose. What is the difference between these structures that makes one indigestible? (Complete sentences required)

In starch, the 1,4-glucosidic bond has the alpha () stereochemistry, but in cellulose it has the beta () stereochemistry. This affects both the crystal structure that forms and the ability of enzymes to hydrolyze the glucosidic bond. Humans and other mammals do not have the proper enzyme to hydrolyze the beta () glycosidic bond. (Ruminants such as cows, as well as termites, have bacteria in their gut that does metabolize cellulose!)

  1. (4 pts) The following are structures of sucrose and sucralose (marketed as Splenda ®) In a July 14, 2004 article in the Chicago Tribune (Section 7, page 3A), the following statement appeared: “The manufacture of sucralose involves replacement of sugar molecules with chlorine.” Also, the ads for Splenda it state that “It’s made from sugar, so it tastes more like sugar.” Are these two statements chemically valid? Explain your answer with complete sentences.

The first statement is at least factually incorrect because it is not molecules that are replaced, it is hydroxyl groups that are replaced with chlorine. If the word “molecules” is changed to “hydroxyl groups” then the statement would be correct. Regarding the second statement, human taste receptors can react similarly to similar structures, but that is not a guarantee that to sucrose would taste like sugar. For example, there are fewer hydrogen bonding interactions possible for sucralose, which could result in a different interaction with the taste receptor. Therefore the second statement is misleading because it implies a clear cause and effect which is not at all clear.