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01:694:301 Lecture 15: Problem Set #10_Carbohydrates and Glycobiology(2)Exam


Department
Molecular Biology and Biochemistry
Course Code
01:694:301
Professor
F.Deis
Study Guide
Final

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CHM 376 Biochemistry I
Spring 2020
Problem Set 10: Carbohydrates and Glycobiology
This first section of this assignment “Self/Home Study Questions” – each of these questions
focuses on a definition or particular structural/functional/chemical features of
carbohydrates, and is designed to help guide you through the slides and your notes from
lectures step by step.
1. Provide a definition for the following terms: monosaccharide, disaccharide, and
oligosaccharide.
Monosaccharide Monomeric (usually 3 9 carbons)
Oligosaccharides Formed by linking two or more saccharides together in a regular order (a
few)
Disaccharide Formed by linking two saccharides together
2. What is the structural difference between an aldose and a ketose? What class of enzyme
would interconvert an aldose and a ketose?
An aldose is a monosaccharide with an aldehyde at 1-position, where a ketose is a
monosaccharide with a ketone at the 2-position.
An isomerase interconverts an aldose and a ketose.
3. What carbon is on “top” of a Fisher projection structure? What is the meaning of the
term chirality determining carbon?
The most ‘oxidized’ carbon is on “top” of a Fisher projection.
The chirality determining carbon is the chiral carbon furthest away from the aldehyde or ketone,
and designates its L or D configuration, which holds true for all carbohydrates.
4. In a carbohydrate with multiple chiral centers, how do we find the chirality determining
carbon? Draw L-glucose.
Find the chiral carbon furthest away from the aldehyde or ketone.

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5. What is an epimer? Draw and name all possible epimers of glucose. Include the special
“L/D” epimer.
Epimers differ in configuration about 1 chiral carbon.
6. What is the structural relationship between glucose and galactose?
They are epimers at the C-4 position.
7. Why are there two different aldotrioses but only one ketotriose?
The ketotriose (dihydroxyacetone) is NOT chiral, which it will not yield any isomers, whereas an
aldotriose has a chiral carbon.
8. Write each step in the chemical mechanism of the enzyme of phosphohexose isomerase.
What is the role of the active site glutamic acid in the process.
The active site glutamic acid takes a proton off glucose to be able to the formation of the enediol
intermediate.
Isomerization: Glucose-6 Phosphate (Aldose) Fructose-6-Phosphate (Ketose)

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9. What would be the products of a reverse aldol reaction on (a) glucose and (b) fructose?
10. Draw the chemical mechanism leading to the formation of an acetal and a ketal. What does
the formation of a hemiacetal or hemiketal do to the chirality of a molecule?
A hemiacetal / hemiketal is chiral, so it will introduce another chiral carbon, the anomeric
carbon.
11. What do we mean by the terms, “-side up ” and “-side down”? How do these terms
relate to the terms L-side and D-side?
If the anomeric –OH is pointing “down”, it is an alpha anomer, and if the –OH is pointing “up”
it is the beta anomer.
12. Given a Fisher projection structure of D-glucose, draw -D-glucopyranose, -D-
glucopyranose, -D-glucofuranose and -D-glucofuranose. In each structure circle the
anomeric carbon. What is an anomer? What is mutarotation?
Anomers are cyclic monosaccharides that are epimers of each other.
Mutarotation is the interconversion of α and β anomers
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