Major biochemicals and enzymes in metabolic biochemistry

87 Pages·2012·3.429 MB·English

by  Denisse Howes

First Edition, 2012

ISBN 978-81-323-3783-6

© All rights reserved.

Published by:
University Publications
4735/22 Prakashdeep Bldg,
Ansari Road, Darya Ganj,
Delhi - 110002
Email: [email protected]
Table of Contents

Chapter 1 - Glucose
Chapter 2 - Fructose
Chapter 3 - Glycogen
Chapter 4 - Starch
Chapter 5 - Pyruvic Acid
Chapter 6 - Urea
Chapter 7 - Adenosine Triphosphate
Chapter 8 - Other Biochemicals and Enzymes in Metabolic Biochemistry
Chapter- 1
Glucose

D-glucose

D-glucopyranose

Chain form
Ball and stick model

Fischer projection of the chain form
Preferred IUPAC name
Dextrose
Systematic name
(2R,3S,4R,5R)-2,3,5,4,6-Pentahydroxyhexanal
Other names
Blood sugar
Corn sugar
D-Glucose
Grape sugar
Identifiers
Abbreviations Glc
CAS number 50-99-7
PubChem 5793
ChemSpider 5589
UNII 5SL0G7R0OK
EC number 200-075-1
KEGG C00031
MeSH Glucose
ChEBI CHEBI:4167
ChEMBL CHEMBL1216
RTECS number LZ6600000
ATC code B05CX01,V04CA02, V06DC01
Beilstein Reference 1281604
Gmelin Reference 83256
3DMet B04623
Properties
Molecular formula C H O
6 12 6
Molar mass 180.16 g/mol
Exact mass 180.063388
Density 1.54 g/cm3
α-D-glucose: 146 °C
Melting point
β-D-glucose: 150 °C
Solubility in water 91 g/100 ml (25 °C)
Solubility in methanol 0.037 M
Solubility in ethanol 0.006 M
Solubility in tetrahydrofuran 0.016 M
Thermochemistry
Std enthalpy of
−1271 kJ/mol
formation ΔHo
f 298
Std enthalpy of
−2805 kJ/mol
combustion Δ Ho
c 298
Standard molar
209.2 J K−1 mol−1
entropy So
298
Hazards
MSDS ICSC 0865

D-glucose or dextrose or grape sugar is the dextro-isomer of glucose (C H O ). The
6 12 6
molecule is the mirror-image of L-glucose. D-glucose is a simple sugar (monosaccharide)
and an important carbohydrate in biology. Cells use it as a source of energy and a
metabolic intermediate. Glucose is one of the main products of photosynthesis and starts
cellular respiration. Starch and cellulose are polymers derived from the dehydration of
glucose. The name "glucose" comes from the Greek word glukus (γλυκύς), meaning
"sweet". The suffix "-ose" denotes a sugar.
Glucose exists in several different structures, but all of these structures can be divided
into two families of mirror-images (stereoisomers). Only one set of these isomers exists
in nature, those derived from the "right-handed form" of glucose, denoted D-glucose. D-
glucose is often referred to as dextrose. The term dextrose is derived from dextrorotatory
glucose. Solutions of dextrose rotate polarized light to the right (in Latin: dexter = "right"
).
Structure
Although it is called a "simple sugar" (meaning that it is a monosaccharide), glucose is a
complicated molecule because it adopts several different structures. These structures are
usually discussed in the context of the acyclic isomer, which exists in only minor
amounts in solution.
Glucose is derived from hexanal, a chain of six carbon atoms terminating with an
aldehyde group. The other five carbon atoms each bear alcohol groups. Glucose is called
an aldohexose. In solution, glucose mainly exists as the six-membered ring containing a
hemiacetal group, which arises from the reaction of the hydroxy group at C-5 and the
aldehyde at C-1. Containing five carbon atoms and one oxygen atom, this ring is a
derivative of pyran. This cyclic form of glucose is called a glucopyranose, of which two
isomers exist.
The asymmetric center at C-1, the site of the hemiacetal, is called the anomeric carbon
atom. The ring closing process can give rise to two isomers, called anomers, which are
labeled α-glucose and β-glucose. These anomers differ in terms of the relative positioning
of the hydroxyl group linked to C-1. When D-glucose is drawn as a Haworth projection or
in the standard chain conformation, the designation α means that the hydroxyl group
attached to C-1 is positioned trans to the -CH OH group at C-5, while β means that it is
2
cis. An inaccurate but superficially attractive alternative method of distinguishing α from
β is observing whether the C-1 hydroxyl is below or above the plane of the ring; this may
fail if the glucose ring is drawn upside down or in an alternative chair conformation. The
α and β forms interconvert over a timescale of hours in aqueous solution, to a final stable
ratio of α:β 36:64, in a process called mutarotation. The ratio would be α:β 11:89 if it
were not for the influence of the anomeric effect.
Isomers
Aldohexoses have four chiral centers in their acyclic forms (i.e. ignoring the anomeric
carbon). Four chiral centers give rise to 24 = 16 stereoisomers. These stereoisomers are
classified into two classes with eight sugars in each, which are mirror images of each
other. One class is labeled L and the other D. Only seven of these isomers are found in
nature, of which D-glucose (Glu), D-galactose (Gal) and D-mannose (Man) are the most
important. These eight isomers (including glucose itself) are diastereoisomers and belong
to the D series.
The Fischer projection of the chain form of D-glucose
The chain form of D-glucose

α-D-
glucopyranose
β-D-
glucopyranose

Chain form: ball-and-stick model
Chain form: space-filling model