carbohydrates - gurudas college...reaction molisch test oxidation–reduction reactions saccharides...
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CARBOHYDRATES
WHAT
IS LIFE?
Koshland’s seven point criteria
The Seven Pillars of Life
“PICERAS”
P= Program
I= ImprovisationI= Improvisation
C= Compartmentalization
E= Energy
R= Regeneration
A= Adaptability
S= Seclusion
Koshland, D.E. (2002) The seven pillars of life. Science 295: 2215-2216.
“The first pillar of life is a Program.
By program I mean an organized plan that describes both the ingredients themselves and the kinetics of the interactions among
ingredients as the living system persists through time. For the living
systems we observe on Earth, this program is implemented by the
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systems we observe on Earth, this program is implemented by the
DNA that encodes the genes of Earth's organisms and that is replicated from generation to generation, with small changes but
always with the overall plan intact. The genes in turn encode for
chemicals--the proteins, nucleic acids, etc.--that carry out the reactions in living systems.
It is in the DNA that the program is summarized and maintained for
life on Earth.”
Central Dogma of Molecular Biology
“The second pillar of life is IMPROVISATION.
Because a living system will inevitably be a small fraction of the larger universe in which it
lives, it will not be able to control all the changes
and vicissitudes of its environment, so it must
Koshland, D.E. (2002) The seven pillars of life. Science 295: 2215-2216.
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and vicissitudes of its environment, so it must
have some way to change its program. If, for example, a warm period changes to an ice age
so that the program is less effective, the system
will need to change its program to survive.
In our current living systems, such changes can
be achieved by a process of mutation plus selection that allows programs to be optimized
for new environmental challenges that are to be faced.”
“The third of the pillars of life is
COMPARTMENTALIZATION.
All the organisms that we consider living
are confined to a limited volume,
Koshland, D.E. (2002) The seven pillars of life. Science 295: 2215-2216.
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are confined to a limited volume, surrounded by a surface that we call a membrane or skin that keeps the
ingredients in a defined volume and keeps
deleterious chemicals--toxic or diluting--on the outside. Moreover, as organisms
become large, they are divided into
smaller compartments, which we call cells
(or organs, that is, groups of cells), in order to centralize and specialize certain
functions within the larger organism.”
Cellular Compartmentalization
“The fourth pillar of life is ENERGY.
Life as we know it involves movement--of chemicals, of the body, of components of
the body--and a system with net movement cannot be in equilibrium. It must be an
open and, in this case, metabolizing system. Many chemical reactions are going on
inside the cell, and molecules are coming in from the outer environment--O2, CO2,
metals, etc. The organism's system is parsimonious; many of the chemicals are
Koshland, D.E. (2002) The seven pillars of life. Science 295: 2215-2216.
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recycled multiple times in an organism's lifetime (CO2, for example, is consumed in
photosynthesis and then produced by oxidation in the system), but originally they
enter the living system from the outside, so thermodynamicists call this an open
system. Because of the many reactions and the fact that there is some gain of
entropy (the mechanical analogy would be friction), there must be a compensation to
keep the system going and that compensation requires a continuous source of
energy. The major source of energy in Earth's biosphere is the Sun--although life on
Earth gets a little energy from other sources such as the internal heat of the Earth--
so the system can continue indefinitely by cleverly recycling chemicals as long as it
has the added energy of the Sun to compensate for its entropy changes.”
Glucose (a monosaccharide)
Plants:
photosynthesis
chlorophyll
6 CO2 + 6 H2O C6H12O6 + 6 O2
sunlight (+)-glucose
(+)-glucose starch or cellulose
respiration
C6H12O6 + 6 O2 6 CO2 + 6 H2O + energy
Energy Transduction
“The fifth pillar is REGENERATION.
Another system for regeneration is the constant resynthesis of the constituents of
the living system that are subject to wear
and tear. For example, the heart muscle of a normal human beats 60 times a minute--
Koshland, D.E. (2002) The seven pillars of life. Science 295: 2215-2216.
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a normal human beats 60 times a minute--
3600 times an hour, 1,314,000 times a year, 91,980,000 times a lifetime. No man-made
material has been found that would not
fatigue and collapse under such use, which is why artificial hearts have such a
short utilization span. The living system,
however, continually resynthesizes and replaces its heart muscle proteins as they
suffer degradation; the body does the same for other constituents--its lung sacs, kidney proteins, brain synapses, etc.”
“The sixth pillar is ADAPTABILITY.
Improvisation is a form of adaptability, but is too slow for many of the environmental hazards that a living organism must face.
For example, a human that puts a hand into a fire has a painful
experience that might be selected against in evolution--but the
Koshland, D.E. (2002) The seven pillars of life. Science 295: 2215-2216.
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experience that might be selected against in evolution--but the individual needs to withdraw his hand from the fire immediately
to live appropriately thereafter.
That behavioral response to pain (a reflex) is essential to survival and is a fundamental response of living systems that we call
feedback.”
“Finally, and far from the least,
Koshland, D.E. (2002) The seven pillars of life. Science 295: 2215-2216.
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“Finally, and far from the least, is the seventh pillar, SECLUSION.
By seclusion, in this context, I mean something rather like privacy in the social world of our
universe.”
Major Classes of Macromolecules
�Carbohydrates
�Proteins�Proteins
�Lipids
�Nucleic Acids
CARBOHYDRATE
CHEMISTRY
�Carbohydrates or saccharides (Greek: sakcharon, sugar)
are essential components of all living organisms and are, infact, the most abundant class of biological molecules.
�The name carbohydrate, which literally means “carbon hydrate,”stems from their chemical composition, which isroughly (C H2O)n, where n 3.
�The basic units of carbohydrates are known as �The basic units of carbohydrates are known as monosaccharides. Many of these compounds are synthesized from simpler substances in a process named gluconeogenesis.
�Others (and ultimately nearly all biological molecules) are theproducts of photosynthesis, the light-poweredcombination of CO2 and H2O through which plants andcertain bacteria form “carbon hydrates.”
Carbohydrates – polyhydroxyaldehydes or polyhydroxy-
ketones of formula (CH2O)n, or compounds that can be
hydrolyzed to them. (aka sugars or saccharides)
Monosaccharides – carbohydrates that cannot be hydrolyzed
to simpler carbohydrates; eg. Glucose or fructose.
Disaccharides – carbohydrates that can be hydrolyzed into Disaccharides – carbohydrates that can be hydrolyzed into
two monosaccharide units; eg. Sucrose, which is hydrolyzed
into glucose and fructose.
Oligosaccharides – carbohydrates that can be hydrolyzed into
a few monosaccharide units.
Polysaccharides – carbohydrates that are are polymeric
sugars; eg Starch or cellulose.
Aldose – polyhydroxyaldehyde, eg glucose
Ketose – polyhydroxyketone, eg fructose
Triose, tetrose, pentose, hexose, etc. – carbohydrates that
contain three, four, five, six, etc. carbons per molecule
(usually five or six); eg. Aldohexose, ketopentose, etc.(usually five or six); eg. Aldohexose, ketopentose, etc.
Figure 11-1 The stereochemical
relationships, shown in Fischer
projection, among the D-aldoses
with three to six carbon atoms.
Figure 11-2 The stereochemical relationships
among the D-ketoses with three to six carbon
atoms.
Kiliani-Fischer synthesis. A series of reactions that extends the
carbon chain in a carbohydrate by one carbon and one chiral center.
Epimers – stereoisomers that differ only in configuration about
one chiral center.
CHO
OHH
HHO
OHH
CHO
HHO
HHO
OHHOHH
OHH
CH2OH
D-glucose
OHH
OHH
CH2OH
D-mannose
epimers
Ruff degradation – a series of reactions that removes the
reducing carbon ( C=O ) from a sugar and decreases the
number of chiral centers by one; used to relate configuration.
CHO
H OH
CH2OH
H OH
CO2H
H OH
CH2OH
H OH
Br2
H2O
CH2OH 2
CO2
H OH
CH2OH
H OH
Ca2+
H2O2
Fe3+
CHO
CH2OH
H OH
D-(+)-glyceraldehyde
Ac = CH3C=O
The Wohl degradation in carbohydrate
chemistry is a chain contraction method
for aldoses.
The reactions of alcohols with (a) aldehydes to
form hemiacetals and (b) ketones to form hemiketals.
Cyclization reactions for hexoses
REACTION
MOLISCH TEST
Oxidation–Reduction Reactions
�Saccharides bearing anomeric carbon atoms that have not
formed glycosides are termed reducing sugars because of
the facility with which the aldehyde group reduces mild oxidizing
agents.
�A reducing sugar is any sugar that is capable of acting as
a reducing agent because it has a free aldehyde group or a free
ketone group. All monosaccharides are reducing sugars, along
with some disaccharides, oligosaccharides, and polysaccharides.
BENEDICT’S TEST
BENEDICT’S TEST
Sucrose
BIAL’S TEST
Fehling's test
This is an important test to detect the presence of reducing sugars. Fehling’s solution
A is copper sulphate solution and Fehling’s solution B is potassium sodium tartrate.
On heating, carbohydrate reduces deep blue solution of copper (II) ions to red
precipitate of insoluble copper oxide.
The α and β anomers are diastereomers of each other and usually have
different specific rotations. A solution or liquid sample of a pure α anomer will
rotate plane polarised light by a different amount and/or in the opposite direction
than the pure β anomer of that compound. The optical rotation of the solution
depends on the optical rotation of each anomer and their ratio in the solution.
For example if a solution of β-D-glucopyranose is dissolved in water, its specific
optical rotation will be +18.7. Over time, some of the β-D-glucopyranose will undergo
mutarotation to become α-D-glucopyranose, which has an optical rotation of +112.2.
Explanation
mutarotation to become α-D-glucopyranose, which has an optical rotation of +112.2.
Thus the rotation of the solution will increase from +18.7 to an equilibrium value of
+52.5 as some of the β form is converted to the α form. The equilibrium mixture is
actually about 64% of α-D-glucopyranose and about 36% of β-D-glucopyranose,
though there are also with traces of the other forms including furanoses and open
chained form. The α anomer is the major conformer, although somewhat
controversially; this is due to the anomeric effect with the stabilisation energy
provided by n-σ* hyperconjugation.
ββββ−−−−furanose (13.2%)
MECHANISM OF MUTAROTATION
CHAIR AND BOAT CONFORMATIONS
CHAIR AND BOAT FORM OF GLUCOSE
MechanismMechanism
The mechanism is not trivial, so attention here is focused
on the actual cleavage step. Prior to this, the alcohol
reacts to form a cyclic periodate ester (shown). The
periodate ester undergoes are arrangement of the
electrons, cleaving the C-C bond, and forming two C=O
OHOH
The principle underlying estimation of DNA using diphenylamine is the reaction of
diphenylamine with deoxyribose sugar producing blue-coloured complex. The DNA
sample is boiled under extremely acidic conditions; this causes depurination of the DNA
followed by dehydration of deoxyribose sugar into a highly reactive ω-
hydroxylevulinylaldehyde. The reaction is not specific for DNA and is given by 2-
deoxypentoses, in general. The ω-hydroxylevulinylaldehyde, under acidic conditions,
reacts with diphenylamine to produce a blue-coloured complex that absorbs at 595 nm.
Reaction of DPA with deoxyribose
O
O
HO
w-hydroxylevulinylaldehyde
Reaction
Diphenylamine
Reaction of ribose with orcinol
Fucose is a hexose deoxy sugar with the chemical formula C6H12O5. It is found on N-
linked glycans on the mammalian, insect and plant cell surface, and is the fundamental
sub-unit of the fucoidan polysaccharide. α(1→3) linked core fucose is a suspected
carbohydrate antigen for IgE-mediated allergy.
O
HO OH
HO
OH
Fucose
carbohydrate antigen for IgE-mediated allergy.
rhamanose
�Rhamnose (Rha, Rham) is a naturally
occurring deoxy sugar.
�It can be classified as either a methyl-
pentoseor a 6-deoxy-hexose.
�Rhamnose occurs in nature in its L-form
as L-rhamnose (6-deoxy-L-mannose). This
is unusual, since most of the naturally is unusual, since most of the naturally
occurring sugars are in D-form. Exceptions
are the methyl pentoses L-fucose and L-
rhamnose and the pentose L-arabinose.
�Rhamnose can be isolated
from Buckthorn (Rhamnus), poison sumac,
and plants in the genus Uncaria.
Rhamnose is also produced by microalgae
belonging to class Bacillariophyceae
(diatoms).
Rhamnose is commonly bound to other sugars in nature. It is a common glycone component of glycosides from many plants. Rhamnose is also a component of the outer cell membrane of acid-fast bacteria in the Mycobacterium genus, which includes the organism that causes tuberculosis
Importance of carbohydrates
1. Metabolic/Nutritional The biological breakdown of carbohydrates
(often spoken of as "combustion") supplies the principal part of the
energy that every organism needs for various processes.
2. Structural Insoluble carbohydrate polymers serve as structural
and protective elements in the cell walls of bacteria and plants and and protective elements in the cell walls of bacteria and plants and
in the connective tissues of animals.
3. Communication Glycosaminoglycans as polymers of derivatives
of carbohydrates are of critical importance in intercellular
communication in organisms.
4. Biosynthesis of other compounds Carbohydrates are source of
carbon for biosynthesis of other compounds.
The term "inverted" is derived from the practice of measuring the concentration
of sugar syrup using a polarimeter. Plane polarized light, when passed through a
sample of pure sucrose solution, is rotated to the right (optical rotation). As the
solution is converted to a mixture of sucrose, fructose and glucose, the amount
of rotation is reduced until (in a fully converted solution) the direction of rotation
has changed (inverted) from right to left.
Inversion of Sucrose
net: +66.5°converts to −19.65°(half of the sum of the specific rotation of
fructose and glucose)
Sucrose Hydrolysis
Disaccharides
Polysaccharides
1. Most carbohydrates found in nature occur as polysaccharides,
polymers of medium to high molecular weight.
2. Polysaccharides, also called glycans, differ from each
other in the identity of their recurring monosaccharide
units, in the length of their chains, in the types of bonds
linking the units, and in the degree of branching.
3. Homopolysaccharides contain only a single type of monomer;
heteropolysaccharides contain two or more different
kindskinds
4. Polysaccharides are generally insoluble in cold water.
5. Some homopolysaccharides serve as storage forms of
monosaccharides that are used as fuels; starch and glycogen are
homopolysaccharides of this type.
6. Heteropolysaccharidesprovide extracellular support for organisms of all
kingdoms.For example, the rigid layer of the bacterial cell envelope (the
peptidoglycan) is composed in part of a heteropolysaccharide built from
two alternating monosaccharide units.
Peptidoglycan
Sialic acid is a generic term for the N- or O-substituted derivatives of
neuraminic acid, a monosaccharide with a nine-carbon backbone. It is also the
name for the most common member of this group, N-acetylneuraminic acid.
Sialic acids are found widely distributed in animal tissues and to a lesser extent
in other organisms, ranging from plants and fungi to yeasts and bacteria, mostly
in glycoproteins and gangliosides (they occur at the end of sugar chains
connected to the surfaces of cells and soluble proteins).That is because it
seems to have appeared late in evolution[citation needed]. However, it has been
observed in Drosophila embryos and other insects and in the capsular
polysaccharides of certain strains of bacteria. In humans the brain has the
highest sialic acid concentration, where these acids play an important role in highest sialic acid concentration, where these acids play an important role in
neural transmission and ganglioside structure in synaptogenesis. In general, the
amino group bears either an acetyl or a glycolyl group, but other modifications
have been described. These modifications along with linkages have shown to
be tissue specific and developmentally regulated expressions, so some of them
are only found on certain types ofglycoconjugates in specific cells. The hydroxyl
substituents may vary considerably; acetyl, lactyl, methyl, sulfate, and
phosphate groups have been found.[4] The term "sialic acid" (from the Greek
for saliva) was first introduced by Swedish biochemist Gunnar Blix in 1952.
Reference Books:
1.Biochemistry – Voet & Voet
2.Biochemistry – Lubert Stryer
3.Lehninger Principles of Biochemistry – Nelson & Cox
4.Organic Chemistry (vol.1&2) – I.L.Finar