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