1Lecture 2

Life (Its Building Blocks & Processes)

Department of Chemical and

Environmental Engineering

H83BCE Biochemical Engineering

2Background

Four main classes of polymeric cell compounds:

1. Polysaccharides Starch, cellulose, etc.

2. Lipids

3. Proteins

4. Nucleic Acids polydeoxyribonucleic and polyribonucleic acids

The elements from which these polymers are

constructed are mainly: C, H, N, O, in addition to: S,

P, K, Na, Ca, Mg, Cl, Fe (and others) in much lesser

amounts.

3Fundamental structure of life

4Carbohydrates: Mono- and Polysaccharides

Key roles:

Structural and storage compounds in cells.

Modulate some aspects of chemical signalling in animals and plants.

Most prevalent of the four groups of compounds

General formula (CH2O)n, where n 3

In photosynthesis, carbon dioxide is converted to simple sugars:

CO2 + H2O Sugars (C3 C9) + O2

These sugars are then polymerised into forms suitable forstorage (starches) and structure (cellulose)

The light energy stored is released by oxidation (respiration) tocarbon dioxide

Light

Energy

5Monosaccharides (Simple Sugars)

Monomeric blocks for

biopolymers

Either aldehyde or ketone

by formula,

However, they do not

behave like them .

The most common

monosaccharide is D-

glucose:

Linear or ring structure.

In solution, D-glucose is in

the form of a ring

(pyranose) structure:

D-glucose, linear structure

D-glucose, ring (pyranose) structure

6Glucose: D- vs. L- forms

D-glucose

Occurs naturally

L-glucose:

Mirror image of D-glucose

Does not occur naturally in higher living

organisms

Not broken down to release energy

Synthesised in lab

Minor role in biological systems.

-D-glucose

-D-glucose

75-carbon ring structured sugar molecules

D-Ribose

A major component

of RNA (an important

nucleic acid)

De-oxyribose

A major component of

DNA (another

important nucleic

acid)

8Disaccharides

The condensation product of two monosaccharides

is a disaccharide.

In D-glucose ring, OH group on the #1 carbon (e.g. a

position) can condense with an H group on the #4

carbon of another sugar to eliminate a water

molecule and form -1,4-glycosidic bond:

Disaccharides

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Maltose:

-D-Glucose + -D-glucose

Sucrose:

-D-Glucose + -D-fructose

Lactose:

-D-glucose + -D-galactose

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Sucrose

Sucrose (table sugar)

is found in all

photosynthetic

plants. Among disaccharides, it is

the easiest to hydrolyse.

Major component in

artificial growth media.

Sucrose

Lactose is found in

milk and whey

Although relatively

rare, it is very a

important disaccharide.

Lactose

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Polysaccharides: Amylose

Continuous polymerisation of glucose can occur by

formation of new 1,4-glycosidic bonds.

Amylose is a straight-chain polymer of glucose

subunits

Molecular weight vary from thousands to 1.5 million

daltons.

Constitutes about 15-20% of starch (reserve food

in plants).

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Amylopectin Constitutes the bulk of starch (80-85%).

Also D-glucose polymer but larger than Amylose

Molecular weight up to 1-2 million daltons.

Soluble in water.

Distinguished by substantial amount of branching, that form when condensation

occurs between the glycosidic OH on one chain with the 6th carbon on another

glucose:

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Glycogen

Glucose reservoirs in animals.

Glycogen resembles amylopectin in that it is

highly branched

the degree of branching is greater

Glycogen molecular weight is above 5

million Da.

Glycogen serves as energy reserve in some

bacteria.

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Cellulose Major structural component in all plant cells from trees to algae (most

abundant compound on earth)

1,000,000,000,000 tonnes produced every year.

Long, unbranched chain of D-glucose subunits, but the bond is a -1,4glycosidic bond which few living creatures can hydrolyse.

MW: 50,000 and 1 million Da.

-1,4 glycosidic bond is resistant to enzymatic hydrolysis. (-1,4 glycosidic bondsin starch/glycogen are relatively easy to break by enzymatic or acid hydrolysis).

Efficient cellulose hydrolysis remains one of the most challenging problems in

attempts to convert cellulosic wastes into fuels or chemicals.

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However, the resistance to degradation derives more from the

crystalline structure.

This tight structure of cellulose comes from intrachain hydrogen

bonding, which occurs between the C-3 hydroxyl and the oxygen

in the pyranose ring and inter-chain hydrogen bonding.

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Structure of Cellulose

Several models for the crystalline structure: Highly ordered:

Chains are tightly packed that even water molecules barely penetrate.

Much more difficult to decompose.

Amorphous: Comprises typically about 15% of cellulose microstructure.

Easily hydrolysed by acids.

Hemicellulose:

Polysaccharides found in cellulosic materials surrounding clusters of microfibrils.

The whole structure is enclosed in cross-linked coating of lignin (polyphenolic material of irregular structure).