By Athene Donald Biological Molecules Sugars, polysaccharides, lipids and fats.

by Athene Donald

Biological Molecules

Sugars, polysaccharides, lipids and fats

Slide 1: Carbohydrates and lipids each represent an enormous family of molecules with some common characteristics. However, small and subtle differences in the placement of an additional group can make a vast difference to their biological properties. (Copyright Athene Donald.)

3a (left) Linear form and Fischer projection in which the two side groups at C1 are reversed. 2b (above) Haworth projection showing the two isomers of D-glucopyranose.

Slide 2: Basic carbohydrate structure. (From Coultate T.P. 1999 Food: the Chemistry of its Components, 2nd edn, Springer, reproduced by permission of the Royal Society of Chemistry.)

lactose

sucrose

Slide 3: Disaccharides. (From Coultate T.P. 1999 Food: the Chemistry of its Components, 2nd edn, Springer, reproduced by permission of the Royal Society of Chemistry.)

Slide 4: Polysaccharides. (From Coultate T.P. 1999 Food: the Chemistry of its Components, 2nd edn, Springer, reproduced by permission of the Royal Society of Chemistry.)

Slide 5: Cellulose and starch.

The helical packing through the wall thickness leads to arcs being seen in cross-sectional images (e.g. in the transmission electron microscopy).

Slide 6: Helical packing in the plant cell wall. (From Neville, A.C.1993 Biology of Fibrous Composites Cambridge University Press, reproduced by permission of Cambridge University Press.)

• C6H12O6 + 6O2 6CO2 +6H2O aerobic conditions

G = –2881 kJ/mol

• Anaerobic respiration (respiration when oxygen supply is limited) proceeds via glycolysis, in which glucose is broken down to pyruvate in a series of stages involving ATP (discussed elsewhere).  

• In plants, the end-product in this process of anaerobic respiration is alcohol, while in many animal cells and bacteria the end-product is lactate.

Slide 7: Glucose metabolism.

• This is a hierarchical model.• One can see how different architectures and compositions of the constituent

molecules may affect the details of the packing.• The amylopectin molecules are aligned radially.

Slide 8: Model for the starch granule.

Schematic of the structure of the collagen triple helix.

Crosslink formation betweencollagen chains. Crosslinking increases with age, causing skin to lose elasticity, for instance.

Slide 9: Collagen. (Left-hand image from Ross-Murphy S.B. (ed) 1994 Physical Techniques for the Study of Food Biopolymers, chapter 3 Blackie Academic, Alan Clarke Figure 23, reproduced with permission of Springer Science + Business Media B.V. Right-hand image from Coultate T.P. 1999 Food: the Chemistry of its Components, 2nd edn, Springer, Figure 5.11 reproduced by permission of the Royal Society of Chemistry.)

Slide 10: Structures of fats and lipids.

SATURATED

Lauric CH3(CH2)10COOH

Palmitic CH3(CH2)14COOH

Stearic CH3(CH2)16COOH

UNSATURATED

Oleic  CH3(CH2)7CH=CH(CH2)7COOH

Linoleic CH3(CH2)4(CH=CHCH2)2(CH2)6COOH

Linolenic  CH3CH2(CH=CHCH2)3(CH2)6COOH

Arachidonic  CH3(CH2)4(CH=CHCH2)4(CH2)2COOH

Slide 11: Examples of fatty acids.

Triglycerides are formed by the addition of three fatty acid chains to glycerol.

Slide 12: Triglycerides.

The fatty acid chains can be wholly saturated or can contain some unsaturated chains, thereby introducing kinks into the tails.