Important Geochemical organic compounds

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Carbohydrates consist of Cn(H20)n. They are organic compounds with C, N and H.

Monosaccharides = single chained sugars

Disaccharides = double chained sugars

Polysaccharides = >10 monosaccharides e.g. cellulose & starch

Longer chained carbohydrates form through condensation reactions.

Cellulose has an important structural function in that it can form cross linkages to add stability to plant cell walls. It can also be broken down into pyruvic acid which enters the krebs cycle.

Cellulose is more stable than starch and it is less easily broken down.

Cellulose is a homogenous polysaccharide in that it is formed from identical monosaccharides.

Amino acids are the basic building blocks of proteins and consist of an amine (NH2) and a carboxylic (COOH) group.

Depending on whether the number of carboxylic groups is equal, less or more than the amine groups determines whether the amino acid is acidic, basic or neutral.

Proteins are formed from condensation reactions of amino acids to form polypeptides (where the functional group is an amide) This is called peptide linkage.

The shape of a protein is governed by it's primary amino acid structure.

Proteins can provide structural roles within organisms - e.g. collagen fibrous proteins or globular proteins such as enzymes.

Organic compounds that are only soluable in organic solvents (e.g. chloroform)

There are many types of lipids including: phospholipids, fatty acids, waxes, trigylcerides etc.

Chlorophyll is a lipid - can be preserved in the rock record (biomarker).

Triglycerides are formed by an esterification reaction of a glycerol alcohol (-OH) with 3 fatty acids (-COOH) This is a dehydration reaction (as water is released) The bond which is formed is -O-. Triglycerides are an efficient form of energy storage. The process of esterification can happen in natural waters.

Phospholipids: important in cell membranes

Fatty acids: Hydrocarbons with a -COOH group. Fatty acids thought to be important in the production of hydrocarbons

Lipids degrade into fulvic acids (humic substances) and then undergo esterification to humic acids.

Lignins and Tannins can be referred to as hydroxy-aromatics. They are found in higher plants but not in aquatic environments.

Lignins surround cellulose in higher order plants to provide structural support. Lignin forms a network around cellulose fibres in the developing xylem.

Lignin is a rigid polyphenol - it is very rigid, stable and refractory - i.e. it is fairly resistant to bacteria decomposition.

2nd most abundant organic compounds in plants (after cellulose).

Tannins are found in wood to make it less palatable to herbivores.

Fungi are important in the decomposition of Lignins.

As most P.P in marine environments is by algae, lignin is a much less important contributer to organic matter in marine environments.

Carbohydrates

Proteins

Lipids

Lignins & tannins