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Phytochemistry intro

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Robyn James

on 26 July 2013

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Transcript of Phytochemistry intro

To deter herbivory by animals or insects

What are secondary metabolites?
Plant roles of secondary metabolites
To seal wounds
Plant roles
of secondary metabolites…
Biosynthetic pathways
The evolution of secondary metabolic pathways
Phytochemistry - Overview
Secondary Metabolites - An Overview
Monoterpenes – taste bitter
Diterpenes – taste bitter, irritant
Triterpenes – specialised toxins such as the cardenolide heart toxins
Lignins and tannins – decrease palatability
Cyanogenics – release cyanide after herbivory
Saponins – reduce fertility of herbivores
Antimicrobial and antifungal agents

Resins – analogous to a scab. They also usually contain antiseptic elements
Isoflavonoids, sesquiterpenes

Inhibit the growth of surrounding plants
Some phenylpropanoids, naphthoquinones
Plant roles
of secondary metabolites
Attractants for pollinators or seed-dispersers
Anthocyanins – provide colour that attracts pollinating insects
Flavones and flavonols provide nectar guides for bees

Each line represents an enzyme, with the end product being a secondary metabolite.

The different pathways
Biosynthetic pathways
are the assembly lines by which secondary metabolites are produced.
These compounds are produced by coupling acetate units.
The main groups produced are:
fatty acids (mostly primary metabolites not secondary)
acetylenic compounds
waxes and hydrocarbons
Some naphthoquinones and anthraquinones

This pathway produces phenolic compounds.
It starts with conversion of shikimic acid into phenylalanine and tyrosine (amino acids). Phenylalanine is then further converted into a range of compounds including:

Simple phenols and phenolic acids
Some anthraquinones, naphthoquinones
Flavanoids, tannins and anthocyanadins
Alkaloids form a large amorphous group with many subgroups. They are defined by the facts that they:
are typically (but not always) basic,
contain one or more nitrogen atoms
(usually in a heterocyclic ring ie, a closed ring of atoms of which at least one is not a carbon atom)
usually have a marked pharmacological action on man or other animals.
This pathway, also known as the mevalonic acid pathway or the isoprenoid pathway, produces terpenoids.These are also known as isoprenoids, isoprenes and terpenes.

Structure: Terpenoids are based on the building block IPP (isopentenyl pyrophosphate), a five-carbon isopene unit.
These basic units are assembled and modified in thousands of different ways to form structures consisting of multiples of C5H8 units.

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