Topic 9 - The role of secondary metabolites; major carbohydrate and phenoloid compounds Flashcards
Primary metabolites
Synthesized directly from inorganic compounds (simple sugars, amino acids etc.)
General plant metabolites (CH, proteins, fatty acids)
Essential compounds for life processes and growth
Secondary metabolites
Non-general compounds, with small proportions in the cells (volatile oils, alkaloids…)
Derived from primary metabolites
Non-essential elements for life processes
Do not take a part of metabolism and energy flow
Their major role is in the interspecific interactions
Produces in specific cells, stored in vacuoles and intercellular cavities
Taxon specific
Universal plant metabolism
Photosynthesis
Respiration
Protein and nucleic acid synthesis (primary and secondary metabolites)
Specific plant metabolism
Taxon specific series of metabolic processes with specific enzymes (secondary metabolites)
Major groups of secondary metabolites
Saccharides Phenoloids Polyketides Terpenoids Azotoids
Role of secondary metabolites in plants
Regulation of growth - plant hormones
Allelopathic compounds - regulating growth of other species
Pollinator attractants - support fertilisation or to catch insects
Insecticides - pyrethroids against lice and fleas
Insect repellents
Defense mechanism against herbivores
Antimicrobial and anti fungal effect (inhibition of growth and reproduction)
Saccharides
= carbohydrates
Monosaccharides
Oligosaccharides
Polysaccharides
Sweet taste, water soluble
Disaccharides
Oligosaccharide
Two joined monosaccharides
Dietery energy source
Oligosaccharides (3-9)
Consists of different monosaccharide units
Storage and transport carbohydrates
components of fibre
Non digestible oligosaccharides
Raffinose, stachyose and verbascose
Mainly in fabaceous plants as stored nutrients
Homopolysaccharides
Starch - storage
Cellulose - structural
Insulin - storage
Heteropolysaccharides
Mucilage - storage
Gums - Storage
Pectins - structural
Non-starch polysaccharides
NSP
Major structural elelments in the cell wall (cellulose, hemicellulose, pectin)
- Mainly in forage legumes
Beta-glucans and arabinoxylans (dietary fibers)
Glycosides
Not a single biosynthetic group
A sugar bound to another functional group via a glycosidic bond
Carbohydrate, nitrogen, and fatty acid metabolic pathways are linked in their biosynthesis
Groups
Based on aglycon part
azotoids → cyanogenic glycosides, glucsinolates
Terpenoids → cardiac glycosides, saponins
Phenoloids → Rutin (rutoside)
Phenoloids
Consist of one or more aromatic rings and a -OH group
Phenoloids biosynthesised mainly from shikimic acid or cinnamic acid
Phenolic compounds are general in many plant taxa
Shikimic acid pathway
Tannis Flavonoids → tannins Quinones Cinnamic acid derivatives - Quinones - Lignoids - Coumarines - Phenolic glycosides
Lignoids
Consists of phenylpropane units
Lignins: polymer molecules of the secondary cell wall
o Degraded only by certain microbes and fungi
Lignans: dimer molecules
Anti-inflammatory and anti-oxydant and estrogen-like
Coumarines
Derived from phenylpropane
Occurs only in members of a few families
o E.g. Apiaceae, Rutaceae, Asteraceae, Fabaceae
Hydroxy coumarins and coumarin dimers (dicoumarol) anticoagulant effect
Furanocoumarine photosensitization, fish venoms
Phenolic glycosides
Widely distributed in nature
The aglycone portion is a phenolic compound with alcoholic or aldehyde groups
Aglycons act as flavours but medicinal effect also possible (salicylic acid can treat warts and a precursor of acetylsalicylic acid)
Quinones
Natural occurrence in species of rosaceae and Ericaceae families
Napthoquinones, hydroquinones
Staining compounds
Urinary antiseptic effect (arbutin)
Some quinones are produced via polyketide pathway
Flavonoids
Phenoloid and polyketide pathways
Universal plant pigments
~6000 different molecules
Subdivided into groups due to position of phenyl ring
Flavonoid groups
Isoflavonoids
Neoflavonoids
True flavonoids
True flavonoids
o Flavones → apigenin – chamomille
o Flavonols → quercetin – lovage
o Flavanones → naringin – grapefruit
o Flavanonols → aromadedrin – Siberian pine
o Flavanols → Catechin – tea
o Anthocyanidins → myrtillin – blueberry
Biological effects of (iso) flavonoids
Activation of cytochrome-P450 enzymes
Antioxidants effect – neutralize free radicals decreasing toxic effect
Immunostimulant effect – exact mechanism is not known
Membrane interaction: some compounds can inhibit histamine release
Reduce risk of atherosclerosis
Anti-inflammatory agents
Used in prevention of cardiovascular deaseases
Isoflavonoids are phyteoestrogens with insecticide activity
In anti-snake venom plants, but they are not frequent
Biflavonoids
Some bioflavonoids are used as a treatment for memory disorders
o Improve cognitive functions and decrease side effects (anxiety, dizziness, tinnitus, memory loss)
Tannins
Tannins are widely distributed in the plant kingdom
Dicot families rich in tannins
o Rosaceae, Fabaceae, Geraniaceae
Tannin containing pants
o Quercus spp., Betula spp., Pinus spp.
Hydrolyzable tannins (Hts) o A glucose with phenolic groups (gallic acid) – low amount in plants
Condensed tannins (proanthocyanidins (Pas)): o Oligomers or polymers of flavonoid units (e.g. catechin)
Biological effect of tannins
Precipitate proteins water insoluble complexes
Antinutritive and poisonous effect
Tretment of diarrhea
