Topic 9 - The role of secondary metabolites; major carbohydrate and phenoloid compounds

Question 1

Primary metabolites

Answer 1

Synthesized directly from inorganic compounds (simple sugars, amino acids etc.)

General plant metabolites (CH, proteins, fatty acids)

Essential compounds for life processes and growth

Question 2

Secondary metabolites

Answer 2

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

Question 3

Universal plant metabolism

Answer 3

Photosynthesis

Respiration

Protein and nucleic acid synthesis (primary and secondary metabolites)

Question 4

Specific plant metabolism

Answer 4

Taxon specific series of metabolic processes with specific enzymes (secondary metabolites)

Question 5

Major groups of secondary metabolites

Answer 5

Saccharides
Phenoloids
Polyketides
Terpenoids
Azotoids

Question 6

Role of secondary metabolites in plants

Answer 6

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)

Question 7

Saccharides

Answer 7

= carbohydrates

Monosaccharides
Oligosaccharides
Polysaccharides

Sweet taste, water soluble

Question 8

Disaccharides

Answer 8

Oligosaccharide

Two joined monosaccharides

Dietery energy source

Question 9

Oligosaccharides (3-9)

Answer 9

Consists of different monosaccharide units

Storage and transport carbohydrates

components of fibre

Question 10

Non digestible oligosaccharides

Answer 10

Raffinose, stachyose and verbascose

Mainly in fabaceous plants as stored nutrients

Question 11

Homopolysaccharides

Answer 11

Starch - storage
Cellulose - structural
Insulin - storage

Question 12

Heteropolysaccharides

Answer 12

Mucilage - storage
Gums - Storage
Pectins - structural

Question 13

Non-starch polysaccharides

Answer 13

NSP

Major structural elelments in the cell wall (cellulose, hemicellulose, pectin)
- Mainly in forage legumes

Beta-glucans and arabinoxylans (dietary fibers)

Question 14

Glycosides

Answer 14

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

Question 15

Groups

Answer 15

Based on aglycon part

azotoids → cyanogenic glycosides, glucsinolates
Terpenoids → cardiac glycosides, saponins
Phenoloids → Rutin (rutoside)

Question 16

Phenoloids

Answer 16

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

Question 17

Shikimic acid pathway

Answer 17

Tannis
Flavonoids → tannins
Quinones
Cinnamic acid derivatives
- Quinones
- Lignoids
- Coumarines
- Phenolic glycosides

Question 18

Lignoids

Answer 18

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

Question 19

Coumarines

Answer 19

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

Question 20

Phenolic glycosides

Answer 20

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)

Question 21

Quinones

Answer 21

Natural occurrence in species of rosaceae and Ericaceae families

Napthoquinones, hydroquinones

Staining compounds

Urinary antiseptic effect (arbutin)

Some quinones are produced via polyketide pathway

Question 22

Flavonoids

Answer 22

Phenoloid and polyketide pathways

Universal plant pigments

~6000 different molecules

Subdivided into groups due to position of phenyl ring

Question 23

Flavonoid groups

Answer 23

Isoflavonoids
Neoflavonoids
True flavonoids

Question 24

True flavonoids

Answer 24

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

Question 25

Biological effects of (iso) flavonoids

Answer 25

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

Question 26

Biflavonoids

Answer 26

Some bioflavonoids are used as a treatment for memory disorders
o Improve cognitive functions and decrease side effects (anxiety, dizziness, tinnitus, memory loss)

Question 27

Tannins

Answer 27

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)

Question 28

Biological effect of tannins

Answer 28

Precipitate proteins water insoluble complexes

Antinutritive and poisonous effect

Tretment of diarrhea