Secondary Metabolites

Question 1

Primary metabolites

Answer 1

Essential for plant growth and development:
Amino acids
Lipids
Carbohydrates
Nucleic acids

Question 2

Secondary metabolites

Answer 2

Derived from products or intermediates of the primary metabolism
Integral to communication of a plant with its environment

Question 3

How are secondary metabolites derived

Answer 3

Products or intermediates of photosynthesis, glycolysis and respiration

Question 4

Main primary metabolite from photosynthesis

Answer 4

3- phosphoglycerate

Question 5

Most common precursors

Answer 5

Erythrose-4-phosphate (Calvin cycle intermediate product)
3-phosphoglycerate (first step in Calvin cycle)
Phosphoenolpyruvate (Glycolysis intermediate product)
Pyruvate (product of glycolysis)
Acetyl-coenzyme A (Citric acid cycle intermediate)
Amino acids

Question 6

Classification of plant secondary metabolites

Answer 6

Terpenes
Phenolics
Nitrogen containing compounds

Question 7

Where are secondary metabolites usually stored

Answer 7

Central vacuoles

Question 8

Terpenes

Answer 8

Largest group, >40.000 known, insoluble in water.

Biosynthesis: from 5-C isoprene units
Mevalonic acid pathway (cytosol)
Methylerythritol phosphate (MEP) pathway (in chloroplasts and other plastids)

Question 9

Examples of terpenes

Answer 9

Monoterpenes
Sesquiterpenes
Diterpenes
…
Polyterpenes

Question 10

Example of phenolics

Answer 10

Lignin
Flavonoids
Tannins
Coumarin

Question 11

Examples of nitrogen containing compounds

Answer 11

Alkaloids
Cyanogenic glucosides
Glucosinolates

Question 12

How are terpenes grouped

Answer 12

By the number of isoprene subunits

Question 13

How many isoprene units does a polyprene have

Answer 13

> 20

Question 14

Essential oils

Answer 14

volatile monoterpenes, give characteristic odor to foliage: limonene, menthol, myrcene, pinene…
Insect repellent properties, accumulate in glandular hairs.

Question 15

Resins

Answer 15

contain mono- and diterpenes and are formed or stored in resin ducts.
With antibacterial activity.
Prevent fungi or bacteria for entering as forms a barrier when the plant is broken

Question 16

Bitter extracts

Answer 16

non-volatile, bitter taste substances. E.g. Azadirachtin, complex limonoid from the Neem tree (Azadirachta indica) used as insecticide. Deterrent to some insects at doses as low as 50 parts per billion!

Question 17

Phytoecdysteriods

Answer 17

triterpenoids, compounds that mimic hormones used by arthropods in the molting process.
More than 500 types.
When ingested, they impede the proper development in insects.

Question 18

Which pathways produce terpenes

Answer 18

Mevalonic acid pathway
MEP pathway

Question 19

Primary carbon metabolites that produce terpenes

Answer 19

3-phosphoglycerate
Pyruvate
Acetyl-CoA

Question 20

Why are secondary metabolites stored in vacuole

Answer 20

Often toxic so it controls their action

Question 21

What pathways produce phenolic compounds

Answer 21

Malonic acid pathway
Shikimic acid pathway
From aromatic amino acids

Question 22

Primary carbon metabolites that produce phenolic compounds

Answer 22

Acetyl-CoA
Erythrose-4-phosphate
Phosphoenolpyruvate

Question 23

Phenolic compounds

Answer 23

Aromatic substances. Nearly 10.000 compounds. Some only soluble in organic solvents, some soluble in water, some insoluble.

Biosynthesis: most derived from phenylalanine
Shikimic acid pathway: most plant phenolics
Malonic acid pathway: less important in plants but important in fungi and bacteria

Question 24

Lignin

Answer 24

most abundant organic compound in plants after cellulose. Found in cell walls, give mechanical rigidity.
Physical toughness deters feeding animals, chemical durability makes it relatively indigestible to herbivores.

Question 25

Flavonoids

Answer 25

pigmentation and defense Anthocyanins: pigments responsible for red, pink, purple, blue colors in flowers and fruits. Attract animals for pollination and seed dispersal. Water soluble, stored in vacuoles. Flavones and flavonols: absorb UV-B light. Form nectar guides in flowers. In leaves, protects cells from excessive UV-B radiation. Excreted to soil by legume roots, mediate interactions with N-fixing bacteria.

Question 26

Flavones and flavonols

Answer 26

absorb UV-B light. Form nectar guides in flowers. In leaves, protects cells from excessive UV-B radiation. Excreted to soil by legume roots, mediate interactions with N-fixing bacteria.

Question 27

Anthocyanins

Answer 27

pigments responsible for red, pink, purple, blue colors in flowers and fruits. Attract animals for pollination and seed dispersal. Water soluble, stored in vacuoles.

Question 28

Tannins

Answer 28

large molecules composed of polymerised flavonoids. Toxins, reduce growth and survival of many herbivores. Feeding deterrents in many animals including mammals. Also defense against microorganisms. They bind on salivary proteins.

Question 29

Nitrogen containing compounds

Answer 29

Synthesised from aromatic and aliphatic amino acids: Alkaloids: from lysine, tyrosine, and tryptophan. Cyanogenic glycosides: from leucine, isoleucine, phenylalanine, tyrosine, valine. Glucosinolates or mustard oil glycosides: from alanine, leucine, methyonine, isoleucine, phenylalanine, trypthofan, tyrosine, valine).

Question 30

Alkaloids

Answer 30

<20.000 compounds, in 20% species of vascular plants. Water soluble. Defense against predators, especially mammals. At lower doses, useful pharmacologically. Many interfere with the nervous system (especially chemical transmitters), other affect membrane transport, protein synthesis or enzymatic activities. Some alkaloids produced by fungal endophytes present in plants! They increase in response to initial herbivore damage.

Question 31

Cyanogenic glycosides

Answer 31

Structurally, a sugar group bonded to another group by a glycosidic bond ~60 compounds, probably synthesised by most plants, but usually metabolised and not accumulated. However, 11% of all plants have appreciable amounts: They liberate hydrogen cyanide (HCN) when hydrolised.

Question 32

Glucosinolates or mustard oil glycosides

Answer 32

Contain sulfur as well as nitrogen. The side group (R) varies: ~150 compounds, found mainly in Brassicales: stored separately in the intact plant. Brought in contact when the plant is crushed, hydrolysis is facilitated by myrosinase, which is stored in localised scattered cells only: Unpalatable and toxic to many generalists feeders (mammals, birds, mollusks, nematodes, insects) and to several specialists feeders living on non-cruciferous plants Certain parasitoids use glucosinolates that are released by feeding herbivores to detect their host

Question 34

Examples of alkaloids

Answer 34

Morphine Caffeine Cocaine Nicotine