Bio 254 Phenolic Compounds

What is a phenolic compound?

A plant compound containing at least one phenol group (benzene ring + hydroxyl group).

What is a phenol group?

A benzene ring (C6H6) with an attached hydroxyl group (OH).

What is the structure of phenol?

C6H5OH.

What is a phenyl group?

C6H5- attached to another molecule.

What is a benzyl group?

C6H5CH2- attached to another molecule.

Why do plants produce phenolic compounds?

Defense, mechanical support, UV protection, attraction of pollinators, attraction of fruit dispersers, allelopathy.

List major functions of phenolic compounds.

Defense, mechanical strength, UV absorption, pigmentation, signaling, allelopathy.

What pathway synthesizes most phenolics?

The shikimic acid pathway.

What does the shikimic acid pathway produce?

Aromatic amino acids: phenylalanine, tyrosine, tryptophan.

What enzyme converts phenylalanine to cinnamic acid?

PAL (Phenylalanine Ammonia Lyase).

Why is PAL important?

It is a key branch-point enzyme between primary and secondary metabolism.

Which pathways contribute to flavonoid synthesis?

Shikimic acid pathway and malonic acid pathway.

What is the basic flavonoid skeleton?

C6-C3-C6 (two benzene rings joined by a 3-carbon bridge).

What are the major classes of flavonoids?

Anthocyanins, flavones, flavonols, isoflavonoids, tannins.

What are anthocyanins?

Pigmented flavonoids producing red, purple, pink, and blue colors in flowers and fruits.

Where are anthocyanins stored?

In the vacuole.

What affects anthocyanin color?

Ring B substituents, pH, and aromatic acids esterified to the structure.

What is an anthocyanidin?

An anthocyanin without a sugar.

Functions of anthocyanins.

Pigmentation, attraction of pollinators and fruit dispersers, antioxidant properties.

What are flavones and flavonols?

UV-absorbing flavonoids found in leaves, flowers, and stems.

Functions of flavones/flavonols.

UV-B protection, nectar guides for insects, regulation of auxin transport, symbiosis with rhizobacteria.

How do flavonols protect against UV-B?

Absorb UV-B light and accumulate in upper epidermal layers.

What happens when plants lack chalcone synthase?

They cannot produce flavonoids and become highly sensitive to UV-B.

What are isoflavonoids?

Flavonoids with the B ring moved to a different position on the C3 bridge.

Where are isoflavonoids mostly found?

Legumes.

Functions of isoflavonoids.

Insecticides, pesticides, fish poisons, phytoestrogens, phytoalexins.

What are phytoestrogens?

Plant isoflavonoids (e.g., genistein, daidzein) that mimic estrogen.

How do phytoestrogens function in humans?

Bind estrogen receptors; may affect menopausal symptoms, cancer risk, cardiovascular health, and bone density.

What are tannins?

Phenolic compounds that bind and precipitate proteins.

List the two types of tannins.

Condensed tannins and hydrolyzable tannins.

What are condensed tannins?

Polymers of flavonoid units; hydrolyze into anthocyanidins.

What are hydrolyzable tannins?

Smaller, easily hydrolyzed phenolic polymers containing gallic acid and sugars.

Major functions of tannins.

Herbivore deterrence, reduced food quality, antimicrobial actions, astringent taste, leather tanning.

Why do tannins deter herbivores?

They bind dietary proteins and reduce nutrient absorption.

How do some herbivores tolerate tannins?

They produce salivary proteins rich in proline that bind tannins.

What is allelopathy?

Chemical inhibition of neighboring plants by phenolics.

Example of allelopathic phenolic.

Juglone from walnut trees.

Examples of simple phenolics.

Caffeic acid, ferulic acid, umbelliferone, vanillin, salicylic acid.

Role of salicylic acid in plants.

Plant hormone involved in pathogen defense (systemic acquired resistance).

Functions of phenolic fruit pigments.

Attract fruit dispersers.

Functions of phenolic flower pigments.

Attract pollinators through visible and UV patterns.

What are UV nectar guides?

Flavonoid-based patterns visible to insects but not humans that guide pollinators to nectar.

What are lignans?

Phenolic dimers with defensive and structural roles.

What are lignins?

Large phenolic polymers providing mechanical support in wood and cell walls.

What do phenolics do in plant-microbe interactions?

Mediate root symbiosis with nitrogen-fixing bacteria.

What types of stress increase phenolic production?

UV-B exposure, pathogen attack, herbivory, drought, and oxidative stress.