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Questions and Answers
What is the role of chalcone synthase (CHS) in this biochemical pathway?
What is the role of chalcone synthase (CHS) in this biochemical pathway?
Which enzyme is responsible for isomerizing chalcone into flavanone?
Which enzyme is responsible for isomerizing chalcone into flavanone?
What is the initial substrate for the formation of chalcone?
What is the initial substrate for the formation of chalcone?
What is the outcome of the pathway after the formation of flavanone?
What is the outcome of the pathway after the formation of flavanone?
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Which of the following statements is true regarding the acetate-malonate pathway?
Which of the following statements is true regarding the acetate-malonate pathway?
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What structure characterizes flavanones?
What structure characterizes flavanones?
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Which of the following is a common example of a flavanone?
Which of the following is a common example of a flavanone?
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What color do anthocyanins primarily impart to fruits and vegetables?
What color do anthocyanins primarily impart to fruits and vegetables?
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Which fruits are particularly high in anthocyanin content?
Which fruits are particularly high in anthocyanin content?
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What are anthocyanidins known as in relation to anthocyanins?
What are anthocyanidins known as in relation to anthocyanins?
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Which vegetable type is likely to contain high levels of anthocyanins?
Which vegetable type is likely to contain high levels of anthocyanins?
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Flavanones are predominantly found in which type of fruit?
Flavanones are predominantly found in which type of fruit?
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Which of the following is not a type of flavonoid mentioned?
Which of the following is not a type of flavonoid mentioned?
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What is the main structural characteristic of flavonoids?
What is the main structural characteristic of flavonoids?
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Which of the following flavonoids is considered a flavonol?
Which of the following flavonoids is considered a flavonol?
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How do isoflavonoids primarily affect the body?
How do isoflavonoids primarily affect the body?
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What is a common plant source for isoflavonoids?
What is a common plant source for isoflavonoids?
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Which of the following does NOT accurately describe flavones?
Which of the following does NOT accurately describe flavones?
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Which is a precursor to anthocyanidin?
Which is a precursor to anthocyanidin?
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Which flavonoid is primarily recognized for having strong antioxidant properties?
Which flavonoid is primarily recognized for having strong antioxidant properties?
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What is the primary function of flavonoids in plants?
What is the primary function of flavonoids in plants?
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What is the chemical structure of catechin?
What is the chemical structure of catechin?
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Which molecules contain chiral centers in their structure?
Which molecules contain chiral centers in their structure?
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What differentiates biflavonoids from other types of flavonoids?
What differentiates biflavonoids from other types of flavonoids?
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Which statement about anthocyanidins is correct?
Which statement about anthocyanidins is correct?
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Which statement accurately describes leucoanthocyanidins?
Which statement accurately describes leucoanthocyanidins?
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What type of configuration do (+)-catechin and (-)-epicatechin represent?
What type of configuration do (+)-catechin and (-)-epicatechin represent?
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Which gene is associated with the synthesis of anthocyanidins?
Which gene is associated with the synthesis of anthocyanidins?
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How are biflavonoids categorized within the flavonoids?
How are biflavonoids categorized within the flavonoids?
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What factors influence the stability of anthocyanins?
What factors influence the stability of anthocyanins?
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Which anthocyanidin is known for producing an orange to red color?
Which anthocyanidin is known for producing an orange to red color?
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How does the presence of hydroxy groups affect anthocyanidin color?
How does the presence of hydroxy groups affect anthocyanidin color?
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What effect do hydroxyl or methoxyl groups have on anthocyanidin stability?
What effect do hydroxyl or methoxyl groups have on anthocyanidin stability?
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Which anthocyanidin produces colors ranging from red to magenta?
Which anthocyanidin produces colors ranging from red to magenta?
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What external environmental factors can degrade anthocyanins?
What external environmental factors can degrade anthocyanins?
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Which of the following statements is true regarding copigments and anthocyanin stability?
Which of the following statements is true regarding copigments and anthocyanin stability?
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What is the role of metal ions in the context of anthocyanin stability?
What is the role of metal ions in the context of anthocyanin stability?
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Which structural component of anthocyanidins is mentioned as influencing their stability?
Which structural component of anthocyanidins is mentioned as influencing their stability?
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What color range is associated with delphinidin?
What color range is associated with delphinidin?
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What is the chemical structure that forms the backbone of flavonoids?
What is the chemical structure that forms the backbone of flavonoids?
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Which sugars are commonly involved in the formation of flavonoid glycosides?
Which sugars are commonly involved in the formation of flavonoid glycosides?
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How are flavonoids classified based on their chemical structure?
How are flavonoids classified based on their chemical structure?
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What is the role of glycosidic linkages in flavonoids?
What is the role of glycosidic linkages in flavonoids?
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Which pathway is involved in the initial biosynthesis of most flavonoids?
Which pathway is involved in the initial biosynthesis of most flavonoids?
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What component is commonly found in the structure of flavonoids?
What component is commonly found in the structure of flavonoids?
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Which statement describes flavonoid aglycones?
Which statement describes flavonoid aglycones?
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In which position can glycosidic linkages be formed in flavonoids?
In which position can glycosidic linkages be formed in flavonoids?
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Which subclass of flavonoids is NOT mentioned in the classification?
Which subclass of flavonoids is NOT mentioned in the classification?
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What structure does an aglycone typically consist of?
What structure does an aglycone typically consist of?
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Study Notes
Flavonoids (Part 1)
- Flavonoids are a group of polyphenolic compounds found in fruits, flowers, seeds, and vegetables.
- They are classified as plant secondary metabolites.
- The name "flavonoid" derives from the Latin word "flavus," meaning yellow, referencing their color in nature.
- Flavonoids are abundant in specific plant families, including Polygonaceae, Rutaceae, Leguminosae, Umbelliferae, and Compositae.
- Flavonoids have a limited role in plant defense mechanisms due to low toxicity compared to other plant secondary metabolites.
- They are pigments in flowers and attract pollinating insects.
- They participate in plant growth control by influencing enzyme activity (inhibiting and activating).
- Flavonoids consist of 15 carbon atoms, with two benzene rings connected by a three-carbon chain (C6-C3-C6 system).
- The C3 can connect the two benzene rings via a furan ring (e.g., aurones) or a pyran ring to form flavonoids, the largest group within this class.
- Flavonoids are often found in aglycone form, glycosides, and methylated derivatives.
- Glycosides are combinations of aglycones (non-sugar part) and glycones (sugar part).
- Common glycosidic linkages occur on carbons 3 and 7 (e.g., D-glucose, L-rhamnose, galactose, and arabinose).
- Flavonoids are divided into six subclasses based on their chemical structures: flavones, isoflavones, flavanones, flavonols, flavan-3-ols, and anthocyanins.
- Flavonoids are frequently conjugated with either an acid or a sugar molecule to form glycosides.
Flavonoid Biosynthesis
- The core synthesis step involves p-coumaroyl-CoA condensation with three molecules of malonyl-CoA to form chalcone.
- Chalcone synthase is the enzyme responsible for this reaction.
- Chalcone is converted to flavanone by the enzyme chalcone flavanone isomerase (CHI).
- The biosynthesis pathway branches into various flavonoid classes.
Chalcones and Dihydrochalcones
- Chalcones act as precursors for all flavonoids.
- Chalcones comprise two aromatic rings linked by a three-carbon chain, forming an α, β-unsaturated carbonyl system.
- The structure of a chalcone is linear or nearly planar.
- Dihydrochalcones are structural precursors to chalcones.
Flavanones and Flavonols
- Flavanones are the first flavonoid products of the flavonoid biosynthetic pathway.
- Flavanones are predominantly found in citrus fruits.
- The structure of flavanones features a 2,3-dihydro-2-phenylchromen-4-one skeleton, with a non-planar pyran ring.
- Examples of flavanones include hesperidin, naringenin, isosakuratenin, and heridictyol.
- Flavonols have a structure similar to that of flavanones, with an additional hydroxyl group.
Anthocyanidins/Anthocyanins
- Anthocyanins are water-soluble pigments that provide red, purple, and blue colors to fruits and vegetables, arising from the phenolic group.
- Common sources of anthocyanins include berries, currants, grapes, and some tropical fruits.
- Anthocyanins are glycosylated pigments with a structural diversity arising from different substituents (R1 and R2).
- Anthocyanin stability depends on pigment types, copigments, light, temperature, pH, metal ions, enzymes, and antioxidants.
- More hydroxyl groups in the B ring of anthocyanins result in bluer colors.
Flavones and Flavonols
- Flavones and flavonols are typically colorless or yellow pigments found in the outer and aerial portions of plants (like leaves and skin).
- These pigments act as co-pigments.
- Apigenin, luteolin, kaempferol, quercetin, and myricetin are some examples of flavonoids in this category.
- These Flavonoids and flavonols contain a 2-phenyl-γ-benzopyrone and a 3-hydroxy-2-phenyl-γ-benzopyrone structure, respectively.
Isoflavonoids
- Isoflavonoids are a class of flavonoid compounds with a 3-phenylchroman backbone.
- Isoflavonoids are phytoestrogens, commonly found in legumes.
- Isoflavonoids and their derivatives are sometimes referred to as phytoestrogens due to their estrogenic activity, which often occurs through the estrogen receptor pathway.
Proanthocyanidins
- Leucoanthocyanidins are the flavan-3,4-diol derivatives preceding anthocyanidins through acid hydrolysis.
- The name "proanthocyanidins" stems from their transformation into anthocyanidins (colored pigments) during acid hydrolysis.
- Proanthocyanidins are often found in edible plants such as berries, roots, tubers, and leafy vegetables.
- Proanthocyanidins are formed from the polymerization of leucoanthocyanidins.
Catechins
- Catechins are polyhydroxy flavan-3-ol structures, part of the wider flavonoid family.
- Catechins feature two chiral centers (carbons 2 and 3).
- Catechin isomers exist either as trans or cis configurations (catechin or epicatechin, respectively)
- These isomers differ by the positioning of hydroxyl groups.
Biflavonoids
- Biflavonoids are composed of two mono-flavonoid molecules joined by covalent bonds (C-C or C-O-C).
- These bonds connect the two mono-flavonoid parts in the biflavonoid molecule.
Tests for Flavonoids
- Shinoda test (sensitive to flavonoids containing the γ-benzopyrone nucleus, flavones, flavanones, and dihydroflavonols) and involve a specific set of reactants (ethanol, Mg or Zn dust, and HCl).
- Pew test is similar to the Shinoda test, but instead of Mg, Zn dust is used.
- Lead acetate test (sensitive to all flavonoids), producing yellow colored precipitation.
- Anthocyanins test determines the presence of anthocyanins using an ethanol extract of petals to observe color changes in acid (HCl) or alkaline (NH4OH) solutions.
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Description
Explore the fascinating world of flavonoids, a group of polyphenolic compounds crucial for plant characteristics and interactions. This quiz covers their classification, structure, and roles in plant defense and pollination. Dive into the science behind these colorful compounds and their significance in nature.
