Secondary metabolites MCQ Quiz in తెలుగు - Objective Question with Answer for Secondary metabolites - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

The correct answer is A, C and D

Explanation:

Statement A: They protect plants against being eaten by herbivores and against being infected by microbial pathogens.
Secondary metabolites serve various ecological functions, primarily defense mechanisms in plants. They help protect plants from herbivores, insects, and microbial pathogens through different strategies. For example:

• Alkaloids like nicotine and morphine can be toxic or deterrent to herbivores.
• Phenolic compounds like tannins can inhibit microbial infection and deter herbivores.
• Terpenes like pyrethroids have insecticidal properties. These compounds often have bitter tastes, toxic properties, or antimicrobial activities that reduce the likelihood of herbivory and infection.

Statement B: Terpenes, the largest class of secondary metabolites, are synthesized by the methylerythritol phosphate (MEP) pathway and shikimic acid pathway.
Terpenes are the largest class of secondary metabolites, are synthesized by two main pathways:

• Methylerythritol phosphate (MEP) pathway: Operates in the plastids and is responsible for the biosynthesis of monoterpenes, diterpenes, and certain other terpenoids.
• Mevalonate (MVA) pathway: Occurs in the cytosol and is responsible for the biosynthesis of sesquiterpenes, sterols, and other terpenoids.

The shikimic acid pathway is not involved in terpene biosynthesis. Rather, it is used for the production of aromatic amino acids (like phenylalanine, tyrosine, and tryptophan) and many phenolic compounds.

Statement C: The most abundant classes of phenolic compounds in plants are derived from phenylalanine.
Phenolic compounds, such as flavonoids, tannins, lignans, and lignin, are derived from phenylalanine. This amino acid undergoes deamination by the enzyme phenylalanine ammonia-lyase (PAL) to form cinnamic acid and subsequent phenylpropanoids. These phenylpropanoids serve as precursors for a wide variety of phenolic compounds, making phenylalanine a key building block in their biosynthesis.

Statement D: Alkaloids are nitrogen-containing secondary metabolites in plants.
Alkaloids are a diverse group of naturally occurring organic compounds that contain nitrogen atoms. They are known for their wide range of pharmacological effects on animals and humans. Examples include:

• Morphine and codeine (isolated from the opium poppy)
• Caffeine (found in coffee, tea, and other plants)
• Nicotine (from tobacco plants)
• Quinine (from the cinchona tree) These compounds often serve protective roles by deterring herbivores and inhibiting microbial growth.

Therefore, the correct statements are A,C and D

The correct answer are 2 and 4

Explanation:

Dhurrin − Phenolic compounds: Incorrect

• Dhurrin is actually a cyanogenic glycoside found in sorghum and other plants. Cyanogenic glycosides can release hydrogen cyanide when metabolized, which serves as a defense mechanism against herbivores. Phenolic compounds, on the other hand, are a diverse group of chemical substances found in plants characterized by the presence of phenol units. Dhurrin doesn't belong to this category.

Farnesene − Terpenoids: Correct

• Farnesene is a sesquiterpene, which is a type of terpenoid. Terpenoids are a large and diverse class of naturally occurring organic chemicals derived from five-carbon isoprene units. Farnesenes are found in the coating of apple skins and other plants, contributing to their aroma and serving as an important chemical in plant defense.

Naringenin − Cyanogenic glycosides: Incorrect

• Naringenin is, in fact, a flavonoid, which is a subgroup of phenolic compounds, and is not related to cyanogenic glycosides. Flavonoids are known for their antioxidant properties and are commonly found in citrus fruits. Naringenin plays a role in plant pigmentation, UV filtration, and symbiotic nitrogen fixation.

Vincristine − Alkaloids: Correct

• Vincristine is an alkaloid, which is a naturally occurring chemical compound containing basic nitrogen atoms. Alkaloids are known for their pharmacological effects, and vincristine, specifically derived from the Madagascar periwinkle (Catharanthus roseus), is used in chemotherapy to treat various types of cancer due to its ability to inhibit cell division.

The correct answer is Scrophulariaceae

Concept:

• Digitalis purpurea, commonly known as foxglove, is a biennial plant species that belongs to the family Scrophulariaceae.
• This plant is well-known for its medicinal properties, particularly its cardiac glycosides, such as digitoxin, which are used to treat various heart conditions.
• Cardiac glycosides are compounds that have a powerful effect on the heart muscle, helping to strengthen and regulate heartbeats.

Explanation:

• Apocynaceae: This family includes plants like oleander and periwinkle, which also produce cardiac glycosides but are not related to Digitalis purpurea.
• Solanaceae: Known as the nightshade family, this group includes plants like potatoes, tomatoes, and bell peppers. Some members produce alkaloids, but they do not contain cardiac glycosides like those found in Digitalis purpurea.
• Scrophulariaceae: This is the correct family for Digitalis purpurea. Plants in this family are often herbaceous and can contain important medicinal compounds like digitoxin.
• Ranunculaceae: Known as the buttercup family, this group includes plants like buttercups and anemones. While some members are toxic, they do not produce cardiac glycosides similar to those in Digitalis purpurea.

The correct answer is Phytoalexins

Concept:

• Phytoalexins are secondary metabolites produced by plants in response to pathogen attacks.
• These compounds exhibit strong antimicrobial activity and accumulate at the site of infection to inhibit the growth of the invading pathogens.
• Phytoalexins play a crucial role in the plant's defense mechanism by providing a rapid and localized response to infection.

Explanation:

• Phytochelatins: These are small, cysteine-rich peptides that chelate heavy metals and are involved in the detoxification of metal ions in plants. They do not have antimicrobial properties and are not synthesized in response to pathogen infection.
• Phytochrome: Phytochromes are photoreceptor proteins in plants that regulate various aspects of growth and development in response to light conditions. They are not related to antimicrobial activity or pathogen response.
• Phytoalexins: These are antimicrobial substances synthesized by plants in response to pathogen attack. They accumulate at the site of infection and help in inhibiting the growth and spread of the pathogen. Examples include resveratrol in grapes and camalexin in Arabidopsis.
• Phytin: Also known as phytic acid, this compound is a storage form of phosphorus in plants, particularly in seeds. It is not involved in antimicrobial activity or pathogen response.

The correct answer is A-i, B-ii, C-iv, D-ii

Explanation:

• Flavonoids (A): Flavonoids are a diverse group of phytonutrients found in fruits and vegetables, contributing to their color and antioxidant properties. They are synthesized via the shikimic acid pathway (i), which involves phenylalanine as a key precursor. The phenylpropanoid pathway, derived from the shikimic acid pathway, leads to the production of flavonoids.
• Alkaloids (B): Alkaloids are nitrogen-containing compounds that often have potent pharmacological effects. Many alkaloids are derived from phenylalanine (ii), an amino acid that serves as a precursor for various alkaloid biosynthesis pathways.
• Terpenoids (C): Terpenoids, also known as isoprenoids, are a large class of natural products built from isoprene units. They are synthesized via the mevalonate pathway (iv), which starts from acetyl-CoA and produces geranylgeranyl diphosphate, a key intermediate for terpenoid biosynthesis.
• Anthocyanins (D): Anthocyanins are water-soluble pigments responsible for red, purple, and blue colors in plants. They are synthesized from phenylalanine (ii) through the phenylpropanoid pathway, similar to flavonoids. Phenylalanine is converted to cinnamic acid, which eventually leads to the production of anthocyanins.

The correct answer is Through co-regulated synthesis and catabolism in response to water stress. 

Explanation:

Glycine betaine is an osmoprotectant that accumulates in plants under osmotic stress conditions, such as high salinity, drought, or extreme temperatures.

By increasing the plant's dependency on sucrose synthesis:

• This is incorrect because glycine betaine does not directly influence sucrose synthesis. Instead, it acts as an osmoprotectant, stabilizing cellular structures and proteins under stress. Sucrose may play a role in stress responses, but it is not directly linked to glycine betaine.

Through co-regulated synthesis and catabolism in response to water stress:

• This is correct. Glycine betaine is synthesized in plants during osmotic stress to protect cells by:
  • Stabilizing protein structures and enzyme activities.
  • Protecting the integrity of membranes by reducing oxidative damage.
  • Maintaining cellular osmotic balance, allowing water retention in cells.

Its synthesis and catabolism are tightly regulated based on stress conditions, ensuring efficient accumulation without overburdening the plant's metabolic processes.
By promoting the breakdown of glycine betaine to release energy for stress response:

• This is incorrect. Glycine betaine is not broken down to provide energy; rather, it accumulates in the cytosol to serve as a stabilizing agent for cellular components.

Genetic alteration that decreases the plant’s ability to synthesize glycine betaine under stress conditions:

• This is incorrect. Genetic modifications aim to enhance glycine betaine synthesis, not decrease it, as increased levels of glycine betaine improve a plant's tolerance to osmotic stress.

The correct answer is Option 2

Explanation:

Abiotic stress refers to the negative impact of non-living factors on living organisms in a specific environment. For plants, abiotic stresses include drought, salinity, extreme temperatures, and heavy metals, among others. These stresses can severely affect plant growth, development, and productivity, ultimately influencing crop yields.

Altered Gene Expression

• Under abiotic stress conditions, plants initiate a complex network of signal transduction pathways that lead to changes in gene expression. These changes enable the production of stress-responsive proteins, including enzymes that detoxify reactive oxygen species (ROS), proteins that protect cellular components (e.g., heat shock proteins), and transporters that help in ion homeostasis. The alteration in gene expression is a crucial early response that sets the stage for downstream physiological adjustments.

Changes in Cellular Metabolism

• Abiotic stresses can lead to a significant reprogramming of cellular metabolism in plants. This reconfiguration aims to produce osmoprotectants (such as proline, glycine betaine, and polyols), antioxidants, and specific secondary metabolites that help in stress tolerance. Osmoprotectants, for instance, help in osmoregulation and protect cellular structures, while antioxidants mitigate oxidative damage caused by increased levels of ROS during stress.

Shifts in Growth Rates

• Growth is an energy-intensive process and under stress conditions, plants often reallocate energy from growth to protective mechanisms. This reallocation can result in reduced growth rates, as observed in both root and shoot development. The reduction in growth is a strategy to minimize water loss during drought stress (through smaller leaf area) and to manage the energy resources more efficiently under unfavorable conditions.

Influence on Crop Yields

• The cumulative effect of these responses to abiotic stress can significantly impact crop yields. While the immediate responses aim to protect the plant and ensure survival, the long-term consequence of reduced growth rates and potential damage to photosynthetic machinery can lead to lower biomass accumulation and reduced reproductive success. 

Clarifications on Incorrect Statements

• Incorrect about osmotic adjustments: Osmotic adjustments involve an increase in solute concentration within plant cells to decrease solute potential Ψs , which helps retain water and maintain cellular functions under drought or salinity stress.
• Incorrect about salinity tolerance: Salinity tolerance in plants often involves the accumulation of compatible solutes like mannitol, glycine betaine, and proline, which help in osmoprotection and detoxification, rather than rapid sucrose synthesis alone.
• Incorrect about ABA's role: Abscisic acid (ABA) plays a crucial role in mediating plant responses to various abiotic stresses, including promoting stomatal closure to minimize water loss and modulating gene expression related to stress resistance mechanisms.

Conclusion:

Therefore, the correct answer is Option 2

The correct answer is The protonated form of alkaloids at physiological pH values allows them to interact with various biological targets.

Explanation:

• Alkaloids are a diverse group of nitrogen-containing organic compounds found in plants (and some fungi and animals) that often have potent effects on the nervous systems of vertebrates. Their pharmacological activity is largely due to their ability to interact with specific enzymes, ion channels, receptors, and other proteins within cells, altering physiological processes.
• Most alkaloids are basic, meaning they tend to accept protons under physiological conditions, forming water-soluble salts.
• At the physiological pH (~7.4) found in most vertebrate body fluids, many alkaloids exist in a protonated form (i.e., with an extra hydrogen ion attached).
• This protonated form is crucial for their interaction with biological targets, many of which are designed to recognize or interact with charged particles.

Other options:

• While some alkaloids may exhibit nonpolar characteristics depending on their structure, the defining feature that enables their biological activity is not their nonpolarity but their ability to exist in a protonated form at physiological pH, which enhances their interaction with biological targets.
• Alkaloids do not primarily exert their effects by binding to water molecules for transport across cell membranes. Their interaction with biological targets is more direct and is related to their structural characteristics and ability to form protonated species.
• The water solubility of alkaloids may influence aspects of their pharmacokinetics, such as absorption and distribution, but saying it is entirely irrelevant disregards the importance of their chemical properties (including solubility and the ability to form protonated species) in determining their interaction with biological targets and mechanisms of action.

Conclusion:

Therefore, the correct answer is Option 2

The correct answer is They act primarily as defense mechanisms against predators.

Explanation:

• Alkaloids, a diverse group of nitrogen-containing compounds found in plants (as well as some fungi and animals), have been extensively studied for their various roles within their natural producers. Current scientific understanding suggests that a primary role of alkaloids in plants is to serve as defense mechanisms against herbivores, pests, and pathogens. By possessing potent biochemical activities, these compounds can deter or harm organisms that attempt to eat or infect the plants producing them.
• The presence of alkaloids can render a plant less palatable or even toxic to many organisms, thereby reducing the likelihood of being consumed and improving the chances of survival and reproduction for the plant. This defensive property also extends to microorganisms, making alkaloids a part of the plant's arsenal against microbial attacks.

They are generally classified based on their common biosynthetic origin, structural similarity, or the natural source from which they are derived. Key structural classes include:

• Indole alkaloids, such as the psychedelic compound psilocybin found in certain mushrooms, and reserpine, an antihypertensive and antipsychotic drug sourced from the Rauvolfia plant.
• Isoquinoline alkaloids, such as morphine and codeine, potent analgesics derived from the opium poppy (Papaver somniferum).
• Pyridine and Piperidine alkaloids, such as nicotine from tobacco plants and coniine from poison hemlock.
• Tropane alkaloids, such as atropine and scopolamine found in deadly nightshade (Atropa belladonna), which have applications in medicine but are also highly toxic.

Alkaloids are typically synthesized by plants through complex biosynthetic pathways, often involving the modification of amino acids like lysine, tyrosine, tryptophan, and phenylalanine. These pathways can differ significantly between different classes of alkaloids 

The correct answer is Lysine, Tyrosine, and Tryptophan 

Explanation:

Alkaloids are a diverse group of plant secondary metabolites characterized by containing at least one nitrogen atom in a heterocyclic structure. They are primarily synthesized from amino acids through various biosynthetic pathways. The amino acids that serve as the primary precursors for the synthesis of alkaloids are Lysine, Tyrosine, and Tryptophan

• Lysine is a precursor for the biosynthesis of alkaloids such as the quinolizidine and piperidine alkaloids found in some families of plants.
• Tyrosine serves as a precursor for the synthesis of isoquinoline alkaloids, which are found in plants like the poppy (Papaver somniferum) that produces morphine and codeine.
• Tryptophan is a precursor for the biosynthesis of indole alkaloids and terpenoid indole alkaloids, found in plants such as Catharanthus roseus, which produces vinblastine and vincristine, compounds used in chemotherapy.

Each of these amino acids undergoes specific biochemical transformations, leading to the vast diversity of alkaloid structures with varying pharmacological activities.