Assignment Code: BBCET-151/TMA/2023

Course Code: BBCET-151

Assignment Name: Plant Biochemistry

Year: 2023

Verification Status: Verified by Professor

PART-(A)

Q1a) Explain the structure and function of plant cell wall. 5

Ans) It is a rigid layer which is composed of polysaccharides cellulose, pectin and hemicellulose. It is located outside the cell membrane. It also comprises glycoproteins and polymers such as lignin, cutting, or suberin.

The primary function of the cell wall is to protect and provide structural support to the cell. The plant cell wall is also involved in protecting the cell against mechanical stress and providing form and structure to the cell. It also filters the molecules passing in and out of it.

The formation of the cell wall is guided by microtubules. It consists of three layers, namely, primary, secondary and the middle lamella. The primary cell wall is formed by cellulose laid down by enzymes.

b) List the diverse roles of plant vacuoles. 5

Ans) Plant vacuoles are large organelles that are full of fluid and have many important jobs to do in plant cells. Among these roles are:

1. Storage: Molecules like sugars, amino acids, and inorganic ions, which the plant can use for energy and growth, are stored in vacuoles.

2. Detoxification: Vacuoles also help detoxify the cell by storing and breaking down harmful molecules, like heavy metals.

3. Protection: Vacuoles can also protect the cell by keeping proteases and pathogens from getting into the rest of the cell.

4. Send Signals: Vacuoles are also organelles that send signals. They help control gene expression, cell division, and programmed cell death.

Q2a) Explain Emerson enhancement effect. 5

Ans) The Emerson enhancement effect is when the amount of CO2 inside a plant cell is higher than the amount of CO2 outside the cell. This makes the rate of photosynthesis in the plant cell go up. This effect is named after Richard L. Emerson, a scientist who first wrote about it in 1957.

It happens because the amount of CO2 inside the cell is a limiting factor for the first step of photosynthesis, the carboxylation of RuBP, which is sped up by the enzyme Rubisco. When the amount of CO2 inside the cell is higher than the amount outside the cell, Rubisco can work more efficiently. This makes the rate of photosynthesis go up.

This effect is especially important for plants that live in places with low CO2 levels, like deserts or high altitudes, because it lets them speed up their rate of photosynthesis and stay alive in these tough conditions.

b) Describe the role of PS I (NADPH Forming) Complex. 5

Ans) Plants, algae, and certain bacteria photosynthesis using the PS I complex. It makes NADPH, a light-activated molecule that stores energy in chemical bonds.

PS My pigments, principally chlorophyll A and phycobilin, receive light energy and send it to complex electron carriers. PS I stimulates chlorophyll an electrons when it absorbs light. Electron carriers receive them. These carriers transfer electrons to the electron transport chain, which produces ATP and NADPH. Photosynthesis's non-light-dependent stages consume NADPH.

PS I am also involved in the proton gradient across the thylakoid membrane, which is used to drive the synthesis of ATP. The PS I complex is in the thylakoid membrane, which is where the photosynthesis reactions that depend on light happen.

Q3) Describe different phases of Calvin cycle. 10

Ans) The Calvin cycle, also called the carbon fixation cycle or the light-independent reactions of photosynthesis, is a series of reactions that happen in the stroma of chloroplasts in plants, algae, and some bacteria.

The three main phases of the Calvin cycle are the carbon fixation, reduction, and regeneration phases.

Carbon Fixation Phase:

In this stage, carbon dioxide is incorporated into ribulose 1,5-bisphosphate (RuBP), which previously consisted of five carbons. A procedure known as carboxylation is used to accomplish this goal. This reaction, which results in the formation of two molecules of 3-phosphoglycerate, is sped up by the enzyme known as RuBP carboxylase/oxygenase (Rubisco) (3-PGA).

Reduction Phase:

In this phase, molecules of 3-PGA made in the carbon fixation phase are changed into molecules of glyceraldehyde 3-phosphate (G3P) through a series of reactions that use ATP and NADPH, which are made in photosynthesis reactions that depend on light. G3P is a sugar that has three carbons and can be turned into glucose and other sugars.

Regeneration Phase:

In this phase, the RuBP that was used in the carbon fixation phase is made ready to be used again in the next round of the cycle. In this process, G3P and ATP are used, and for every molecule of G3P used, one molecule of RuBP is made. One molecule of glucose, a sugar with six carbons, is made when the cycle is turned six times. One molecule of CO2 is "fixed" at the beginning of the cycle. After six turns, one molecule of glucose is made.

Q4a) What are the alternate reactions of cytosolic plant glycolysis that permit it to bypass many of the steps of conventional glycolysis. 5

Ans) In cytosolic plant glycolysis, there are alternative reactions that allow the pathway to skip over many of the steps of traditional glycolysis. Among these other responses are:

1. The normal enzyme, hexokinase, is not used to turn fructose-6-phosphate into fructose-1,6-bisphosphate. Instead, aldolase is used.

2. The change from 1,3-bisphosphoglycerate to 3-phosphoglycerate is done by 3-phosphoglycerate kinase instead of the usual phosphoglycerate kinase.

3. The normal enzyme, 2,3-bisphosphoglycerate, is not used to turn 2-phosphoglycerate into phosphoenolpyruvate. Instead, the enzyme enolase is used.

These different reactions make a shorter and more efficient pathway that skips several steps of normal glycolysis. This speeds up the process of making ATP, which is a form of energy.

Cytosolic plant glycolysis uses different reactions that let it skip many of the steps of traditional glycolysis. This makes for a shorter, more efficient pathway that lets ATP, which is a form of energy, be made faster.

b) Point out the basic difference (s) in the regulation of glycolysis in plants and animals. 5

Ans) The main difference between how plants and animals control glycolysis is that plants can change the levels of protein expression to change the activity of enzymes in the glycolytic pathway, while animals mostly change the levels of phosphorylation to change the activity of enzymes.

In plants, the activity of enzymes in the glycolytic pathway can be changed by changing how much of the corresponding mRNA is present. This, in turn, changes how much of the corresponding enzyme protein is present. This kind of control is called transcriptional control.

In animals, on the other hand, changes in the amount of phosphorylation on certain enzyme residues control the activity of enzymes in the glycolytic pathway. Post-translational regulation is the name for this kind of control.

Another difference is that in plant cells, the activity of enzymes in the glycolytic pathway is controlled by changes in the amount of the enzyme protein. This is not the case in animal cells.

Q5a) Regulation of TCA Cycle in Plants. 5

Ans) The tricarboxylic acid (TCA) cycle, which is also called the citric acid cycle or the Krebs cycle, is the way that plants get energy from acetyl-CoA by oxidising it. Plants control the TCA cycle in a number of ways, such as:

Controlling the Activity of Enzymes: In the TCA cycle, the activity of enzymes can be changed by changing the amount of the enzyme protein.

Substrate Level Regulation: The level of the substrate, such as acetyl-CoA, can also change the activity of enzymes in the TCA cycle.

Allosteric Regulation: Enzymes in the TCA cycle can also be controlled by molecules called allosteric modulators, which bind to certain spots on the enzymes and change how they work.

Hormonal Control: Hormones like cytokinins and abscisic acid can also control how enzymes in the TCA cycle work.

Metabolic Regulation: The levels of other metabolites like NADH and ATP, which act as feedback inhibitors, can also control the activity of enzymes in the TCA cycle.

b) Describe the structure of F-ATPase and mechanism of ATP synthesis. 5

Ans) F-ATPase, which is also called ATP synthase, is a complex enzyme that is in charge of making ATP. F-ATPase has two main parts that make up its structure: the F1 part, which is on the surface of the mitochondria or chloroplast, and the F0 part, which is in the inner membrane.

The F1 part of F-ATPase is made up of a spinning rotor in the middle and three catalytic subunits (alpha, beta, and gamma) that make ATP. The F0 part of F-ATPase is made up of a proton channel that goes across the inner membrane and a stator that holds the rotor in place.

F-ATPase makes ATP by letting protons flow from the intermembrane space through the F0 part of the enzyme and into the matrix. This flow of protons spins the rotor in the F1 part, which in turn spins the three catalytic subunits and speeds up the process of making ATP from ADP and Pi.

PART-(B)

Q1a) Indicate three ways by which filamentous cyanobacteria protect nitrogenase. 5

Ans) Filamentous cyanobacteria protect nitrogenase, an enzyme complex responsible for nitrogen fixation, in several ways:

1. Physical Protection: Many filamentous cyanobacteria form specialized structures called heterocysts, which are thick-walled cells that protect nitrogenase from the oxygen produced during photosynthesis.

2. Genetic Regulation: Cyanobacteria can also regulate the expression of genes encoding nitrogenase in response to changes in the availability of nitrogen. This allows them to turn off nitrogenase when there is enough nitrogen in the environment and prevent the enzyme from being damaged by oxygen.

3. Metabolic Control: Cyanobacteria can also control the metabolic pathways that produce oxygen, such as photosynthesis, to minimize the production of oxygen and protect nitrogenase. They can also use alternative metabolic pathways such as cyclic electron flow around photosynthetic electron transport chain to reduce the production of oxygen.

b) Give the reactions catalysed by nitrogenase in vivo. 5

Ans) Nitrogenase is a complex of enzymes that helps fix nitrogen in living things. The MoFe protein and the Fe protein are the two parts that make up the enzyme complex. The MoFe protein speeds up the change from dinitrogen (N2) to ammonia (NH3), while the Fe protein carries electrons. The overall process that nitrogenase speeds up is:

N2 + 8H+ + 8e- + 16ATP → 2NH3 + H2 + 16ADP + 16Pi

This reaction generates heat and requires ATP and electrons. Nitrogenase reacts poorly to oxygen and high temperatures, hence it needs a specific environment. Heterocysts in filamentous cyanobacteria prevent these inhibitors from reaching the enzyme complex.

Nitrogenase accelerates dinitrogen (N2) to ammonia conversion (NH3). A very exothermic process takes 16 ATP and 8 electrons. The enzyme complex consists of MoFe and Fe proteins. The Fe protein transports electrons and the MoFe protein accelerates N2 to NH3 conversion.

Q2a) Explain nitrate assimilation. 5

Ans) Nitrate assimilation is the process by which plants and some microorganisms convert nitrate (NO3-) into a form that can be used for growth and metabolism. The process is typically carried out by a series of enzymes and transporters that are located in the roots and/or leaves of plants. Nitrate is taken up by the plant via specific transporters and then is reduced to nitrite (NO2-) by the enzyme nitrate reductase. Nitrite is then converted to ammonia (NH3) by the enzyme nitrite reductase. The ammonia is then incorporated into amino acids, nucleotides and other nitrogen-containing compounds via a process called amination.

b) Indicate the unique features of biological nitrogen fixation. 5

Ans) Biological nitrogen fixation is the process by which nitrogen gas (N2) is converted into forms that can be used by plants and other organisms, such as ammonia (NH3) or nitrate (NO3-). It is unique in several ways:

1. Nitrogen fixation is a highly energy-intensive process, requiring the input of large amounts of energy in the form of ATP and electrons.

2. Nitrogen fixation is carried out by a small group of microorganisms, such as certain bacteria and cyanobacteria, which possess the specialized enzyme complex nitrogenase.

3. Nitrogen fixation can occur in a variety of environments, including soil, water and symbiotic relationships with plants.

4. Nitrogen fixation is crucial for the growth of plants and other organisms, as nitrogen is a key component of many biomolecules, such as amino acids and nucleic acids.

5. Nitrogen fixation is a natural process that helps to maintain the balance of nitrogen in the ecosystem, providing a vital source of nitrogen for plants and other organisms.

Q3) Illustrate GS-GOGAT pathway of ammonium assimilation. 10

Ans) The GS-GOGAT pathway, which is also called the glutamine synthetase-glutamate synthase pathway, is a keyway for plants and microorganisms to take in ammonium. Ammonium (NH4+) is changed into glutamate (an amino acid) by this pathway. Glutamate can then be used to make other amino acids, nucleotides, and other nitrogen-containing compounds.

The two most important enzymes in the GS-GOGAT pathway are glutamine synthetase (GS) and glutamate synthase (GOGAT). Ammonium and glutamate are changed into glutamine by GS, while glutamine is changed back into glutamate and ammonium by GOGAT.

The overall reaction can be represented as:

NH4+ + 2-oxoglutarate + ATP → glutamine + ADP + Pi

glutamine + 2-oxoglutarate + NADPH → 2 glutamate + NADP+

The GS-GOGAT pathway is a cyclical process that helps the plant keep a balance between taking in ammonium and making glutamate. Several things, like the amount of ammonium in the soil, the amount of nitrogen in the plant, and the rate of photosynthesis, control the pathway.

The GS-GOGAT pathway is a very important process for plants because it gives them a source of nitrogen that they can use to make amino acids and other compounds that contain nitrogen. The pathway also helps the plant keep its nitrogen balance, which is important for the plant to grow and stay alive. In addition, the GS-GOGAT pathway is a key part of how the plant controls its carbon metabolism. By controlling the rate of ammonium assimilation, the pathway helps to keep carbon and nitrogen metabolism in balance. This makes sure that the plant has the right amount of nutrients to grow and stay alive.

Q4a) Indicate the effects of growth hormones like auxins, gibberellins, cytokinins, on growth and development of plants. 5

Ans) Plants need growth hormones, which are also called plant growth regulators, to grow and develop. Auxins, gibberellins, cytokinins, and abscisic acid are the four main types of growth hormones.

Auxins help cells grow longer and make stems and roots grow longer. They also help control apical dominance, which is when the top bud stops the growth of the side buds, and phototropism, which is when the plant bends toward a light source.

Gibberellins help cells grow and divide, which is why stems get longer and seeds start to grow. They also play a part in getting some plants to bloom.

Cytokinins help cells divide and help buds, and roots grow. They also keep leaves from turning yellow and help plants handle stress better.

Abscisic acid slows or stops growth in times of drought or water stress by closing stomata and stopping or slowing the flow of water into and out of the plant.

b) Describe role of alkaloids in plants. 5

Ans) Alkaloids are a group of naturally occurring chemicals that are found in many plants. They have been used for hundreds of years as medicine and for fun because of how they make animals and people feel. Alkaloids in plants are not completely understood, but it is thought that they protect plants from herbivores and disease-causing organisms and also attract pollinators and animals that spread seeds.

Alkaloids can also stop plants from growing, and they may have something to do with how plants compete with each other. They can also be used to treat diseases, and both modern and traditional medicine make use of them. Some alkaloids are also used in the industrial world to make dyes, insecticides, and other things. People and animals can also get sick from eating too many alkaloids.

Q5a) Give any five applications of plant cell and tissue culture. 5

Ans) Plant cell and tissue culture are a technique used to grow plant cells, tissues or organs in a controlled environment, outside of their natural growth conditions. It has a wide range of applications in agriculture, horticulture, and biotechnology.

1. Propagation: Plant cell and tissue culture can be used to clone plants, produce genetically identical plants, or create new plant varieties. This technique is commonly used for the mass production of crops such as bananas and pineapples.

2. Preservation: Endangered plant species can be preserved by growing them in culture and maintaining a living gene bank.

3. Biotechnology: Plant cell and tissue culture is used in the production of secondary metabolites such as alkaloids, flavonoids, and terpenoids, which have medicinal and industrial applications.

4. Plant Breeding: Tissue culture can be used to induce genetic variations, to produce new varieties of plants with desired characteristics.

5. Agriculture: Tissue culture can be used to produce disease-free plantlets, which can be used to produce high-yielding crops. Also, it can be used to produce virus-free plantlets and induce genetic improvement in plants.

b) Describe ways by which plants sense stressors. 5

Ans) Plants have developed different ways to sense and react to stressors like changes in the environment, pathogens, and herbivores.

1. Receptors: Plants have receptors that can tell when the light, temperature, or humidity changes. These receptors make the plant do things that help it adjust to changes in its environment.

2. Hormones: Changes in hormone levels are another way that plants can tell when they are under stress.

3. Pathogen-Associated Molecular Patterns: PAMPs are molecules that are unique to certain types of pathogens and let plants know they are there. This makes the plant's immune system react to the pathogen so it can fight it off.

4. Damage-Associated Molecular Patterns: DAMPs are molecules that are released when a plant is hurt by herbivores or abiotic stressors. This makes the plant defend itself, so it doesn't get hurt any more.

5. Signal Transduction: Signals from receptors, hormones, PAMPs, and DAMPs are turned into changes in gene expression that allow the plant to respond to stressors.