BCHET-149 Solved Assignment 2025
Part-A
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a) Describe the biochemical composition of a living organism
b) Explain the structure and functions of mitochondria.
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a) Why do monosaccharides form cyclic structure? Draw the structures of open chain and cyclic forms of glucose.
b) Taking D-glucose as an example explain the term mutarotation.
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a) What is the principal structural difference between amylose and cellulose? Explain giving structures.
b) What is the difference between a fat and a fatty acid? Give definition of iodine number.
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a) Describe the structural differences between a triacylglycerol and a phospholipid. Give one example in each case.
b) What are the similarities in composition amongst the four DNA nucleotides.
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a) Describe the isoelectric point. With the help of an example explain the utility of this property of amino acids and how is it useful in maintaining pH in human systems.
b) How are the peptides named? Write the structure of a tripeptide of your choice and write its full and abbreviated name.
Part-B
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a) What is meant by active site of an enzyme? How do the binding groups and catalytic groups of an active site differ from each other?
b) What is the basic principle involved in the mechanism of enzyme action in biological reactions? Explain.
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a) What is the significance of oxidative phosphorylation? Illustrate with the help of two examples.
b) How is the enzyme, pyruvate dehydrogenase complex different from other enzymes ? How does it function in the conversion of pyruvate to acetyl- CoA?
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a) What are the similarities between DNA replication and RNA transcription?
b) Describe the factors that affect the immune response.
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a) Describe the interrelationship amongst the metabolic pathways.
b) Write the steps of the degradation of amino acids and give a diagrammatic representation.
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a) Describe the energetic of the degradation of fatty acids.
b) Explain the mechanism of drug action.
Answer:
Part-A
Question:-1(a)
Describe the biochemical composition of a living organism.
Answer:
1. Overview of Biochemical Composition
Living organisms are complex systems primarily composed of biochemical molecules that sustain life. These molecules include water, organic compounds (carbohydrates, lipids, proteins, and nucleic acids), and inorganic ions. The precise composition varies across species, but the fundamental building blocks remain consistent. Water, making up 60-90% of most organisms, serves as a solvent and medium for biochemical reactions. Organic molecules provide energy, structure, and genetic information, while inorganic ions regulate physiological processes. This intricate balance enables metabolism, growth, and reproduction.
The biochemical makeup reflects evolutionary adaptations and environmental interactions. For instance, a human cell differs from a plant cell due to specialized molecules like chlorophyll in plants. Understanding this composition reveals how life functions at a molecular level, from single-celled bacteria to multicellular organisms like humans.
2. Water: The Universal Solvent
Water is the most abundant molecule in living organisms, constituting about 70% of a typical cell’s mass. Its unique properties—polarity, hydrogen bonding, and high heat capacity—make it essential for life. As a solvent, water dissolves ions and polar molecules, facilitating chemical reactions like hydrolysis and enzymatic processes. It also maintains cellular structure by providing turgor pressure in plant cells and volume in animal cells.
Beyond its solvent role, water participates directly in metabolic reactions, such as photosynthesis (where it’s split to release oxygen) and cellular respiration (where it’s a byproduct). Its ability to regulate temperature and pH ensures homeostasis, allowing enzymes and other molecules to function optimally. Without water, the biochemical machinery of life would cease.
3. Carbohydrates: Energy and Structure
Carbohydrates, composed of carbon, hydrogen, and oxygen (typically in a 1:2:1 ratio), are a primary energy source and structural component. Simple sugars like glucose (C₆H₁₂O₆) are broken down during cellular respiration to produce ATP, the cell’s energy currency. Polysaccharides, such as starch in plants and glycogen in animals, store energy for later use.
Structurally, carbohydrates like cellulose form rigid plant cell walls, while chitin strengthens fungal cells and arthropod exoskeletons. Glycolipids and glycoproteins on cell membranes aid in recognition and signaling. Carbohydrates’ versatility—ranging from quick energy release to long-term storage—underscores their importance in biochemical systems.
4. Lipids: Energy Storage and Membranes
Lipids are hydrophobic molecules, including fats, phospholipids, and steroids, made of carbon, hydrogen, and oxygen. Fats, or triglycerides, store energy more efficiently than carbohydrates, yielding twice as many calories per gram. This makes them vital for organisms requiring long-term energy reserves, like hibernating animals.
Phospholipids form the backbone of cell membranes, with hydrophilic heads and hydrophobic tails creating a bilayer that controls what enters and exits cells. Steroids, such as cholesterol, stabilize membranes and serve as hormone precursors (e.g., testosterone). Lipids also insulate organisms and cushion organs, highlighting their diverse roles beyond energy storage.
5. Proteins: The Workhorses of Life
Proteins, polymers of amino acids, are the most functionally diverse biomolecules. Composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur, they perform tasks ranging from catalysis to structural support. Enzymes, a protein subset, accelerate biochemical reactions—e.g., amylase breaks down starch into sugars. Structural proteins like collagen provide strength to tissues, while hemoglobin transports oxygen in blood.
Proteins’ functionality depends on their three-dimensional shape, determined by amino acid sequences and bonding (hydrogen bonds, disulfide bridges). They also mediate cell signaling (e.g., insulin) and immune responses (e.g., antibodies). Life’s complexity hinges on proteins’ ability to adapt and specialize.
6. Nucleic Acids: The Blueprint of Life
Nucleic acids—DNA and RNA—store and transmit genetic information. Built from nucleotides (sugar, phosphate, and nitrogenous base), they encode instructions for protein synthesis. DNA, with its double-helix structure, is stable and resides in the nucleus, while RNA, single-stranded, translates DNA into proteins via transcription and translation.
Nucleotides like ATP also act as energy carriers, linking nucleic acids to metabolism. The sequence of bases (adenine, thymine, cytosine, guanine in DNA; uracil replaces thymine in RNA) dictates an organism’s traits, making nucleic acids the foundation of heredity and evolution.
7. Inorganic Ions and Trace Elements
Inorganic ions (e.g., Na⁺, K⁺, Ca²⁺, Cl⁻) and trace elements (e.g., iron, zinc) are minor but critical components. Sodium and potassium regulate nerve impulses and osmotic balance, while calcium strengthens bones and triggers muscle contraction. Iron in hemoglobin binds oxygen, and magnesium in chlorophyll captures light for photosynthesis. These elements, though less abundant than organic compounds, are indispensable for enzymatic activity and cellular signaling.
Conclusion
The biochemical composition of living organisms is a harmonious blend of water, organic molecules, and inorganic ions, each contributing to life’s processes. Water provides the medium, carbohydrates and lipids fuel and structure, proteins execute tasks, nucleic acids store information, and ions fine-tune reactions. This molecular symphony, refined over billions of years, enables organisms to thrive in diverse environments. Understanding this composition not only illuminates life’s mechanics but also inspires advancements in medicine, biotechnology, and ecology, revealing the unity underlying Earth’s biodiversity.
Question:-1(b)
Explain the structure and functions of mitochondria.
Answer:
Structure of Mitochondria
Mitochondria are double-membraned organelles found in the cytoplasm of eukaryotic cells, often referred to as the "powerhouses" of the cell due to their role in energy production. Their structure is highly specialized to support their functions, and they vary in size (typically 0.5–1.0 micrometers wide and up to 10 micrometers long) and shape (oval, rod-like, or thread-like), depending on the cell type and energy demands.
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Outer Membrane: The outer mitochondrial membrane is smooth and permeable, containing proteins called porins. These porins form channels that allow small molecules (up to 5,000 daltons), such as ions and sugars, to pass freely into the intermembrane space. This permeability connects the mitochondrial interior to the cytosol, facilitating material exchange.
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Intermembrane Space: This narrow compartment between the outer and inner membranes acts as a reservoir for protons (H⁺ ions) during energy production. It plays a critical role in the proton gradient that drives ATP synthesis.
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Inner Membrane: The inner membrane is highly folded into structures called cristae, which increase its surface area. Unlike the outer membrane, it is selectively permeable and rich in proteins, including those of the electron transport chain (ETC) and ATP synthase. The inner membrane’s impermeability to most ions and molecules ensures a controlled environment for energy generation.
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Cristae: These invaginations of the inner membrane maximize the space available for chemical reactions. In cells with high energy demands (e.g., muscle cells), cristae are more numerous and densely packed.
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Matrix: The innermost compartment, enclosed by the inner membrane, contains a gel-like fluid rich in enzymes, mitochondrial DNA (mtDNA), ribosomes, and other molecules. The matrix is the site of the citric acid cycle (Krebs cycle) and houses circular mtDNA, which encodes some proteins essential for mitochondrial function.
Mitochondria are unique in possessing their own genetic material and protein-synthesizing machinery, a remnant of their evolutionary origin as endosymbiotic bacteria. Their double-membrane structure reflects this heritage and supports their multifaceted roles.
Functions of Mitochondria
Mitochondria are central to cellular metabolism and perform several critical functions beyond energy production. Below are their primary roles:
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ATP Production (Cellular Respiration): The most well-known function of mitochondria is generating adenosine triphosphate (ATP), the cell’s energy currency, through cellular respiration. This process occurs in three stages:
- Glycolysis (in the cytoplasm) breaks down glucose into pyruvate, which enters the mitochondria.
- Citric Acid Cycle (in the matrix) oxidizes pyruvate into CO₂, producing electron carriers (NADH and FADH₂).
- Oxidative Phosphorylation (on the inner membrane) uses the ETC to transfer electrons from NADH and FADH₂ to oxygen, creating a proton gradient across the inner membrane. ATP synthase then harnesses this gradient to produce ATP. This process yields up to 36-38 ATP molecules per glucose molecule, making mitochondria highly efficient energy producers.
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Regulation of Cellular Metabolism: Mitochondria integrate metabolic pathways beyond ATP synthesis. They oxidize fats and amino acids, feeding their intermediates into the citric acid cycle. This flexibility allows cells to adapt to varying energy sources, such as during fasting when fatty acids become a primary fuel.
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Calcium Homeostasis: Mitochondria regulate intracellular calcium levels by taking up and releasing Ca²⁺ ions. This function influences signaling pathways, enzyme activity, and muscle contraction. Calcium storage in the matrix also buffers cytosolic levels, preventing toxicity.
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Heat Production: In specialized tissues like brown fat, mitochondria produce heat instead of ATP through a process called thermogenesis. Proteins like uncoupling protein 1 (UCP1) dissipate the proton gradient, releasing energy as heat to maintain body temperature in mammals.
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Apoptosis (Programmed Cell Death): Mitochondria play a pivotal role in apoptosis by releasing pro-apoptotic factors, such as cytochrome c, from the intermembrane space into the cytosol. This triggers a cascade of events leading to cell death, essential for development (e.g., shaping embryos) and eliminating damaged cells.
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Biosynthesis: The matrix hosts enzymes that synthesize biomolecules, including heme (for hemoglobin) and certain amino acids. Mitochondria also contribute to steroid hormone production by providing precursor molecules.
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Reactive Oxygen Species (ROS) Management: During the ETC, mitochondria generate ROS as byproducts. While excessive ROS can damage cells, controlled levels serve as signaling molecules. Mitochondria contain antioxidants like superoxide dismutase to mitigate oxidative stress.
Integration of Structure and Function
The mitochondria’s structure is intricately tied to its functions. The large surface area of the cristae accommodates the ETC and ATP synthase, optimizing energy production. The matrix’s enzyme-rich environment supports the citric acid cycle, while the outer membrane’s permeability ensures nutrient influx. This compartmentalization enhances efficiency and protects the cell from harmful byproducts like ROS.
In summary, mitochondria are dynamic organelles that not only power cellular activities but also regulate metabolism, calcium, and cell fate. Their structural complexity and functional versatility make them indispensable to eukaryotic life.