BCHET-149 Solved Assignment 2024 | IGNOU

Molecules of Life
Elective Course in Chemistry

Part-A

Cells are the basic structural and functional units of life, and they can be broadly classified into two categories: prokaryotic and eukaryotic. This distinction is primarily based on their structural differences, which are crucial for understanding their functions, complexity, and the evolution of life on Earth.

Prokaryotic Cells: Prokaryotic cells are generally smaller and simpler in structure compared to eukaryotic cells. They typically range in size from 0.1 to 5 micrometers in diameter. Due to their small size, prokaryotic cells have a larger surface area-to-volume ratio, which facilitates efficient nutrient uptake and waste removal.

Eukaryotic Cells: Eukaryotic cells are larger and more complex, usually ranging from 10 to 100 micrometers in diameter. This increased size allows for greater internal complexity, including the presence of various organelles that perform specific functions within the cell.

Prokaryotic Cells: Prokaryotic cells lack a true nucleus. Their genetic material, which is usually a single circular chromosome, is located in a region called the nucleoid, which is not enclosed by a membrane.

Eukaryotic Cells: Eukaryotic cells have a well-defined nucleus, which is enclosed by a double-membraned nuclear envelope. This nucleus contains the cell’s genetic material organized into linear chromosomes.

Prokaryotic Cells: Prokaryotic cells do not possess membrane-bound organelles. Their cellular processes, such as respiration and photosynthesis, occur directly in the cytoplasm or are associated with the plasma membrane.

Eukaryotic Cells: Eukaryotic cells contain numerous membrane-bound organelles, each with specific functions. These include the endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, and, in plant cells, chloroplasts. The compartmentalization provided by these organelles allows for more efficient and specialized cellular processes.

Prokaryotic Cells: Most prokaryotic cells have a rigid cell wall that provides structural support and protection. The composition of the cell wall varies among different prokaryotic groups, with bacteria typically having a peptidoglycan layer.

Eukaryotic Cells: Not all eukaryotic cells have a cell wall. When present, the composition is different from that of prokaryotes. For example, plant cell walls are primarily made of cellulose, while fungal cell walls contain chitin.

Prokaryotic Cells: Prokaryotic cells contain 70S ribosomes, which are smaller than those found in eukaryotic cells. These ribosomes are responsible for protein synthesis and are found freely floating in the cytoplasm.

Eukaryotic Cells: Eukaryotic cells contain 80S ribosomes, which are larger and more complex. These ribosomes can be found free in the cytoplasm or bound to the endoplasmic reticulum, forming the rough endoplasmic reticulum, which is involved in protein synthesis and processing.

Prokaryotic Cells: Prokaryotic cells typically have a single, circular chromosome that is not enclosed in a nuclear membrane. They may also contain small, circular DNA molecules called plasmids, which carry additional genes.

Eukaryotic Cells: Eukaryotic cells have multiple, linear chromosomes contained within a nucleus. The genetic material is organized and packaged with proteins into chromatin, which helps regulate gene expression and DNA replication.

Prokaryotic Cells: Prokaryotic cells reproduce asexually through a process called binary fission, where the cell divides into two genetically identical daughter cells. This process is relatively simple and fast.

Eukaryotic Cells: Eukaryotic cells can reproduce both asexually and sexually. Asexual reproduction involves mitosis, a more complex process than binary fission, resulting in genetically identical daughter cells. Sexual reproduction involves meiosis, leading to the production of gametes with half the number of chromosomes.

Prokaryotic Cells: Prokaryotic cells have a simple cytoskeleton composed of a few protein filaments, which provide structural support and help maintain cell shape.

Eukaryotic Cells: Eukaryotic cells have a well-developed cytoskeleton made up of microtubules, microfilaments, and intermediate filaments. This complex network provides structural support, facilitates cell movement, and plays a crucial role in intracellular transport and cell division.

In summary, prokaryotic and eukaryotic cells differ significantly in terms of size, complexity, and structural organization.

b) How are lysosomes formed in the cells. Describe their role within the cell.

Lysosomes are membrane-bound organelles found in the cytoplasm of eukaryotic cells. They are often referred to as the cell’s "digestive system" because they contain enzymes that break down biomolecules. Understanding how lysosomes are formed and their role within the cell is crucial for comprehending cellular homeostasis and the recycling of cellular components.

Origin from the Endomembrane System: Lysosomes originate from the endomembrane system, specifically from the trans-Golgi network (TGN). The TGN sorts and packages proteins into vesicles. Some of these vesicles become lysosomes.

Enzyme Precursors: The enzymes destined for lysosomes are synthesized in the rough endoplasmic reticulum (ER) and transported to the Golgi apparatus. In the Golgi, they undergo modifications, such as the addition of mannose-6-phosphate (M6P) tags, which target them to lysosomes.

Formation of Primary Lysosomes: The tagged enzymes are packaged into vesicles that bud off from the TGN. These vesicles, known as primary lysosomes, contain inactive enzymes to prevent digestion of cellular components during transport.

Maturation and Activation: Primary lysosomes fuse with endosomes or phagosomes, forming secondary lysosomes where the acidic environment activates the enzymes. This activation is crucial for the lysosome’s digestive function.

Intracellular Digestion: Lysosomes break down macromolecules such as proteins, lipids, carbohydrates, and nucleic acids. This process is essential for recycling cellular components and removing damaged organelles or foreign materials.

Autophagy: Lysosomes play a key role in autophagy, a process where cells degrade and recycle their own components. This is vital for cellular maintenance, adaptation to stress, and survival during nutrient deprivation.

Phagocytosis: In immune cells, lysosomes digest foreign particles or pathogens engulfed during phagocytosis, contributing to the body’s defense mechanism.

Apoptosis: Lysosomes can release enzymes that trigger apoptosis, or programmed cell death, which is important for development and the removal of harmful cells.

Bone Remodeling: In osteoclasts, lysosomes secrete enzymes that break down bone tissue, allowing for bone remodeling and calcium homeostasis.

Lipid Metabolism: Lysosomes are involved in lipid metabolism, including the breakdown of cholesterol and other lipids, which is crucial for cell membrane maintenance and energy production.

Lysosomes are essential organelles that play a crucial role in maintaining cellular health through their involvement in digestion, recycling, and defense mechanisms. Their formation from the endomembrane system ensures the proper targeting and activation of hydrolytic enzymes, while their diverse functions highlight their importance in various cellular processes. Understanding lysosomes’ role within the cell is fundamental to comprehending cellular homeostasis and the pathology of lysosomal storage diseases.