Unit 1: Biomolecules & Cell Biology Notes

Biomolecules and cell biology

1.1: Biomolecules – Introduction and Functions

Biomolecules are organic molecules essential for the structure, function, and regulation of living organisms. They encompass a diverse range of molecules, each with specific roles critical for life processes.

1. Carbohydrates:

  • Functions:
  • Energy Source: Carbohydrates serve as the primary energy source for cellular metabolism, providing readily available fuel for cellular processes.
  • Structural Role: Certain carbohydrates, such as cellulose in plant cell walls and chitin in fungal cell walls, provide structural support and rigidity to cells and tissues.
  • Cellular Recognition: Carbohydrates on the surface of cells participate in cell-cell recognition and adhesion processes, essential for immune responses, cell signaling, and development.

2. Proteins:

  • Functions:
  • Enzymatic Catalysis: Proteins act as enzymes, catalyzing biochemical reactions by lowering the activation energy required for the reaction to proceed.
  • Structural Support: Structural proteins, such as collagen in connective tissues and keratin in hair and nails, provide strength and support to cells and tissues.
  • Transport: Certain proteins, such as hemoglobin, transport molecules like oxygen and carbon dioxide in the bloodstream.
  • Cell Signaling: Signaling proteins, such as hormones and receptors, regulate cellular processes by transmitting signals between cells or within cells.
  • Immune Response: Antibodies, a type of protein, recognize and neutralize foreign substances (antigens) to protect the body from infections.

3. Lipids:

  • Functions:
  • Energy Storage: Lipids, particularly triglycerides, serve as a concentrated energy reserve in adipose tissue, providing a long-term source of metabolic fuel.
  • Cell Membrane Structure: Phospholipids are major components of cell membranes, forming a lipid bilayer that regulates the passage of substances into and out of cells.
  • Insulation: Lipids, such as adipose tissue, provide thermal insulation, helping to maintain body temperature in vertebrates.
  • Hormone Production: Steroid hormones, derived from cholesterol, regulate various physiological processes, including metabolism, immune response, and reproduction.

4. Nucleic Acids:

  • Functions:
  • Genetic Information Storage: DNA (deoxyribonucleic acid) stores the genetic information necessary for the development, growth, and functioning of organisms.
  • Gene Expression: RNA (ribonucleic acid) mediates the expression of genetic information by transcribing DNA into messenger RNA (mRNA) and translating mRNA into proteins.
  • Regulation of Gene Expression: Non-coding RNAs, such as microRNAs (miRNAs) and small interfering RNAs (siRNAs), regulate gene expression by controlling mRNA stability and translation.

5. Minerals:

  • Functions:
  • Structural Role: Minerals, such as calcium and phosphorus, contribute to the formation and maintenance of bone and tooth structure, providing strength and rigidity.
  • Electrolyte Balance: Sodium, potassium, and chloride ions maintain electrolyte balance in cells and tissues, essential for nerve function, muscle contraction, and fluid balance.
  • Cofactors for Enzymes: Some minerals, such as iron and zinc, serve as cofactors for enzymes, facilitating their catalytic activity in biochemical reactions.

6. Enzymes:

  • Functions:
  • Catalysis: Enzymes accelerate biochemical reactions by lowering the activation energy required for the reaction to proceed, without being consumed in the process.
  • Specificity: Each enzyme exhibits specificity for its substrate(s), recognizing and binding to specific molecules to catalyze a particular reaction.
  • Regulation: Enzyme activity is regulated through various mechanisms, including allosteric regulation, covalent modification, and feedback inhibition, to maintain metabolic homeostasis.

7. Water:

  • Functions:
  • Solvent: Water is the universal solvent, facilitating the dissolution and transport of ions and polar molecules in biological systems.
  • Temperature Regulation: Water’s high specific heat capacity and heat of vaporization contribute to temperature regulation in organisms, preventing rapid fluctuations in body temperature.
  • Chemical Reactant: Water participates in biochemical reactions, serving as a reactant or product in metabolic processes such as hydrolysis and dehydration synthesis.

1.2: Cell Structure

The cell is the fundamental unit of life, exhibiting remarkable complexity and diversity in its structure and function. Understanding the intricacies of cell structure provides insights into cellular organization and the processes that sustain life.

1. Introduction to Cells:

Cells are the basic building blocks of living organisms, capable of independent existence and carrying out essential life processes. They vary widely in size, shape, and complexity, reflecting their specialized functions within multicellular organisms.

2. Concepts of Prokaryotic and Eukaryotic Cells:

Cells can be classified into two main categories based on their structural organization and complexity:

  • Prokaryotic Cells:
  • Characteristics:
    • Lack a membrane-bound nucleus; the genetic material is typically located in a nucleoid region.
    • Lack membrane-bound organelles.
    • Typically smaller and simpler in structure compared to eukaryotic cells.
  • Examples: Bacteria and archaea.
  • Eukaryotic Cells:
  • Characteristics:
    • Contain a membrane-bound nucleus that houses the genetic material (DNA).
    • Possess membrane-bound organelles, each with specific functions and compartments.
    • Generally larger and more complex than prokaryotic cells.
  • Examples: Plant cells, animal cells, fungal cells, and protist cells.

3. Detailed Structure of Eukaryotic Cells:

Eukaryotic cells exhibit a high degree of structural organization, with various organelles performing specialized functions essential for cellular processes. The following is an in-depth exploration of the major organelles found in eukaryotic cells:

  • Cell Wall:
  • Composition: Found primarily in plant cells, composed of cellulose fibers embedded in a matrix of other polysaccharides and proteins.
  • Function: Provides structural support, protection against mechanical stress, and helps maintain cell shape.
  • Cell Membrane (Plasma Membrane):
  • Structure: Composed of a phospholipid bilayer embedded with proteins, cholesterol, and carbohydrates.
  • Function: Regulates the passage of substances in and out of the cell, maintains cell integrity, and facilitates cell signaling and communication.
  • Cytoplasm:
  • Composition: Gel-like matrix composed of water, salts, organic molecules, and various organelles.
  • Function: Houses organelles, facilitates cellular processes, and provides structural support.
  • Organelles:
  • Mitochondria:
    • Structure: Double membrane-bound organelles with an outer membrane and inner membrane folded into cristae.
    • Function: Site of aerobic cellular respiration and ATP production, which provides energy for cellular processes.
  • Plastids:
    • Types: Chloroplasts, chromoplasts, and amyloplasts.
    • Function: Chloroplasts are involved in photosynthesis, chromoplasts synthesize and store pigments, and amyloplasts store starch.
  • Endoplasmic Reticulum (ER):
    • Types: Rough ER (with ribosomes) and smooth ER (lacks ribosomes).
    • Function: Rough ER is involved in protein synthesis and modification, while smooth ER participates in lipid synthesis, detoxification, and calcium ion storage.
  • Golgi Apparatus (Golgi Bodies):
    • Structure: Consists of flattened membrane-bound sacs (cisternae).
    • Function: Modifies, sorts, and packages proteins and lipids synthesized in the ER for secretion or transport to other cellular locations.
  • Lysosomes:
    • Structure: Membrane-bound vesicles containing hydrolytic enzymes.
    • Function: Digestion of macromolecules, recycling of cellular components, and programmed cell death (apoptosis).
  • Ribosomes:
    • Structure: Composed of ribosomal RNA (rRNA) and protein.
    • Function: Site of protein synthesis, translating mRNA into polypeptide chains.
  • Nucleus:
    • Structure: Membrane-bound organelle containing chromatin (DNA and proteins) and a nucleolus.
    • Function: Stores genetic material, regulates gene expression, and controls cellular activities.
  • Cilia and Flagella:
    • Structure: Microtubule-based structures projecting from the cell surface.
    • Function: Involved in cell motility, movement of fluids over cell surfaces, and sensing environmental stimuli.

4. Cell Inclusions:

In addition to organelles, eukaryotic cells may contain various non-membrane-bound structures called cell inclusions, which serve diverse functions:

  • Storage Granules: Accumulate and store reserve materials such as starch granules (amyloplasts) or lipid droplets.
  • Pigment Granules: Store pigments responsible for coloration, such as melanin granules in skin cells.
  • Vacuoles: Membrane-bound organelles involved in storage, waste management, and maintaining turgor pressure in plant cells.

1.3: Cell Division

Cell division is a fundamental process in biology that ensures the growth, development, and reproduction of organisms. It involves the replication and distribution of genetic material to produce daughter cells with identical or diverse genetic information.

1. Cell Cycle:

The cell cycle is a highly regulated process that encompasses the series of events from the formation of a new cell to its division into daughter cells. It consists of distinct phases, each crucial for the successful completion of cell division.

  • Interphase:
  • G1 Phase (Gap 1): The cell grows and performs its normal functions, preparing for DNA replication.
  • S Phase (Synthesis): DNA replication occurs, resulting in the duplication of genetic material.
  • G2 Phase (Gap 2): The cell continues to grow and prepares for cell division by synthesizing proteins and organelles necessary for mitosis.
  • M Phase (Mitotic Phase):
  • Mitosis: The nucleus divides into two daughter nuclei, each containing an identical set of chromosomes.
  • Cytokinesis: The cytoplasm divides, resulting in the formation of two daughter cells.

2. Types of Cell Division:

Cell division can occur through various mechanisms, each serving specific purposes in different organisms and physiological contexts.

  • Amitosis:
  • Description: Amitosis, also known as direct cell division, is a simple process in which the cell divides into two daughter cells without undergoing nuclear division (karyokinesis).
  • Occurrence: Commonly observed in unicellular organisms such as bacteria and some protists for reproduction.
  • Process: The parent cell elongates and undergoes constriction, leading to the formation of two daughter cells with equal cytoplasmic contents.
  • Mitosis:
  • Description: Mitosis is a complex process of nuclear division that results in the formation of two genetically identical daughter nuclei.
  • Phases of Mitosis:
    1. Prophase: Chromatin condenses into visible chromosomes, the nuclear envelope breaks down, and spindle fibers form.
    2. Metaphase: Chromosomes align at the metaphase plate, attached to spindle fibers at their centromeres.
    3. Anaphase: Sister chromatids separate and move toward opposite poles of the cell.
    4. Telophase: Chromosomes decondense, nuclear envelopes reform around each set of chromosomes, and spindle fibers disassemble.
  • Significance: Mitosis plays a crucial role in growth, tissue repair, and asexual reproduction in multicellular organisms.
  • Meiosis:
  • Description: Meiosis is a specialized form of cell division that occurs in germ cells (e.g., sperm and egg) and results in the formation of haploid gametes.
  • Phases of Meiosis:
    1. Meiosis I: Reduction division, where homologous chromosomes pair, exchange genetic material (crossing over), and segregate into separate daughter cells.
    2. Meiosis II: Resembles mitosis but involves the separation of sister chromatids, resulting in the formation of four haploid daughter cells.
  • Significance: Meiosis ensures genetic diversity in sexually reproducing organisms by shuffling genetic material and producing genetically unique gametes.

3. Regulation of Cell Division:

Cell division is tightly regulated by various cellular mechanisms to maintain genomic integrity and prevent aberrant proliferation.

  • Cell Cycle Checkpoints:
  • G1 Checkpoint: Ensures conditions are favorable for DNA synthesis before entering the S phase.
  • G2 Checkpoint: Verifies DNA replication and checks for any DNA damage before proceeding to mitosis.
  • Metaphase Checkpoint: Monitors proper chromosome alignment and attachment to spindle fibers before anaphase onset.
  • Regulatory Proteins:
  • Cyclins and Cyclin-Dependent Kinases (CDKs): Key regulators of cell cycle progression, activating various checkpoints and controlling transitions between cell cycle phases.
  • Tumor Suppressors and Oncogenes: Genes involved in the regulation of cell growth and division, mutations in these genes can lead to uncontrolled cell proliferation and cancer development.

Certainly! Here are some exam-based questions covering Unit 1, including all chapters on biomolecules and cell biology:

Biomolecules & Cell Biology – Exam Questions

1. Biomolecules:

  1. Define biomolecules and provide examples of different classes of biomolecules. Discuss their roles in living organisms.
  2. Explain the structural differences between carbohydrates, lipids, proteins, and nucleic acids. How do these structural differences relate to their functions in cells?
  3. Describe the importance of enzymes in biological systems. Discuss how enzymes facilitate biochemical reactions and their specificity for substrates.

2. Cell Biology:

  1. Compare and contrast prokaryotic and eukaryotic cells. Highlight their structural differences and similarities, as well as their significance in biological systems.
  2. Explain the structure and function of the following organelles in eukaryotic cells: mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes.
  3. Discuss the significance of the cell membrane (plasma membrane) in maintaining cell integrity and regulating the passage of substances. How does its structure contribute to its functions?

3. Cell Division:

  1. Describe the stages of the cell cycle and the key events that occur during each phase. Discuss the significance of checkpoints in regulating the cell cycle.
  2. Differentiate between mitosis and meiosis. Explain the processes involved in each type of cell division and their respective outcomes.
  3. Discuss the implications of errors in cell division, such as chromosomal abnormalities and mutations, on organismal development and health.

Bonus Question:

  1. Consider a scenario where a new species of single-celled organism is discovered. Design an experiment to determine whether the organism undergoes mitosis, meiosis, or a combination of both during cell division. Provide a hypothesis, experimental design, and expected results.

These exam-based questions cover various topics within Unit 1, allowing students to demonstrate their understanding of biomolecules, cell structure, and cell division processes. Adjustments can be made based on the specific focus and level of the exam.