_Biology_-Entrance_Exam___Universidad_de_Navarra__unit_4

Biology - Entrance Exam (Universidad de Navarra)

Unit 4 - Morphology, Structure, and Cellular Functions

Cell Morphology

• Definition: Cell morphology refers to the distinctive structural features and shapes of cells which are essential for defining their functions and roles in biological processes.

• Techniques: Various microscopy methods are employed to assess cellular characteristics, including:

  • Shape: The geometric appearance of a cell, indicative of its function.

  • Structure: The internal organization, detailing the arrangement of organelles.

  • Form: Overall outline and appearance of a cell.

  • Color: Often indicates certain metabolic states or structural attributes.

  • Texture: Surface characteristics impacting cell interactions with their surroundings.

  • Pattern: Organizational layout of cells within tissues, critical for organ functionality.

  • Size: Measurement of cell dimensions, which influences interactions and functionalities.

• Bacteriology: A specialization within microbiology focused on classifying bacteria based on their shape and size, assisting in taxonomy and understanding their pathogenicity.

Classification of Bacterial Cells by Morphology

• Bacterial cells are unicellular organisms categorized mainly by their shape:

  • Coccus (cocci): Spherical-shaped bacteria, which may cluster (staphylococci) or form chains (streptococci).

  • Bacillus (bacilli): Rod-shaped bacteria, which can occur singly or in chains.

  • Spiral: Twisted form, classified into spirilla (rigid) and spirochetes (flexible).

  • Vibrio: Comma-shaped bacteria, some of which are associated with diseases like cholera.

Eukaryotic Cell Morphology

• Overview: Eukaryotic cells are defined by the presence of a true nucleus and membrane-bound organelles, facilitating the compartmentalization of cellular functions.

• Plant Cell Morphology:

  • Featuring a rigid cell wall composed of cellulose, which gives structural support and shape. Variations include:

    • Epidermal cells: Rectangular-shaped, providing a protective barrier and minimizing water loss.

    • Cortex cells: Isodiametric forms, primarily involved in storage and structural support.

    • Sclerenchyma cells: Stone-like cells that provide mechanical strength.

    • Parenchyma cells: Round to brick-like cells that perform storage and metabolic activities.

Mammalian Cell Morphology Differences

• Types of Mammalian Cells:

  • Epithelial Cells: Characterized by regular rectangularity, forming barriers and protective layers.

  • Fibroblast-like Cells: Spindle-shaped cells that are crucial for connecting tissues.

  • Lymphoblast-like Cells: Globular cells capable of growing in suspension, playing major roles in the immune system.

• Epithelial Cell Example: Synovial fibroblasts have a spindle shape and are significant for joint health.

Microscopy Techniques

• Light Microscopes: Allow for studying stained or live cells, magnifying up to 1,000x, enabling the observation of cell shapes.

• Electron Microscopes: Provide greater magnification (up to 1 million times), revealing fine details of internal cellular structures.

Types of Cells

• Prokaryotic Cells:

  • Size: Generally smaller and simpler than eukaryotic cells, mainly represented by bacteria and archaea.

  • Characteristics:

    • Composed of cytoplasm, with genomic material organized in a nucleoid region.

    • The cell wall contains peptidoglycans, offering protection and stability.

    • Lack membrane-bound organelles, allowing for a simplified organization.

    • May possess flagella for movement and protective capsules against environmental conditions.

• Eukaryotic Cells:

  • Complexity: More intricate than prokaryotic cells, inclusive of fungi, protists, plants, and animals.

  • Organelles: Eukaryotic cells contain specialized organelles, many unique to this group, enabling various functions.

  • Plasma Membrane:

    • Comprising a bilayer of phospholipids and proteins that regulate substance movement across the membrane.

    • Fluid-Mosaic Model: Describes the arrangement of lipids and proteins in the membrane, critical for signaling and interactions.

Functions of Cell Membrane

• Provides mechanical support and defines cell shape.

• Regulates the exchange of substances due to its semi-permeable nature, ensuring controlled material flow.

• Facilitates communication between cells and their environment, essential for responding to external stimuli.

The Nucleus

• Largest organelle, serves as the control center for cell activities including growth, metabolism, and replication.

• Houses DNA organized into chromosomes, which hold genetic instructions vital for cell functioning.

• Nucleolus: A specialized region for synthesizing ribosomal RNA (rRNA) and assembling ribosomes essential for protein synthesis.

Ribosomes

• Sites for protein synthesis made of ribosomal RNA and proteins; can be found free in the cytoplasm or bound to the endoplasmic reticulum (ER), which indicates their role in either cytosolic or membrane-associated protein synthesis.

Endoplasmic Reticulum (ER)

• A continuous membrane network offering structural support and transport within cells:

  • Rough ER: Studded with ribosomes, involved in synthesizing and transporting proteins.

  • Smooth ER: Lacks ribosomes, takes part in lipid synthesis and detoxification, vital for metabolic processes.

Golgi Complex

• Modifies, processes, and sorts proteins received from the rough ER.

• Packages materials into vesicles for transport, critical for both secretion and intracellular distribution.

Mitochondria

• Often called the cell's powerhouses, convert energy from organic compounds into ATP during cellular respiration.

• Composed of inner and outer membranes, and play key roles in maintaining calcium balance and apoptosis (programmed cell death), contributing to cellular functionality.

Lysosomes

• Membrane-bound vesicles with digestive enzymes; responsible for breaking down cellular waste, organelles, and external particles through hydrolysis techniques.

• They are vital for executing apoptosis, ensuring removal of damaged cells while maintaining homeostasis.

Vacuoles

• Fluid-filled compartments used for storage of substances like water, waste, and nutrients, essential for maintaining cell turgor in plant cells.

Peroxisomes

• Organelles that detoxify harmful metabolic by-products, generating hydrogen peroxide, which is in turn decomposed into water and oxygen.

• Engage in fatty acid oxidation and lipid synthesis, crucial for cellular health.

Cytoskeleton

• A dynamic network of protein filaments that determines cell shape, provides structural support, and aids in cellular movements:

  • Microtubules: Hollow tubes that offer rigidity and structural integrity; involved in cell division and intracellular transport.

  • Microfilaments: Thin fibers that facilitate cellular movements, primarily composed of actin, which aid muscle contraction and motility.

Plant vs. Animal Cells

• Plant Cells:

  • Possess a rigid cell wall, chloroplasts for photosynthesis, large central vacuoles for storage, and lack centrioles. The chloroplasts contain chlorophyll essential for converting sunlight into chemical energy.

• Animal Cells:

  • Do not have cell walls or chloroplasts but may contain centrioles that assist in organizing cell division processes.

Plasmodesmata

• Specialized channels connecting plant cells to permit direct communication and exchange of substances, essential for coordinating physiological responses within plant tissues.

Vesicles

• Can be formed naturally through membrane processes or artificially in laboratory conditions; essential for transporting materials and substances within cells, serving various cellular functions.

Membrane Transport Mechanisms

• Passive Transport: Involves movement of substances down a concentration gradient without energy input (e.g., diffusion and osmosis) to maintain cellular equilibrium.

• Facilitated Diffusion: Requires transport proteins to assist in the movement of polar or charged substances across membranes without expending energy.

• Active Transport: Moves substances against their concentration gradient, using energy (typically from ATP) to maintain concentration gradients (e.g., sodium-potassium pump).

• Endocytosis and Exocytosis: Processes that allow larger molecules to move into (endocytosis) or out of (exocytosis) the cell through vesicles, crucial for nutrient uptake and waste management.

Glycolysis

• The initial phase of cellular respiration that occurs in the cytosol, where glucose is broken down into two molecules of pyruvate, generating ATP and NADH as by-products.

Fermentation

• An anaerobic metabolic process that occurs when oxygen is absent, allowing glycolysis to continue by regenerating NAD+ from NADH, sustaining energy production.

Lactic Acid Fermentation

• A specific type of fermentation where pyruvate is converted into lactate, taking place mainly in muscle cells during low oxygen conditions, leading to the short-term buildup of lactate.

Chemosynthesis

• A process through which certain organisms synthesize organic compounds using chemical energy derived from inorganic substances, distinguishing it from photosynthesis, which utilizes sunlight for energy.

Laboratory Practices in Cell Studies

• Emphasizing safe laboratory methodologies is essential before performing experiments, ensuring accurateness in results and safety for all personnel involved.

• Employing various microscopy techniques (both light and electron) alongside subcellular fractionation is critical for isolating and studying organelles, helping comprehend cellular functions thoroughly.

Mitosis and Meiosis

• Mitosis: A crucial process of somatic cell division in eukaryotes that results in two genetically identical daughter cells, maintaining the same chromosome number as the original cell. The process is vital for growth, repair, and asexual reproduction and includes several phases:

  • Prophase: Chromatin condenses into visible chromosomes, and the nuclear envelope begins to disintegrate. Spindle fibers start to form from the centrosomes.

  • Metaphase: Chromosomes align along the metaphase plate, ensuring each sister chromatid is attached to spindle fibers from opposite poles.

  • Anaphase: Sister chromatids are pulled apart toward opposite poles of the cell, ensuring each new cell will receive an identical set of chromosomes.

  • Telophase: Chromatids arrive at the poles, the nuclear envelope reforms around each set of chromosomes, and chromosomes begin to decondense back to chromatin.

  • Cytokinesis: The cytoplasm divides, resulting in two distinct daughter cells, each with a complete set of chromosomes.

• Meiosis: A specialized type of cell division crucial for sexual reproduction, producing four non-identical daughter cells known as gametes, with half the chromosome number of the parent cell (haploid). Meiosis enhances genetic variation through two successive divisions:

  • Meiosis I: This reduction division includes several phases:

    • Prophase I: Homologous chromosomes pair up and exchange genetic material through crossing-over, increasing genetic diversity.

    • Metaphase I: Paired chromosomes align at the metaphase plate, the orientation is random, contributing to genetic variation in the resulting gametes.

    • Anaphase I: Homologous chromosomes are pulled apart to opposite poles, reducing the chromosome number by half.

    • Telophase I: Chromosomes reach the poles, and the cell divides through cytokinesis, resulting in two haploid cells.

  • Meiosis II: Similar to mitosis but operates on the two haploid cells produced from Meiosis I, including:

    • Prophase II: Spindle formation occurs in each haploid cell, and the nuclear envelope disintegrates if it was present.

    • Metaphase II: Chromosomes align on the metaphase plate in each cell.

    • Anaphase II: Sister chromatids are separated and pulled to opposite poles.

    • Telophase II: Chromatids reach the poles, and nuclear envelopes reform around each set, leading to the final division of the cells.

    • Cytokinesis: The cytoplasm divides, yielding a total of four non-identical haploid gametes, each genetically unique due to the processes of crossing-over and independent assortment.

This detailed understanding of mitosis and meiosis is crucial for comprehending cellular reproduction and the mechanisms that underpin genetic inheritance.