A Tour of the Cell Study Notes

Lecture Overview

  • Presenters: Nicole Tunbridge and Kathleen Fitzpatrick

  • Subject: A Tour of the Cell

  • Publication Year: 2017

  • Publisher: Pearson Education, Inc.

Fundamental Units of Life

  • All organisms are made of cells: The cell is recognized as the basic unit of life.

  • Simplest living matter: The cell represents the simplest collection of matter that can sustain life.

  • Descent of cells: All cells are connected through their evolutionary history, sharing common ancestry.

  • Diversity of cells: While cells vary significantly in structure and function, they also exhibit common features.

Microscopy and Study of Cells

Concept 6.1: Cell Visualization Techniques

  • Microscopes: Essential tools for studying cells due to their small size, typically not visible to the naked eye.

Types of Microscopes

  • Light Microscopes (LM): Utilize visible light passing through specimens. Image magnification occurs through glass lenses that bend the light.

    • Parameters in Microscopy:

    • Magnification: Ratio of image size to actual size.

    • Resolution: Clarity measure of an image; indicates the minimum distance between two distinguishable points.

    • Contrast: Variability in brightness between different parts of the sample.

Comparison of Cell Sizes and Microscopy Types

  • Cell sizes: Examples include frog eggs (approx. 1 mm), human height (1.7 m), most plant and animal cells (10–100 µm), and organelles like ribosomes (20 nm).

  • Types of microscopy: Evolvement of microscopy tools has led to various methods that enhance image quality (e.g., Electron Microscopy (EM) and Confocal Microscopy).

    • Light microscopy provides up to 1,000 times magnification but cannot resolve organelles efficiently, especially in eukaryotic cells.

  • Examples of Imaging Techniques:

    • Brightfield microscopy: Commonly used for both stained and unstained specimens.

    • Phase-contrast and Differential interference contrast (Nomarski): Techniques that enhance the contrast of transparent specimens.

Advances in Light Microscopy

  • Fluorescence Microscopy: Allows visualization of specific cellular components using fluorescent markers.

  • Super-resolution Microscopy: Enables observations at nanometer scales (10–20 nm).

Cell Fractionation and Organelles

Concept 6.2: Eukaryotic Cells

  • Compartmentalization: Eukaryotic cells include internal membranes that compartmentalize their functions.

  • Types of Cells: Prokaryotic cells (Bacteria and Archaea) vs. eukaryotic cells (Protists, fungi, animals, and plants).

  • Basic components of all cells:

    • Plasma Membrane: Selective barrier for entry and exit of materials.

    • Cytosol: Semi-fluid substance within cells.

    • Ribosomes: Sites for protein synthesis.

Cell Fractionation Methodology

  • Definition: The process of separating cellular components by breaking down cells and using centrifugation.

  • Centrifuge utilization: To separate organelles based on their size and density through differential centrifugation.

Structure of Eukaryotic and Prokaryotic Cells

Comparative Features

  • Prokaryotic Cells:

    • No nucleus; DNA located in nucleoid region.

    • Absence of membrane-bound organelles; cytoplasm bound by plasma membrane.

    • Generally smaller than eukaryotic cells.

Eukaryotic Cells**:

  • Possess a nucleus bounded by a double membrane.

  • Contain various membrane-bound organelles and are generally larger than prokaryotic cells.

Cellular Dimensions and Scaling

  • Metabolic requirements: Limit cell size, governed by the surface area-to-volume ratio.

  • As cell size increases, its volume grows more than its surface area, enforcing structural limits.

Overview of Key Organelles

Nucleus

  • Contains the majority of a eukaryotic cell's DNA.

  • Surrounded by a double membrane, separating it from the cytoplasm, with nuclear pores for material exchange.

Ribosomes

  • Composed of ribosomal RNA and proteins; can be found freely in the cytosol or bound to the endoplasmic reticulum.

  • Cellular locations impact their functions in protein synthesis.

Endomembrane System

  • Comprises several interconnected organelles:

    • Nuclear envelope

    • Endoplasmic reticulum (smooth and rough)

    • Golgi apparatus

    • Lysosomes

    • Vacuoles

    • Plasma membrane

  • Functions in regulating traffic of proteins and performing metabolic duties.

Organelle Functions

Endoplasmic Reticulum (ER)

  • Smooth ER: Involved in lipid synthesis, metabolic processes, and detoxification of drugs.

  • Rough ER: Has ribosomes that synthesize glycoproteins, distribute transport vesicles, and serve as a membrane factory.

Golgi Apparatus

  • Modifies, sorts, and packages proteins and macromolecules for transport.

  • Composed of flattened membrane sacs (cisternae) that have a receiving (cis) and shipping (trans) side.

Lysosomes

  • Membranous sacs containing hydrolytic enzymes that digest macromolecules; function optimally in their acidic environments.

  • Involved in phagocytosis (engulfing cells) and autophagy (recycling organelles).

Vacuoles

  • Large vesicles with various functions depending on cell type (e.g., food vacuoles, contractile vacuoles in protists, central vacuoles in plants).

Energy Conversion Organelles

Mitochondria

  • Sites for cellular respiration; generate ATP using oxygen for energy.

  • Structure: double membrane with an inner membrane folded into cristae for increased surface area for ATP production associated with metabolic enzymes.

Chloroplasts

  • Conduct photosynthesis; contain chlorophyll for capturing light energy and converting it into chemical energy in plants and algae.

  • Structure includes thylakoids stacked as granum and liquid stroma.

Peroxisomes

  • Bounded by a single membrane, involved in oxidation reactions, converting hydrogen peroxide to water.

  • Still under study for their functional relationship with other organelles.

Cytoskeleton Structure and Function

Concept 6.6: Roles of Cytoskeleton

  • Cytoskeleton components: Optical framework extended throughout the cytoplasm. Key responsibilities include maintaining the cell's shape and supporting organelle positioning.

  • Types of fibers:

    • Microtubules: Thickest; composed of tubulin; involved in shape maintenance, organelle movement, and chromosomal separation during cell division.

    • Microfilaments: Thinnest; composed of actin; involved in maintenance of cell shape, muscle contraction, and cellular motility.

    • Intermediate Filaments: Provide structural support and are more permanent fixtures than other components.

Cell Motility and Support

  • Interaction with motor proteins: Microtubules provide tracks for vesicle movement facilitated by motor proteins, like dyneins and kinesins.

Extracellular Structures and Cell Junctions

Concept 6.7: Cellular Coordination

  • Extracellular components: Cells often synthesize external materials, influencing their operational dynamics through interactions with neighboring cells.

Plant Cell Walls

  • Structure distinguishes plant cells; made of cellulose fibers; provides shape and prevents excessive water uptake.

  • Layers of the cell wall include primary cell wall, middle lamella, and in some cases, secondary cell wall.

Extracellular Matrix (ECM) in Animal Cells

  • Made of glycoproteins (collagen, proteoglycans, fibronectin) that bind to integrins on the plasma membrane, affecting cellular behavior and gene regulation.

Cell Junction Types in Animal Cells

  • Tight Junctions: Prevent fluid leakage between neighboring cells.

  • Desmosomes: Anchor cells into strong sheets.

  • Gap Junctions: Allow communication via cytoplasmic channels between adjacent cells.

Integration Within Cells

Concept 6.8: Holistic Functionality

  • Integration of cellular structures and organelles allows for efficient functioning; for example, macrophages utilize coordinated components like lysosomes and the cytoskeleton to engulf bacteria efficiently.