A Tour of the Cell Study Notes

Chapter: A Tour of the Cell

  • Introduction to Cells

    • All cells have certain key components:

    • Nucleic Acids: Store and transmit genetic information.

    • Proteins: Perform most of the cell's functions, synthesized by ribosomes.

    • Carbohydrates: Provide chemical energy, structural support, and cellular identity.

    • Plasma Membrane: A selectively permeable barrier that encloses the cell.

Grouping Different Types of Cells

  • Cells can be grouped based on morphology and phylogeny:

    • Morphological Groupings:

    • Prokaryotes: Lack a membrane-bound nucleus.

    • Eukaryotes: Have a membrane-bound nucleus.

    • Phylogenetic Groupings: Three domains of life:

      • Bacteria

      • Archaea

      • Eukarya

Structure of Prokaryotic Cells

  • Key Components of Prokaryotic Cells:

    • Fimbriae: Attachment structures on some prokaryotic surfaces.

    • Ribosomes: Complexes that synthesize proteins.

    • Plasma Membrane: Encloses the cytoplasm.

    • Cell Wall: Rigid structure outside the plasma membrane.

    • Glycocalyx: Outer coating, can be in the form of a capsule or slime layer.

    • Flagella: Locomotion organelles in some prokaryotes.

    • Nucleoid: Region where the cell's DNA resides, not membrane-bound.

    • DNA Packaging: Chromosomal DNA is elongated and supercoiled, e.g., E. coli chromosome and plasmids.

Introduction to Eukaryotic Cells

  • Key Differences Between Eukaryotic and Prokaryotic Cells:

    • Eukaryotic chromosomes are enclosed within a membrane-bound nucleus.

    • Eukaryotic cells tend to be larger than prokaryotic cells.

    • Eukaryotic cells have extensive internal membranes containing numerous organelles, enhancing reaction efficiency and separating incompatible reactions.

    • Eukaryotic cells possess a diverse and dynamic cytoskeleton.

Animal Cell Structure

  • Key Components of Animal Cells:

    • Flagellum: Motility structure made of microtubules within the plasma membrane.

    • Endoplasmic Reticulum (ER): Network of membranous sacs and tubes involved in synthesis:

    • Rough ER: Studded with ribosomes, synthesizes proteins.

    • Smooth ER: Involved in lipid synthesis, detoxification, reservoir for Ca2+ ions.

    • Nucleus: Contains chromatin (DNA and proteins).

    • Nuclear Envelope: Double membrane enclosing the nucleus, contains pores.

    • Nucleolus: Produces ribosomes.

    • Golgi Apparatus: Modifies, sorts, and secretes cell products.

    • Mitochondrion: Site for cellular respiration and ATP generation.

    • Lysosome: Digestive organelle that hydrolyzes macromolecules.

    • Centrosome: Initiates microtubule formation.

    • Peroxisome: Contains enzymes for specific metabolic processes.

    • Microvilli: Projections increasing surface area for absorption.

    • Cytoskeleton Components:

    • Ribosomes: Sites of protein synthesis.

    • Microfilaments, Intermediate Filaments, Microtubules: Support the cell's shape, movement, and transport functions.

Plant Cell Structure

  • Key Components of Plant Cells:

    • Similar to animal cells but includes:

    • Chloroplast: Site of photosynthesis, converting sunlight to chemical energy.

    • Cell Wall: Maintains cell shape and protects from mechanical damage.

    • Central Vacuole: Storage and waste breakdown, critical for plant growth.

    • Plasmodesmata: Cytoplasmic channels connecting adjacent cells for communication.

The Nucleus and Its Envelope

  • Structure of the Nucleus:

    • Nuclear Envelope: Composed of inner and outer membranes with nuclear pores.

    • Nuclear Pores: Ringed by protein complexes regulating molecular transport.

    • Nuclear Lamina: A network lining the inner surface, providing structural support.

    • Chromatin: The complex of DNA and proteins in the nucleus; condensed into chromosomes during cell division.

Nuclear Import Mechanism

  • Protein Import into the Nucleus:

    • Nuclear localization signal (NLS): A specific sequence of 17 amino acids that directs proteins to the nucleus.

Ribosomes and the Endoplasmic Reticulum (ER)

  • Ribosome Structure: Composed of large and small subunits, can be free in the cytosol or bound to the rough ER.

  • Functions of the ER:

    • Rough ER: Protein synthesis.

    • Smooth ER: Lipid synthesis, catalyzes reactions involving lipids, and calcium ion storage.

Golgi Apparatus Functionality

  • Structure:

    • Composed of cisternae with distinct sides:

    • Cis face: Receiving side for vesicles.

    • Trans face: Shipping side for vesicle transportation.

  • Cisternal Maturation: Movement of Golgi cisternae from cis to trans, with vesicles transporting products between ER and Golgi.

Lysosomes

  • Function of Lysosomes:

    • Engage in autophagy (recycling cellular components) and phagocytosis (digestion of engulfed materials).

    • Hydrolytic enzymes facilitate the digestion of organelle components by fusing with vesicles containing damaged organelles.

Endomembrane System Relationships

  • Components include:

    • Nuclear envelope connected to rough ER, which is continuous with smooth ER.

    • Vesicles transport proteins to Golgi for processing and from Golgi to plasma membrane for secretion or to lysosomes for digestion.

Protein Sorting and Delivery**

  • Steps During Sorting:

    1. Ribosome deposits protein in ER.

    2. Protein exits ER.

    3. Protein enters Golgi.

    4. Protein exits Golgi.

    5. Protein exits cell (via exocytosis).

The Plant Cell's Central Vacuole

  • Functions:

    • Storage of various substances, breakdown of waste products, and contributes to plant growth through vacuole enlargement.

Structure and Function of the Cytoskeleton

  • Microtubules:

    • Dimension: 25 nm diameter with hollow tubes made of tubulin.

    • Functions: Maintenance of cell shape, motility, and organelle movement.

  • Microfilaments:

    • Dimension: 7 nm diameter comprised of actin.

    • Functions: Maintenance of cell shape, muscle contraction, cytoplasmic streaming, and cell motility.

  • Intermediate Filaments:

    • Dimension: 8-12 nm, made of various proteins like keratins.

    • Functions: Provide structural support and anchorage for organelles.

Motor Proteins and Cellular Motion

  • Functionality of Motor Proteins:

    • Facilitate movement along microtubules and microfilaments, powered by ATP.

    • Essential for transporting vesicles, especially in neurons.

Cell Wall Structure

  • Cell Wall: Present in fungi, algae, and plants, providing rigid protection and maintaining cell shape.

Extracellular Matrix (ECM) of Animal Cells

  • Components: Fibronectin, integrins, proteoglycans, and collagen fibers.

    • Functions: ECM facilitates cell communication, structural support, and attachment of cells.

Cell Junctions in Animal Tissues

  • Types of Junctions:

    • Tight Junctions: Prevent fluid movement between cells.

    • Desmosomes: Anchor adjacent cells together.

    • Gap Junctions: Allow communication between cells through small pores.

Plasmodesmata in Plant Cells

  • Functionality: Cytoplasmic channels facilitate communication and transport between adjacent plant cells.

Dynamic Nature of Eukaryotic Cells

  • Cellular Activity:

    • Approximately 10 million ATP molecules are used and synthesized per second in human cells.

    • Cellular enzymes can catalyze over 25,000 reactions per second, showcasing high metabolic activity.

    • Membrane phospholipids can traverse the cellular compartment within one minute, indicating dynamic membrane properties.

    • Continuous replacement of mitochondria occurs approximately every 10 days, maintaining cellular energy supply throughout life.

    • Ongoing changes in plasma membrane composition reflect active cellular processes.