Cell Structure and Function Study Notes

Cellular Function and Microscopy

  • Cell Size and Functionality
    • The relationship between cell size and functionality shows that closer proximity among components optimizes cell function.
    • As cell size increases, the functional ratio diminishes leading to decreased effectiveness.

Types of Microscopes

  • Light Microscope
    • Standard microscope used in laboratory settings.
  • Transmission Electron Microscope (TEM)
    • Provides higher resolution for internal visualization through thin sections of cells.
  • Scanning Electron Microscope (SEM)
    • Offers surface viewing; can visualize structures like the tracheal villi.

Resolution in Microscopy

  • Resolution refers to the clarity and detail visible in the microscope image.
  • Higher resolution allows better observation of structures such as cell membranes and organelles.

Cell Membrane Composition

  • Extracellular Fluid (ECF)
    • The medium surrounding the cell, essential for cellular processes.
  • Phospholipid Bilayer
    • Composed of approximately 70% phospholipids, forming the fundamental structure of the cell membrane.
  • Proteins in Cell Membrane
    • Cholesterol: Embedded within the membrane contributing to fluidity.
    • Peripheral Proteins: Located on the inner and outer surfaces of the membrane.
    • Transmembrane Proteins: Span the bilayer, involved in transport and communication.
  • Glycolipids and Glycoproteins
    • Serve as cell identification markers, crucial for cellular recognition processes.

Membrane Transport Mechanisms

  • Aquaporins: Specialized transmembrane proteins facilitating water movement into and out of cells due to the lipid nature of the membrane.
  • Protein Functions in Membrane
    • Serve as receptors, enzymes, channels, and carriers.
    • Can enable binding and assist in cell signaling pathways like the second messenger system.
    • Chemical messengers bind to receptors, activating G-proteins that influence cellular biochemistry through pathways involving ATP.

Microvilli and Cilia

  • Microvilli
    • Extensions of the cell membrane increasing surface area for absorption (up to 15-40x).
    • Predominantly found in the small intestine, facilitating nutritional absorption.
  • Cilia
    • Non-Motile Cilia: Found in sensory cells, such as those in the nasal cavity.
    • Motile Cilia: Active in respiratory tracts, they help move mucus and foreign particles out through coordinated movement.
    • Cilia possess a structure described as ‘nine plus two’ arrangement of microtubules.
    • Example: Cystic fibrosis is associated with dysfunctional cilia leading to respiratory complications.

Flagella and Pseudopods

  • Flagella
    • Longer appendages found in sperm cells aiding motility; characterized by undulating movement.
  • Pseudopods
    • Temporary extensions of some cells (like amoebas) used for movement and food engulfing.

Membrane Transport Types

  • Diffusion
    • Movement of molecules from high to low concentration without energy expenditure.
    • Simple Diffusion: Molecules traverse a membrane if small and nonpolar.
  • Passive Transport
    • Consists of simple diffusion, facilitated diffusion, and osmosis without ATP use.
  • Active Transport
    • Molecular movement against the concentration gradient requiring ATP.
    • Examples include the sodium-potassium pump (Na+/K+ ATPase).
  • Carrier-Mediated Transport
    • Involves specific protein carriers for molecule transport, showing saturation characteristics.

Osmosis

  • Osmosis: Special type of diffusion specifically for water, enhanced by aquaporins.
  • Osmotic Pressure: The pressure needed to prevent water movement across a semipermeable membrane.
  • Tonicity Types:
    • Hypotonic Solutions: Lower concentration of solutes outside, causing cells to swell or burst.
    • Hypertonic Solutions: Higher solute concentration outside, leading to cell shriveling.
    • Isotonic Solutions: Equal solute concentration, maintaining cell stability.

Carrier-Mediated Transport Types

  • Uniport: Carries a single solute.
  • Symport: Carries two solutes in the same direction.
  • Antiport: Carries two solutes in opposite directions.
  • Facilitated Diffusion: No ATP consumed; utilizes existing energy gradients.

Cell Organelles

  • Nucleus
    • Contains genetic material, the nucleolus, and nuclear pores for communication.
    • Nucleolus produces ribosomes, crucial for protein synthesis.
  • Mitochondria
    • ATP production site, featuring its own DNA and ribosomes.
    • Responsible for cellular respiration and energy metabolism.
  • Endoplasmic Reticulum (ER)
    • Rough ER: Studded with ribosomes, involved in protein synthesis.
    • Smooth ER: Lacks ribosomes, associated with lipid synthesis and detoxification.
  • Golgi Apparatus
    • Functions as a processing and packaging center for proteins and lipids, determining their destinations.
  • Lysosomes
    • Contain hydrolytic enzymes for digestion of cellular waste and extracellular material.
  • Peroxisomes
    • Break down peroxides; often involved in detoxification activities within the liver and kidneys.