BSC2010 - Exam #2 Study Guide

Robert Hooke and Anton van Leeuwenhoek

  • Robert Hooke:

    • Coined the term "cell" after observing cork under a microscope in 1665.

    • His observation marked the beginning of cell biology.

  • Anton van Leeuwenhoek:

    • Considered the father of microbiology.

    • First to observe and describe single-celled organisms, which he called "animalcules," in the 1670s.

    • His work opened up a new world of microscopic organisms.

Cell Theory

  • Developed by Matthias Schleiden, Theodor Schwann, and Rudolf Virchow.

  • Three Principles:

    • All organisms are composed of one or more cells.

    • This principle emphasizes the universality of cells in living organisms.

    • The cell is the basic unit of structure and organization in organisms.

    • Cells are the fundamental building blocks of life, performing all essential functions.

    • All cells come from pre-existing cells.

    • This principle, known as "Omnis cellula e cellula," refuted spontaneous generation.

Microscopy

  • Magnification: Amplification of the image, allowing for visualization of small structures.

  • Resolution:

    • Minimum distance two objects can be distinguished as separate.

    • Depends on the wavelength of the light source; shorter wavelengths provide better resolution.

    • Influenced by the quality of lenses and specimen preparation.

  • Contrast:

    • Enhanced by staining techniques to distinguish cellular components.

    • Dyes and stains increase the visibility of transparent structures.

  • Types of Microscopes:

    • Light Microscope:

    • Uses visible light and lenses to magnify images.

    • Limited resolution but suitable for live cells and basic structures.

    • Electron Microscope:

    • Uses electron beams for higher magnification and resolution.

    • TEM (Transmission Electron Microscopy):

      • For viewing internal structures at high resolution.

      • Requires thin specimens and complex preparation.

    • SEM (Scanning Electron Microscopy):

      • For viewing surface details with a 3D appearance.

      • Samples are coated with metal for imaging.

Prokaryotic Cell Structures

  • Cytoplasm: The internal content of the cell, including cytosol, organelles, and inclusions.

  • Nucleoid: Region containing the DNA, which is not enclosed by a membrane.

  • DNA: Genetic material, typically a single circular chromosome.

  • Ribosomes: Site of protein synthesis, smaller than eukaryotic ribosomes.

  • Plasma Membrane: Outer boundary of the cell, regulating entry and exit of substances.

  • Cell Wall: Provides structure and protection, composed of peptidoglycan.

  • Capsule: Additional protective layer (not always present), aiding in attachment and preventing dehydration.

  • Flagella: Used for movement, simpler in structure than eukaryotic flagella.

  • Pili: Involved in attachment to surfaces and genetic exchange through conjugation.

Animal and Plant Cell Structures

  • Ribosomes: Protein synthesis, either free in the cytosol or bound to the endoplasmic reticulum.

  • Cytosol:

    • Metabolism:

    • Catabolism: Breakdown of molecules, releases energy.

      • Includes processes like glycolysis and cellular respiration.

    • Anabolism: Building of molecules, requires energy.

      • Includes processes like protein synthesis and DNA replication.

    • Cytoskeletal Elements:

    • Microtubules:

      • Composed of tubulin.

      • Dynamic instability (+ and – ends).

      • Centrosome: Microtubule organizing center.

      • Roles: Cell division (formation of the mitotic spindle), intracellular transport, movement (cilia and flagella).

      • Cilia vs. Flagella: Understand similarities and differences in structure and function.

    • Intermediate Filaments:

      • Keratin forms coiled coils (rope-like).

      • Found in cells requiring mechanical strength, such as nuclear lamina (support).

    • Microfilaments (Actin Filaments):

      • Composed of actin.

      • + and – ends.

      • Roles: Cleavage furrow formation during cell division, amoeboid movement, and muscle contraction.

    • Importance, structure, and function of motor proteins in some of the cytoskeletal elements (dynein and myosin):

    • Motor proteins use ATP to move along cytoskeletal filaments, enabling cellular movement and transport.

Motor Proteins

  • Dynein: Associated with microtubules, involved in movement of cilia and flagella, and intracellular transport.

  • Myosin: Associated with microfilaments, involved in muscle contraction and cell motility.

Nucleus

  • Double bilayer nuclear envelope, separating the nucleus from the cytoplasm.

  • Chromatin (DNA + proteins), the complex of DNA and histone proteins.

  • Nuclear pores: Regulate transport of molecules in and out of the nucleus.

  • Nucleolus: Assembly of ribosome subunits.

  • Nuclear matrix: Provides structural support within the nucleus.

Endomembrane System

  • Endoplasmic Reticulum (ER):

    • Rough ER (RER):

    • Ribosomes present on the surface.

    • Protein synthesis and sorting.

    • Glycosylation: Addition of carbohydrates to proteins.

    • Smooth ER (SER):

    • Synthesis of lipids, including phospholipids and steroids.

    • Detoxification of drugs and poisons.

    • Calcium (Ca2+Ca^{2+}) storage, important for cell signaling.

    • Glycogen metabolism, particularly in liver cells.

  • Golgi Apparatus:

    • Cis vs. Trans faces: Receiving and shipping sides, respectively.

    • Receives, modifies, packages, sorts, and secretes proteins.

    • Involved in glycosylation and formation of glycoproteins and glycolipids.

  • Lysosomes:

    • Hydrolytic enzymes and low pH for intracellular digestion.

    • Autophagy: Self-eating; breaking down damaged organelles.

    • Involved in the breakdown of cellular waste and debris.

  • Vesicles/Vacuoles:

    • Transport vesicles: Move molecules between different parts of the endomembrane system.

    • Food vacuoles: Formed by phagocytosis, containing ingested particles or cells.

    • Central vacuole (tonoplast) in plant cells: Stores water, ions, and other molecules, maintaining cell turgor.

    • Contractile vacuole in Paramecium: Pumps out excess water, maintaining osmotic balance.

    • Phagocytic vacuoles: Engulf bacteria or cellular debris for degradation.

Peroxisomes

  • Catalase: Breaks down hydrogen peroxide (H<em>2O</em>2H<em>2O</em>2) into water (H<em>2OH<em>2O) and oxygen (O</em>2O</em>2), preventing oxidative damage.

Semiautonomous Organelles

  • Endosymbiosis Theory: Mitochondria and chloroplasts originated from bacteria.

    • Evidence: double membranes, have their own DNA, divide independently, have ribosomes similar to bacteria.

  • Mitochondrion:

    • Cellular respiration (ATP production).

    • Outer membrane, intermembrane space, inner membrane (cristae), and matrix.

  • Chloroplast:

    • Photosynthesis.

    • Thylakoids (thylakoid membrane).

    • Granum (stack of thylakoids).

    • Stroma.

Protein Sorting

  • Sorting Signals: Direct proteins to specific locations within the cell.

  • Co-translational Sorting (Endomembrane System):

    • SRP (Signal Recognition Particle) and SRP-receptor.

    • Signal peptidase: Cleaves signal peptide from the protein.

  • Post-translational Sorting (Nucleus, Peroxisomes, Mitochondria, Chloroplast):

    • Proteins are synthesized in the cytoplasm and then transported to their target organelles.

Plasma Membrane

  • Extracellular vs. Cytosolic leaflets: Different lipid compositions and protein distributions.

  • Components of a membrane: Phospholipids, cholesterol, proteins, and carbohydrates.

  • Fluid Mosaic Model (Singer and Nicolson): Describes the membrane as a fluid lipid bilayer with proteins embedded or attached to it.

  • Integral (intrinsic) proteins vs. Peripheral (extrinsic) proteins: Based on their association with the lipid bilayer.

  • Phospholipid movement (lateral, on its own axis, and flip flops with the help of ATP and flippases):

    • Lateral movement is rapid, while flip-flopping requires energy and flippases.

  • 3 factors that affect membrane fluidity: Temperature, lipid composition, and cholesterol content.

  • Protein movement: Lateral movement is more restricted and slower; some proteins are anchored and cannot move.

  • Membrane carbohydrates, functions, types of glycosylation, and location: Involved in cell recognition and signaling.

Membrane Transport

  • Selective permeability: The membrane allows some substances to cross more easily than others.

  • Passive transport (simple diffusion vs. facilitated diffusion) and active transport:

    • Passive transport does not require energy, while active transport requires energy.

  • Concentration gradient vs. Electrochemical gradient: Influence the movement of ions and molecules across the membrane.

  • Osmosis and tonicity (hypertonic, hypotonic, isotonic):

    • Osmosis: Movement of water across a semipermeable membrane.

    • Tonicity: The ability of a solution to cause a cell to gain or lose water.

    • Animal cells prefer isotonic solutions, while plant cells prefer hypotonic solutions.

    • What happens to cells when placed in isotonic, hypotonic, or hypertonic solutions?

    • Role of contractile vacuoles in protists in osmoregulation.

  • Channels: Provide a hydrophilic passage for specific ions or molecules to cross the membrane.

  • Transporters: Uniporters, symporters, and antiporters facilitate the movement of specific molecules across the membrane.

  • Active transport: Primary and secondary active transport mechanisms.

  • Know the Sodium-Potassium pump: Maintains ion gradients across the plasma membrane.

  • Important functions of ion electrochemical gradients: Nerve impulse transmission, muscle contraction, and nutrient transport.

  • Exocytosis vs. Endocytosis: Mechanisms for bulk transport of substances into or out of the cell.

Cell Communication

  • Cell communication as a response to changes in the environment.

  • Cell-to-cell communication: Example of phototropism in plants.

  • 5 ways of signals relayed between cells: Autocrine, paracrine, endocrine, direct contact, and synaptic signaling.

  • 3 Stages in cell communication and cell signaling: Reception, transduction, and response.

Different types of receptors:
Cell-surface receptors:

  • Enzyme-linked receptor (RTKs – receptor tyrosine kinases):

    • Know and understand the difference between a kinase and a phosphatase.

    • Involved in cell growth, differentiation, and survival.

  • G-protein coupled receptors (GPCRs):

    • G proteins (active vs. inactive).

    • Adenylyl cyclase vs. Phosphodiesterase.

    • cAMP as secondary messenger (advantages).

    • Importance and function/regulation of PKA.

    • Know example of epinephrine receptor.

  • Ligand-gated ion channels: Open or close in response to ligand binding, allowing ions to flow across the membrane.

Intracellular receptor:

  • Estrogen receptor: Binds to estrogen and regulates gene expression in the nucleus.