Exercise 2: Cells and cycle

• Plasma membrane


  Phospholipid bilayer, contains cholesterol and proteins; Acts as physical barrier to enclose cell contents; Regulates material movement into and out of cell; Functions in cell communication
• Cilia


  • Short, numerous membrane extensions supported by microtubules; Moves substances (e.g. mucus, and dissolved materials) over the surface; Usually seen in organs of respiratory system
• Flagellum


  • Long, singular membrane extension supported by microfilaments; present on sperm; Propels sperm
• Microvilli


  • Numerous thin membrane folds projecting from the free cell surface; supported by microfilaments; Increase membrane surface area for greater absorption
• Nucleus


  • Large structure enclosed within a double membrane; contains chromatin, nucleolus, and nucleoplasm; Stores genetic material: DNA and RNA
• Nuclear envelope


  • Double membrane boundary between cytoplasm and nuclear contents; continues with rough ER
• Nuclear pore


  • Openings through the nuclear envelope; Allows passage of materials bet. Cytoplasm and nucleoplasm
• Nucleolus


  • Large, prominent structure within the nucleus; Functions in synthesis of ribosomes
• Cytoplasm


  Contents of cells bet. the plasma membrane and nuclear envelope; Responsible for many cellular processes
• Cytosol


  Viscous fluid medium with dissolved solutes (e.g. ions, proteins, carbohydrates, lipids); Supports organelles
• Organelles


  • Membrane-bound and nonmembrane-bound structures; Carries out specific metabolic activities of the cell
• Rough Endoplasmic Reticulum


  • Presence of ribosomes; Modifies, transport, and stores protein – produced by ribosomes
• Smooth Endoplasmic Reticulum


  • Lacks ribosomes; Synthesizes, transports and stores lipids (e.g. steroids); metabolizes carbohydrates, detoxifies drugs, alcohol, and poisons; forms vesicles and peroxisomes
• Golgi Apparatus


  • Series of elongated, flattened saclike membranous structures; Modifies, packages, and sorts materials, that arrive from the ER in transport vesicles; forms secretory vesicles and lysosomes
• Vesicle


  • Spherical-shaped membrane-bound sacs; contains various types of materials to be transported through cell; Transports cellular material
• Lysosomes


  • Spherical-shaped membrane bound organelles formed from the Golgi apparatus; contain digestive enzymes; Digest microbes or materials (e.g. ingested by the cell, worn-out cellular components, or the entire cell)
• Peroxisomes


  • Smaller, spherical-shaped membrane-bound organelles formed from the ER or though fission; contain oxidative enzyme; Detoxify specific harmful substances either produced by a cell or taken into cell
• Mitochondria


  • Double membrane-bound organelles containing a circular strand of DNA; Powerhouse of the cell (synthesize most ATP during aerobic cellular respiration
• Ribosomes


  • Organelles are composed of both protein and ribosomal RNA (rRNA); Site of protein synthesis
• Cytoskeleton


  • Organized network of protein filaments and hollow tubules, includes microfilaments, intermediate filaments, and microtubules; Maintains intracellular structural support and organization of cells; participates in cell division; facilitates movement
• Microfilaments


  • Actin protein monomers organized into two thin, intertwined protein filaments (actin filaments); Maintain cell shape; support microvilli; separate two cells during cytokinesis (a process of cell division); facilitate change in cell shape; participate in muscle contraction
• Intermediate filaments


  • Various protein components; Provide structural support; stabilize junctions between cells
• Microtubules


  • Hollow cylinders composed of tubulin protein; Maintain cell shape and rigidity; organize and move organelles; support cilia and flagella; participate in vesicular transport; separate chromosomes during the process of cell division
• Centrosome


  • Amorphous region adjacent to nucleus; contains a pair of centrioles; Organizes microtubules; participates in mitotic spindle formation during cell division
• Proteasomes


  • Large, barrel-shaped protein complexes located in both the cytosol and nucleus; Degrade and digest damaged or unneeded proteins; ensure quality of exported proteins
• Inclusions


  • Aggregates of specific types of molecules (eg, melanin protein, glycogen, or lipid); Serve as temporary storage for these molecules
• Sodium-potassium pump


  A protein pump found in the cell membrane of all animal cells
• Sodium-potassium pump


  • Its main function is to transport sodium ions out of the cell and potassium ions into the cell
  • It helps to maintain a higher concentration of sodium ions outside the cell, and a higher concentration of potassium ions inside the cell
  • Preserving these differences in ion concentrations helps to stabilize the cell's membrane potential
  • It is critical for the neuron to be able to fire an action potential, which is the basis of the electrical signaling of neurons
• How the sodium-potassium pump works

  1. Binding of ATP to the pump

  2. Binding of 3 sodium ions and release of 2 previously bound potassium ions

  3. ATP is broken down and transfers a phosphate group to the pump

  4. Pump undergoes a conformational change, causing the bound sodium ions to be released into the extracellular fluid

  5. Pump binds 2 potassium ions, which prompts another conformational change that returns the pump to its previous configuration

  6. Each cycle of the pump causes 3 sodium ions to move out of the cell and 2 potassium ions to move into the cell

  7. There is a net loss of positive ions, making the resting membrane potential of the cell slightly more negative
• Membrane-associated enzyme


  The sodium-potassium pump is a large membrane-associated enzyme that uses the energy of adenosine triphosphate (ATP) to transport sodium and potassium ions across the cell membrane
• The details of how the sodium-potassium pump achieves its function are not yet fully clear