Cells and the cytoskeleton

Cards (45)

  • Organelles are membrane-bound
    Like “mini cells” with a big cell
  • Each organelle contains specific molecules for specific chemical reactions and cellular processes
  • Why organelles are so great
    • Compartmentalization! Incompatible chemical reactions can be separated things the cell wants to keep intact
    • For example, digestive enzymes can be kept away from
  • Why organelles are so great
    • Specialization! Increased efficiency of chemical rxs and cellular processes
    • Substrates required for chemical reactions can be clustered in one compartment and/or embedded in the organelle membrane for easy access, thus speedier rxs
  • Why organelles are so great
    • Complexity
    • With the help of a supportive cytoskeleton, cells can become bigger, perform more diverse functions, give rise to multicellularity
  • The nucleus houses the DNA and is the site of RNA synthesis
  • Some ribosomes float freely in the cytosol, where they make proteins that function in the cytosol
  • Other ribosomes are attached to the rough endoplasmic reticulum, where they synthesize proteins that will be:
    1. embedded in a cell membrane
    2. secreted from the cell
    3. put inside of an organelle
  • The rough endoplasmic reticulum gets its name from the rough appearance of the ribosomes on its surface
  • The attached ribosomes grab RNA strand from nucleus and start injecting protein product directly into the lumen of the rough ER as its being translated
  • The smooth ER (which is “smooth” because it’s not associated with ribosomes) is where lipids such as phospholipids and fatty acids are synthesized
  • The Golgi apparatus receives proteins and lipids from the rough and smooth ER and:
    • further modifies them (e.g., by attaching a sugar molecule) and
    • sorts and packages them for delivery to their final locations in the membrane or outside of the cell
  • The Golgi apparatus is also where most of the cell’s carbohydrates are synthesized
  • The nucleus, ER and Golgi make up a continuous “endomembrane system” (or “secretory pathway”)– connected by vesicles –
    • to streamline synthesis and delivery of proteins and lipids to their final destinations
  • Lysosomes break down damaged or unneeded macromolecules (large molecules) into smaller components
  • Lysosomes form from the fusion of Golgi vescicle containing enzymes and the vesicle containing macromolecules to be broken down
  • Mitochondria synthesize most of the ATP (“energy currency”) used by the cell
  • Chloroplasts (in plant cells) capture energy from sunlight and synthesize simple sugars
  • The biconcave shape of a red blood cell maximizes its surface area for gas exchange and allows it to deform as it passes through the circulatory system
  • Long, slender extensions of the plasma membrane allow neurons to communicate with other cells
  • Thin, comb-like projections, called microvilli, on intestinal cells increase their absorptive surface area
  • Long flagellum facilities movements, packed with a lot of mitochondria to support this energy-intensive swimming function
  • Peroxisomes break down specific organic molecules, such as fatty acids, and synthesize other organic molecules such as cholesterol and some types of phospholipids
  • Cytoskeleton (the "bones of the Cell)
  • The cytoskeleton provides internal structural support and enables movement of substances within the cell
    • 3 types
    • Each type is formed from long chains of protein subunits joined together
    •The cytoskeleton is DYNAMIC! (unlike bones)
  • Microtubules
    • Subunits (“Building Blocks”):
    • • Tubulin dimers
  • Microtubules
    • Structure:
    • Hollow tube
    • • Directional: plus end and minus end
  • Microtubules
    • Major Microtubule Functions:
    • • Cell shape and support
    • Vesicle transport and organelle arrangement
    • Cell movement (by cilia, flagella)
    • • Cell division (chromosome segregation)
  • Microtubules: vesicle transport
    • Motor proteins kinesin and dynein “walk” on microtubule tracks to carry cargo-filled vesicles through the cell.
  • Microtubules: Cell movement
    • Microtubules are a key part of the structures of eukaryotic cilia and flagella.
    • Cilia and flagella beat to either propel a cell or allow it to move fluidly across the cell surface
  • Microtubules are dynamic
    • Microtubules lengthen and shorten at their ends
  • Microfilaments
    Subunits (“Building Blocks”):• Actin monomers
  • Microfilaments
    Structure:
    • Thin double helix of actin protein monomers
    • Directional: plus end and minus end
  • Microfilaments
    Major Microfilament Functions:
    • Cell shape and support
    • Cell movement (by crawling)
    Vesicle transport
    • Muscle contraction
    • Cell division (cytokinesis)
  • Microfilaments: Cell shape and support
    • Actin microfilaments help maintain cell shape
    • Lots of actin microfilaments at plasma membrane!
  • Microfilaments: Cell movement (by crawling)
    • Elongating actin filaments at the edge of the cell membrane allow crawling motion of cells
  • Microfilaments: Vesicle transport
    • Actin microfilaments work together with myosin motor proteins to carry out important functions.
    • Myosin motor proteins can “walk” along microfilaments carrying cargo-filled vesicles (similar to kinesin and dynein on microtubules)
  • Microfilaments: Muscle contraction
    • Interactions between actin microfilaments and myosin motor proteins are responsible for muscle contractions
  • Microfilaments: Cell division (cytokinesis)
    • Actin microfilaments play a key role in cell division.
    • A band of actin contracts, causing the two new cells to “pinch” apart
  • Intermediate Filaments
    Subunits (“Building Blocks”):
    Diverse, cell - type - specific protein subunits
    Major Intermediate Filament Function:
    • Provide mechanical strength to cell