AP Bio Unit 4: Cell Communication and Cell Cycle

Signal Transduction

• Signal Transduction - When cells do not pass any molecules through the membrane, but instead they just pass a message

  • Ligand binds to receptor on the outside of the cell and causes changes to the inside of the cell

  • Ligand-gated ion channels, catalytic receptors, and G-protein-linked receptors are common examples

• Usually involved 3 steps:

  • signaling molecule binding to a specific receptor

  • activation of a signal transduction pathway

  • production of a cellular response

• Plasma membrane receptor - integral membrane protein that transmits signals from the extracellular space into the cytoplasm

  • 3 classes:

  • Ligand-gated ion channels

    • open or close an ion channel in response to binding a particular ligand

  • Catalytic (enzyme-linked) receptors

    • enzymatic active site on interior site of the membrane

    • initiated by ligand binding at the extracellular surface

  • G-protein-linked receptor

    • does not act as enzyme

    • binds a different version of a G-protein (GTP or GDP)

    • activates secondary messengers within the cell

      • Ex: cyclic AMP (cAMP)

• Ex: Insulin

  • When insulin binds to its receptor, it initiates a series of events inside the cell leading to various cellular responses

  • The receptor involved is a type of catalytic (enzyme-linked) receptor, which activates an intracellular signaling cascade

  • This cascade ultimately results in the regulation of glucose uptake and metabolism in cells

• Signal transduction in Eukaryotic cells usually involve many steps and regulations

  • signal transduction cascades are helpful to amplify a signal

Feedback

• Positive feedback pathway - end product further stimulates the pathway

• Negative feedback pathway - end product inhibits further production on the pathway

  • More common

Cell Cycle

• Divided into interphase and mitosis

  • I Pick My Apples To Cook

  • Interphase

  • Prophase

  • Metaphase

  • Anaphase

  • Telophase

  • Cytokinesis

• Three stages of interphase

  • S phase - “synthesis,“ when chromosomes replicate

    • chromatid replicates itself into two sister chromatids conjoined by a centromere

  • Growth and preparation for mitosis occur in G1 and G2

    • Preform metabolic actions and produce organelles, proteins, and enzymes

• Checkpoint pathways and CDK/cycling complexes - control cell cycle progression

• Cancer occurs when cells grow abnormally and spread to other parts of the body

  • tumor-suppressor genes - genes that prevent the cell from dividing when it shouldn’t

  • Proto-oncogenes - genes that help the cell divide

    • Mutated proto-oncogenes are called oncogenes

  • If either of the two types of genes above are mutated it can lead to uncontrolled cell growth

• G0 phase - a state outside the replicative cell cycle, where cells are neither actively dividing nor preparing to divide

Mitosis/Cellular Division

• 4 stages (+Cytokinesis):

• Prophase

  • nuclear envelope disappears and chromosomes condense

• Metaphase

  • chromosomes align at the metaphase plate and mitotic spindles attach to kinetochores

• Anaphase

  • sister chromatids separate at the centromere are pulled away from the center by spindle fibers

  • Spindle fibers - microtubules attached to the kinetochores (protein structures on the centromeres)

• Telophase

  • terminates mitosis, and the two new nuclei form

• Cytokinesis

  • Occurs during telophase and ends mitosis, as the cytoplasm and plasma membranes pinch to form two distinct, identical daughter cells