AP Biology - Cell Communication and Cell Cycle

Cell Communication

  • Signal Transduction Pathway – A series of molecular steps by which a signal on a cell’s surface is converted into a specific cellular response.
  • Ligand – A molecule that binds to a receptor.
  • Receptor – Protein on/in a cell that binds to a ligand and initiates a response.
  • Second Messenger – Small molecules (e.g., cAMP, Ca2+Ca^{2+}, IP3IP_3) that help amplify and distribute signals inside the cell.
  • G Protein-Coupled Receptor (GPCR) – A receptor that activates a G protein when a ligand binds.
  • Protein Kinase – An enzyme that adds phosphate groups to proteins (phosphorylation).
  • Protein Phosphatase – An enzyme that removes phosphate groups from proteins.
  • Amplification – When one signal molecule activates many molecules inside the cell.
  • Autocrine – Signaling to the same cell that secreted the signal.
  • Paracrine – Signal acts on nearby cells.
  • Endocrine – Signal (often a hormone) travels through the bloodstream to distant cells.

Cell Cycle

  • Interphase – The phase where the cell grows and prepares to divide (G₁, S, G₂).
    • G₁ Phase – Cell grows and carries out normal functions.
    • S Phase – DNA is replicated.
    • G₂ Phase – Cell prepares for mitosis; checks for DNA errors.
  • Mitosis – Division of the nucleus into two identical nuclei.
  • Cytokinesis – Division of the cytoplasm into two daughter cells.
  • Checkpoints – Control points (G₁, G₂, M) where the cell decides whether to continue.
  • Cyclin – Protein that regulates the timing of the cell cycle.
  • CDK (Cyclin-Dependent Kinase) – Enzyme that is active only when bound to cyclin.
  • MPF (Maturation Promoting Factor) – A cyclin-CDK complex that triggers mitosis.
  • Apoptosis – Programmed cell death, important for development and damaged cells.

Mitosis Stages (PMAT)

  • Prophase – Chromatin condenses into chromosomes; spindle forms.
  • Metaphase – Chromosomes line up at the metaphase plate.
  • Anaphase – Sister chromatids separate and move to opposite poles.
  • Telophase – Nuclear envelope re-forms; chromosomes decondense.
  • Centrosome/Centriole – Organizes spindle fibers in animal cells.
  • Spindle Fibers – Microtubules that help separate chromosomes.

Cancer and Cell Cycle Errors

  • Oncogene – A mutated gene that causes uncontrolled cell growth.
  • Tumor Suppressor Gene – A gene that prevents uncontrolled cell division; ex: p53.
  • Metastasis – Spread of cancer cells to other parts of the body.