BIOLOGY 111 1st Edition Lecture 23 Outline of Last Lecture I. Gene regulationII. OperonsIII. Negative and Positive ControlIV. Chromatin level regulationV. Protein StabilityOutline of Current Lecture I. Proto-oncogenesII. Tumor Suppressor GenesIII. Cell Signaling Current Lecture- Proto-oncogenes o Control the cell cycle by providing signals to cells when it is the appropriate time for them to divide o Oncogenes are genes that are cancerous for some reason (something went wrong in cell division) and were initially found on viruses  They are a result of a point mutation: within a control element (normal growth stimulating protein) or within the gene (hyperactive or degradation resistant protein) Gene amplification and movement of a gene within a genome, either by translocation of by transposition will result in normal growth-stimulating proteins in excess- Tumor suppressor genes (i.e. p53) o These prevent, or at least attempt to prevent, abnormal cell divisiono With p53, the cell will not go on until the error is fixed. Once the error is resolved, the cell can proceed to division. o Defective or missing transcription factors, such as p53, cannot activate transcriptiono i.e. BRCA 1 and BRCA 2 are tumor suppressor genes. A mutation with these suppressor genes would contribute to genetic disposition of breast cancer.- Cancer usually entails the activation of oncogenes and requires defects in tumor suppressor genes, ultimately increasing cell division. Most cancers require multiple mutations (typically one single mutation will not lead to cancer). This provides an opportunity to catch tumors at an early stage, before they become fully cancerous and metastasize. Cell communication These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- For cell junctions, in animal cells there are GAP junctions and in plant cells there is plasmodesmata that allow cell to cell communication. There are also cell-cell recognition(local signals that work with cell receptors on the surface)- Short Distance Signaling o Paracrine Signaling is short distance (longer than cell junction signaling) secretiono Synaptic Signaling is the transmission of electrical charges and messages sent in between two cell’s neurotransmitters- Long distance Signalingo The only long distance signaling between cells is done by hormones Plant hormones: auxins, ethylene, some cytokinins, plant growth factors Animal hormones: testosterone, estrogen, adrenalin, insulin- Regardless distance of signaling (junction, short, or long distance), they each undergo the same specific mechanism (Sutherland)o Reception – a signaling molecule binds with a receptor  Ligand is the most common signaling molecule and since it is too big or too polar, it must bind with the receptor proteins (G protein-coupled receptor) at the membrane surface৹ There is a ligand ion channel that allows passing of substances across the membrane down a concentration gradient  Many extracellular signals are transmitted via a pathway that involves GTP. ৹ Inactive form (GDP) is activated by phosphorylation ৹ Active form (GTP) can be deactivated by dephosphorylation  Receptor Tyrosine Kinases are another major cell surface receptor and it usually triggers many signals at once And there are also Intracellular receptors ৹ Hydrophobic hormones diffuse across the plasma membrane and bind to a intracellular receptor, changing in conformation.৹ This new complex is transported to the nucleus where it binds DNA with protein and activates specific hormone responsive geneso Transduction - relaying molecules in a signal transduction pathwayo Response – activation of cellular