Bio college board slides 4.1-4.5

4.1

Cells communicate by generating, transmitting, receiving, and responding to chemical signals. 

  • Cells communicate with one another through direct contact with other cells or from a distance via chemical signaling

    • Cells communicate by cell to cell contact

    • Immune cells interact by cell to cell contact, antigen presenting cells (APCs), helper T cells, and killer T cells

    • Plasmodesmata between plant cells allow material to be transported from cell to cell

  • Cells communicate over short distances by using local regulators that target cells in the vicinity of the signal emitting cell

    • Signals released by one cells type can travel long distances to target cells of another cell type

    • Cells communicate using local regulators -

      • Neurotransmitters

      • Plant immune response

      • Quorum sensing in bacteria

      • Morphogens in embryonic development

4.2

  • Components of a signal transduction pathway

    • Signal transduction pathways link signal reception with cellular responses

    • Many signal transduction pathways include protein modification and phosphorylation cascades

  • Describe the role of the components above in producing a cellular response

    • Signaling begins with the recognition of a chemical messenger ( a ligand ) by a receptor protein in a target cell 

      • The ligand binding domain of a receptor recognizes a specific chemical messenger, which can be a peptide, a small chemical, or protein, in a specific one to one relationship

      • G protein coupled receptors are an example of a receptor protein in eukaryotes

    • Signaling cascaded relay signals from receptors to cell targets often amplifying the incoming signals, resulting in the appropriate responses by the cell, which could include cell growth, secretion of molecules, or gene expression

      • After the ligand binds, the intracellular domain of a receptor protein changed shape, initiating transduction of the signal

      • Second messengers (cAMP) are molecules that relay and amplify the intracellular signal

      • Binding of ligand to ligand gated channels can cause the channel to open or close

4.3

  • Describe the role of the environment in evoking a cellular response

    • Signal transduction pathways influence how the cell responds to its environment

  • Describe the different types of cellular responses evoked by a signal transduction pathway

    • Signal transduction may result in changes in gene expression and cell function, which may alter phenotype or result in programmed cell death also known as apoptosis

  • Use of chemical messengers by microbes to communicate with other nearby cells and to regulate specific pathways in response to population density also known as quorum sensing

  • Cytokines regulate gene expression to allow for cell replication and division

  • Mating pheromones in yeast trigger mating gene expression

  • Expression of the SRY gene triggers the male sexual development pathway in animals

  • Ethylene levels cause changed in the production, of different enzymes allowing fruits to ripen

  • HOX gene and their roles in development 

4.4

  • Changes in signal transduction pathways can alter cellular response

    • Mutations in any domain of the receptor protein or in any component of the signaling pathway may affect the downstream components by alerting the subsequent transduction of the signal

  • Chemicals that interfere with any component of the signaling pathway may activate or inhibit the pathway

4.5 

  • Timing and coordination of biological mechanisms involved in growth, reproduction, and homeostasis depend on organisms responding to environmental cues

  • Organisms use feedback mechanisms to maintain their internal environments and respond to internal and external environmental changes

  • Negative feedback mechanisms maintain homeostasis for a particular condition by regulating physiological processes. If a system is troubled, negative feedback mechanisms return the system back to its target set point. These processes operate at the molecular and cellular levels

    • Blood sugar regulation by insulin/glucagon

  • positive feedback mechanisms amplify responses and processes in biological organisms. The variable initiating the response is moved farther away from the initial set point. Amplification occurs when the stimulus is further activated, which in return initiates an additional response that produces system change

    • Lactation in mammals

    • Onset of labor in childbirth

    • Ripening of fruit