C2.1  Chemical Signaling

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• How do cells distinguish between the many different signals that they receive?
• What interactions occur inside animal cells in response to chemical signals? 

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​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• What patterns exist in communication in biological systems?
• In what ways is negative feedback evident at all levels of biological organization?

Resources:

• At SHS, Topic C2.1 is taught in the Chemical Signaling, Epigenetics, Signaling Between Neurons, Homeostasis and Reproductive Hormones units. 
• Quizlet study set for this topic.  Coming soon!
• View the general sequence of the SHS course
• View the SHS units mapped to the IB Biology curriculum roadmap

AHL ​C2.1.1— Receptors as proteins with binding sites for specific signaling chemicals.

• Define ligand.
• Outline the structure and function of receptor molecules.
• Outline the relationship between receptor and a specific ligand.​

AHL ​C2.1.2— Cell signaling by bacteria in quorum sensing.

• Describe the process of quorum sensing in a population of bacteria, including the role of signaling molecules, receptors and a threshold for gene expression.
• Outline the process of bioluminescence in Vibrio fischeri as an example of quorum sensing in bacteria.

AHL ​C2.1.3— Hormones, neurotransmitters, cytokines and calcium ions as examples of functional categories of signaling chemicals in animals. 

• Compare the action of different functional categories of animal chemical signaling molecules, including hormones, neurotransmitters, cytokines and calcium ions.

AHL ​C2.1.4— Chemical diversity of hormones and neurotransmitters.

• Outline the properties shared by all signaling chemicals.
• State that signaling systems have evolved repeatedly, leading to a wide range of chemical substances being used as signaling chemicals. 
• List chemical categories of hormones.
• List chemical categories of neurotransmitters.​

AHL ​C2.1.5—  Localized and distant effects of signaling molecules.

• Contrast the location of action relative to release location of hormones and neurotransmitters.​​

AHL ​C2.1.6- Differences between transmembrane receptors in a plasma membrane and intracellular receptors in the cytoplasm or nucleus.

• Distinguish between structure of transmembrane receptors and intracellular receptors, including distribution of hydrophilic and hydrophobic amino acids.
• Compare the ligands ability to enter the target cell for transmembrane and intracellular receptors.

AHL ​C2.1.7- Initiation of signal transduction pathways by receptors.

• Define signal transduction.
• Describe the signal transduction pathway that is activated when a ligand binds to a transmembrane receptors.
• Describe the signal transduction pathway that is activated when a ligand binds to an intracellular receptor.

AHL ​C2.1.8- Transmembrane receptors for neurotransmitters and changes to membrane potential.

• Outline the mechanism of synaptic transmission occurring at a post-synaptic cell, including the role of the neurotransmitter, transmembrane receptor, gated ion channel, threshold potential and action potential. 
• State that acetylcholine is one of the most common neurotransmitters in both invertebrates and vertebrates and is used as the neurotransmitter in many synapses including between neurons and muscle fibers.

AHL ​C2.1.9- Transmembrane receptors that activate G proteins.

• Describe the structure and function of the G-protein coupled receptors.
• List ligands of the G-protein coupled receptors.
• Outline the activation of the signal cascade triggered by the G-protein subunits.

AHL ​C2.1.10- Mechanism of action of epinephrine (adrenaline) receptors.

• State that epinephrine is secreted by adrenal glands in preparation for vigorous activity.
• Describe the activation of the cAMP second messenger system by the epinephrine receptor. 
• Outline the effects of epinephrine on a body.

AHL ​​​C2.1.11- Transmembrane receptors with tyrosine kinase activity.

• Define phosphorylation and kinase.
• Describe the action of receptors with tyrosine kinase activity.
• State that insulin is secreted by pancreas cells when blood glucose levels are high.
• Describe the cause and effect of the activation of the insulin receptor.

AHL ​​​C2.1.12- Intracellular receptors that affect gene expression.

• Describe the mechanism of steroid hormone action.
• List example steroid hormones.
• Outline one example of a steroid hormone promoting transcription of a specific gene.

AHL ​​​C2.1.13- Effects of the hormones oestradiol and progesterone on target cells.

• State the oestradiol and progesterone are steroid hormones. 
• Describe the role of oestradiol in the regulation of the release of FSH and LH from the anterior pituitary, including the role of the hypothalamus, the oestradiol receptor, transcription factor and gonadotropin releasing hormone. 
• Describe the role of progesterone in the formation and maintenance of the endometrium, including the progesterone receptor, transcription factor and growth factor protein.

AHL ​​​C2.1.14- Regulation of cell signaling pathways by positive and negative feedback.

• Compare the processes and consequences of positive and negative feedback.
• Outline one example each of hormonal regulation via positive feedback and negative feedback.