C2.1  Chemical Signaling

Theme:  Interaction and Interdependence

Interaction refers to the physical binding of a signaling chemical to its receptor, triggering a subsequent "domino effect" within the cell.

• Interaction begins with a ligand (the signal) binding to a receptor (the sensor). This is a highly specific interaction based on complementary shapes and chemical properties.
• Once a receptor is activated, it interacts with intracellular proteins to set off a cascade where "secondary messengers" like cAMP or calcium ions interact with various enzymes to amplify the signal, ensuring a small interaction at the surface leads to a large-scale cellular response.
• In bacteria like Vibrio fischeri, the interaction is between the population and its own secreted signaling chemicals. This allows individual cells to "sense" the presence of others through molecular collisions.

Interdependence focuses on how chemical signals allow cells and systems to rely on one another to maintain homeostasis or perform complex tasks.

• The endocrine system (hormones) and nervous system (neurotransmitters) create a web of interdependence. For example, the pancreas depends on blood glucose levels to to release insulin, and muscle cells depend on that insulin signal to take up glucose for energy.
• The signal and response of a feedback loop are interdependent. 

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? 

​
​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?

Key Terms to Know: all are higher level only

Acetylcholine
Acetylcholine Receptor
Adrenal Gland
Amines
Amino Acid
Bacteria
Binding Site
Bioluminescence
Blood
Calcium Ion
Cyclic AMP (cAMP)
Cytokine
Cytoplasm
Deoxyribonucleic Acid (DNA)
Endometrium
Epinephrine
Epinephrine Receptor
G-Protein

G-Protein Coupled Receptor
Gene Expression
Glucose Transporter
Gonadotropin Releasing Hormone
Hormone
Hydrophilic
Hydrophobic
Hypothalamus
Insulin
Intracellular Receptor
Ion Channel
Ligand
Membrane Potential
Negative Feedback
Neurotransmitter
Nitrous Oxide
Nucleus
Oestradiol

Peptide
Phosphorylation
Plasma Membrane
Positive Feedback
Progesterone
Protein
Quorum Sensing
Receptor
Signal Transduction
Signaling Chemical
Steroid
Synaptic Gap
Testosterone
Transmembrane Receptor
Tyrosine
Tyrosine Kinase
Vesicles
Vibrio fischeri
Voltage

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

• 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. 

• State that signaling systems have evolved repeatedly, leading to a wide range of chemical substances being used as signaling chemicals. ​
• Define ligand.
• Compare the structure and function of different categories of animal chemical signaling molecules, including hormones, neurotransmitters, cytokines and calcium ions.

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

• State the properties shared by all signaling chemicals.
  
• Outline the chemical categories of hormones.
• Outline chemical categories of neurotransmitters.​

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

• Contrast the location of effect relative to the location of release between 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.

• Outline the steps of a signaling pathway. 
• Define first messenger, transduction, signaling cascade, and second messenger.
• Outline the three pathways that can be activated when a ligand binds to a transmembrane receptor.
• Outline the effect of a ligand binding to an intracellular receptor.
• List the general cell responses to the binding of a signaling molecule.

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

• Outline the mechanism by which the receptor for the neurotransmitter acetylcholine changes membrane potential in a postsynaptic cell membrane.

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

• Describe the structure and function of the G-protein coupled receptors (GPCRs) and of the G-proteins.
• Outline activation of G-protein coupled receptors (GPCRs).
• Outline how binding of a signaling ligand to a G-protein coupled receptor (GPCR) can cause change in the target cell. 
• List example signaling ligands that target G-protein coupled receptors (GPCRs).
  

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.