Chemical Signalling

(Topic C2.1 – AHL Only)

Essential Idea(s): Chemical signaling is the process by which cells communicate using molecules (ligands) that bind to specific receptors, triggering a series of responses that drive cell-to-cell communication.

 Unit Length: 4 Lessons (AHL Only)

  Guiding Questions

◊ How do cells distinguish between the many different signals that they receive?

◊ What interactions occur inside animal cells in response to chemical signals?

Materials:

Self-Teaching Slides   Quizlet Vocab Set
Teaching Slides   Notes Template

 

IB Statement(s) and Objective(s)

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

 

C.2.1.2: Cell signaling by bacteria in quorum sensing

  • Describe the process of quorum sensing in a population of bacteria
  • Outline the process of bioluminescence in Vibrio fischeri as an example of quorum sensing in bacteria

 

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

  • Compare the structure and function of different categories of animal chemical signaling molecules, including hormones, neurotransmitters, cytokines and calcium ions

 

C2.1.4: Chemical diversity of hormones and neurotransmitters

  • Outline the basic mechanism by which hormones and neurotransmitters act on target cells
  • Outline the 3 main classes of hormones

 

C2.1.5: Localized and distant effects of signaling molecules

  • Contrast the localized vs distant effects of hormones vs neurotransmitters

 

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

  • Distinguish between transmembrane receptors and intracellular receptors
  • Describe how the composition of amino acids in receptor proteins determines their respective location in the cell 

 

C2.1.7: Initiation of signal transduction pathways by receptors

  • Outline the 3 main steps of a chemical signaling pathway

 

C2.1.8: Transmembrane receptors for neurotransmitters and changes to membrane potential

  • State that acetylcholine is one of the most common neurotransmitters in both invertebrates and vertebrates 
  • 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

 

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
  • List example signaling ligands that target G-protein coupled receptors (GPCRs)

 

C2.1.10: Mechanism of action of epinephrine (adrenaline) receptors

  • Describe the mechanism of epinephrine action
  • NOS: Outline how naming conventions are an example of international cooperation

 

C2.1.11: Transmembrane receptors with tyrosine kinase activity

  • Define phosphorylation and kinase
  • Describe the cascade activated by insulin receptors and tyrosine kinase enzymes, including 2 examples of outcomes from this process
  • Describe the movement of vesicles containing glucose transporters to the plasma membrane

 

C2.1.12: Intracellular receptors that affect gene expression

  • Describe the mechanism of steroid hormone action
  • List 3 examples of steroid hormones
  • Outline one example of a steroid hormone promoting transcription of a specific gene

 

C2.1.13: Effects of the hormones oestradiol and progesterone on target cells

  • Outline the basic functions of oestradiol and progesterone 
  • Describe the role of oestradiol in the regulation of the release of FSH and LH from the anterior pituitary
  • Describe the role of progesterone in the formation and maintenance of the endometrium

 

C2.1.14: Regulation of cell signaling pathways by positive and negative feedback

  • Compare the processes and consequences of positive and negative feedback
  • Outline examples positive feedback and negative feedback
  • Explain why positive feedback loops must have a maximal point

Activities: ⓟ = podcast / ⍰ = inquiry 5 / ⓦ = Write it /  Ӕ = The academy  / Ⓡ = Read it

ⓟ: Thanks, Evolution…But No Thanks (💁/ 👭 max 3)

Epinephrine (adrenaline) and cortisol (the main “stress hormone”) evolved as chemical signals to help keep our ancestors alive. They could very well be the reason that we still exist to this day. And yet today, with our relatively safer lifestyles, these hormones all too often are the cause of many unwanted effects: crippling anxiety, nervousness for exams, social awkwardness in new settings – they’re all a product of these hormones. As a result, humans invented beta blockers – drugs that block the effects of these hormones. This leads to a question: Is it possible that a trait that was life-saving for our cave-dwelling ancestors is now a burden in modern society? Partner up and discuss this, including: 

  1. What cortisol and adrenaline do in these modern unwanted situations 
  2. How beta blockers work to counteract this
  3. Any other examples of bodily parts or functions that are no longer wanted in the modern world. 
  4. Discuss: Now that they’re no longer needed as much, is it possible that we are currently evolving to get rid of these unwanted traits? Why or why not?

Ⓛ LAB! You Are What You (Can) Taste: Reading Evolution in Receptor Genes (💁/ 👭 max 2)

Using real protein and DNA sequence data, investigate how taste receptors evolved, why some animals have lost taste abilities entirely, and what the genome of a giant panda can tell us about the relationship between diet and DNA. Work through the exercises in this student guide, (teacher guide here) then discuss the following with your partner(s):

  1. The adaptive logic of taste — For each taste (sweet, sour, salty, bitter, umami), explain what it was detecting in the environment and why that information was worth having.
  2. What the phylogenetic tree tells us about receptor evolution — Use the tree to argue whether umami or sweetness detection is the more ancient ability — and explain what that might tell us about the diets of the earliest vertebrates.
  3. Discuss: The chicken, the panda, and the cat. In each case, discuss which came first: the dietary change or the genetic change? Is there a single answer that works for all three, or does the direction of causation differ? What does each case tell us about how evolution actually works — is it always driven forward by new adaptations, or can it also move by loss?

ⓟ/ⓦ: Accidental Gourmets: How Desert Cats Fell in Love with Ocean Fish (💁/ 👭 max 3)

Domestic cats evolved from desert-dwelling wildcats — animals that would never have encountered a tuna in their lives. And yet, given the choice, many cats will pick tuna over almost anything else. How is that even possible? It turns out the answer lies in an elegant and unexpected overlap between what cats evolved to detect and the specific chemistry of fish they never evolved around. Watch this video and then partner up to discuss:

  1. The five basic tastes and what cats can (and can’t) detect.
  2. The molecular basis of the tuna obsession  – Explain, at the receptor level, why cats respond so strongly to tuna specifically — and why they don’t show the same enthusiasm for chicken or beef.
  3. The evolutionary puzzle — Cats evolved in deserts, not oceans. So why do their umami receptors happen to respond so powerfully to a deep-sea fish?
  4. What does this case study reveal about the relationship between genes, receptors, and behaviour?

Teachers…send me more! Email me at sph@wolfert.nl if you have solid lesson plans for this unit.