1. Hormonal Communication

2. The Process of Communication: Signal-Transduction Pathway
Three stages of the Signal- Transduction Pathway
1. reception
2. transduction
3. response
Most cell communication involves three basic steps, reception, transduction and response. Today, we will see this signal transduction pathway being initiated by hormones. We will look at specific examples of how communication is completed using this pathway.

3. Typical Signal Transduction Pathway
The diagram shows a typical signal transduction pathway. In our example today, we will consider a ligand or signal molecule to be a hormone produced by one of the endocrine glands we discussed earlier.
The word transduce means to convert. A signal transduction pathway “converts” the original signal molecule into a cellular response. This conversion requires several intermediate messenger molecules (sometimes called “second messengers”), so the signal is actually “converted” or transduced several times, as shown in the blue box above labeled Transduction. The concept of signal transduction pathways will be seen over and over again in AP Biology and is certain to be on the exam.

4. Ligand = Chemical Messenger
Three major classes of molecules function as hormones in vertebrates (ligands)
Polypeptides (proteins and peptides)
Amines derived from amino acids
Steroid hormones
The hormones we consider today fall into three main categories. Polypeptides, amines and steroid hormones. The chemical make up of each is different so it is not surprising that these ligands impact cells very differently.

5. LIGAND: a molecule that binds to a larger molecule
The transduction pathway at the target cell begins when the ligand binds to the receptor forming a temporary ligand/receptor complex. This stimulates transduction which leads to a response from the cell. Have students cite some examples of ligands.

6. Typical Signal Transduction Pathway
Emphasize that “Reception” begins when the ligand establishes an IMF (intermolecular force) or electrostatic attraction to a specific site on the “Receptor”. Point out these IMFs are NOT covalent chemical bonds but rather a strong attraction that can be overcome with far less energy than it would take to “break” an actual covalent chemical bond.

7. Phase 1: Reception The target cell detects the ligand
Membrane proteins
G-protein linked receptors
Ion channel receptors
Tyrosine Kinase
Intracellular receptor
Steroid hormone receptors
Receptor proteins may be found ON the cell or IN the cell.

8. Type of Receptor : G-protein linked
G protein linked receptors are located in the membrane of the cell. When activated, the G-protein linked receptor sets off a chain of events inside the cell.

9. Type of Receptor: Ion Channel
Ion channel receptors, integral proteins found within the cell membrane undergo a conformational (which is fancy for “shape”) change when the ligand binds to the receptor. Ions bear a charge and cannot enter the cell by diffusion across the membrane. Instead, ions are allowed to enter the cell when the ligand is present and bound to the receptor. This allows the influx of ions to be a regulated process. Emphasize that any time charged particles (ions) are transported a difference in electric potential (as in potential energy) is established. This electric potential is now available to do “work”!

10. We saw an example of ion channel communication when we studied the transmission of impulses from one neuron to the next via neurotransmitters. The neurotransmitters serve as ligand molecules allowing the influx of sodium ions when the channel is open.

11. Intracellular Receptor
Type of Receptor:
Intracellular Receptor
Some receptors are located inside the cell and are described as intracellular receptors. The receptor for testosterone, for example is found inside the cell.
Testosterone is a steroid hormone. Challenge students to explain why steroid hormones have intracellular receptors, while protein hormones have extracellular receptors. (Steroids are lipids and therefore easily diffuse through the membrane and into the cell. Proteins will not diffuse through the membrane due to both charge and size, so they must bind with receptors on the cell’s surface.)

12. Name three types of receptors in the signal transduction pathway
G-protein-linked receptors
Ion channel receptors
Intracellular receptors
You should be able to give examples of membrane bound receptors (G-protein linked and ion channel receptors) as well as intracellular receptors) .

13. Ask students to explain what this image represents – what is “transduction?”
Answers:
Signal transduction, any process by which a biological cell converts one kind of signal or stimulus into another OR A process by which a transducer converts one type of energy to another (chemical to electrical for example)

14. Action of G-Protein Linked Receptor
Note that the GDP is replaced by higher energy GTP in order for the process to continue.

15. Transduction Binding changes the receptor protein.
Can set off a cascade reaction

17. Response Set any of a variety of cell activities in motion.
Activation of an enzyme
Rearrangement of cytoskeleton features
Activation of a specific gene

18. EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 Reception Receptor
Overview of cell signaling.
Signaling molecule

19. Relay molecules in a signal transduction pathway
EXTRACELLULAR FLUID
CYTOPLASM
Plasma membrane 1
Reception 2
Transduction
Receptor
Relay molecules in a signal transduction pathway
Overview of cell signaling.
Signaling molecule

20. Relay molecules in a signal transduction pathway
EXTRACELLULAR FLUID
CYTOPLASM
Plasma membrane 1
Reception 2
Transduction 3
Response
Receptor
Activation of cellular response
Relay molecules in a signal transduction pathway
Overview of cell signaling.
Signaling molecule

22. Types of Receptors +

23. Which is the receptor? G-Protein? Ligand?
A—Ligand or signal molecule such as epinephrine
B—receptor molecule
C—relay molecule or second messenger, G protein

24. Which Is A Receptor Through Which Ions Would Pass?
Answer D—note the channel appearance

25. Which Of These Acts As A Second Messenger?
D acts as the second messenger

26. Water-soluble (hydrophilic) Lipid-soluble (hydrophobic)
Polypeptides
Steroids
0.8 nm
Insulin
Cortisol
Amines
Hormones differ in structure and solubility.
Epinephrine
Thyroxine

27. Cellular Response Pathways
Water- and lipid-soluble hormones differ in their paths through a body
Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell- surface receptors
Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells
Protein/peptide hormones are released by exocytosis, steroid hormones are able to leave their secretory cells by way of diffusion. Once in the blood stream, both travel to their target cells.. Upon arrival at the target cell, these two types of hormones have different methods of communicating with the target cells.

28. Water- soluble hormone Lipid- soluble hormone
SECRETORY CELL
Water- soluble hormone
Lipid- soluble hormone
VIA BLOOD
Transport protein
Signal receptor
TARGET CELL
Signal receptor
Receptor location varies with hormone type. Notice that the water soluble hormones, such as epinephrine or insulin, bind with a membrane bound receptor protein while the lipid soluble hormone can pass directly through the membrane of the target cell to dock with an intracellular receptor..
NUCLEUS
(a)
(b)

29. Water- soluble hormone Lipid- soluble hormone
SECRETORY CELL
Water- soluble hormone
Lipid- soluble hormone
VIA BLOOD
Transport protein
Signal receptor
TARGET CELL OR
Signal receptor
Receptor location varies with hormone type.
Cytoplasmic response
Gene regulation
Cytoplasmic response
Gene regulation
NUCLEUS
(a)
(b)

30. Pathway for Water-Soluble Hormones
Binding of a hormone to its receptor initiates a signal transduction pathway leading to responses in the cytoplasm, enzyme activation, or a change in gene expression

31. Pathway for Water-Soluble Hormones
The animation should play once you show this slide.

32. Specific Example Notice the presence of the second messenger
Go through the numbered steps in this pathway emphasizing the presence of a second messenger and the amplification of the response inside the cell. Click the blue tip of the arrow to link to a video clip that explains the process of amplification. (The link will only be active in “presentation” mode). Once the video has been viewed ask students to discuss the role of the second messenger and the value of amplification.
Click here to view the animation

33. Pathway for Lipid-Soluble Hormones
The response to a lipid-soluble hormone is usually a change in gene expression
Steroids, thyroid hormones, and the hormonal form of vitamin D enter target cells and bind to protein receptors in the cytoplasm or nucleus
Protein-receptor complexes then act as transcription factors in the nucleus, regulating transcription of specific genes

34. Pathway for Lipid-Soluble Hormones
The animation should play once you show this slide.

35. Steroid Hormone Example: Testosterone
Explain the pathway of a steroid hormone using testosterone as an example. Pick a male student with a moustache as your example and explain how testosterone from the testes is secreted and moves into the blood stream The testosterone would move around the male’s body. However, follicular cells have testosterone receptors and respond to the presence of this hormone. Once inside the follicle cell of the lip, the testosterone stimulates the cell to produce keratin by “turning on” the segment of DNA that codes for the protein.”

36. In this case the protein produced could be keratin.

37. Model Steroid Hormone Action using the Testosterone Manipulative
Have students take turns explaining the action of a steroid hormone using the model provided. (Pig hair from a paint brush can serve as the keratin produced in this pathway). Hold students accountable for the activity by having them write a list of steps in the pathway from secretory cell to keratin produced.

38. Compare protein and steroid hormones by completing this T chart
Characteristic
Protein Hormone
Steroid Hormone
Speed of response
Primary biomolecule composition
Method of leaving secretory cell
Location of receptor
Example
Students should complete the chart on their own or working with a partner.

39. Compare protein and steroid hormones by completing this T chart
Characteristic
Protein Hormone
Steroid Hormone
Speed of response
Rapid response, cascade
Response is slower, gene expression
Primary biomolecule composition
Amino acid
cholesterol
Method of leaving secretory cell
Exocytosis
diffusion
Location of receptor
Membrane bound
Intracellular
Example
Epinephrine
Testosterone
Compare their responses to these suggested responses

40. Multiple Effects of Hormones
The same hormone may have different effects on target cells that have
Different receptors for the hormone
Different signal transduction pathways
The same hormone can cause different reactions depending upon the cell it has targeted.

41. Multiple Effects of Hormones
The hormone epinephrine has multiple effects in mediating the body’s response to short-term stress
Epinephrine binds to receptors on the plasma membrane of liver cells
This triggers the release of messenger molecules that activate enzymes and result in the release of glucose into the bloodstream
For example, epinephrine can be stimulatory is some parts of the body and stimulatory in others.

42. Epinephrine inhibits the glycogen synthesizing work of a liver cell while promoting the breakdown of glycogen

43. Same receptors but different intracellular proteins (not shown)
Different receptors
Different cellular responses
Different cellular responses
Epinephrine
Epinephrine
Epinephrine
 receptor
 receptor
 receptor
Glycogen deposits
Vessel dilates.
One hormone, different effects.
Vessel constricts.
Glycogen breaks down and glucose is released from cell.
(a) Liver cell
(b)
Skeletal muscle blood vessel
Intestinal blood vessel
(c)

44. Did you know…
One reason that kittens sleep so much is because a growth hormone is released only during sleep.
The levels of two stress hormones, cortisol and epinephrine which suppress the body's immune system, will actually drop after a dose of laughter.
Chocolate is associated with the release of serotonin, the hormone that makes you feel relaxed, calm, and happy. So are hugs.
Just for fun!