1. Big Idea 3 - Genetics and Information
Concept 3D. Cell Signaling
Lesson 1: Cell communication processes share features that reflect a shared evolutionary history
Lesson 2: Cells communicate with each other through
direct contact or from a distance via chemical signaling.
Lesson 3: Signal transduction pathways link signal reception with cellular response
Lesson 4: Changes in signal transduction pathways can alter cellular response.

2. Communication involves transduction of signals.
Signals pass from one cell to another
can stimulate or inhibit a response

3. The signal and the response must be correct
Why are the genes for cell signaling under strong evolutionary selective pressure?

4. Signaling in single-celled organisms
Signals influence how the cell responds to the environment.
Example - Quorum sensing
Bacteria produce low concentration of inducing agents
can signal production of a substance or slow the growth of the colony

5. Signaling in single-celled organisms (cont)
Signals influence how the cell responds to the environment.
Example - Chemotaxis
Bacteria will move “up” or “down” the concentration gradient of a substance.

6. Signaling in multicellular organisms
Signal transduction pathways coordinate the activities within individual cells
support the function of the organism as a whole
Example DNA repair
Damage to the DNA is detected
Typically: change in shape or base pair mis-match
Repairs are attempted
repair using template - translesion synthesis if a template is absent
If damage cannot be repaired
Cell goes dormant (senescence), or destroyed via apoptosis

7. Signaling in multicellular organisms (cont)
Example - Temperature-dependent sex determination
Cells detect temperature and produce hormones
Can be mother’s cells or cells of the forming organisms (in ovo)
Other cells respond to those hormones and determine sex
Patterns of temperature-dependent sex determination (TSD) in reptiles. Pattern I is found in turtles, e.g. Red-eared slider turtles (Trachemys scripta), Olive Ridley sea turtles (Lepidochelys olivacea), or Painted turtles (Chrysemys picta). Pattern II has been found in American alligators (Alligator mississippiensis and Leopard geckos (Eublepharis macularius).

8. Big Idea 3 - Genetics and Information
Concept 3D. Cell Signaling
Lesson 1: Cell communication processes share features that reflect a shared evolutionary history
Lesson 2: Cells communicate through direct contact or from a distance via chemical signaling.
Lesson 3: Signal transduction pathways link signal reception with cellular response
Lesson 4: Changes in signal transduction pathways can alter cellular response.

9. Cells communicate by cell-to-cell contact
Called Juxtacrine signals
Example:
Immune cells interact by cell-cell contact, antigen-presenting cells (APCs), helper T-cells and killer T-cells

10. Cells communicate by cell-to-cell contact
Called Juxtacrine signals
Example:
Plasmodesmata between plant cells that allow material to be transported from cell to cell.

11. Cells communicate over short distances by using local regulators that target cells in the vicinity of the emitting cell
Called paracrine signals
Examples:
Quorum sensing in bacteria
Neurotransmitters

12. Signals released by one cell type can travel long distances to target
cells of another cell type
called Endocrine signals
Example:
Insulin and other endocrine system signals

13. Signals released by cells on one organism can target cells of another organism
Called pheromones
Example:
Yellow bee-orchid releases female bee allomones

14. Big Idea 3 - Genetics and Information
Concept 3D. Cell Signaling
Lesson 1: Cell communication processes share features that reflect a shared evolutionary history
Lesson 2: Cells communicate through direct contact or from a distance via chemical signaling.
Lesson 3: Signal transduction pathways link signal reception with cellular response
Lesson 4: Changes in signal transduction pathways can alter cellular response.

15. Signaling begins with a ligand
Chemical messengers
peptides
small chemicals
proteins
Specific to the receptor

16. Receptor protein Signal molecules binds to the receptor protein
protein changes shape
conformation change
Initiates transduction of the signal

17. Receptor protein example: G protein-coupled receptors
After ligand binds:
The cytosol-facing portion of the protein undergoes a conformation
activate g-protein
GDP → GTP
affects another (target) protein
Which may (for example)
relay signal to other proteins
release products
catalyze other reactions
youtu.be/V_0EcUr_txk

18. Receptor protein example: Ion channel linked receptors
After ligand binds:
conformation change
ions flow down the concentration gradient
youtu.be/A1sdk7hyGz8

19. The process of signal transduction
Converts signal to cellular response
signal cascade
relays signal from receptor to cell target
often amplifying signal

20. Secondary messengers Often essential to cascade function Example:
cyclic AMP
activated by g-protein target
activates protein
kinases
which phosphorylate other proteins/enzymes

22. Many signal transduction pathways include:
Protein modifications
conformational changes (H-bonds)
additions (covalent bonds)
Phosphorylation cascades
series of protein kinases
phosphorylate (add a phosphate group to) the next protein in the cascade sequence