1. 2E2 – Timing and coordination of physiological events are regulated by multiple mechanisms.
3B2 – A variety of intercellular and intracellular signal transmissions mediate gene expression.
3D – Cells communicate by generating, transmitting, and receiving chemical signals.
1 – Cell communication processes share common features that reflect a shared evolutionary history.
2 – Cells communicate with each other through direct contact with other cells or from a distance via chemical signaling.
3 – Signal transduction pathways link signal reception with cellular response.
4 – Changes in signal transduction pathways can alter cellular response.

2. Chapter 11~ Cell Communication

3. Signal-transduction pathway I
Def: Process by which a signal on a cell’s surface is converted into a specific cellular response
Local signaling (short distance):
Messenger moleucles are secreted and travel short distances
Paracrine signaling (growth factors)
Single cell produces factors that are received and responded to by numerous cells simultaneously
Synaptic (neurotransmitters)
Electrical signal stimlates secretion of chem signal which moves across the synapse to another cell

4. Signal-transduction pathway II
Long distance: hormones
Animals - aka endocrine signaling
Hormones released into circulatory system to travel to target cells
Nervous system – signal continues along a series of cells
Plants – growth regulators
Travel by vessels, diffusion through cells, or the air as a gas

5. Stages of cell signaling
Discovered by Earl Sutherland (‘71)
Glycogen depolymerization by epinephrine
3 steps:
(1) Reception: target cell detection
(2) Transduction: single-step or series of changes
(3) Response: triggering of a specific cellular response

6. Reception I
A signal molecule binds to a receptor protein and causes a conformation change
Ligand – molecule that specifically binds to another
Compare to a key in a lock – similar to enzymes
Intracellular receptors
Proteins found in cytoplasm or nucleus of target cell
Messenger must pass through plasma membrane
Must be hydrophobic or small enough
Ex. Steroids, thyroid hormones
Testosterone – released by testis
Target cells have receptor in nucleus
Binds w/ protein activating it
Active form enters nucleus and turns on specific genes

7. Reception II Plasma membrane receptors (pg 206-208)
Water soluble signal molecules
Receptor transmits info by changing shape
3 main types
(1) G-protein-linked receptors
Receptor is made of 7 transmembrane α helices
Works w/ the help of a G protein which is just inside the membrane
Is on or off depending on which of 2 guanine nucleotides is attached (GDP or GTP)
Signal molecule binds to receptor and changes its shape
Binds to GDP causes GTP to replace it
GTP binds to an enzyme and activates it
Reverts to GDP

8. Reception III (2) Receptor Tyrosine Kinases
Can trigger simultaneous signal transduction pathways
Regulates cell growth and reproduction
Malfunction may lead to cancer
Kinase – enzyme catalyzes phosphate transfers in cytoplasm
Portion of receptor acts as a tyrosine kinase
Signal molecule causes 2 receptors to move close together (dimerization)
Activates tyrosine kinase
Attaches phosphates to tyrosines
Different inactive proteins bind to phosphorylated tyrosine and become activated

9. Reception IV (3) Ligand-gated ion channels
Important for nervous system
When receptor changes shape a “gate” opens/closes allowing ions through or blocking flow
Cause changes in Na+ and Ca- concentration levels

10. Transduction I
Series (cascade) of molecular interactions relay signals from receptors to target molecules
Begins when receptor changes
Relay molecules = proteins
@ each step info is transduced into a different form
Usually a conformation change in protein
Caused by phosphorylation

11. Transduction II
Protein kinase – enzyme that transfers a phosphate from ATP to protein – many different kinds
Addition of phosphate activates protein
Dephosphorylation – removal of phosphate
Inactivates proteins – turn off pathway
Caused by enzymes called protein phosphatases

12. Second Messengers I Small molecules and ions that are not proteins
1st is the extracellular signal molecule that binds to membrane
Are able to diffuse through cells
2 most common:cyclic AMP &calcium ions

13. Second Messengers II (1) cyclic AMP (cAMP)
Adenylyl cyclase (enzyme in membrane) converts ATP to cAMP
Concen. increases and spreads through cell
Only lasts while signal molecule is attached
Concen. decreases because phosphodiesterase changes cAMP back to ATP

14. Second Messengers III (2)Calcium ions and Inositol Triphosphate (IP3)
Ca concen. increases triggered by other secondary messengers
Phospholipid in membrane is broken into IP3 and diaglycerol (DAG)
IP3 goes on to stimulate Ca increase

15. Response Regulation of cellular activities In cytoplasm
Ex. Open/close ion channel; change in metabolism
May cause synthesis of enzymes

16. Specificity of Cell Signaling
Get different results from different cells because they have different collections of proteins
Ex. Epinephrine – a liver cell breaks down glycogen; heart cells contract for faster heart beat

17. Signaling Efficiency
Scaffolding proteins – large relay proteins w/ other relay proteins attached
Increases efficiency