1. Cell Communication
CHAPTER 11
Unit 4

2. Evolution
Molecular details of signal transduction in yeast and mammals are very similar
Early versions of today’s mechanisms evolved well before the first mutlicellular organism
First evolved in ancient prokaryotes and single-celled eukaryotes, then were adopted for new uses by multicellular descendants

3. Cell Signaling Direct contact (gap junctions) Local regulators
Paracrine signaling: numerous cells receive signal
growth factors
Synaptic signaling:
neurotransmitters
Long distance (hormones)
Endocrine signaling:
cells release hormone and travels through circulatory system to target cell

5. 3 Stages of Cell Signaling:
Reception: Detection of a signal molecule (ligand) coming from outside the cell
Transduction: Convert signal to a form that can bring about a cellular response
Response: Cellular response to the signal molecule

6. Reception

7. Transduction

8. Response

9. 1. Reception
Binding between signal molecule (ligand) and the receptor is highly specific.
Types of Receptors:
Intracellular receptors (cytoplasm, nucleus)
hydrophobic or small
EX: testosterone
Plasma membrane receptor
Receptor proteins in plasma membrane
water-soluble ligands

10. 3 Major Types of Plasma Membrane Receptors
G-Protein Coupled Receptor (GPCR)
Tyrosine Kinase
Ligand-Gated Ion Channels
G protein + GTP activates enzyme  cell response
Attaches (P) to tyrosine
Signal on receptor changes shape
Widespread, diverse in function (embryonic dev., sensory reception)
Activate multiple cellular responses at once
Regulate flow of specific ions
(Ca2+, Na+)

11. G Protein Coupled Receptors
Largest family
Transmembrane with a G protein that binds with GTP
EX: epinephrine, senses, embryonic development

12. Cholera
Toxin modifies G-protein involved in regulating salt & water secretion
G protein stuck in active form  intestinal cells secrete salts, water
Infected person develops profuse diarrhea and could die from loss of water and salts
Disease acquired by drinking contaminated water (w/human feces)
Bacteria (Vibrio cholerae) colonizes lining of small intestine and produces toxin

13. Receptor Tyrosine Kinase
One receptor can activate 10 or more different transduction pathways
EX: cell growth and reprodcution
Abnormal function associated with cancer
Excessive levels of HER2 and breast cancer

14. Receptor Tyrosine Kinase

15. Ligand-Gated Ion Channel

16. 2. Transduction
Cascades of molecular interactions relay signals from receptors to target molecules
Protein kinase: enzyme that phosphorylates and activates proteins at next level (turns on)
Phosphorylation cascade: enhance and amplify signal
Protein Phophatases: enzyme that rapidly removes phosphate groups from proteins (turns off)

18. Second Messengers
small, nonprotein molecules/ions that can relay signal inside cell
Eg. cyclic AMP (cAMP) and Ca2+

19. 3. Response
Regulate protein synthesis by turning on/off genes in nucleus (gene expression)
Regulate activity of proteins in cytoplasm

20. Apoptosis = cell suicide
Cell is dismantled and digested
Triggered by signals that activate cascade of “suicide” proteins (caspase)
Why?
Protect neighboring cells from damage
Animal development & maintenance
May be involved in some diseases (Parkinson’s, Alzheimer’s); interference may contribute to cancers

21. Apoptosis of a human white blood cell
Figure Apoptosis of human white blood cells
Left: Normal WBC
Right: WBC undergoing apoptosis – shrinking and forming lobes (“blebs”)

22. Effect of apoptosis during paw development in the mouse
Figure Effect of apoptosis during paw development in the mouse