1. Cell Signaling A. Types of Cell Signaling
B. Intracellular Receptor Signaling: Steroid Hormones
C. Cell Surface Receptors: Types
D. Cell Surface Receptors: G-protein linked receptors

2. A. Types of Cell Signaling
Direct cell-cell signaling vs. signaling via secretion

4. A. Types of Cell Signaling
Cell surface receptors vs. Intracellular receptors

6. A. Types of Cell Signaling
Three forms of signaling by secreted molecules
Paracrine
Synaptic
Endocrine

9. A. Types of Cell Signaling
Gap junctions

11. A. Types of Cell Signaling
The same signal can produce different effects in different cells

13. A. Types of Cell Signaling
Proper signaling generally depends on a signal molecule being degraded rapidly

14. A. Types of Cell Signaling
Types of Signals based on Where they Bind
To an intracellular receptor: e.g. Steroid hormones
To a cell-surface receptor: G-protein linked, enzyme-linked, or ion channel-linked

15. B. Intracellular Receptor Signaling: Steroid Hormones
Overview of Steroid Hormone Action:
Steroid hormone (small, hydrophobic) is secreted by glandular cells and released into bloodstream (usually transported via shuttle proteins)
The hormone enters the cytoplasm of cells
In the cytoplasm of target cells, the hormone binds to steroid hormone receptor protein

16. B. Intracellular Receptor Signaling: Steroid Hormones
Overview of Steroid (cont.):
The steroid-receptor conplex is translocated into the nucleus, where it activates the transcription of the primary response genes
Transcription of the primary response genes, followed by translation, results in the production of primary response proteins

17. B. Intracellular Receptor Signaling: Steroid Hormones
Overview of Steroid (cont.):
The primary response proteins usually inhibit further transcription of their own genes, and they may activate transcription of secondary response genes.

21. C. Cell Surface Receptors: Types
Three known classes of cell surface receptors
Ion channel-linked, G-protein-linked, Enzyme-linked
An activated cell-surface receptor triggers a phosphorylation cascade

25. D. Cell Surface Receptors: G-protein linked receptors
Largest family of cell surface receptors
Different ones respond to a wide variety of mediators including different hormones, neurotransmitters, local mediators
Examples: Receptors to epinephrine, acetylcholine, serotonin

27. B. G-linked Receptors What do G-protein receptors do?
G-protein receptors activate trimeric G-protein
Activated G-protein alters the cellular concentration of a “second messenger”: usually cyclic AMP or Ca2+
The second messenger activates a protein kinase enzyme
The protein kinase phosphorylates another enzyme and alters its activity

32. B. G-linked Receptors Trimeric G-proteins disassemble when activated
Three chains: a, b, and g
a chain binds and hydrolyzes GTP
b & g chains form a tight complex bg that anchors G-protein to the plasma membrane

33. B. G-linked Receptors Trimeric G-proteins disassemble when activated
Inactive G-protein has a bound GDP
When activated: GDP dissociates, new GTP is bound
This causes a to dissociate from bg
a binds to adenylate cyclase, altering its activity
Gs protein stimulates activates adenylate cyclase, Gi inhibits it

36. B. G-linked Receptors Action of epinephrine on glycogen metabolism
Epinephrine (adrenaline) is released from the adrenal gland in times of stress. It has two overall actions on glycogen metabolism: it inhibits glycogen synthesis, and it promotes glycogen breakdown
This is mediated by a protein phosphorylation cascade