biolA 190 - ch 8

8.1

8.1

all living organisms require

cell communication/cell signaling to survive

signals are often

chemical molecules

signals can also be

physical parameters like light or temperature

1. direct intercellular signaling

where cell junctions allow signals to directly pass from one cell to another

2. contact-dependent signaling

where molecules bound to the surface of cells serve as signals to other cells encountering them

3. autocrine signaling

where cells secrete signaling molecules that bind to their own surface receptors

4. paracrine signaling

where cells release signals that affect nearby cells

5. endocrine signaling

where signals (called hormones) are released into the blood and affect target cells that are far away

5 types of cell signaling

3 common stages of cell signaling are

receptor activation

signal transduction

cellular response

often a gorup of proteins form a signal transduction pathway

8.2

8.2

ligand

signaling molecule that binds noncovalently to its receptor with high specificity

ligand binding changes the receptor structure

this conformational chanfe transmits the signal across the membrane t

he complec that forms between the ligand and its receptor is stable for a finite period of time

the complex will dissociate

generally, binding and release between a ligans and a receptor is relatively

rapid and equilibrium is reached

Kd, the dissociation constant, is used to

quantify the affinity receptors have for their ligands

Kd also reflects the ligand concentration where

half of the receptors have bound ligand

When the ligand is above the Kd value

most receptors are likely to have ligand bound to them

if the ligand is substantially below the Kd value, most receptors will not be bound to their ligand

8.3

8.3

most signaling molecules are small and hydrophilic or

too large to pass through the plasma membrane

cell surface receptors that are embedded in the plasma membrane

detect these types of extracellular signals

enzyme-linked receptors

typically have 2 important domains

an extracellular signal-binding domain and an intracellular catalytic domain

G protein-coupled receptors (GPCRs) interact with

intracellular proteins called G proteins

when signaling molecule binds a ligand-gated ion channel

the channel opens and allows the flow of ions across the membrane

8.4

8.4

intracellular receptors

found in the cytosol or nucleus

bind signal molecules thaty are small and hydrophobic

activation of an intracellular receptor typically leads to a change in

gene expression