Chapter 7 Cell Communication and Multicellularity Flashcards
Signal transduction pathway
A sequence of molecular events and chemical reactions that lead to a cell’s response to a signal
A signal transduction pathway includes
A signal, a receptor and a response
In multicellular organisms, chemical signals are often made in one part of the body and arrive at target cells by (3 ways
Local diffusion
Circulation im the blood
Plant vascular system
Autocrine signals
Diffuse to and affect the cells that make them
e.g, tumor cells
Juxtacrine signals
Affect only cells right next to and in contact with the cell producing the signal
Paracrine signals
Diffuse to and affect nearby cells
e.g, histamine, (inflammation when the skin is cut, signals from skin cells are sent to nearby blood cells to aid in healing
Hormones
Signals that travel through the circulatory systems of animals or vascular systems of plants are generally called hormones
(Hormones are chemical signals that act on distant cells
Crosstalk
Interactions between different signal transduction pathways
Ligand
A specific chemical signal molecule that fits into a 3D site on its protein receptor
Binding of the signaling ligand causes
The receptor to change its 3D shape, and that conformational change initiates a cellular response (ligand contributes no further
The binding is reversible because
Receptors bind to ligands according to chemistry’s law of mass action
Why is reversibility important
Otherwise the receptor would be continuously stimulated and the cell will never stop responding
Dissociation constant is a measure of
The affinity of the receptor for its ligand
Low Kd, high affinity, bind to ligands at low ligand conc.
The change in receptor’s shape may expose
A previously hidden group of amino acids on the protein that participates in a biochemical activity
Membrane receptors
Large or polar ligands cannot cross the lipid bilayer
e.g, insulin
Binds to a transmembrane receptor with an extracellular binding domain
Intracellular receptors
Small or nonpolar ligand can diffuse across the nonpolar phospholipid bilayer of the cell membrane and enter cell
e.g, the hormone estrogen
3 types of cell membrane receptors
Ion channels
Protein kinase receptors
G protein-coupled receptors
Ion channels
e.g, acetylcholine (Na+)
Protein kinase receptor
e.g, insulin
Insulin is a hormone made by pancreas
Adding phosphate
Phosphorylation (v important in biology
G protein-coupled receptors
7-transmembrane domain receptors
Many roles including light detection
Detection of odors
Regulation of mood and behavior
e.g, oxytocin, vasopressin
Many G proteins have 3 polypeptide subunits and can bind three different types of molecules:
The receptor
GDP and GTP (guanosine diphosphate and triphosphate)
An effector protein
Effector protein:
Causes an effect in the cell
Intracellular receptors are located
In the cytoplasm of the nucleus
Intracellular receptors respond to
Physical signals such as light
Chemical signals that can diffuse across cell membrane (e.g, steroid hormones
Many intracellular receptors are transcription factors
After binding to their ligands, these transcription factors move to the nucleus and bind to DNA and alter expression for specific genes
Another group of intracellular receptors is always in to nucleus
Ligands must enter nucleus to bind
Second messenger
Can amplify signals between receptors and target molecules
The balance between the activities of enzymes that activate and inactivate transducers determines the ultimate cellular response to a signal. Cells can alter this balance by
Synthesis or breakdown of the enzymes
Activation or inhibition of the enzymes by other molecules
