Chapter 11: Cell Communication

Word Roots:

liga- = bound or tied to

trans- = across

Ligand – a small molecule that specifically binds to a larger one.

Transduction – the transmission and conversion of a message.

www.chem.cmu.edu

www.aisee.com

Signal Transduction Pathways•Local Signaling

•Direct contact

•Local Regulators

•Paracrine signaling

•Synaptic signaling

•Long Distance Signaling

•Hormones

•Nervous

Direct Contact

Local Signaling

•Less specific

•Growth factors

•More Specific

•Neurotransmitters

Long Distance Signaling •Very Specific

•Target cells

•Hormones

•Nerves – electrical transmission of impulses

www.arikah.com

Three Stages of Cell Signaling•3 Steps

•Reception

•Transduction

•Response

•Earl W. Sutherland – 1971

•Signal Transduction Pathway for glycogen breakdown.

Step 1: Reception

•Receptor Proteins:

•Membrane

•Cytoplasm

•Nucleus

•Signal Molecule

•Ligand-general term for chemical signal

•Small/hydrophobic

• nucleus/cytoplasm

•Large/water soluble

• Usually Membrane

Plasma Membrane Receptors•G-Protein Linked

•Receptor Tyrosine Kinases

•Ion Channel

G-Protein Linked•Embryonic development and sensory reception.

•GTP – guanosine triphosphate

Receptor Tyrosine Kinases

Receptor Tyrosine Kinases cont.•Kinase

•Regulates growth and reproduction

•Multiple pathways stimulated

•Branched pathways

Ion Channel Receptors•Nervous system

•Sodium-Potassium Pump

Sodium Potassium Pump

Step 2: Transduction•Multi-step

•Amplifies signal

•Require Relay Molecules

•Protein Kinases

•Serine/threonine kinases

•Phosphorylation cascade

•Conformational change

•Increase or decrease

•Protein Phosphatases

•Recycle and reuse

Second Messengers•Small,nonprotien water soluble

•Diffuse easily

•Easily Amplified

•Cyclic AMP (cAMP)

•Calcium ions (Ca2+)

•Inositol triphosphate (IP3)

•Diacylglycerol (DAG)

Cyclic AMP•Cyclic adenosine monophosphate

•Created by Adenylyl Cyclase from ATP

•Many cAMP molecules – amplification

•Phosphodiesterase

•Activates Protein Kinase A

‘Locking’ the pathway

Cholera – Vibrio cholerae

Locks G-Protein for water and salt regulation ‘on’.

Diarrhea

Vasodilatation

Cyclic GMP – relaxes artery walls

Viagra – blocks cyclic GMP – increases blood flow

Calcium Ions and Inositol Triphosphate•Ca2+ low in cytosol, high in ER and ECF

•Active transport and membrane proteins

•Controlled by gated ion channels

•Regulates:

•Muscle contraction

•Secretion of other substances

•Cell division

•Used:

•G-protein

•Receptor Tyrosine Kinases

Step 3: Response•Cytoplasmic or Nuclear

•Regulates:

•Enzyme/Protein activity

•Enzyme/Protein creation

•Transcription factors

•Growth factors

•Hormones

Cytoplasmic Response

Nuclear Response

Benefits of Transduction Pathways•Signal Amplification

•Each step – more amplification

•Specificity

•Branched pathways – Receptor Tyrosine Kinases

Signaling Efficiency•Scaffolding Proteins (kind of like a relay molecule)

•Can cause different phosphorylation cascades

•Signaling Complexes

•Proteins can participate in:

•More than one pathway in 1 cell

•Many pathways in different cells

Step 4: Signal Termination•Reversible binding

•Signal molecule unbinds

•GTPase activity

•Phosphodiesterase

•Phosphatases