Lecture 20: Signal Transduction – Part 1

Cells need to respond how often to changes in external environment?

constantly

What detectd and respond to changes in nutrients, chemicals, light, heat,mechanical forces, etc.

cells

Which organisms must coordinate these responses to different external signals across different cell types

Multicellular

Order of Signal Transduction

1. Receive Signal ---------> 2. Transduce Signal -----------> 3.Respond to Signal

The complex process by which a cell converts a signal from outside (or from inside the cell) to a functional change within the cell

Signal Transduction

Location of Signal Transduction

Signaling Cell ---------> Signal ---------> Receptor ---------> Target Molecule ---------> Response

whereby a protein in the signal transduction pathway (S5) or an effector protein modifies either the receptor or an early protein in the pathway

feedback controls

Ex: hormones (insulin secreted by pancreatic cells travels through blood and acts on target cells in liver, muscles, etc)

Endocrine signaling

Ex: neuron releasing a neuro transmitter, growth factors et

Paracrine signaling

Ex: tumor cells secrete growth factors that act on itself

Autocrine signaling

Signaling by plasma membrane attached proteins

Ex: notch signaling pathway

Signaling by plasma membrane attached proteins

typically consequences of modifications to specific preexisting enzymes and other proteins that alter their activity or function

Rapid changes

effector proteins are typically transcription factors and results in
changes in gene expression

Slower, long-term changes

Often initiated by covalent modifications such as phosphorylation or ubiquitination or by binding of ions or molecules such as Ca2+ or cAMP

Rapid changes

Induces changes in cell proliferation, cell differentiation, and organismal development

Slower, long-term changes

Such modifications can induce changes in cellular metabolism, secretion of hormones, firing of action potentials in nerve cells etc

Rapid changes

Diffuse through the plasma membrane

Bind to cytosolic receptors

Hydrophobic signaling molecules

Cannot diffuse across the cell membrane

Bind to specific cell-surface receptor proteins

Hydrophilic signaling molecules

Receptor-signal complex moves into the nucleus – binds

promoter regions in DNA to regulate gene expression

e.g., Estrogen – Estrogen Receptor

Hydrophobic signaling molecules

triggers receptor conformational change that activates the receptor

Ligand receptor interaction can be extracellular or intracellular

small molecules [adrenaline, acetylcholine], peptides [yeast

mating factors, glucagon], and proteins [insulin, growth

hormone]

Hydrophilic signaling molecules