Signal Transduction: Ligand-Receptor Interactions Cell and Developmental Biology Group

Goals – Integration of quantitative skills in cell biology Modeling cellular responses

Class setup First or second year majors in cell biology Co-requisite with Calculus Middle of the course ~1 hour lecture Learning outcomes 1) Relate the concept of threshold to cellular responses 2) Understand how these components affect threshold - ligand and receptor concentrations - binding affinity 3) Apply knowledge of quantitative models of cellular response

A driver returned to his car after a 3 hour shopping spree to see the following sight. His car would not start. Why?

Battery current thresholds Battery power 0% 100%

Draw how the battery / ignition threshold would look on this graph Battery current Response (ignition) lowhigh No ignition ignition

Cell Signaling EXTRACELLULAR FLUID Reception Receptor Signal molecule Plasma membrane Transduction CYTOPLASM Relay molecules in a signal transduction pathway Response Activation of cellular response Tomorrow’s presentation

What happens when you see this?

Effects of adrenaline on different tissues in the body

Threshold as it relates to ligand  receptor binding and cellular function Basic response threshold Maximum response threshold [Adrenaline] Fight - Flight response lowhigh Ligand / receptor concept Reception

A.1 Ligand receptor complex B Ligand receptor complexes C ,000 Ligand receptor complexes D.10, ,000 Ligand receptor complexes E.100, million Ligand receptor complexes How many ligand / receptor complexes are required to elicit a cellular response?

Binding Affinity [L] + [R][LR] Dissociation Constant (K d ): is the free ligand concentration at which 50% of receptor is occupied. Affinity is defined by the association constant (K a ) =1/K d Each ligand / receptor complex has its own specific binding affinity. k1k1 k -1 K d = k -1 / k 1

[ligand] response Which graph represents a cell with a receptor with the highest affinity? lowhigh A B CD

(Think-Pair  1 minute essay) What is the relationship between affinity and threshold? [ligand] response lowhigh ABCD

Affinity and the curves Which of these factors can the cell control? How might a cell be able to control its own threshold? Affinity = 1 / K d

Affinity and the curves [Ligand] Response Affinity = 1 / K d Associate each of the following with the appropriate graph above A. [L]=1 µM, [R]=0.5 µM, K d =.25 µM B.[L]=1 µM, [R]=1.25 µM, K d =.25 µM BA

Affinity and the curves [Ligand] Response Affinity = 1 / K d Associate each of the following with the appropriate graph above A. [L]=1 µM, [R]=1.25 µM, K d =.25 µM B. [L]=1 µM, [R]=1.25 µM, K d =.5 µM AB

Relationship between [R],[LR],K d In general, What happens to [LR] when [R] increases and K d stays the same? What happens to [LR] when K d increases and [R] stays the same?

Affinity and the curves [Ligand] Response Associate each of the following with the appropriate graph above A. [L]=1 µM, [R]=0.5 µM, K d =.25 µM B.[L]=1 µM, [R]=1.25 µM, K d =.25 µM C.[L]=1 µM, [R]=1.25 µM, K d =.5 µM Affinity = 1 / K d BAC

Affinity and the curves [Ligand] Response Associate each of the following with the appropriate graph above A. [L]=1 µM, [R]=0.5 µM, K d =.25 µM B.[L]=1 µM, [R]=1.25 µM, K d =.25 µM C.[L]=1 µM, [R]=1.25 µM, K d =.5 µM Affinity = 1 / K d BCA

Think-Pair-Share (2 minutes) Assume the order of response events to an adrenaline spike is: 1st) heart rate increase, 2nd) blood vessel constriction, 3rd) sweating [ligand] response lowhigh Which of the following associates the response curves with the physiological response? A)Heart = blue, blood = black, sweat = green B) Heart = green, blood = black, sweat = blue C) Heart = black, blood = blue, sweat = green D) All tissues would have the same response curve

What happens when your adrenaline rush goes away??

Off-switch (negative threshold ) Basic response threshold Maximum response threshold [Adrenaline] Fight - Flight response lowhigh

Ligand-receptor interactions are widespread and have varied roles in organisms. The immune system Development Environmental sensing

A.1 Ligand receptor complex B Ligand receptor complexes C ,000 Ligand receptor complexes D.10, ,000 Ligand receptor complexes E.100, million Ligand receptor complexes How many ligand / receptor complexes are required to elicit a cellular response?

Summative Assessment 1)Explain the concept of threshold 2)Relate changes in dissociation constants to cellular responses – Correlate changing K d values to how they affect the graph 3) Describe the effects that drug A would have on the fight or flight response if drug A: – Lowered the concentration of adrenaline – Blocked the receptor 4)Relate the importance of understanding mathematics to experimentally analyzing cellular responses