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Signal Transduction Lab

Investigate how cells detect and amplify chemical signals through receptor binding and enzyme cascades. Vary ligand concentration, cascade length, and amplification to build dose-response curves, measure signal amplification, and explore the molecular logic of cell signaling.

Guided Experiment: Signal Amplification Investigation

If you increase the number of cascade steps while keeping the ligand concentration constant at EC50, how will the total amplification change?

Write your hypothesis in the Lab Report panel, then click Next.

Signal Cascade (3 steps, 1,000× amplification)

Ligand (10.0 nM)Receptor (50%)Step 15%10×Step 239%10×Step 399%10×

Controls

Ligand Concentration10.0 nM
Dissociation Constant (Kd)10.0 nM
EC5010.0 nM
Hill Coefficient (n)2.0
Max Response100 %
Cascade Steps3
Fold per Step10 ×

Results

E=Emax⁡⋅[C]nEC50n+[C]n=50.0%E = E_{\max} \cdot \frac{[C]^n}{EC_{50}^n + [C]^n} = 50.0\%
Receptor Occupancy
50.0%
Amplification
1,000×
Response
50.0%
EC50
10.0 nM
Signal Path
Ligand (10.0 nM)→Receptor (50%)→3 steps (1,000×)→50.0%

Dose-Response Curve

Data Table

(0 rows)
#TrialLigand Conc.(nM)Receptor Occ.(%)Cascade StepsAmplification(fold)Response(%)EC50 Est.(nM)
0 / 500
0 / 500
0 / 500

Reference Guide

Receptor-Ligand Binding

Signaling begins when a ligand binds to a receptor on the cell surface. The fraction of receptors occupied follows a saturation curve governed by the dissociation constant Kd.

θ=[L]Kd+[L]\theta = \frac{[L]}{K_d + [L]}

At [L] = Kd, 50% of receptors are occupied. The Kd represents the ligand concentration needed for half-maximal binding.

Cascade Amplification

Each step in a signaling cascade activates multiple molecules of the next component. Total amplification is the product of all individual step amplifications.

Atotal=f1×f2×⋯×fn=fnA_{total} = f_1 \times f_2 \times \cdots \times f_n = f^n

For uniform amplification, n steps with f-fold each gives f^n total amplification. Three steps at 10-fold each yields 1000-fold amplification.

Dose-Response and EC50

The dose-response relationship follows the Hill equation, producing a sigmoidal curve that characterizes how strongly a cell responds to different ligand concentrations.

E=Emax⁡⋅[C]nEC50n+[C]nE = E_{\max} \cdot \frac{[C]^n}{EC_{50}^n + [C]^n}

The EC50 is the concentration producing 50% of the maximum response. The Hill coefficient n determines the steepness. Higher n values create sharper thresholds.

GPCR vs RTK Pathways

G-protein coupled receptors (GPCRs) activate G-proteins, which stimulate enzymes like adenylyl cyclase to produce second messengers (cAMP). This cascade provides massive amplification.

Receptor tyrosine kinases (RTKs) like the insulin receptor dimerize upon ligand binding and activate the Ras/MAPK cascade. RTK pathways often regulate gene expression and cell growth.

Both pathway types use sequential enzyme activation to amplify signals, but differ in their mechanisms and downstream targets.