Use matplotlib to plot two data series on separate y-axes.

secondary_axis.py

from matplotlib import pyplot as plt

fractions = range(1, 16)
mcgs = [0,0,0,0,0,190,145,10,0,0,0,0,0,0,0]
dpms = [0,0,0,0,0,290,390,0,0,0,0,5,20,80,350]

#check lists for length
for list in [dpms, mcgs]:
    assert len(list) == len(fractions), "lists should be same length"


fig, ax1 = plt.subplots(figsize=(6,4))
ax2 = ax1.twinx()

def my_plot(ax, fractions, alist, color = "red", ylabel = "ylabel"):
    ax.scatter(fractions, alist, color=color, label=ylabel, alpha=0.5)
    ax.plot(fractions, alist, color=color, ls=":")
    ax.set_ylabel(ylabel)

my_plot(ax1,
        fractions, 
        dpms, 
        ylabel=r"Total Radioactivity count (DPM) $10^{3}$", 
        color="orange")

my_plot(ax2, 
        fractions, 
        mcgs, 
        ylabel= r"Total Protein $\mu$g", 
        color="blue")

fig.legend(bbox_to_anchor=(1, 1), loc='upper left', borderaxespad=0.)
ax1.set_title(r"Incorporation of ${}^{14}$C into X")
ax1.set_ylim(0, 450)
ax2.set_ylim(0, 200)
ax1.set_xlabel("fraction")

fig.tight_layout()