# Cumulative growth curve - how to calculate CPD(cumulative population doubling)? (Mar/09/2011 )

I want to do a cumulative growth curve as I want to see, if siRNA-mediated knockdown of my protein has any effects on proliferation.

I do a 9-day protocol:

day 0: seed cells in the morning, transfect with siRNA late in the afternoon

day 3/6/9: trypsinize, count cells, seed again with same density as on day 0, transfect again some hours later

For each 3-day-interval, I would calculate (cell number at the end) divided by (cell number at beginning). So for CPD at day 6 it would be: {(day3 density)/(seeding density)}x{(day 6 density)/(seeding density)}

So how do I calculate my cumulative population doubling? Is it okay to multiply the PD-values for each 3day-interval? Or does it have to be added? I have also seen this formula: PD={ln (day 3 density)-ln (day 0 density)}/ln2. But I have no idea why logarythmic values should be used...

Any help or publications are very much appreciated.

Thanks!

Do determine your population doubling you will need to calculate your growth rate and doubling time. This is info would help you calculate your integral viable cell density (cumulative)

cheers

Why re-transfect - surely that is re-starting the experiment at each time point, so essentially you are doing 3 -3 day experiments.

You would be better off setting up plates such that you can harvest cells at 1, 2, 3 days and plotting an increase in cell number over time - which will give you a growth curve and allow you to calculate the actual population doubling time.