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# Cumulative growth curve

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### #1 Taranaki

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Posted 09 March 2011 - 04:58 AM

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!

### #2 sbyrne27

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Posted 09 April 2011 - 03:30 PM

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

### #3 bob1

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Posted 10 April 2011 - 04:02 PM

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.