Gene expression question - (Sep/30/2017 )

Im studying gene expression

I want to test a plant extract against bacteria, then studying the gene exprssion changes in bacterial DNA.

Now my question, Im really confused about designing the experiment

For example

If I want to study a gene for the production of lipase that degrade host tissues, someone told me to use a control gene or refrence

how to choose this control gene ?

I thought if I did the cDNA before plant treatment then after treatment and meassuring the quantity or changes of this gene, wouldnt that be enough ? why I should use a control gene ?

The control gene is to account for differences in preparation of the sample - for instance in one case you might have 10^6 bacteria in one sample, in the next you might have 1.5x10^6 - how do you account for having more in one sample than another... use a control! The expression is measured on the RNA (converted to cDNA) the bacteria produce, so reference genes need to be stable under experimental conditions.

How you choose the control is up to you - you should check the literature to see if there are commonly used ones for the species you are using for the experiments. You should then test to see if they vary under your conditions and that they give good amplification efficiency. 

I recommend that you find a good real-time PCR guide and have a read!