how do we determine primers? basic question

[nananvatip]

I have no experience in Molecular biology and would like to get into the field. I am reading about PCR and I dont understand how we can know which primers to use and how do we make primers?
Thanks

[shamim khaja]

primers are short stretch of nucleotides whose sequence has been picked from the template strand.
We have a "forward primer" and a "reverse primer". The forward primer has a sequence similar to the template strand for 5'--3'. Where as the reverse primer has a sequence complementary to the strand 3'---5'.
To design a primer first u have to know the sequence of your template strand i.e. the sequence of ur desire gene.
hope that has helped u

[nananvatip]

Thanks a lot, this helps.

[kk]

I my lab we follow these criteria:

1. primer length should be 18-24 base
2. GC content should be 55-60%
3. the melting temperature of the two primers should be similar
4. G or C are preferred, especially at the 5' end of the primers

5'-XXXX.......-3'

- the first and second (from the 5') should be both G or C
- at least 3 G or C in the first 4 base

5. avoid runs of 4 bases the same (e.g. AAAA)
6. check primers for hairpin or dimer formation (shouldn't form)
7. blast the sequence

[robertlee_ioz]

thanks for the question and answers especially that form kk.
I am a beginner and this helps me