SC-FDMA in LTE system
First of all, in refering to standard specification, please mention the version because the numeration between versions can be different.

My answer should be only a comment but I think with images it would be easier for you. Everything in my answer is for 36.211 v8.7.0.

The section 5.6 SC-FDMA baseband signal generation and 6.12 OFDM baseband signal generation are IDFT. The difference is the values of $\left\lbrace a_{k,n} \right\rbrace$. Ignoring MIMO stuffs in DL, in OFDM case, $\left\lbrace a_{k,n} \right\rbrace$ are mapped directly to subcarrier. In SC-FDMA case, $\left\lbrace a_{k,n} \right\rbrace$ are outputs of a supplementary block Transform precoder as in the image below.



This transform precoder is implemented as a DFT and its formula can be found in the section 5.3.3 of 36.211 v8.7.0. It is specified only for PUSCH data (if my memory is correct, among UL physical channels, only PUSCH data uses frequency-generated SC-FDMA).

I hope my answer covers what have been asked in your question. For more details (k+1/2, null DC, ...) I suggest a very good book "LTE – The UMTS Long Term Evolution From Theory to Practice" which is surprisingly can be found by a simple Google search.