乳剂制备时油相、水相混合后加入到乳化剂中迅速研磨成初乳，再加水稀释的方法

乳剂制备时，使植物油与含碱的水相发生皂化反应，生成新生皂乳化剂，随即进行乳化的方法

乳剂制备时，乳化剂与油混合，加入一定量的水乳化成初乳，再逐渐加水至全量的方法

向乳化剂中每次少量交替地加入水或油，边加边搅拌形成乳剂的方法

乳化剂制备时，将油相逐渐加到含乳化剂的水溶液中的方法

Ligases

Exonucleases

Endonucleases

Modifying enzymes

正确

错误

把叶子拿回家

把叶子画下来

acridine

5-bromouracil

mitomycin

nitrous oxide

黄山

泰山

三清山

龙虎山

雁荡山

湿胶法

干胶法

新生皂法

两相交替加入法

机械法

Base analogs 碱基类似物

DNA modifying agents DNA修饰剂

Intercalating agents 插入剂

氨基酸

In eukaryotic cells, activator and repressor proteins can exploit the mechanisms used to package DNA to help turn genes on and of.

Chromatin structure can be altered by chromatin-remodeling complexes and by enzymes that covalently modify the histone proteins that form the core of the nucleosome. Many gene activators take advantage of these mechanisms by attracting such chromatin-modifying proteins to promoters.

For example, the recruitment of histone acetyltransferases promotes the attachment of acetyl groups to selected lysines in the tail of histone proteins; these acetyl groups themselves attract proteins that promote transcription, including some of the general transcription factors. And the recruitment of chromatin-remodeling complexes makes nearby DNA more accessible. These actions enhance the efficiency of transcription initiation.

In a similar way, gene repressor proteins can modify chromatin in ways that reduce the efficiency of transcription initiation. For example, many repressors attract histone deacetylases—enzymes that remove the acetyl groups from histone tails, thereby reversing the positive effects that acetylation has on transcription initiation.