DNA 复制叉机制图

一张 DNA 复制叉侧视扁平矢量图。亲代双链螺旋从左侧以深蓝与青绿色进入；解旋酶为六聚体灰色环；前导链（深蓝）上钴蓝 C 形 Pol III 夹持滑动，合成青色新链；滞后链（青绿）上三段淡金色冈崎片段，每段以珊瑚色 RNA 引物起始，绿色椭圆 DNA 连接酶封口，RNase H 移除一段引物。叉前方 Topo I 以 8 字结释放超螺旋。领线细标注，右上角色码图例，白色背景，无阴影。

A detailed flat vector diagram of an active DNA replication fork, viewed from the side as a close-up cross-section. The parental double helix enters from the left as two intertwined strands in complementary navy and teal. At the fork junction, a helicase enzyme is shown as a hexameric ring (6 pale grey subunits) actively unwinding the strands. The leading strand (navy, top) runs continuously rightward, with DNA polymerase III depicted as a C-shaped clamp in cobalt blue sliding along it, reading 3′→5′ and synthesising 5′→3′ with a growing new strand in cyan. The lagging strand (teal, bottom) runs in the opposite direction; three Okazaki fragments in pale gold are shown, each starting with a short RNA primer in coral and being extended by a second pol III clamp. RNase H removes a primer in one fragment, and DNA ligase (a green oval) seals the nick. Topoisomerase I ahead of the fork is shown as a figure-8 knot releasing a supercoil. All components are annotated with thin leader lines and 9 pt labels. Colour-coded legend at top-right. White background, no drop shadows.