What are lagging strands?

A lagging strand is like the part of a ladder that gets built backwards while the other side is being made forwards.

Imagine you and your friend are building a ladder together. One of you starts at one end, putting rungs on in order, first rung, second rung, third rung, just like when you count from 1 to 10. That’s like the leading strand. But your friend is doing something different. They’re starting at the other end and adding rungs, but they can’t go backwards, so they have to wait until the rest of the ladder is built before they can add their rungs in order, first, second, third, just like you.

That’s how lagging strands work during DNA copying. While one side of DNA (the leading strand) gets copied smoothly and steadily, the other side (the lagging strand) has to wait a little bit and copy in pieces called Okazaki fragments, like your friend waiting until they can put their rungs in order.

So the lagging strand is just a part of DNA that gets built a little slower, kind of like building a ladder from one end while someone else starts at the other.