Stitches in Time: Okazaki Fragments Explained

If DNA polymerase absolutely cannot begin a new chain without a 3'-OH group to attach to, then every time it starts a new segment on the lagging strand, it needs a new starting point. If primase provides that point, then every one of the okazaki fragments has a primer.

If the fragments are physically next to each other but not bonded, then there is a "nick" in the backbone. If a bond is formed to seal this, then the okazaki fragments become one continuous strand.

If DNA is antiparallel and polymerase is unidirectional, then a physical conflict exists at the replication fork. If the cell builds the lagging strand in short segments to overcome this, then okazaki fragments are the structural solution to that problem.

If DNA polymerase is restricted to moving in a 5' to 3' direction, and the two strands of DNA are antiparallel, then the enzyme must move away from the replication fork on one strand. If it moves away from the fork, then it must restart in short bursts as new DNA is unzipped.

If the lagging strand is built discontinuously, then it consists of many small pieces. If these pieces were discovered by Reiji and Tsuneko Okazaki, then they are logically named okazaki fragments.

If the lagging strand consists of multiple disconnected segments, then a molecular "glue" is needed to create covalent bonds between them. If DNA ligase performs this sealing function, then it is the enzyme that connects the segments.

If the leading strand is oriented so it can be built toward the opening replication fork, then it can be synthesized without stopping. If the lagging strand is oriented the opposite way, then it must be built in pieces called okazaki fragments.

If a fragment is a piece of DNA, then it needs a starting point (primer) and a builder (polymerase). If it is being built at the replication fork, then the fork must be opened by helicase. If it needs to be connected to the next piece, then ligase is required.

If the leading strand is continuous, then it only needs one primer to start. If the lagging strand is made of many separate okazaki fragments, then each individual fragment needs its own primer to begin.

If DNA polymerase cannot start a strand from scratch, then primase must provide an RNA foundation. If this happens for every discontinuous segment on the lagging strand, then it happens for every one of the okazaki fragments.

If the replication fork opens in one direction, but the 5' to 3' orientation of the lagging strand template points the opposite way, then DNA polymerase must move away from the fork to build.

If the RNA primers are temporary, then they must be removed and replaced with DNA. If DNA polymerase I and exonucleases handle this removal and replacement, and ligase seals the gaps, then they are the processing enzymes.

If eukaryotic DNA is wrapped tightly around histones, then the replication machinery has less "room" to move before hitting an obstruction. If it has less room, then the resulting okazaki fragments will be shorter than those in bacteria.

If a specific enzyme is the main "workhorse" for building new DNA strands at the fork, then it is DNA polymerase III. If it adds to the primer on the lagging strand, then it is building the okazaki fragments.

If ligase is the only enzyme that can create the final phosphodiester bond between DNA segments, then its absence means the segments remain disconnected. If they are disconnected, then the genetic code is broken and the molecule is unstable.

If the strands run in opposite directions, then the DNA polymerase (which only goes one way) can only follow the fork on one strand. If it can't follow the fork on the other, then it must create okazaki fragments.

If DNA replication is the process of copying the genome, and if this process happens during the S (Synthesis) phase, then all parts of replication, including the building of okazaki fragments, occur in this phase.

If the leading strand moves smoothly and the lagging strand must wait for the fork to open before starting a new segment, then the discontinuous strand is slower. If it is slower, then it "lags" behind.

If the segments on the lagging strand are named okazaki fragments, then they are named after the scientists who discovered them. If those scientists were Reiji and Tsuneko Okazaki, then they are the correct discoverers.

If the final DNA molecule must be pure DNA, then the RNA primer is a temporary "placeholder." If enzymes remove it and fill the gap with DNA, then the primer is removed, replaced, and its components are recycled.