Question

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Answer 1

Answer:

The five steps of DNA replication are (1) DNA unzips, (2) complementary bases come in, (3) the sugar-phosphate backbone is constructed, (4) the backbone bonds to bases and bases bond to each other, and (5) the bases are proofread.

The process of DNA replication.

You may thus remember that your cells produce enzymes as catalysts to carry out activities. Your cells turn on an enzyme called DNA helicase for DNA replication. Your DNA is grabbed by the helicase molecule, which then gently unravels and unwinds the entire DNA molecule. Another group of enzymes known as DNA polymerase follow behind it as it moves.

There are also free-floating nucleotides present in your cell. Normally, your cell utilizes them to build RNA for communications, but now the DNA polymerase enzymes take them up and assemble them into new DNA. If the polymerase tries to insert the incorrect nucleotide, it won't fit since each nucleotide can only ever link to its matching nucleotide (A->T, G->C), which stops the process. Another nucleotide is taken after discarding the erroneous one. The leading edge is created in this manner.

Another enzyme, which should be mentioned, primes the nucleotides with phosphate groups that the polymerases grasp onto and then discard when the nucleotides are integrated into at the DNA strand.

It becomes a little trickier with the lagging strand. The polymerase will move in the same direction as the helicase on one side because the polymerases can only move in one way (5'-3'), but it cannot move in the opposite direction on the other. The open DNA on that side is instead read by a different enzyme known as DNA primase (there are many of them), which then synthesizes RNA segments that are identical. A different polymerase converts the RNA primer to DNA, followed by a third enzyme (DNA ligase) that joins the ends of those DNA segments to create the new whole DNA from the lagging strand. This process starts with one polymerase using the primer to attach and build DNA in the opposite direction of the helicase.

The two new complete sets of DNA are therefore formed from the leading and lagging strands. The other half is composed of the old DNA that was divided in half, while the first half is entirely new and formed of free nucleotides.

The process by which your cells divide then involves bundling up the DNA, dividing, and a whole bunch of other things.

Little more info that might answer some extra questions:

The primase is not what puts the extra phosphate groups onto the loose nucleotides. As far as I'm aware, that's part of their construction. Those phosphate groups are what provides the energy for the polymerase to attach them to the DNA strand, after which they're discarded to be picked up and reused later to build more nucleotides. The nucleotides themselves are made with a different series of enzymes.  Suffice it to say, enzymes are like tiny molecular robots in a factory using chemical reactions to build what your cell needs, each enzyme responsible for one of the often many reactions needed. The process for constructing nucleotides is over my head, but it boils down to a series of enzymes putting molecules together and changing their shape.

What primase does is construct the RNA primers that the polymerase fuses to the DNA strand to become the other half of that side of the DNA.

The lagging strand isn't smaller, it's just being constructed in the opposite direction from the way the DNA is being unzipped by the helicase. Typically, you picture DNA like a twisted ladder, but that's not quite right. The reason it has the twist has to do with the structure of the base pairs. The two chains of the DNA run opposite from each other. If you're looking at it like a ladder, one side is "upside down". The helicase starts unzipping from either end of the DNA strand, but for one side of the DNA it's unzipping 3'-5', and for the other side it's unzipping 5'-3'.

The polymerase only constructs DNA going from the 5' end to the 3' end. For half the DNA, this works perfectly fine - it follows merrily along behind the helicase as it unzips the DNA strand. As each base pair separates, the polymerase just pops a new base onto the half it's attached to. For the other half, though, from its perspective the DNA is getting unzipped 3'-5', which is opposite the direction the polymerase can go. It can't follow behind the helicase. Instead, primase comes in and builds RNA segments in the 5'-3', "backwards" from the helicase, giving the polymerase something to grab and go the direction it wants to go.