By Kaytlin Avina

DNA

There are 2 different types of cells that we will be talking about today: prokaryotes and eukaryotes. We will be taking a closer look at how eukaryotes replicate their DNA later on, but first we will learn how prokaryotes and eukaryotes are different when it comes to DNA replication.

Welcome to the DNA Zoo! My name is Sam and I will be you're guide today. We will be exploring how DNA is replicated, or copied, with a little help from all of our animals here.

One of our brightest elephants here has come up with a list of things that prokaryotes have or do that eukaryotes don't. I'll let him explain, he's much better at comparing and contrasting than me!

Prokaryotes

Eukaryotes

Hello! Here are some of the main differences between the two types of cells:

PROKARYOTES

-Replication occurs in cytoplasm

-1 origin of replication per DNA molecule

-2 replication forks & 1 replication bubble formed

-Occurs faster

-Transcription & translation occur in same place

EUKARYOTES

-Replication occurs in nucleus

-Occurs during S phase of cell cycle

-Many origins of replication

-Many forks and bubbles formed

-Occurs slower

-Transcription occurs in nucleus, translation occurs in cytoplasm

Thanks Mr. Elephant! Now we can focus more on how exactly DNA replicates in eukaryotic cells.

Before we learn the steps of replication, it is important to know what DNA is. The DNA double helix is a long molecule inside cells that contains genetic information. It acts like the blueprints for our bodies and other organisms, such as the animals here at the zoo. It is made of deoxyribose (sugar), phosphate, and nitrogen bases. Here is a picture of what DNA looks like:

Now that we know what DNA is, let's talk about the steps of replication. Before a cell can divide, it needs to create an exact DNA copy to give to the new cell.

This is done by matching nucleotides, in complimentary pairs. The nucleotides are like mini puzzle pieces; only Adenine (A) and Thymine (T) can fit together, and only Guanine (G) and Cytosine (C) can fit together.

There are lots of parts that go into unraveling and copying the DNA, and there are many enzymes that help each step happen. Here at the DNA Zoo, all of the animals do the jobs of the enzymes, but I will teach you the scientific names of the enzymes, too.

When you think of all the different kinds of animals together, it is called the zoo. Similarly, when you think of all the enzymes involved in DNA replication together, it is called the replisome.

The first step in DNA replication is unwinding and unzipping the strands of DNA. This is done by the enzyme called helicase as it breaks the hydrogen bonds. In the DNA Zoo, this job is done by the rhinoceros, because it is very good at pushing through the strand and splitting up the nucleotides.

Once the strands of DNA are separated, they can be used as templates for new DNA strands. We don't want the two strands to attach to each other again though, so single strand binding proteins attach to them to keep them apart. At the DNA Zoo, these proteins are birds that land on the strands.

The next step in DNA replication is the RNA primers preparing the template strands. This is done by the enzyme primase, which uses uracil (U) to bind to the A's instead of T's as primers. Primase is important because it tells another enzyme where to start the replication process. In the DNA Zoo, the kangaroo acts as primase because it is so good at jumping around on the strand and placing the primers.

Primer

Primer