Hello everyone I am Sir DNA, a DNA molecule.Today I will be talking to you about my job. My job is very important because I hold all of the important genetic information for the cell. I carry genes which tell you what colour your hair is, what colour your eyes are,  and even more. The genes I carry also contain the information that tells you which proteins to make in protein synthesis which is a process we will talk about in a little bit. 

First I’m going to talk about what I am made up of. I am a double helix structure that is made up of three molecules, a phosphate, a deoxyribose sugar, and a nitrogen base (A, C, G or T).  These three molecules form a group called a nucleotide. Hydrogen bonds are like glue that hold nucleotides together with each other. A and T always pair together and C and G always pair together. I kind of look like a twisty staircase.

    Part of my job is to have kids because cells reproduce through cell division so I have to go through the process of DNA replication. To replicate DNA, first I have to unwind into two strands. My friend helicase helps me do this. I don’t like having my strands separated, so I try to pull them back together,  but single strand binding proteins (SSBPs) hold on to each strand and keep them apart. Then my enzyme friend RNA primase lays down RNA primers to mark where the DNA replication will start

    The 2 different strands that I am split into replicate DNA at different speeds.  This is because DNA polymerase III can only work in the 5’ to 3’ direction so my leading strand can make more DNA very quickly where my lagging strand is slower. The leading strand is in the lead of the race and the lagging strand is lagging behind. As helicase keeps unwinding me,  more primers are put down on the lagging strand and DNA polymerase III works backwards. Okazaki fragments are pieces in between the primers. This process continues until a new piece of DNA is formed.

However I’m not finished yet! We must remove the primers and replace them with nucleotide bases (A,C,T and G). My friend polymerase I does this for me. We also need something to act like a glue to hold everything together so this is DNA ligase’s job. Finally, we need someone to proofread and make sure there are no mistakes (mutations) that can change the way a cell acts. This is polymerase II’s job. We all work together to help me replicate so I can have children.

Sounds pretty harmless and easy right? Well every time I go through this process part of me can get lost. To prevent this from happening I have something called telomeres to protect my important coding strands. Instead of losing parts of me I lose part of my telomere. Telomeres shorten over time meaning I can only make more DNA for so long.  This is called the Hayflick limit.

You might be wondering how I can actually result in a trait such as eye colour. Well the genes that are inside me can code for proteins through the process of protein synthesis like I mentioned in the beginning. Now I am going to talk to you about how I make these proteins with the help of more of my friends. First, the information from the genes needs to get out of the nucleus and into the cell to start making the proteins it needs. There are two major steps to this process, transcription and translation.

Transcription happens in the nucleus. My friend,  an enzyme called RNA polymerase, binds with me to form mRNA (messenger RNA.) mRNA comes from me DNA so I am considered the director of the process. The mRNA is special because it gets to go out of the nucleus and attach to a ribosome. Ribosomes are made up of rRNA (ribosomal RNA) and ribosomes make protein. 

Initiation is the first step of transcription. RNA polymerase attaches to me and starts unwinding near the beginning of my genes. It detects an area with many Ts and As, this is called the promotor. It unwinds here because the hydrogen bonds between T and A are easier to break than the ones between C and G.

The next step of transcription is elongation. Once I am unwound, RNA polymerase starts building RNA in the 3' to 5' direction. This is the strand that is being copied and the other strand is called the coding strand because it has the same bases as the RNA except with a T instead of a U. RNA polymerase adds new nucleotides which makes the RNA longer. It then winds for a short period of time with the template strand to make a hybrid double helix of me and my bestie RNA.  

The last step of transcription is termination. Termination happens when RNA polymerase stops copying the DNA because it reaches a termination sequence. Now RNA polymerase can move on to transcribe another gene. We can now move on to the next step which is translation. But first let's talk about tRNA. tRNAs are shaped like a cross and at the end of the cross are anticodons. These anticodons bind with a codon on mRNA to make amino acids this makes tRNA aminoacyl-tRNA.

In translation, the cytoplasm of the cell has a lot of tRNAs (transfer RNA) and these carry amino acids on them. An amino acid is a building block for a protein, and a bunch of amino acids together make a polypeptide chain. The tRNA brings the amino acids in order to make the protein. But how does it know which amino acid to bring? This is why the mRNA is so important because it tells the tRNA which amino acids to bring. tRNA reads the mRNA in threes or codons. When the tRNA finds its complementary base it will join up with it. Once the tRNAs attach their amino acids they will leave.

Something called a start codon will tell the tRNAs where to start dropping off their amino acids. The start codon is AUG. Which codes for methionine (in green on the chart). There are also three stop codons which tell the tRNA to stop bringing amino acids (in red on the chart). To figure out which amino acid a codon will code for, you can use a codon chart. Different codons can code for the same amino acids.