How does DNA make a copy of itself in order to travel outside to make protein?

Answer 1

DNA is double stranded, in the shape we know as the "double helix." One strand of DNA is the coding strand, while the other is called the complementary strand. The coding strand is what has the protein codes, the complementary strand just bonds to that strand. DNA is also located inside the nucleus, which is protected by a nuclear membrane. This nuclear membrane is porus, but the double helix is too big to fit through these pores. So, the DNA has to be copied into mRNA (messenger ribonucleic acid.) Now, DNA is made up of nucleotides, all of which are either Adenine, Thymine, Guanine, and Cytosine; or just A, T, G, and C. A and T always pair together in the double helix, and G and C always pair together. But, the mRNA has ribonucleotides. There are still A, G, and C; but instead of a T bonding to an A, a Uracil, or U, will bond to all the A nucleotides. Okay, confusing basics, but heres the fun part. The DNA molecule "unzips," or the two strands pull apart when its time to make a protein. Then, a molecule called an mRNA polymerase will attach to the coding strand of the DNA and start "reading" it. Once it reaches the sequence "TAC" (remember the little parts that make up the DNA strand,) it will start to attach the ribonucleotides. This "TAC" is know as a start codon, because it tells the mRNA polymerase to start. Now, the mRNA polymerase will bond "AUG" to the "TAC". Then mRNA will continue to bond it's ribonucleotides to the corresponding nucleotides of the coding strand of DNA, until it reaches a "stop" codon. This stop codon is either ATT, ATC, or ACT on the DNA; which becomes UAA, UAG, or UGA on the mRNA. This is when the mRNA stops pairing ribonucleotides to the DNA nucleotides, because the code for the protein is complete. Every set of 3 nucleotides in between the start and stop codons are called a codon, and they code for one specific amino acid that will make up the protein. Now that the mRNA strand has been made, it is sent out of the nucleus because it is single-stranded, and can fit through the pores. This process of making the mRNA is called Transcripiton. But how can the protein be made? As soon as the mRNA strand exits the nucleus, a ribosome, or rRNA molecule, bonds to it. This ribosome "reads" the mRNA, and begins to attach "anti-codons" to the mRNA codons (remember a codon is 3 ribonucleotides that code for an amino acid.) The anti-codons and the amino acids come in a "package" called a tRNA, or transfer RNA, molecule. This consists of the anti-codon that will pair up to the mRNA codon, and an attached amino acid that is specific to the mRNA codon. For example, the start codon AUG will pair to the anti-codon UAC, and AUG codes for the amino acid methionine; so the tRNA molecule will have UAC at the base, and methionine attached at the top. The ribosome will do this to each codon within the strand, so each codon has an anti-codon and amino acid attached. But, ribosomes can only fit 3 codons inside them at any time, so it has to move down the mRNA 3 codons at a time. As a codon exits the ribosome after being attached to it's tRNA molecule, the anti-codon part of the tRNA breaks off and the amino acid attaches to the other amino acids using a peptide bond. So the ribosome leaves behind a string of amino acids bonded together using peptide bonds. To find out which codons on the mRNA code for which amino acids, you need to use an "amino acid wheel," which is a wheel that is read by looking at the innermost circle and finding the ribonucleotide that the codon begins with, then looking in that section to find the second ribonucleotide in the codon, then looking in that small section of the outermost circle to find the last ribonucleotide of the codon, which will then show you the protein. This chart is attached in the image below. Anyways, once the ribosome reaches a stop codon on the mRNA, it stops attaching the tRNA molecules, and the result is all the amino acids that correspond to the codons, bonded together to create the finished protein! This process of creating the protein is called Translation, so the entire process from DNA to protein is called Transcription and Translation.