AUG is the start codon on which depends on the position in the mRNA. The Helicase separates the DNA strand making a bubble with a leading strand and a lagging strand. A leading strand of replication fork, this strand runs in a continuous direction as it opens.The fork has to wait for a long segment of DNA to become exposed first before adding a primer. Start by adding nucleosides and attaching to an RNA primer. The lagging strand is the DNA not running in a opposite as it opens. Protein synthesis starts of with a DNA strand (template) goes into transcription; the process of making a working copy of an original. They make a DNA copy but in RNA form known as mRNA. Primary Transcription is modified to produce the secondary transcript; sent out of the nucleus to the ribosome. The mRNA must be modified before translation can occur. This turns the mRNA into a primary sequence of amino acids for making protein. Transcription is carried out by a RNA polymerase and a number of accessory proteins called transcription factors. Transcription factors bind to specific DNA sequences that are enhancers and promoter sequences in order to recruit RNA polymerase to an apposite transcription initiation complex . This complex initiates transcription, and the RNA polymerase begins mRNA synthesis by matching complementary bases to original DNA strand. The mRNA molecule is elongated and, once the strand is completely synthesized, transcription is terminated. The newly formed mRNA copies of the gene then serve as blueprints for protein synthesis during the process of translation. The transport of RNA molecules from the nucleus to the cytoplasm is fundamental for gene expression. The different species that are produced in the nucleus are exported through the nuclear pore complexes via mobile export receptors The correct tRNA with its attached amino acid selected at each step because each specific tRNA molecule contains a three base sequence that can base pair with its complementary code word in the mRNA. Then part of protein synthesis is translation; process from taking from one language and changing to another language. The cell is turning nucleotide language into amino acid language to make proteins. This occurs in ribosomes, since this is building a protein. Translation of a mRNA molecule by the ribosome occurs in three stages. First initiation the ribosomal subunit binds to the start of the mRNA molecules has the sequence AUG and codes for methionine. The other ribosomal subunit binds to form the complete initiation complex. Next Elongation, ribosome continues to translate each codon in turn. Amino acid is added to the growing chain and linked via a bond call a peptide bond. It continues until all of the codons are read. Third is termination occurs when the ribosome reaches a stop codon; UAA, UAG, and UGA. There is no tRNA molecules that can recognize these codons, ribosome recognize that translation is complete. New protein is released and the translation complex comes apart. Middle modification of mRNA molecule, during this step remove the non-coding introns using spliceosomes. Then rearrange the separated coding exons to the needed configuration, this is alternative. Exons can be rearranged in different orders. Then the pieces together to make the finalized secondary mRNA transcript that is ready for transport to the ribosomes for translation into proteins. Also mutations can occur in protein synthesis. Point mutations is a single nucleotide mutations thus affecting a single codon, which includes silent, missense, and nonsense. Silent is the mutation causes no change in the amino acid coded for. Missense is the changes the amino acid coded for. Lastly nonsense changes from coding for an amino acid coding for a stop codon. The second type of mutation is reading frameshift mutation which is mutation alter the codon sequence, which includes insertion and deletion. Insertion is the adding nucleotides to the sequences. Deletion is taking out nucleotides from the sequence.