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DNA to Protein
DNA is found in the nucleus, and in unique cases, in the mitochondria and chloroplast. DNA has the bases Adenine, Guanine, Cytosine, and Uracil, where Adenine pairs with Uracil and Guanine pairs with Cytosine. Along with those nitrogenous bases, a DNA nucleotide also has a sugar and a phosphate. The two strands of the DNA molecules are held together by the hydrogen bonds between the nitrogenous bases of each strand to create a double helix structure. DNA has ends labelled for the carbon that ends the strand. The 5' end has a phosphate group and 3' end has a hydroxyl group. The 5' end is always opposite of the 3' end of the other strand, which is why the DNA strands are said to be antiparallel.
DNA replication two identical replicas of DNA from the original DNA molecule. It starts with topoisomerase uncoiling DNA. Next, enzymes, called helicases, unwinds the double helix. After the double helix is unwound, proteins stabilize the DNA. Nucleotides can only go through the DNA polymerase from 5' to 3', called the leading strand. The leading strand is synthesized continuously by DNA polymerase. The strand that goes from 3' to 5' is called the lagging strand. The lagging strand is synthesized discontinuously. The lagging strand is made in pieces of nucleotides known as Okazaki Fragments. The Okazaki Fragments are made when the RNA polymerase synthesizes a short RNA primer, which is then extended by DNA polymerase. The fragments are linked together by the enzyme DNA ligase to create a continuous strand. Replication is known as being semi-conservative because the created DNA molecule contains one new strand, and one original strand.
Transcription is the synthesis of an RNA molecule with a base sequence complementary to a section of DNA. Unlike replication, transcription only copies a gene from DNA in the form of mRNA instead of the whole strand. The first step of transcription is to unwind and unzip the DNA strands using helicase. One strand of DNA is copied. RNA nucleotides line up against one DNA strand to create an mRNA strand. RNA polymerase brings the RNA nucleotides to the DNA strand. Once the mRNA finishes adding nucleotides and stops, it separates from the DNA template and completes the process of transcription. NDSU Virtual Cell Animations Project animation 'mRNA Splicing'. For more information please see Before being used in transla... NDSU Virtual Cell Animations Project animation 'mRNA Processing'. For more information please see After being transcribed, m...
The mRNA molecule carries the message from DNA in the form of codons. Codons are a group of three bases that correspond to one of the twenty amino acids.
Initiation: The first step of translation is initiation. This happens when a tRNA molecule carrying the codons AUG (methionine), also known as the start codon, associates with the small ribosomal subunit. The methionine is often removed so that the first the first amino acid in every protein isn't the same. The ribosome is then completed by the large ribosomal subunit. One of the two sites of the large ribosomal subunit bonds to the growing peptide chain called the P site, while the other binds to the incoming aminoacyl tRNA. Next, the second amino acid is delivered to the A site adjacent to the correct codon on the mRNA. A peptide bond is formed between the two adjacent amino acids. At the same time, th covenant bond between the amino acid in the P site and its tRNA site is hydrolysed. The unbound tRNA leaves the P site and the ribosomes move along the mRNA by one codon. Elongation: Ribosome A site is located over a new codon so that it can bind to a new aminoacyl tRNA. The peptide continues to grow in length by two amino acids. Termination: the ribosome reaches a terminator (stop) codon which codes for a releasing factor. The hydrolysis of tRNA to amino acid now releases completed peptides. The parts of the translation complex are disassembled.

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