Topics: DNA, Protein, RNA Pages: 2 (635 words) Published: March 23, 2013
Biology Assignment
Proteins are large, complex molecules that are made up of hundreds or thousands of smaller units called amino acids, which are attached to one another in long chains. There are 20 different types of amino acids that can be combined to make a protein. The sequence of amino acids determines each proteins unique structure and specific function. They play many critical roles in the cells. They can be grouped as enzymes, antibodies, messengers, structural components or transporters, according to their functions. These proteins are made through a process called protein synthesis. Some of the organelles involved in it are the ribosomes, the Rough Endoplasmic Reticulum and the Golgi Apparatus. There are a few steps in the process of protein synthesis. The two commonly known steps are transcription and Translation. However, the step of translation can be divided into 3 other steps known as Initiation, Elongation and Termination. Before the beginning of the process, the corresponding RNA molecule is produced by RNA transcription by a DNA gene in the nucleus. A strand of the DNA double helix is used by the RNA polymerase to synthesize a messenger RNA (mRNA). This mRNA migrates from the nucleus to the cytoplasm. During this step, mRNA goes through different types of maturation including one called splicing when the non-coding sequences are eliminated. The coding mRNA sequence can be described as a unit of three nucleotides called a codon. During Initiation, the ribosomes bind to the mRNA at the start codon (AUG) that is recognized only by the tRNA as it is the initiator. At the elongation phase, complexes, composed of an amino acid linked to tRNA, sequentially bind to the appropriate codon in mRNA by forming complementary base pairs with the tRNA anticodon. As the ribosomes, move from codon to codon one by one, the amino acids are added. In the end, at the termination phase, the stop signal of the mRNA will be reached and the last...
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