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By Prithis98 Mar 23, 2013 635 Words
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 amino acid will be hydrolyzed from the tRNA. The whole peptide will move out of the cell. The ribosomes that begin to do the synthesis all over again. One of the essential proteins in the body is haemoglobin. It is found in the red blood cells and produced in the blood marrow. It is an iron containing oxygen-transporting metalloprotein in the red blood cells. In mammals, the protein makes up about 97% of the red blood cells’ dry content, and around 35% of the total content (including water). It also gives the red blood cells their red colour. (The picture on the left is the structure of the haemoglobin) It transports oxygen from the lungs to the rest of the body. In the lungs, Haemoglobin bonds with oxygen, exchanges it for carbon dioxide at cellular level, and then transports the carbon dioxide back to the lungs to be exhaled. Whether haemoglobin binds with oxygen or carbon dioxide depends on the relative concentration of each around the red blood cell. When it reaches the oxygen-rich lungs, it releases the less-abundant carbon dioxide to bind with oxygen; when it goes back out into the body where cells are producing carbon dioxide, it releases the oxygen and binds with carbon dioxide. Other cells that contain hemoglobin include the A9 dopaminergic neurons in the substantia nigra, macrophages, alveolar cells, and mesangial cells in the kidney. In these tissues, hemoglobin has a non-oxygen-carrying function as an antioxidant and a regulator of iron metabolism. In all, the proteins in our body play a very important role. They are present in almost every cell and all of them are unique and different. There are also needed in different ways.


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