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Protein_Synthesis_Notes

Protein_Synthesis_Notes - Introduction to protein synthesis...

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Introduction to protein synthesis: Nucleus, Ribosome, Endoplasmic Reticulum, and Golgi Complex. Protein synthesis involves two processes: 1) transcription- the synthesis of messenger RNA from a DNA template and 2) translation: the synthesis of a polypeptide from the messenger RNA sequence. This idea is called the one-gene-one-polypeptide hypothesis. It was the one-gene-one- enzyme hypothesis, but not all proteins are enzymes. It was then the one-gene-one-protein hypothesis, but some proteins are made up of more than one polypeptide chain. Now it’s the one- gene-one-polypeptide hypothesis. Proteins are composed of amino acids; proteins are made in the ribosome. The DNA sequence determines which proteins are made. mRNA delivers the information from the DNA to the ribosome. RNA: ribonucleic acid. Three main differences between RNA and DNA. 1) The RNA sugar is ribose vs. deoxyribose for DNA. 2) Uracil replaces Thymine in RNA. 3) RNA is single stranded. There are 5 types of RNA: 1) rRNA: ribosomal RNA, the principle component of ribosomes. Amino acids are synthesized into polypeptides in the ribosome. This is produced in the nucleolus. 2) mRNA: messenger RNA, carries the DNA code to the ribosome. The information is encoded in the DNA, but the DNA doesn't make the proteins or move to the ribosome. mRNA is the physical link in protein synthesis between the blueprints (DNA) and the factory (ribosomes). 3) tRNA: transfer RNA, carries amino acids to ribosome. This is produced in the nucleolus. 4) hnRNA: heterogeneous nuclear RNA, the pre-edited transcribed RNA found in the nucleus. 5) snRNA: RNA found in small nuclear ribonucleoproteins (snurps). These will form the larger spliceosome. Also produced in the nucleolus. How hnRNA is formed: The two DNA strands unwind, and only one of the two strands is copied. The two DNA strands rewind. The base pairing rules of RNA synthesis are very similar to those of DNA replication except that RNA contains uracil instead of the thymine found in DNA. Instead of T, a U is matched up to adenine in making RNA. For every G in DNA, RNA polymerase puts in a C. For every T in DNA, RNA polymerase puts in A. For every A in DNA, RNA polymerase puts in U. When the process is completed, RNA has the same order of bases as the appropriate non-copied (non- transcribed) strand of DNA except that all thymines have been replaced with uracil. This process is called transcription. RNA is synthesized in a 5'-3' direction using triphosphonucleotides and RNA polymerase. Many RNA molecules can be transcribed simultaneously from different parts of the same DNA molecule. 1
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There are also spaces, called spacer regions, between DNA that are not transcribed. The length of the DNA molecule on which RNA is being transcribed is equivalent to a gene-- or a gene that codes for a polypeptide. Only a specific portion of the DNA molecule is being copied.
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