How your cell makes very important proteins- part 1

The information content of DNA is in the form of specific sequences of nucleotides along the DNA strands. The DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins. The process by which DNA directs protein synthesis, gene expression includes two stages, called transcription and translation. Cells are governed by a cellular chain of command
– DNA --> RNA--> protein
Transcription:- Is the synthesis of RNA under the direction of DNA, Produces messenger RNA (mRNA)
Translation:- Is the actual synthesis of a polypeptide, which occurs under the direction of mRNA, Occurs on ribosomes. In prokaryotes transcription and translation occur together. In a eukaryotic cell the nuclear envelope separates transcription from translation. Extensive RNA processing occurs in the nucleus. Transcription is the DNA-directed synthesis of RNA. RNA synthesis, Is catalyzed by RNA polymerase, which pries the DNA strands apart and hooks together the RNA nucleotides, Follows the same base-pairing rules as DNA, except that in RNA, uracil substitutes for thymine. RNA is single stranded, not double stranded like DNA. RNA is short, only 1 gene long, where DNA is very long and contains many genes. RNA uses the sugar ribose instead of deoxyribose in DNA. RNA uses the base uracil (U) instead of thymine (T) in DNA. The stages of transcription are, Initiation, Elongation, Termination. Promoters signal the initiation of RNA synthesis. Transcription factors help eukaryotic RNA polymerase recognize promoter sequences. A crucial promoter DNA sequence is called a TATA box. RNA polymerase synthesizes a single strand of RNA against the DNA template strand (anti-sense strand), adding nucleotides to the 3’ end of the RNA chain. As RNA polymerase moves along the DNA it continues to untwist the double helix, exposing about 10 to 20 DNA bases at a time for pairing with RNA nucleotides. Specific sequences in the DNA signal termination of transcription. When one of these is encountered by the polymerase, the RNA transcript is released from the DNA and the double helix can zip up again. Most eukaryotic mRNAs aren’t ready to be translated into protein directly after being transcribed from DNA. mRNA requires processing. Transcription of RNA processing occur in the nucleus. After this, the messenger RNA moves to the cytoplasm for translation. The cell adds a protective cap to one end, and a tail of A’s to the other end. These both function to protect the RNA from enzymes that would degrade. Most of the genome consists of non-coding regions called introns. Non-coding regions may have specific chromosomal functions or have regulatory purposes, Introns also allow for alternative RNA splicing. Thus, an RNA copy of a gene is converted into messenger RNA by doing 2 things: Add protective bases to the ends, Cut out the introns, Each end of a pre-mRNA molecule is modified in a particular way, The 5¢ end receives a modified nucleotide cap, The 3¢ end gets a poly-A tail.

To be continued.......