From DNA to ProteinChapt. 12.ppt

From DNA to ProteinChapt. 12 Central Dogma DNA carries the genetic code and transcribes an RNA copy of the code The RNA copy is translated by ribosomes to make protein DNA RNA Protein Step 1: RNA SYNTHESIS- TRANSCRIPTION The process of converting the information contained in a DNA segment into proteins begins with the synthesis of mRNA molecules containing anywhere from several hundred to several thousand nucleotides, depending on the size of the protein to be made. Each of the 100,000 or so proteins in the human body is synthesized from a different mRNA that has been transcribed from a specific gene on DNA. Why do we need mRNA if DNA holds all the genetic instructions for the proteins the cell is supposed to produce? DNA must be protected…If DNA is damaged in any way, then the coding sequence is changed and a mutation could result which could greatly affect a cell or even the whole organism! Transcription If a protein is required by a cell, that gene is activated (turned on).. The gene makes an RNA copy of itself in the form of a messenger RNA molecule (mRNA) Enzyme RNA polymerase runs along open DNA strand and synthesizes RNA complementary to the DNA Transcription Messenger RNA is synthesized in the cell nucleus by transcription of DNA, a process similar to DNA replication. As in replication, a small section of the DNA double helix unwinds, and the bases on the two strands are exposed. RNA nucleotides (ribonucleotides) line up in the proper order by hydrogen-bonding to their complementary bases on DNA, the nucleotides are joined together by a DNA dependent RNA polymerase enzyme, and a piece of mRNA is produced. UNLIKE what happens in DNA replication where both strands are copied, only ONE of the two DNA strands is transcribed into mRNA (remember that RNA is a single-stranded molecule). The DNA strand that is transcribed is called the template strand and is a copy of the DNA informational strand! Transcription RNA Polymerase