Replication, Transcription, and Translation Before a cell can divide, the DNA in the nucleus of the cell must be duplicated. Since the DNA molecule consists of two complimentary stands, if those two strands separate and the right conditions are present, two new stands that are the compliments of the originals will be produced. Each new DNA molecule will consist of one old stand, and a new complimentary strand. he gray strands in the figure to the right are new strands in the process of being assembled. Assembling the New Bases The term semiconservative replication means that in the new DNA molecule there is one old and one new strand. This is seen in the figure below. DNA Replication Since the DNA molecule is very large, there must be a way to copy it faster than just unwinding from one end to the other This happens when the DNA molecule separates at many sites, forming thousands of replication bubbles.This allows parts of the DNA message to be replicated simultaneously in many locations. DNA polymerase adds new nucleotides , while DNA ligase joints the DNA segments together. Why the fuss about DNA replication?? As you will note when you read the te!tboo" #if you haven$t already%the process of DNA replication involves a number of en&ymes and proteins, and it a bit more complicated than seen in the previous slide. The important idea is that an e!act duplication of the DNA message is re'uired, so that each new cell in the body has the same set of genetic instructions as the cells that preceded it. This also insures that every new generation of individuals has the same genetic information as his(her parents. DNA carries information that can be used to construct the proteins which form structures and regulate the bodys activities. )rotein synthesis involves two processes*transcription and translation. +n transcription the DNA message is converted into an ,NA molecule. +n translation the ,NA message is used to assemble amino acids into a protein chain. times they are a changing -or many years biologists referred to the one gene.one en&yme hypothesis.+t was believed that each gene controlled the production of a single protein. This was changed to the one gene.one protein hypothesis because many proteins are structural proteins, not en&ymes. Since some proteins consist of several polypeptide chains that are lin"ed together, the hypothesis was changed again.This time one gene.one polypeptide seemed more accurate. As a result of the /uman 0enome )roject, the one gene.one polypeptide hypothesis has had to be changed again1e now "now that a gene can produce more than one polypeptide depending upon how the information in the gene is read.2ore about this later !he genetic code The genetic code is written in the se'uence of the 3 bases of DNA* A, T, 4, and 0. Three bases read in se'uence specify one of the 56 amino acids found in protein molecules. A codon is the 7.base se'uence for an amino acid. The message in the DNA is transcribed into an ,NA molecule, and then translated into a polypeptide !he "enetic #ode $$ There are 83#39393% possible triplet codes, but only 56 amino acids. As seen in the table, more than : triplet may code for the same amino acid.This is no problem, as long as no triplet can code for more than one amino acid. Note that several codons can also act as start #A;0% or stop #;AA% signals. Why do we need RNA too? There are three types of ,NA produced in the nucleus* m,NA, t,NA, r,NA. 2essenger ,NA #m,NA% is a copy of the DNA that codes for a polypeptide. 1hen the two DNA strands of a gene separate, one of the strands is transcribed into an ,NA molecule with the aid of the en&yme ,NA polymerase. The ,NA strand elongates until it reaches a termination signal #a se'uence of bases in the DNA strand%.At this time the ,NA molecule is released from the DNA, allowing the DNA strands to reunite. After production the ,NA molecules leave the nucleus and enter the cytoplasm. #leaning up the %essage 1hen the genetic message is copied to ma"e m,NA, the message contains unwanted base se'uences. The