But each gene can also be transcribed and translated with a different efficiency, allowing the cell to make vast quantities of some proteins and tiny quantities of othersHow Cells Read the Genome: From DNA to ProteinGenes can be expressed with different efficiencies. Because many identical RNA copies can be made from the same gene, and each RNA molecule can direct the synthesis of many identical protein molecules, cells can synthesize a large amount of protein rapidly when necessary.
The flow of genetic information from DNA to RNA (transcription) and from RNA to protein (translation) occurs in all living cells Transcription and translation are the means by which cells read out, or express, the genetic instructions in their genes. This primer is erased by a special DNA repair enzyme (an RNAse H) that recognizes an RNA strand in an RNA/DNA helix and fragments it this leaves gaps that are filled in by DNA polymerase and DNA liqaseFROM DNA TO RNA The pathway from DNA to protein. In eucaryotes, RNA primers are made at intervals spaced by about 200 nucleotides on the lagging strand, and each RNA primer is approximately 10 nucleotides long. On the lagging strand, the Okazaki fragments are synthesized sequentially, with those nearest the fork being the most recently made.The synthesis of one of many DNA fragments on the lagging strandThe synthesis of one of many DNA fragments on the lagging strand. Because both daughter DNA strands are polymerized in the 5’ to 3'direction, the DNA synthesized on the lagging strand must be made initially as a series of short DNA molecules, called Okazaki fragments. The original strands therefore remain intact through many cell generationsThe structure of a DNA replication forkThe structure of a DNA replication fork. In a round of replication, each of the two strands of DNA is used as a template for the formation of a complementary DNA strand. As shown, base-pairing between an incoming deoxyribonucleoside triphosphate and an existing strand of DNA (the template strand) guides the formation of the new strand of DNA and causes it to have a complementary nucleotide sequence.Review: Replication The semiconservative nature of DNA replication.
The addition of a deoxyribonucleotide to the 3' end of a polynucleotide chain (the primer strand) is the fundamental reaction by which DNA is synthesized.
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