Replication, Transcription, and Translation: From DNA to Protein

This post is be a chart comparing the Initiation, Elongation, and Termination stages for Replication, Transcription, and Translation.

	Process
	Replication	Transcription	Translation
Initiation	·      Helicase unzips the DNA double helix ·      Single-strand binding proteins (SSBP) keep unpaired template strands apart during replication ·      Gyrase releases tension brought about by unwinding and twisting the DNA ·      Primase synthesizes a short RNA primer to start DNA synthesis [A=U, C≡G]	·       Starts at TATA box (part of promoter region) ·       Transcription factors (TFs) bind to promoter region ·       RNA Polymerase II binds to TFs to form initiation complex at the promoter region, upstream of the gene ·       *Note: Gene = transcription unit	·       Small ribosomal subunit binds with mRNA and special initiator tRNA carrying methionine which attaches to start codon (AUG) (anticodon on tRNA) ·       Initiation factors bring in large subunit such that tRNA occupies the P site
Elongation	·       DNA Polymerase III synthesizes new DNA strand; reads DNA 3ʹ→5ʹ; makes DNA 5ʹ→3ʹ ·       Leading and Lagging strands on both sides of replication bubble, but with alternate orientations	·       RNA Pol II synthesizes RNA strand; reads DNA template 3ʹ→5ʹ, creating RNA transcript 5ʹ→3ʹ ·       New RNA strand is similar to coding strand	·       Codon recognition: elongation factor assists bonding b/w codon of mRNA under A site with matching anticodon of tRNA carrying amino acid ·       Peptide bond formation: rRNA catalyzes formation of peptide bond b/w polypeptide in P site with new amino acid in A site ·       Translocation: ribosome moves tRNA with attached polypeptide from A site to P site; mRNA moves with tRNA; tRNA at P site is moved to E site and leaves ribosome ·       mRNA is read 5ʹ→3ʹ codon by codon
Termination	·       DNA Polymerase I proofreads new DNA and replaces RNA primers with DNA nucleotides ·       Ligase “glues” the gaps b/w Okazaki fragments by forming phosphodiester bonds	·       AAUAA sequence on RNA (terminator region)(downstream) stops production of RNA; causes new RNA strand to break off and RNA Pol II falls off DNA molecule ·       After transcription: 5ʹ cap is added to 5ʹ end of RNA transcript, consisting of a modified form of guanine; poly-A polymerase adds poly-A tail to 3ʹ end of RNA transcript; also, introns are removed via RNA splicing done by spliceosomes containing snRNPs and snRNA	·       Occurs when stop codon reaches A site (UAA, UAG, UGA) ·       Release factor hydrolyzes bond b/w polypeptide and its tRNA in P site, freeing polypeptide and causing translation complex to disassemble

Super-Important People in the History of Genetics

Real scientific work in the field of genetics began in earnest in the mid-1800s with the work of the Austrian monk Gregor Mendel who studied the inheritance of certain traits in pea plants. Since those humble beginnings, genetics has since become an integral branch of modern science. Many brilliant scientists were responsible for crucial developments made throughout the history of genetics. Yesterday in class, we went over some of the big names in the history of genetics. However, I am going to pick 5 of them to write about in this blog post:

James D. Watson and Francis Crick (count as 1 person)

Watson (Left) and Crick (right)

James Watson and Francis Crick were the two co discoverers of the structure of DNA. Working out of the Cavendish Laboratory at the University of Cambridge in England, the pair managed to deduce the double helical structure of DNA. They published their results in Nature in April 1953, and subsequently won the 1962 Nobel Prize in Medicine along with another scientist, Maurice Wilkins. However, it is interesting to note that Watson and Crick did not actually perform any significant experiments to determine the structure of DNA, but they merely collected experimental data from other scientists and reached their conclusion based on those data.

Rosalind Franklin

Franklin (Left) along with Watson and Crick

Rosalind Franklin was one of the key scientists from whom Watson and Crick took experimental data. In 1952, while Franklin was working at King's College London she took an X-ray diffraction image of a DNA molecule. This image was eventually used by Watson and Crick to determine the double helical structure of DNA. Unfortunately, Franklin did not receive a Nobel Prize for her work because she died of ovarian cancer soon after her work on DNA, likely due to her exposure to large amounts of x-ray radiation.

George Wells Beadle

George Wells Beadle

George Wells Beadle was an American geneticists who co-discovered that genes are involved in regulating biochemical processes within cells. Along with his lab partner Edward Tatum, they exposed bread mould to x-rays, causing mutations in the bread mould's DNA. They then observed that the mutations caused changes in specific enzymes involved in cell metabolism. The results of their experiments led Beadle and Tatum to propose the "one gene, one enzyme" hypothesis, which states that there is a direct connection between a cell's genes and the enzymes it produces. For their efforts, they were awarded the 1958 Nobel Prize in Medicine.

Hermann Joseph Muller

Hermann Joseph Muller

Whereas Beadle and Tatum used radiation to induce mutations in DNA to study their effects on cell enzymes, Hermann Joseph Muller was the scientist who, during the late 1920s, discovered that radiation, specifically x-ray radiation, was capable of causing mutations in a process called "x-ray mutagenesis". For his discovery, he was awarded the 1946 Nobel Prize in Medicine. He was also a politically vocal scientist, warning people about the dangers of radiation exposure in humans and campaigning tirelessly against nuclear weapons.

Andrew Fire

Andrew Fire

Andrew Fire is one of the more contemporary scientist on this list. He is the co-discoverer of RNA interference, a process in which genes are silenced by short double-stranded RNA molecules in a cell's cytoplasm. He published his research in Nature in 1998. He won the 2006 Nobel Prize in Medicine along with his colleague Craig Mello.

First Entry

Hey guys, this is my new bio blog which I'll be using to keep track of everything that we're learning in class.