Compare and Contrast: Replication, Transcription, Translation

	Initiation	Elongation	Termination
Replication	Enzymes involved: Helicase unwinds the DNA strands. Single-strand binding proteins (SSBP) keeps the two untwisted strands separate, and protects it from damage. Gyrase releases the tension and cut the DNA. Primase, an enzyme that codes for RNA (primer) kicks starts the elongation process.	DNA polymerase III helps catalyze, and is responsible for the elongation of new DNA strand from 5 prime to 3 prime. Two daughter strands are replicated simultaneously. The leading strand elongates into the fork, the lagging strands grows away from the fork. Each segment on the lagging strand is called an Okazaki fragment.	DNA polymerase I is responsible for proof reading the replicated sequence and replacing RNA with DNA. Ligase acts as the glue at the end of the replication process and joins the fragments of DNA together.
Transcription	The upstream of the template DNA strand contains the promoter, which signals the start of transcription. The promoter region contains transcription factors, which recognizes the TATA box which initiates the transcription process. The transcription factors (TF), TATA box, and RNA polymerase II forms the initiation complex.	RNA polymerase II is responsible for the elongation portion of the transcription process. RNA polymerase II untwist the double helicase of DNA, reads the DNA sequence from the template and transcribe it into a RNA strand with corresponding sequences, and lastly it joins the DNA back together.	Once the RNA polymerase II encounters the TTATT sequence on the antisense DNA strand the transcription will come to an end with the formation of the AAUAA sequence on the RNA transcript. Around 50-250 adenine nucleotides are added to the pre-mRNA, the poly (A) tail. A modified guanine is added to the front of the sequence, called the 5, cap which protects the RNA sequence. A large portion of the RNA transcript is cut from the strand, the introns which have little function. The remaining sequences are called the exons. This process is called RNA splicing.
Translation	At the start of the translation process tRNA or transfer RNA reads the codon from the mRNA and forms the anticodon. Each anticodon consists of three bases. The last base on the anticodon is usually flexible, for example UAC and UAU could code for the same amino acid. This reduces the effect of small errors along the translation process.	The first codon that is recognized and translated is AUG; this is the universal starting codon. After the starting codon is read the ribosome reads the codons 3 bases at once and forms a polypeptide chain with the correct amino acid sequence.	The ribosome will encounter three stop codons, which do not code for amino acids. These three codons are UGA, UAG, and UAA. A protein called the release factor will help with the release of the polypeptide chain once the translation has come to a halt.

Big Names in the Field of Genetics

The study of genetics has brought great scientific advancement to the field of biology. The discovery of DNA as the building block of life in the last century gave scientists keys to unlock the mysteries of life and could potentially answer fundamental questions of our existence. The discipline of genetics was built upon the works of brilliant minds spanning many generations.

Gregor Mendel (1822-1884)

It is impossible to introduce the study of genetics without mentioning Gregor Mendel who many consider as the “Father of Genetics”.  Mendel was born in the Austrian Empire (now the Czech Republic) and studied practical and theoretical philosophy and physics in the University of Olomouc as a young man. After graduation Mendel became a priest and worked in a monastery, and it is during this time that he made his greatest discoveries and kicked start the study of genetics. Mendel conducted studies on the pea plants in the monastery’s garden and noticed interesting phenomenon between the pea plants of successive generations. He noticed that when two pea plants with different traits were cross-bred the second generation pea plants only took one of the two traits. However when the second generation plants were cross-bred the third generation plants exhibits both traits from the first generation plants and the traits existed in a fixed ration. This discovery led to Mendel’s Law of Segregation and Law of Independent Assortment which laid down groundwork for modern genetics. Gregor Mendel published these findings in 1866.

Oswald Avery (1877-1955)

By the early 1900s scientists already know that there is a link between parents and offspring and that some traits and characteristics were passed down from one generation to the next but the exact nature of such a linkage was still a mystery, this is where Oswald Avery comes in. Avery was a Canadian-born American medical researcher who was one of the pioneers in immunochemistry. In 1944 Avery studied strains of bacteria and managed to transfer disease causing material from one strain of bacteria to another previously harmless strain, the material that was moved was the nucleic acid. Avery wrote in his 1944 paper that genes and chromosomes were made of DNA and this is the hereditary material.

Erwin Chargaff (1905-2002)

Erwin Chargaff was an Austrian biochemist who later moved to the United States. Chargaff read Oswald Avery’s work on DNA and was inspired to work out the chemical composition of DNA. At the time it was hypothesized that DNA consists of four bases adenine, thymine, cytosine, and guanine. Chargaff discovered that in any species the ratio of adenine and thymine were roughly equal, so was cytosine and guanine. This was later known as Chargaff’s Rule. He concluded that there exists a complementary relationship between the pairs. Chargaff did not realize the significance of his work; it is based on his work that Francis Crick and James Watson were able to develop the double helix model for DNA.

Rosalind Franklin (1920-1958) 

Rosalind Franklin was a British biophysicist and crystallographer. In 1951 Franklin was appointed to King’s College London to work on the structure of DNA. Franklin was an expert at crystallography; she used X-Ray diffraction to photograph structure of DNA. In the 1940s and 50s Franklin along several other scientist were working on DNA at the college, including Francis Crick, James Watson, and Maurice Wilkins. An x-shaped graph of DNA taken by Franklin was shown to Crick and Watson which helped them to develop the double helix model for DNA. Rosalind Franklin is also known as the “dark lady of DNA” mainly because her work was not recognized and she died an early death from ovarian cancer due to prolonged exposure to X-ray. Maurice Wilkins later took credit for her work and shared a Nobel Prize of Physiology or Medicine with Crick and Watson in 1962. 

Francis Crick (1916-2004) and James Watson (1928- )

By the 1950s scientist were convinced that DNA is the genetic material and a race was on to build the first model of DNA. In the 1953 English molecular biologist Francis Crick and American molecular biologist/geneticist James Watson came up with the double helix model for DNA and unravelled the blueprint of life. Previous ladder model of DNA could not work in real life as it was easily broken by water, it was Watson and Crick that discovered the secret to DNA’s structure was the twist in the ladder. In a paper they published wrote: "It has not escaped our notice that the specific pairing (of purine and pyrimidine bases) that we have postulated immediately suggests a possible copying mechanism for the genetic material."  In 1962 Watson, Crick and Maurice Wilkins shared the noble prize for Physiology or Medicine.