CH3 -cell replication-

• Proteins are good for the body, especially in building muscles and repairing tissues.
• The deoxyribonucleic acid (DNA) is a biomolecule that has an essential role on how our cells produce proteins.
• 1928

  Frederick Griffith

  He hypothesized that there is a "factor" that can change a harmless bacteria into a harmful one.
• 1944

  Oswald Avery

  He discovered that the "transforming factor" is the DNA.
• 1950

  Erwin Chargaff

  He introduced the "Chargaff's rule," which is the basis of the base pairing of nucleotides.
• 1952

  Alfred Hershey and

  Martha Chase

  They concluded that DNA is the genetic material present in bacteriophages.

  Rosalind Franklin and

  Maurice Wilkins

  They studied the structure of DNA using the X-ray diffraction technique.
• 1953

  Francis Crick and

  James Watson

  They created the double-helix model of the DNA
• DNA is made up of chains of nucleotides.

  Each nucleotide consists of a five-carbon sugar called deoxyribose (deoxy- means "without oxygen") and a sugar-phosphate backbone group, which make up the nitrogenous bases of DNA. The nucleotide also contains the nitrogenous bases that extend Sideways
• There are four nitrogenous bases found in DNA. They are cytosine (C), guanine (G), adenine (A), and thymine T).
•  Adenine and guanine are considered purines because their structure has two rings, whereas cytosine and thymine are pyrimidines because their structure only has one ring. A pyrimidine always pairs with a purine, which was first observed by Chargaff, leading him to formulate Chargaff's Rule.
•  So, cytosine pairs with guanine and adenine pairs with thymine.

  This is called the Chargaff's rule.
• DNA is described as a double helix, whose structure is similar to a twisted ladder.

  The five-carbon sugar and the phosphate group form the handles of the ladder, and the nitrogenous base pairs create the steps of the ladder.
•  This structure was first presented by James Watson and Francis Crick when they formed the three-dimensional model of DNA based on the X-ray pattern of the DNA made by Rosalind Franklin and Maurice Wilkins.
• Replication is the process wherein DNA produces new copies of itself. This process is described as semiconservative because, after DNA replication, the new copies contain both the old strand and the new strand.
• There are different proteins that help along the process of DNA replication. It happens inside the nucleus of the cell. A helicase (an enzyme) will attach to one part of the DNA and opens it up (unzip), exposing the nitrogenous bases. The unzipped parts will constitute the leading strand and the lagging strand. To stabilize the unzipped part of the DNA, the molecules of a single-strand binding protein will attach to the open strands.
•  The ribonucleic acid primer will attach to one part of the leading strand in a 5'→3' direction (the apostrophe is read as prime). It will be synthesized continuously by DNA polymerase (another enzyme). This happens simultaneously with the lagging strand of the DNA in a 3'→5' direction.
• Because the lagging strand cannot be synthesized continuously, it creates Okazaki fragments, which will be joined together by another enzyme called DNA ligase.