Structure of DNA
Structure of DNA DNA is the code for life, the key to unlocking this code lies in the structure of DNA. Many different people have been involved in the discovery of the structure of DNA, and many different ideas have been discussed. Francis Crick and James Watson have made a momentous discovery about the structure of DNA, but where did their ideas originate and where will they lead? Early ideas about DNA came in 1951 from Rosalind Franklin who was an X-ray crystallographer. She suggested that DNA had a helical structure and that the phosphate groups of the nucleic acids were positioned on the outside of the chain. She also thought that each helical unit had 2,3 or 4 nucleic acid chains. In 1951/1952 Francis Crick an English physicist and James Watson an American biologist began their work to discover the structure of DNA. They set about finding how many polynucleotide chains were in the DNA molecule. Using X-ray data they decided that DNA was made up of three chains twisted about each other. They also thought that the forces that held the chains together were salt bridges in which cations such as Mg++ held two or more phosphate groups. In 1952 Franklin responded to Watson and Crick's findings by dismissing the helical structure that she had initially proposed. She also dismissed the way in which the phosphate groups were held together. If they were held together with Mg++
Nucleic Acids, DNA Replication and Protein Synthesis.
Jasmeet Singh Bhambra Nucleic Acids, DNA Replication and Protein Synthesis In side the nuclear membrane is the nucleoplasm. The nucleoplasm consists of two main substances, which are nucleic acids and proteins. There are two nucleic acids, which are ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). RNA translates the genetic code into instructions for making proteins in the cytoplasm of the cell. Making these proteins is a process called protein synthesis - a production line that turns out enzymes to carry out the instructions and build a new cell. DNA is the basic genetic material, the blueprint for the cell to be passed on when it divides. This makes up the chromosomes in the nucleus of the cell. DNA carries a code in its molecules, which is read by RNA. DNA replicates itself to be sure that the genetic code is passed on to each new cell - it needs to produce another molecule exactly the same as itself. Protein Synthesis - What's it all about? Firstly, the genetic code of the nucleus is transcribed onto messenger RNA. This RNA moves out of the nucleus into the cytoplasm and becomes attached to a ribosome. Molecules of tRNA carry individual amino acids to the surface of the ribosome. The process translation now occurs, which is when tRNA molecules complementary to the codons in the mRNA strand line up, and enzymes link the amino acids together. When this is done,
Protein Synthesis
PROTEIN SYNTHESIS Proteins are used in the cell for a variety of reasons. They may have a structural or a functional role, or they may act as enzymes controlling cell metabolism. Protein synthesis is a very complex process; therefore it is necessary to understand the structures of DNA and RNA which are involved in the process of protein synthesis. DNA and RNA are nucleic acids formed from nucleotides. Individual nucleotides are comprised of three parts: * Phosphoric acid (Phosphate H3PO4). This has the same structure in all nucleotides. * Pentose sugar: These are of two types - Ribose (which occurs in RNA) and Deoxyribose (which occurs in DNA) * Organic bases: There are five different bases which are divided into two groups - Pyrimidines - these are single rings with six sides. i.e., cytosine, thymine and uracil. Purines - these are double rings comprising a six-sided and a five-sided ring, i.e., adenine and guanine. The three components are combined by condensation reactions to give a nucleotide. By a similar condensation reaction between the sugar and phosphate groups of two nucleotides, a dinucleotide is formed. Continued condensation reactions lead to the formation of a polynucleotide. DNA is a double stranded polymer made up of two polynucleotide chains, where the pentose sugar is always deoxyribose and the organic bases are adenine, guanine, cytosine and
