What is the central dogma?
Classic views of the central dogma can be notes as genetic information that has been hardwired into DNA being codes and transcribed into messenger RNA (mRNA). Each mRNA contains information that will allow for the synthesis of a particular protein. DNA replication is the first stage of the central dogma. DNA replication is semi-conservative, meaning that one complete strand within the new âdaughterâ DNA is derived from the parent molecule. Helicase breaks the hydrogen bonds that hold the complementary bases together, and the separation of the two strands mean that they then act as a template for the new strands of DNA1. Transcription then occurs, a DNA strand is split by RNA polymerase. This enzyme allows the passage for mRNA. Messenger RNA is not identical to the DNA strand, but is complementary to the DNA. Therefore, the mRNA forms a complementary strand where instead of thymine, uracil is present. This mRNA can then be modified before it leaves the nucleus ready for translation2. Within translation, the information that has been transcribed is read as triplets, each coding for one amino acid. The amino acids are linked together by transfer RNA, and will later be folded into a protein.
Who stated the central dogma?
The central dogma was first stated by Francis Crick in 1956, before later being re-stated in the paper âNatureâ which was published in 1970.
âThe central dogma of molecular biology deals with the detailed residue-by-residue transfer of sequential information. It states that such information cannot be transferred back from to protein to either protein or nucleic acidâ â” Francis Crick3.
DNA consists of a phosphate and a deoxyribose sugar, which forms the sugar-phosphate backbone. This deoxyribose has a significant importance in DNA being a long term information storage molecule because DNA doesnât contain a hydroxyl group at the 2â carbon. The presence of a hydroxyl group at the 2â means that the molecule is more susceptible to breakage. Therefore, the DNA molecule is more resistant to hydrolysis meaning that genetic information is better protected. In DNA, there are four nucleotides, these are; Adenine Guanine, Thymine and Cytosine. These nucleotides are placed into two categories, purines and pyrimidines. Adenine and Guanine are purines, whereas Thymine and Cytosine are pyrimidines. Purine molecules form hydrogen bonds with their corresponding pyrimidine pairs. This is known as complementary base pairing. There are two separate strands within the DNA molecule, each containing the complementary nucleotides (A-T,G-C) needed in order to form a double helix4. The sugar-phosphate backbone of the DNA strands wind around the helical axis forming a âspiralâ structure. The nucleotides are then contained within this molecule, giving them protection from the outside chemical and physical factors and thus preventing the genetic information being damaged. This double helix structure means that if one of the strands becomes damaged, then the remaining strand can be utilised to act as a template for repair. The importance of passing on information from generation to generation is that it allows for favourable genetic characteristics to be passed on to the offspring and future generations. DNA is associated with histone proteins, which they are âwrappedâ around, this allows the DNA to be compacted. This compaction is important because it enables the compaction of a large genome in the nucleus.
RNA consists of a phosphate and a ribose sugar which forms the sugar phosphate backbone. In RNA, the presence of a ribose with an OH group on the 2â carbon means that RNA is more susceptible to breakage. This means that RNA is not as effective in storing genetic information like DNA, however RNA is only needed when a protein is needed, therefore it is easily broken down to allow for the transcription of new protein molecules5. There are 4 nucleotides present in RNA, these are; Adenine, Guanine, Cytosine and Uracil. Thymine is not incorporated into RNA, as it is believed that the presence of Thymine makes DNA more stable; as Thymine contains a methyl group. Uracil is not used in DNA as the nucleotide Cytosine can be deanimated to uracil. The cell can recognise this and it can then be ârepairedâ by substituting the Uracil with a Cytosine. This is done by DNA glucosylase, which excises uracil from the DNA double strand6. RNA is very unstable, and this is because it is constantly being broken down to make new proteins. RNA is an intermediate product between DNA and Protein, and so by being unstable it means that it can easily be broken down. This is important because if a mutation occurs in the mRNA then it will be degraded by an enzyme and wonât have a long term effect like it would in DNA.
During translation, tRNA carries amino acids to their complementary codons forming the primary structure of a protein, this structure is an amino acid chain (the polypeptide) and this allows for the construction of the secondary structure. The secondary structure can either be be Î±-helix or the Ã-sheet. The tertiary structure is the overall three-dimensional shape of the protein which allows a protein to perform a specific function. Many proteins, like haemoglobin, have a quaternary structure and this refers to how the protein subunits interact with each other and how they form a larger protein complex7. Each protein has a specific function within the body and this is important to biology as many biological reactions would not occur without them, for example; antibodies. Antibodies are proteins that are specialised in defending the body from antigens which can cause disease. This is important because without antibodies our bodies are susceptible to illness. Enzymes are another example of proteins which catalyse biochemical reactions8. An example of this is Pepsin, which works within the stomach to break down the proteins in food molecules. This is important as it allows for the digestion of food. The importance of proteins is that they play a part in many processes, and without them these processes would not occur.
In conclusion, the importance of central dogma to modern biology is that without this process reproduction of species would not occur as genetic information wouldnât be able to be stored and produce proteins which are essential in biochemical processes.
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