Protein synthesis is the process, which produces the proteins, which make up the Genetic Code, and this consists of two processes, which are transcription and translation. Transcription happens in the nucleus and during this the section of the DNA molecule (a gene) uncoils and the two polynucleotide strands separate, as hydrogen bonds are broken. RNA nucleotides line up against the DNA nucleotide bases on the template strand by specific complementary base pairing. RNA polymerase enzyme joins the nucleotides together to form a strand of messenger RNA. This mRNA leaves through the nuclear pore and attaches to a ribosome in the cytoplasm where translation occurs. Translation is carried out at the ribosomes in the cytoplasm and each tRNA molecule has three exposed bases known as an anticodon. During translation an mRNA attaches to the ribosome and then a tRNA molecule with the complementary anticodon binds to the first codon on the mRNA strand bringing with its specific amino acid. The anticodon binds to the codon by specific complementary base pairing and then another tRNA then binds to the second codon on the mRNA strand. The amino acid on the first tRNA molecule is joined to the amino acid on the second tRNA molecule by a peptide bond. The tRNA moves away from the ribosome leaving its amino acid behind and this process continues until all the codons have been read and the primary structure of the polypeptide has been produced and then this is folded into the secondary and tertiary structure.
Meiosis is an important process, which involves diploid organisms i.e. humans, who have cells, which have pairs of homologous chromosomes, dividing to produce haploid gametes, containing one chromosome of each homologous pair. The cells produced are genetically different to the parent cell and to each other. Meiosis is an important process in terms of the genetic code because it ensures that haploid gametes are produced in diploid organisms, during sexual reproduction. The haploid gametes fuse to form a zygote during fertilisation and the diploid number is restored. Meiosis ensures that there are a constant number of chromosomes in each generation i.e. 46 chromosomes, because if it didn’t the number of chromosomes would double after every generation. Meiosis also produces genetic variation.
The Genetic Code contains DNA, which is a very stable molecule. However sometimes mutations can occur, which is when there are changes in the sequence of nucleotide bases in DNA which results in the formation of a different polypeptide and an altered base sequence which codes for a different sequence of amino acids. There are a number of ways in which the base sequence of the bases in DNA can be altered. These are Substitution (the replacement of one or more bases by one or more different base, often resulting in a non-functional protein being produced) Deletion, (the removal of one or more bases) and Addition (the addition of one or more bases). Addition and Deletion both result in a frame shift, which is the alteration in the codons from the point of deletion/addition and then results in a different protein being produced which is often non-functional. This is one type of genetic variation, but there are others, such as, producing new alleles of genes, during meiosis which produces new combinations of maternal and paternal origin alleles on homologous chromosomes through crossing over at chiasmata, through independent assortment which produces new combinations of maternal and paternal origin alleles on homologous chromosomes and their alleles, by producing variation in gametes in sexual reproduction and random fusion of gametes at fertilisation which brings about new combinations of alleles. These mutations and genetic variations are the basis for Natural Selection and Evolution.
Natural Selection is the process by which one or more environmental factors affect the survival rates of different phenotypes in the population. Intraspecific competition is concerned with Natural Selection and is when two populations of the same species compete for the same resources in an ecosystem in order to survive. An example of intraspecific competition taking place is the effects of pollution on the survival of the peppered moth. In Britain, 1850 the large population of moths had white wings with black scales in an irregular pattern but after the industrial revolution the melonic moths, which were moths with entirely black wings became more common. This could have been because there could have being a chance mutation, which meant that the offspring were melonic. The air became sooty and black during the industrial revolution; therefore the melonic moths couldn’t be seen by predators and survived more successfully than speckled moths. This will have occurred due to the melonic allele being dominant to the speckled allele. Evolution is when existing species are a result of changes in the frequency of alleles in a population over millions of year; therefore this can also alter the make up of the genetic code. Evidence for evolution exists because fossils have been found and these give evidence of the changes in forms of life over time and vast numbers of now extinct species, they also give evidence of development of more complex forms with time, some fossils records show the evolution of new, modern species from previously existing species and fossils also show the structural similarities between the extinct and living species.
Speciation is when new species arise from existing species, through altering the frequency of alleles in a population. A species is a group of organisms that interbreed to produce fertile offspring and evolution states that new species arise by the process of speciation. A species is made up of one or more populations each living in different environmental conditions. Natural selection takes place in each population leading to changes in allele and phenotype frequencies in each population. Over time this process makes each population different from all the others. Sometimes individuals move from one population to another by emigration and immigration, which moves alleles between populations and prevents big differences from occurring between populations. If a population becomes geographically isolated they adapt to the environment through natural selection. These changes in genotypes and phenotypes in an isolated population may lead to reproductive isolation and the formation of the new species, because the species cannot breed with other species to produce variable offspring. Darwin has demonstrated this idea by discovering finches on different islands of the Galapagos groups. Four species of finch were found who had evolved from one ancestral species. These were the woodpecker finch, cactus finch, warbler finch and ground finch and these were closely related but differed as they had different beaks and ate different food.
The Genetic code has been used for many applications in gene technology. Genetic engineering is a technique, which allows genes to be removed from the DNA of one organism and then inserted into the DNA of another species. This is a useful technique because genes can be injected into humans to cure genetically inherited diseases such as cystic fibrosis, which is caused by a defective gene. Plants and animals have been cloned by vegetative propagation and the splitting of embryo’s to produce better crop yield or meats, which are more profitable. However ethical issues have been raised about the use of genetic engineering.
In conclusion it can be seen that the Genetic Code is fundamental for all living organisms. The processes such as protein synthesis and DNA replication that occur in terms of the Genetic Code are vital for the growth and reproduction of organisms. Mutations can occur which alter DNA sequences and produce genetic variation. This variation is related to Natural Selection and Evolution, which are changes in the frequency of alleles in a species. The main use of the Genetic Code is its applications in gene technology, such as genetic engineering which replaces defective genes to cure genetically inherited diseases. These ideas are continuing to be researched, even though a number of ethical issues have been raised.