Write a series of paragraphs that shows your knowledge of the following: the biochemical structure of dna, how dna replicates, how the dna structure forms the genetic code, and how that genetic code comes to be expressed as a phenotype.

The answers are as follows:
1. THE BIOCHEMICAL STRUCTURE OF DNA
The DNA is composed of molecules called nucleotide. Each nucleotide is made up of a phosphate group, a sugar group and a nitrogenous base. The nitrogenous bases are four in number, they are adenine, cytosine, guanine and thymine. The genetic code of a DNA molecule depend on the manner in which the bases are arranged. It has been reported that the nitrogenous bases in DNA molecules of humans is approximately 3 billion in number. Double stranded DNA is made up of two spiral nucleic acid chains, which are twisted into double helix shape. The DNA is packed into tightly coiled structure called chromatin and are stored in the nucleus of cells. Chromatin usually condense to form chromosomes during cell division.

2. DNA REPLICATION
DNA replication is the biochemical process by which two identical DNA molecules are produced from a single original double stranded DNA parent molecule. This is the basic way by which the DNA molecule makes copies of itself. This process is the basis of inheritance and it occurs in all living organisms. DNA replication is a semi conservative process, this means that, each strand in the double helix DNA acts as a template for the formation of a new complementary strand. The major enzyme that catalyses this process is DNA polymerase and other enzymes that are involved include: DNA ligase, DNA primase, DNA helicase and topoisomerase. 

3. HOW DNA STRUCTURE FORM GENETIC CODE
The genetic code is the route via which the DNA molecule carry genetic information in living cells. The genetic code refers to the rules by which the genetic information that is encoded inside the DNA molecule is translated into different type of proteins by the cells of living organisms. The translation process involves the ribosomes, which links up amino acids in the specific manner specified by messenger RNA. Transfer RNA participate in the process by carrying amino acids and by reading the messenger RNA three nucleotides at a time. In genetic code, a group of three DNA bases, called codon, codes for one particular amino acid. For instance, the codon CGT codes for the amino acid alanine. 

4. HOW GENETIC CODES COME TO BE EXPRESSED AS PHENOTYPE
Phenotype refers to a set of observable features of an individual, that is formed as a result of the interaction of the genotype with the environment. Examples of phenotype are: eye color, hair color, skin colour, nose shape, etc.  The genotype refers to the set of genes in a DNA, which is responsible for a particular trait in a man.The phenotype is the physical expression of that trait. Each gene in living organisms typically code for a particular trait, for exmaple eye color. Each gene have different alleles, which code for the same trait.The allele may be dominant or recessive. The phenotype that will eventually be formed will depend on the whether the alleles are dominants or recessive.

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