DNA Replication Transcription and Translation

The replacement of dead cells and the repair of worn out tissues, as well as growth, are the results of cell division. Prior to division, the cell must duplicate its DNA in order to give identical DNA to its daughter cells. This process is done through DNA replication which requires transcription and translation processes. During replication, the DNA unwinds, as aided by the DNA polymerase, and generates two identical DNA molecules. In the synthesis of protein, the DNA also unwinds and synthesizes the messenger RNA or mRNA.

This mRNA, then goes to the ribosome and serves as a template for protein synthesis. In the ribosome, the genetic information encoded by the DNA on the mRNA is decoded by the ribosomal RNA or rRNA. On the other hand, the transfer RNA or tRNA finds amino acid in the cytoplasm and attaches it to the mRNA template based on the genetic code transcribed. DNA Polymerase DNA polymerase is the enzyme responsible for the accurate duplication of genetic information.

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During cell division, this enzyme makes an exact copy of the DNA of the parent cell that will be turned over to the daughter cells.

In such way, the exact DNA attributes of the parent cell is passed through the generations of its daughter cells. In addition, the DNA polymerase makes an identical copy of the parent cell’s DNA with less than one possible error for every one billion of bases. It strengthens the specific pairing of the DNA bases: thymine to adenine, guanine to cytosine by proofreading and deleting mismatched bases.

tRNA, rRNA, and mRNA Although the DNA holds the genetic code, the RNA transforms this genetic information into the synthesis of proteins.

In fact, with the RNA types: tRNA, rRNA, and mRNA, 80% of the cell’s RNA are ribosomal or rRNA which indicated the RNA’s role in the protein synthesis (Enger, Ross, and Bailey, 2009). As the mRNA carries the genetic code into the ribosome and serves as a template for protein synthesis, the tRNA hunts for amino acids in the cytoplasm and attaches it to the mRNA template. Nitrogenous base, Nucleotide and Codon A nitrogenous base is a heterocyclic organic molecule which has two or more nitrogen atoms in its ring structure. There are eight nitrogenous bases in every DNA and RNA which are classified as purine bases and pyrimidine bases.

These bases differ in their ring substituents; each has a nitrogen atom bonded to two carbon atoms and a hydrogen atom. The nitrogen-hydrogen portion of both purine and pyramidine bases react with sugar molecule forming a nucleoside. The nucleoside then can further react with phosphate group to form nucleotide. Thus, a nucleoside is a nitrogenous-sugar molecule combination while a nucleotide is a phosphate ester of a nucleoside. On the other hand, a codon is made of three nucleotides; the triplet codons of mRNA call for a specific amino acid. Gene Expression and Control

Gene expression is comprised of three interrelated processes, wherein the gene transcribed and processed by the mRNA is translated generally into protein. The control of gene expression causes variation in the phenotype and functions of the cells which eventually affect the tissues as well as the appearance of the organism. In the case of multicellular organisms, their respective cells have identical genetic material for they came from a single diploid zygote (Enger, Ross, and Bailey, 2009). However, cells may vary in forms and functions due to genetic expression.

For instance, the epithelial cells and the nerve cells have different morphology, functions, and other characteristics because of genetic expression characteristics. The control of gene activity commences at the transcription stage where the specific portion of the DNA is transcribed into the mRNA. As well, gene expression is largely controlled through the protein and DNA interactions along with their binding sites. The first level of gene expression control occurs as the sequence of the series of DNA nucleotides changes. Although, the cells in our body are the products of the original zygote’s mitosis, DNA scrambling is possible.

In particular, the development of the immune system’s B cells involves DNA scrambling in specific regions which in turn reflect in the attributes of the antibodies generated by the system. In such process, the cells divide in a certain phase of the embryonic development with rearrangement in the specific regions of the DNA. At the end of the embryonic phase, as the cells undergo division, the DNAs of the daughter cells are identical but are different from that of the parent cells. As a consequence, clones of antibody producing cells which generate different antibodies are created (Enger, Ross, and Bailey, 2009).

Mutation In the natural course of time, the appearance of traits in an organism which are different from or not even manifested in its ancestors happens. These unique traits are directly caused by the genetic or chromosomal changes called mutations. Mutations are generally harmful and since they are genetically imprinted, the impacts of such are inherited by the next generations of the organism. Meanwhile, mutations are classified as either point or chromosomal mutations. In point mutation, either substitution or frame shift, the DNA base sequence is altered.

Whereas substitution mutation involves the replacement of a DNA nucleotide with a nucleotide having a different nitrogenous base, a frame shift mutation is a result of insertion or deletion of nucleotide in the DNA. Still, silent mutation is a type of substitution mutation wherein the base substitution in the DNA does not affect the coded amino acid. For instance, when the mutation resulted to the transcription from the codon “CCG” to “GGC”, the protein synthesis will not be altered. This substitution has only led to a codon which codes for the same amino acid---glycine (Enger, Ross, and Bailey, 2009).

Hence, the resulting mutation is “silent” for the amino acid sequence in the protein-ending gene is not affected. On the other hand, chromosomal mutations are triggered by the chromosomal rearrangements with alteration or non-alteration in the chromosomal number. Chromosomal mutations induce birth defects in humans such as in “cry of the cat” syndrome which involves deletion in the chromosome 5 and in Down syndrome which is caused by an extra copy of chromosome 21 (Enger, Ross, and Bailey, 2009). Reference Enger, E. D. , Ross, F. C. , and Bailey, D. B. (2009). Concepts in biology, 13th ed. New York: McGraw-Hill.