Question

List the parts of the structure of a nucleotide. Explain in depth what the purpose of ONE of these parts is to the structure or function of Nucleic Acids 3.

Answer 1

A nucleotide consists of a pentose sugar (ribose or deoxyribose), a nitrogenous base and a phosphate group. The nucleotides serve as monomers in forming nucleic acids (DNA or RNA), which are essential biomolecules of all living beings.

The pentose sugar in RNA is ribose and in DNA, it is deoxyribose. Ribose is an aldopentose (a monosaccharide containing five carbon atoms) that, in its open chain form, has an aldehyde functional group at one end. In the conventional numbering scheme for monosaccharides, the carbon atoms are numbered from C1' (in the aldehyde group) to C5'. The deoxyribose derivative found in DNA differs from ribose by having a hydrogen atom in place of the hydroxylgroup at C2'. This hydroxyl group performs a function in RNA splicing.

The nitrogenous bases are of two types - the purines and the pyrimidines. The purine bases adenine and guanine and pyrimidine base cytosine occur in both DNA and RNA, while the pyrimidine bases thymine (in DNA) and uracil (in RNA) in just one. Adenine forms a base pair with thymine with two hydrogen bonds, while guanine pairs with cytosine with three hydrogen bonds. The nucleic acids are then assembled from these nucleotides.

Though, all parts of the nucleotide are important, the pentose sugar determines whether, it will be a DNA or RNA and their function will vary accordingly. The DNA carries all the genetic information in its base sequence. m-RNA is formed from this DNA, and then proteins will be formed which will carry out the functions of body. It, is the base sequence, in DNA which is responsible for forming the proteins. The four roles DNA plays are replication, encoding information, mutation/recombination and gene expression.

Replication- DNA exists in a double-helical arrangement, in which each base along one strand binds to a complementary base on the other strand. Bacteria and mitochondria may also have single-strand DNA arranged in a ring. When a cell divides, the chromosomes containing the DNA strands must replicate, or make copies, of themselves so that both daughter cells receive the full set of genetic material. During replication, the DNA double helix unwinds, allowing each strand to act as a template for a newly synthesized complementary strand that forms a new double helix. The enzyme DNA polymerase assists in the process.

Encoding Information- The base sequences of A, T, C and G along a DNA strand are organized into units called genes. An adjacent trio of bases, called a codon, specifies a particular amino acid. Therefore, the sequence of bases in genes determines the sequence of amino acids in proteins, which are the biochemical units of a cell’s structure and function. RNA, a chemical similar to DNA, is an intermediary in protein synthesis.

Mutation and Recombination-DNA plays a role in the evolution of a species. Chromosomal DNA helices don’t usually interact with each other. However, through the process of genetic recombination, segments of different chromosomes swap places with each other, creating new sequences of genetic material. If changes occur to the DNA sequences of sex cells, the changes can be inherited by the next generation. The new sequences might produce new proteins, some of which are beneficial to the organism. In this way, the characteristics of the organism might evolve over time. Natural selection of beneficial traits can produce changes that make an organism more fit for survival and reproduction. DNA can also repair itself through recombination. A mutation happens when an unusual base pairing occurs -- for example, when an A lines up opposite a G instead of opposite a T. An inheritable mutation must occur in the chromosomes of the sex cells. Mutations and recombinations can be beneficial but can also create genetic diseases and malformed offspring.

Gene Expression- Each cell contains a full complement of genes, yet cells from different tissues and organs look and behave differently. The reason is that only some of the DNA of each cell is used to make proteins. DNA plays a role as a traffic cop for the types of proteins a cell will make. It does this through interactions with proteins in the cells that cause only certain genes to express themselves. This is how a single fertilized egg cell differentiates into the many types of cells, tissues and organs found in complex organisms. The DNA can respond to the need for a particular protein by exposing the appropriate genes for transcription while keeping other genes inactive.