Explain The Structure And Inheritance O

Topics: Gene, DNA, Allele Pages: 3 (1013 words) Published: December 3, 2014
Explain the structure and inheritance of genes (15 marks) A cell’s nucleus contains chromosomes, which are long, coiled packaged and organized chromatin (molecules of DNA). Chromatin is a complex of molecules found in cells, consisting of DNA, protein and RNA. Proteins are polypeptides (a large sequence of amino acids). The chief protein component of chromatin are histones, which package and order the DNA into structural units called nucleosomes in order to fit in the cell, as well as reinforce the DNA molecule to allow mitosis to occur to prevent DNA damage. Another primary function of chromatin is to control gene expression and DNA replication. Chromosomes are made up of two homologous (meaning carrying the same characteristics) sister chromatids and are connected by a centromere in the middle, these chromatids are divided into regions called genes. A gene is a section of DNA that holds information, that is, a sequence of nucleotide bases, that’s usually determines a single characteristic of an organism. Each gene in a molecule of DNA contains a different sequence of bases and codes for a particular protein. The information contained in genes is in the form of coded instructions called the genetic code. The genetic code controls cell activity, which means that it also controls some characteristics of the organism. Nucleotide bases are composed of a nitrogenous base, a five carbon sugar, and at least one phosphate group and are, in essence, the building blocks of DNA. Base pairs exist between different nitrogenous bases. There are two of these, being Adenine and Thymine which are connected by two hydrogen bonds and Guanine and Cytosine which are connected by three hydrogen bonds. In DNA, two DNA strands coil together to create a double-helix, this is where base pairing occurs between the two strands when hydrogenous bonds are created between two bases. Genes also have variants, which are called alleles, which play a large part in the inheritance of genes via...
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