Genetics: Dna and Dna Molecules Essay

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Code of Life

Topic 1 - Genetic material
Plants and animals have different cellular structures and so do different tissues and organs within the same organism. All cells have DNA, a membrane and cytoplasm. A cell's nucleus is a very important organelle. It controls all the processes within the cell. Some cells have a nucleus and some do not. All cells are divided into two large groups: cells with a nucleus, called eukaryotic cells, or simply eukaryotes; and cells without a nucleus, called prokaryotic cells, or prokaryotes.
All biological cells store their genetic information in the form of DNA. DNA is an abbreviation of deoxyribonucleic acid. DNA molecules determine the types of protein synthesised within the cell. Eukaryotes store their DNA in their nucleus and prokaryotes store their DNA in their nucleoid.
A nucleus is composed of the following parts: nuclear envelope; nucleoplasm; nucleolus and chromatin. Prokaryotic cells do not have a defined nucleus. Their DNA freely 'floats' in a more-or-less specified area of the cytoplasm called the nucleoid. A bacterial nucleoid usually consists of a single molecule of DNA. Topic 2 - Inheritance
A cell's genetic information is stored in the form of DNA molecules. DNA molecules and associated proteins form the chromatin of the nucleus. During cell division, the chromatin forms thread-like DNA structures called chromosomes.
Each chromosome is made up of DNA molecules tightly coiled many times around proteins called histones. The spiral shape of DNA is called a helix. Each strand of the DNA double helix is a linear arrangement of repeating similar units called nucleotides. When a cell divides, its DNA takes a more compact form called a chromosome. Eukaryotic organisms have many chromosomes, while prokaryotes usually have just one in the form of circular DNA.
Normal human cells have 46 chromosomes: 44 autosomes and 2 sex chromosomes. Autosomes are chromosomes that contain just genetic information and are not involved in sex determination. Chromosomes that determine an organism's sex are called sex chromosomes.
James Watson and Francis Crick discovered the true genetic information carriers - molecules of DNA and RNA. This double helix model of DNA is referred to as the Watson-Crick model of DNA. DNA is an abbreviation of deoxyribonucleic acid. DNA is a polymer, which means it is a large molecule composed of monomers called nucleotides. Nucleotides are made of one nitrogenous base, one phosphate molecule and one sugar molecule (deoxyribose in DNA and ribose in RNA) There are four different types of nucleotides found in DNA: adenine, guanine, cytosine and thymine. 
During cell division, the DNA molecule is copied for future generations of cells. This process of DNA copying is called replication. RNA is an abbreviation of ribonucleic acid. RNA is a single-stranded polymer. Its structure is similar to DNA except it has sugar ribose in place of deoxyribose and base uracil in place of thymine.
Genes are found on chromosomes within the nucleus of every cell. During the process of protein synthesis, genes are 'read' by RNA molecules that later function as templates for protein structure. The type of protein determines the type of organism. Proteins are polymers made of monomers called amino acids. A group of three nucleotides within DNA or RNA specifying a single amino acid is called a codon. A larger section of nucleotides that specifies the sequence of amino acids in proteins is called a genetic code. Most living organisms use the same genetic code, which is called a standard genetic code.
An organism's genetic characteristics are called its genotype. Genotype is encoded in DNA molecules and is often (but not always) expressed in an organism's phenotype. A phenotype is a set of visible characteristics of the organism. An organism's phenotype is always an expression of its genotype.
When reproductive cells, called gametes, combine to form a new organism they both contribute their
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