INTRODUCTION life on Earth is composed of a basic set of All chemical components The most fundamental fundamental of these are water H2O charged particles known as ions and small molecules namely nucleic acids amino acids fatty acids and carbohydrates Small molecules are of special significance in understanding understanding the structure function and behaviour of living things particularly because they have such enormous influence on the biochemical phenomena phenomena from genetically programmed activities to physical appearance that characterize organisms Of the small molecules nucleic acids are among the most fundamental They combine to form an organism’s genetic code therefore they determine an organism’s genetic makeup which in turn governs governs physical makeup Nucleic acids are also the molecules of evolution susceptible to change in response to environmental factors thereby enabling adaptation and survival For life to persist after becoming established there must have been polymers polymers long-stranded molecules capable of replicating 8
glucose a sugar glycine an amino acid myristic acid a fatty acid adenine triphosphate ribose adenosine triphosphate a nucleotide Examples of members of the four families of small organic molecules sugars e g glucose amino acids e g glycine fatty acids e g myristic acid and nucleotides e g adenosine triphosphate or ATP 9
replicating or making copies of themselves Presumably these first self-replicating polymers were like nucleic acids Once polymers could replicate those best able to cope with their surroundings survived After certain other basic adaptations were achieved the most primitive cells arose From then on only natural selection was needed to give rise to the many species species that would inhabit Earth The fundamental component of a gene is DNA a nucleic acid made up of two strands of biochemical units called nucleotides Each nucleotide consists of a phosphate deoxyribose a sugar and one of four nitrogen-bearing bases adenine guanine cytosine or thymine Chemical bonds connect bases on one strand with bases on the other forming base pairs The molecule resembles a ladder with the two DNA strands for sides and chemical bonds forming steps The nucleotide ladder winds around itself forming a double helix Equally important for cell and organ function is ribonucleic acid RNA This nucleic acid is markedly similar to DNA except for three key features RNA consists of a single strand except in some viruses in RNA the nucleotides contain ribose instead of deoxyribose and the base uracil replaces the thymine found in DNA The information locked in the genetic code of nucleic acids is translated into amino acids a molecular form that renders genetic information more accessible to cells All living organisms from 10 EXAMINING BASIC CHEMICAL MOLECULES
INTRODUCTION protozoa to plants and animals have in common the fact that they synthesize protein by using the same 20 amino acids even though more than 100 different amino acids occur in nature If proteins are the bricks from which the body is made then amino acids are the grains of sand and clay that make up those bricks Amino acids are defined chemically by the presence of an amino group which is made up of a nitrogen atom and two atoms of hydrogen NH2 as well as carbon C and oxygen O These amino acids join together to form proteins with the sequence in which they join being a direct translation translation of the sequence of the nucleic acids from which they were formed Examples of proteins created by amino acids include keratin the principal component component of hair egg albumin present in egg whites casein a major milk protein enzymes venoms hormones and other molecules of special biological activity Most of the common proteins contain more than 100 amino acids For example hemoglobin the oxygen-carrying component of blood is made of 287 amino acids arranged into four chains Proteins because they inherit the nitrogen N molecules of amino acids are characterized as nitrogenous compounds They are an extraordinarily diverse group of molecules and serve many different functions within cells Many proteins are enzymes compounds that accelerate chemical reactions in and around cells By following the instructions 11
