There are 4 main macromolecules that make up life on Earth. In the following paragraphs I will talk about nucleic acids, lipids and carbohydrates. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essay There are 2 structures of nucleic acids, which are DNA, or deoxyribonucleic acid, and RNA, or ribonucleic acid. Both of these molecules are composed of monomers called nucleotides that bond covalently to form a polymer. Nucleotides are composed of three basic functional groups, a phosphate group, a nitrogen base and a pentose. DNA is made up of 5-carbon pentose or deoxyribose sugar which is covalently linked to a phosphate group. This phosphate group is covalently bonded to a nitrogen base. There are 5 nitrogenous bases, however, DNA is only made up of 4 of them, namely adenine, thymine, cytosine and guanine. Adenine and cytosine are purines, which means they are made of 2 nitrogen rings. Thymine and guanine are pyrimidines because they both have a single nitrogen ring. As a polymer, DNA has a double helix, because DNA is made up of 2 chains of nucleotides, linked by phosphodiester bonds, which are held together by hydrogen bonds formed between purines and pyrimidines on opposite chains . On the other hand, RNA is different from DNA. RNA, instead of containing the nitrogenous base Thymine, it contains Uracil, which is also a pyrimidine. Additionally, RNA is a single-stranded polymer, meaning it does not form hydrogen bonds with any other strand in its normal state. Two examples of molecules belonging to nucleic acids are chromosomes and transfer RNA or tRNA. Chromosomes are condensed DNA structures wrapped around histone proteins. It is these molecules that have the information necessary to synthesize the proteins that will give a cell its phenotype. Additionally, chromosomes contain the information to determine a person's sex as male or female. This is generally stored in the last pair of chromosomes. In fact, chromosomes contain alleles, which are alternative forms of genes coding for a specific trait. Another example of a molecule that is a nucleic acid is transfer RNA. These molecules perform the function of reading the triplet of mRNA that enters the ribosome to be translated into protein and bringing one of the 20 types of proteins that match the codon with the anticodon. Thus, tRNA is able to help the ribosome synthesize a polypeptide. Lipids, another type of macromolecule, are composed primarily of carbon, oxygen, hydrogen, and phosphorus. There are types of lipids: phospholipids, steroids and fats. The main monomers of lipids are glycerol and fatty acids. Fatty acids are hydrocarbon chains: carbon chains either saturated with hydrogen atoms. Sometimes hydrocarbons can be saturated, in which two hydrogens are produced or not and the two adjacent carbon atoms form a double bond. At the end is a carboxyl group. Glycerol is a type of alcohol composed of three carbons with a hydroxyl attached to one end and a hydrogen to the other. These two bonds bond by forming covalent ester bonds between the hydroxyl of the carboxyl group of the fatty acid and the hydrogen through dehydration synthesis. When three fatty acids are attached to a glycerol, the remaining molecules are called triglycerides. In short, steroids are formed in a carbon ring structure,.