Pyrimidines: The Basic Structure Of DNA And RNA

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1. Pyrimidines are heterocyclic aromatic amines which, together with purines, form nucleotides. Nucleotides are the building blocks of nucleic acids, the basic structural component of DNA and RNA. The pyrimidines in DNA are cytosine and thymine, and in RNA uracil replaces thymine (Bettelheim, Brown, Campbell, Farrell & Torres, 2013). 
DNA and RNA are found in the nuclei of all cells and their job is to transmit the information needed for cellular growth and reproduction (Averill & Eldredge, 2007).

2. The number of carbons and the branching determines the boiling point, where the higher of either increases the boiling point. The reason behind this is hydrogen bonding (Clark, 2003). In ethanol there is an -OH group present. The oxygen pulls
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Phospholipids, such as lecithin, make up the basic structure of cell membranes and are the major constituents (Whitney et al., 2014). They consist of two groups, a head and a tail group. The head contains a hydrophilic phosphate group (meaning “water loving”, attracted to water). 
The tail group is made up of two strings of hydrogen and carbon atoms, called fatty acid chains (Cooper, 2000). These chains are hydrophobic, meaning they do not like to interact with water molecules. Because of this, phospholipids of a cell membrane form a double layer, where the hydrophilic ends are exposed to both the extracellular fluid and the intracellular fluid, and the hydrophobic tails are buried within the membrane to avoid contact with water (Cooper, 2000). This arrangement represents the formation of cell membranes and is referred to as the lipid bilayer (Cooper, 2000). Because phospholipids are amphipathic molecules, meaning both water-soluble and water-insoluble, they can help lipids move back and forth across the cell membranes into the watery fluids on both sides (Cooper, 2000). This enables fat-soluble substances, including vitamins and hormones, to pass in an out of cells easily (Whitney et al., 2014).

Sterols, and more specifically cholesterol, also have an important role in maintaining cell membranes (Whitney et al., 2014). Cholesterol are found among the hydrophobic tails in the lipid bilayer, where it function as a structural component and strengthens the membrane by preventing some small molecules from crossing. Cholesterol also prevent the tail ends of the phospholipids from interfering with each other, thereby maintaining membrane fluidity at lower temperatures (Cooper,

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