Another group of lipids is based off of isoprenoids, which are the building blocks of sterols (such as cholesterol). Glycerophospholipids and sphingolipids are essential constituents of cellular plasma membranes. Glycerolipids (triacylglycerols) are important for energy storage and thermal insulation. In addition, combining fatty acids with different bases, including glycerol, phosphate, and shingosine, results in different lipids with varied functions within the human body. Eicosanoids are a family of cell-signaling molecules with important physiologic properties derived from the fatty acid, arachadonic acid. Fatty acids are integral building blocks of lipids, and can be classified as unsaturated or saturated based on the presence/absence of carbon-carbon double bonds within their nonpolar chains. Lipids are a diverse group of hydrophobic organic molecules, which include fats, oils, sterols, and waxes. Degradation of nucleotides result in xanthine then uric acid production in purines, while pyrimidines produce the amino acids, β-alanine, and β-aminobutyrate. For thymine, a part of deoxyribonucleotides, ribonucleoside reductase is required to reduce the ribose moiety. Synthesis of pyrimidine nucleotides also follows different reactions, producing uridine monophosphate (UMP), which is converted to uridine triphosphate (UTP) and cytidine triphosphate (CTP). Purine synthesis is regulated in the 1st 2 steps. The de novo pathway generates inosine monophosphate (IMP), which is the precursor of adenosine monophosphate (AMP) and guanosine monophosphate (GMP).
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Purine nucleotide synthesis follows a series of reactions using carbon donors, amino acids (e.g., glutamine, aspartate), and bicarbonate. Purines include adenine and guanine, while pyrimidines include thymine (in DNA), uracil (in RNA), and cytosine. Purines and pyrimidines are heterocyclic aromatic compounds, which, along with sugar and phosphate groups, form the important components of nucleotides.
Compared with karyotyping, FISH is much more sensitive and specific in determining several abnormalities (except for point mutations) but is limited by the currently available gene probes. Fluorescence in situ hybridization utilizes fluorescent probes to identify and locate specific genes on chromosomes. However, chromosomal microarray analysis is not useful in identifying certain variations such as balanced translocations. Chromosomal microarray analysis is a comparative technique that utilizes fluorescence to identify and quantify specific genetic sequences and is much more sensitive in identifying copy number variants, such as microdeletions or microduplications. Karyotyping is not sensitive in identifying small abnormalities and is a labor-intensive process. Karyotyping is the staining, organization, and visualization of chromosomes, which can help identify aneuploidy and major structural changes. Chromosomal testing can be accomplished using several techniques, all of which can identify chromosomal abnormalities.
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