Cellular and Molecular Basis of Human Biology
Lawrence S. Chan, William C. Tang in Engineering-Medicine, 2019
The human genome is consisted of 20,000 different genes and nucleic acids composed of 3 billion base pairs (Green et al. 2015). For the basic components of nucleic acid, the nucleotides, there are only 4 distinct nitrogenous bases: adenosine (short for A), thymine (T), guanine (G), and cytosine (C) and each nucleotide also contains a phosphate group and a sugar deoxyribose. One interesting and important fact is that virtually all differentiated cells have the identical and entire genome. Yet some proteins are produced by certain cell types and not by other cell types. The key factor is transcriptional factors, which function to bind to promoter region of DNA in initiating mRNA transcription. The binding of transcriptional factors enables the binding of RNA polymerase to DNA for the transcription. Activation and inactivation of certain transcriptional factors during human development determine the ability and inability to express certain proteins, and by extension their phenotype expressions, respectively (Hillis et al. 2014). Another interesting and also essential fact is that reactivation of cell-specific transcriptional factors could change a cell’s phenotype. For example, transgenic introduction of neuron-specific transcription factors into fibroblasts turn these connective tissue protein-producing cells into functional neurons with characteristic neuronal synapses (Hillis et al. 2014).
Introduction to Cell Biology
Anthony R. Mundy, John M. Fitzpatrick, David E. Neal, Nicholas J. R. George in The Scientific Basis of Urology, 2010
Deoxyribonucleic acid (DNA) is a polymer of single nucleotides linked by phosphodiester bonds. Nucleotides consist of a five-carbon sugar with a phosphate group attached to carbon 5 and a purine or pyrimidine base attached to carbon 2 (Fig. 1B). There are four nucleotide bases—thymine, cytosine, adenine, and guanine—and the nucleotide itself is often referred to as the base subunit that it contains. RNA, or ribonucleic acid, also comprises these bases except for thymine, which is replaced by uracil. Nucleotides are arranged as two complimentary antiparallel strands in a double helix and the order in which they are linked is referred to as its primary structure. In the cell nucleus, DNA helices are tightly coiled into protein-associated chromosomes, whereas RNA exists predominantly as single-stranded polymers and are found both in the nucleus and cytoplasm.
Biological Basis of Behavior
Mohamed Ahmed Abd El-Hay in Understanding Psychology for Medicine and Nursing, 2019
A strand of DNA serves as a template for the synthesis of ribonucleic acid (RNA) molecules. There are four types of RNA, each encoded by its own type of gene. Messenger RNA serves as a template for the synthesis of protein molecules. DNA contains four bases (adenine, guanine, cytosine, and thymine). The order of those bases determines the order of corresponding bases along an RNA molecule (adenine, guanine, cytosine, and uracil). In turn, the order of bases along an RNA molecule determines the order of amino acids that compose a protein, e.g., if three RNA bases are, in order, cytosine, adenine, and guanine, then the protein adds the amino acid glutamine. If the next three RNA bases are uracil, guanine, and guanine, the next amino acid on the protein is tryptophan. In total, proteins consist of 20 amino acids, and the order of those amino acids depends on the order of DNA and RNA bases.
Chromosome aberration in typical biological systems under exposure to low- and high-intensity magnetic fields
Published in Electromagnetic Biology and Medicine, 2020
Emanuele Calabrò, Hit Kishore Goswami, Salvatore Magazù
Chromosomes are molecules composed of the deoxyribonucleic acid (DNA) that represents the genetic material of a living being. In human beings, there are 22 pairs of chromosomes and 2 sex chromosomes for a total of 46. DNA is an organic polymer composed of monomers that are called nucleotides. They consist of a phosphate group and a nitrogenous base linked to deoxyribose by the so-called N-glycoside bond. The nitrogenous bases that can be used in nucleotide formation are adenine, cytosine, guanine and thymine disposed in base pairs of adenine-thymine (A-T) and guanine-cytosine (G-C) that in aqueous solutions are linked one each other by hydrogen bonds forming a double helix structure because of the repulsions between the negative charge of phosphate groups. This double helix structure is bound to proteins (the histones) that have positively charged amino acids in order to bind the DNA which is negatively charged and is wrapped around the core of histone of eight protein subunits forming the nucleosome. About 200 base pairs of DNA are coiled around each histone. This coil is untwisted generating a negative superturn per nucleosome that is the active chromatin.
siRNA: an alternative treatment for diabetes and associated conditions
Published in Journal of Drug Targeting, 2019
Ribonucleic acid (RNA) consists of a single stranded linear structure has crucial role in regulation and expression of specific gene and also stores genetic information. RNA structure consists of four ribonucleotide base pairs namely, adenine, guanine, cytosine and uracil in which purines like adenine and guanine binds which complementary pyridines like uracil and cytosine, respectively [8]. RNA is classified into three types, messenger RNA (mRNA), ribosomal RNA (rRNA) and transfer RNA (tRNA) which are involved in protein synthesis in human body, whereas RNA like short interfering RNA (siRNA) and micro RNA (miRNA) are mainly involved in regulation and expression of genes. Both siRNA and miRNA are similar in their structure as well as in their function of silencing and regulation of gene expression by binding with complementary messenger RNA (Figure 2). In contrast, they differ in their mechanism of action and also siRNA targets only one specific mRNA while miRNA has multiple complementary targets [9].
Comprehensive overview of the recently FDA-approved contraceptive vaginal ring releasing segesterone acetate and ethinylestradiol: A new year-long, patient controlled, reversible birth control method
Published in Expert Review of Clinical Pharmacology, 2019
The most critical component that accounts for the success of this new CVR is the new progestin segesterone acetate. Segesterone acetate is a 19-nor-progesterone derivative, known as 19-norpregn-4-ene-3,20-dione, 17-hydroxy-16-methylene-19-nonpregn-4-ene-3,20-dione acetate ester and 16-methylene-17α-acetoxy-19-nor-pregn-4-ene-3,20-dione (see Figure 3). Its molecule formula is C23H3004 (see Figure 3). It is a white or yellowish-white powder with a molecular weight of 370.5 Dalton. This compound has significant potency; only low doses are needed for ovulation suppression. However, it is rapidly metabolized when administered orally, so a slow release, transdermal or transmucosal delivery system, such as the contraceptive vaginal ring, represents an excellent delivery system to utilize its strengths [11].