“Chromatin” is the combination of DNA and proteins that make up the contents of the nucleus of a cell. To define another way, Chromatin is DNA wound tightly around proteins called histones. The primary functions of chromatin are 1) to package DNA into a smaller volume to fit in the cell, 2) to strengthen the DNA to allow mitosis (splitting of chromosomes), 3) to prevent DNA damage, and 4) to control gene expression and DNA replication. The primary protein components of chromatin are histones that compact the DNA. Chromatin is only found in eukaryotic cells. DNA or deoxyribonucleic acid is a double helix structure containing genetic materials. Combination of a base such as adenine (A), thymine (T), Guanine (G) and Cytosine (C) and sugar and phosphate is called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. This looks like a twisted ladder and the base pairs form the rungs of the ladder, (A) paring with (T) and (G) paring with (C) and the sugar and phosphate molecules form the sides of the ladder. When a cell is getting ready to divide, the chromatin coils and condenses into individual, distinguishable chromosomes. Because the nuclear envelope consists of two bilayer membranes, there is a space between these two membranes called a lumen. The importance of chromatin lies in the fact that DNA assumes this form when the cell is ready to divide, as opposed to its loose counterpart, chromosomes, which are used for the process of transcription, a process by which a RNA (ribonucleic acid) molecule is made using DNA template. Only during the cell division the chromosomes are visible.
Humans normally have 23 pairs of chromosomes, for a total of 46. Twenty-two of these pairs, called autosomes, look the same in both males and females. The 23rd pair is called the sex chromosomes and differs between males and females. Females have two copies of the X chromosomes or XX, while males have one X and one Y chromosomes. It is interesting to note here that sperms do not pass on mitochondria to the offspring; the mitochondrial DNA comes from the mother. Y-chromosome comes only from the father in which case the child will be a boy.
How are proteins synthesised? The building blocks of proteins are amino acids, which are small organic molecules. The journey from gene to protein is complex and tightly controlled within each cell. It consists of two major steps: transcription and translation. Together, transcription and translation are known as gene expression. During the process of transcription, the information stored in a gene’s DNA is transferred to a similar molecule called RNA in the cell nucleus. The type of RNA that contains the information for making a protein is called messenger RNA (mRNA) because it carries the information, or message, from the DNA out of the nucleus into the cytoplasm. Translation, the second step in getting from a gene to a protein, takes place in the cytoplasm. The mRNA interacts with a ribosome (already discussed above), which “reads” the sequence of mRNA bases. Each sequence of three bases, called a codon, usually codes for one particular amino acid. A type of RNA called transfer RNA (tRNA) assembles the protein, one amino acid at a time. Protein assembly continues until the ribosome encounters a “stop” codon, a sequence of three bases that does not code for an amino acid. The flow of information from DNA to RNA to proteins is one of the fundamental principles of molecular biology. It is so important that it is sometimes called the “central dogma.”
The discovery of the double helix structure of DNA put an end to an age-old debate if life has some magical mystical essence or it is just the product of physical and biochemical processes. Now all serious scientists, even those religiously inclined agree that life is just the matter of physics and chemistry. DNA contains the genetic materials and directs use of energy that a cell needs to sustain itself. DNA self-replicates according to instructions contained in genes as computer viruses and worms self-replicate. DNA performs tasks to sustain life through productions of proteins, life’s active molecules. These proteins form enzymes that catalyze biochemical reactions and they also provide the body’s major structural components like keratin, of which skin, hair and nails are made. Cells communicate with each other via small signalling molecules that are produced by specific cells and received by target cells. This communication system operates on both a local and long-distance level. The signalling molecules can be proteins, fatty acid derivatives, or gases. Nitric oxide is an example of a gas that is part of a locally based signalling system and is able to signal for a human's blood pressure to be lowered. Hormones are long-distance signalling molecules that must be transported via the circulatory system from their production site to their target cells.
According to one theory, many symbiotic cells join together to form multicellular organisms. The human body maintains a steady internal environment for the proper functioning of the body. Maintaining a constant internal environment requires the body to make many adjustments. Adjustments within the body are referred to as regulation of homeostasis. Homeostatic regulation comprises three parts: a receptor, a control center (brain) and an effector. The receptor functions by receiving information about any changes that are occurring in the environment while the control center processes that information and the effector executes the commands of the control center by making changes in response. The whole organ system of the body works in tandem to maintain homeostasis within the body. DNAs, especially human DNAs are fitting examples of how nature or evolutionary processes create molecules that possess so much remarkable feats as to store instructions to sustain human lives, pass on one copy each of two persons’ (a male and a female) DNA to form a one-celled human embryo that splits up, grows and becomes a human being simple by following the instruction in genes. While genes contained in DNA molecules store instruction for life to originate (reproduction), grow and function, the study of genome is not the only way to control various maladies that we suffer from. As I have said earlier, a cell does all the tasks through proteins produced from genetic instructions following processes we know as transcription and translation. Therefore, the study of proteomics and transcriptomics are very important to learn how our body reacts to environmental cue. As for example, C- reactive protein in the blood is the marker of inflammation in the body. Defective or mutated genes will produce wrong proteins to perform tasks that are injurious to our health. Transcriptomics can tell us where and when genes are expressed thereby giving us clues if a mutated gene is going to be expressed and how we can fix it. Many branches of science emerge in the post-genome era to deepen our knowledge how we inherit genes, how they are expressed and how are proteins produced normally and how some are produced to respond to environmental cue, sometimes good and at times bad.
Another branch named metabolomics, which is the study of chemical processes involving metabolites (byproducts of metabolism), determines how our metabolic functions advances and if there is any malfunction. Many bloods tests are now available to understand how healthy a person is by studying some of the proteins and metabolites in the blood. Gaining knowledge is the only way we can keep track of what is happening in the scientific arena and how we can take advantage of them.
The writer is a mathematician and a former ambassador
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