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The Law

Belief - III

Our Cellular Biology - II

A cell needs to spend a lot of energy to maintain its constituents for its survival. An estimate is that a cell spends 30% of its energy for maintaining the constituents of its cytoplasm. 

The typical constituents of cytoplasm are illustrated in the diagram. The 30% part of the cytoplasm consists of various organic molecules and organelles. An organelle is a part of cell that has a specific function. The name organelle comes from the idea that these structures are to a cell what an organ is to a human body. Organelles have their own membrane separating them from the rest of the cytoplasm. The major classes of the organic molecules include nucleic acids, proteins, carbohydrates, and lipids all of which are essential to the cell's function. 

The nucleic acids are large bimolecules essential for all forms of life. Nucleic acids, which include DNA and RNA, are made from nucleotides.

Nucleic acids are the molecules that contain the genetic code of the cell. The two major classes of nucleic acids are Deoxyribonucleic Acids (DNA) and Ribonucleic Acid (RNA). 

The diagram shows the configuration of DNA and RNA. 

DNA molecules contain all information required to maintain the cell. RNA is associated with expressing the information stored in DNA. The nucleic acid molecules are not the only molecules which preserve and express the genetic material. The protein molecules are also used by the cells to help replicate the genome accomplish the profound structural changes that underlie cell division. 

A genome is an organism's complete set of DNA, including all of its genes. Each genome contains all of the

information needed to build and maintain that organism. In humans, a copy of the entire genome — more than 3 billion DNA base pairs — is contained in all cells that have a nucleus. Our bodies contain 50 trillion or more cells with their own set of instructions for making us, like a recipe for the body. This set of instruction is known as the Genome. Each cell in the body, a skin cell of a liver cell, contains the same set of instructions. While explaining Genome, a diagram is illustrated alongside. In this diagram two new terms are indicated - Genes and Chromosomes.  As we have understood earlier, DNA is the chemical information database that carries the complete set of instructions for the cell as to the nature of the proteins produced by it, its life span, maturity, function and death. Genes are the working sub-units of DNA. Each gene contains a particular set of instructions, usually coding for a particular protein or for a particular function. The DNA in each chromosome constitutes many genes. The DNA also contains large sequences that do not code for any protein and their function is not known. 

Every human cell has 46 molecules of double-stranded DNA in the nucleus. This DNA is coiled and supercoiled to form chromosomes. Each chromosome has around 50 to 250 million bases.Human cells contain two sets of chromosomes, one set inherited from the mother and one from the father. The egg from the mother contains half of the 46 (23) and the sperm from the father carries the other half 23 of 46 chromosomes. Together the baby has all 46 chromosomes. 

We will examine the term nucleotide before we revert to the other cytoplasm constituents.

A nucleotide is one of the structural components, or building blocks, of DNA and RNA. A nucleotide consists of a base (one of four chemicals: adenine (A), thymine (T), guanine (G), and cytosine (C)) plus a molecule of sugar and one of phosphoric acid.

If you look at teh structure of the double-helix of DNA, you will see that the two long stacks of building blocks fit together like a zipper, but there's a rule involved. (A) can only pair with (T), and (C) can only pair with (G). So each rung in the DNA structure is a pair of nucleotides and each pair  is either an (A) stuck into (T), or a (G) mating with (C).

Each of your cell has six billion pairs of nucleotides, and among these six billion pairs of nucleotides are roughly 23000 genes. To recapitulate, a gene is a distinct stretch of DNA that determines something about who you are. Genes vary in size from just over a few thousand pairs of nucleotides to over two million pairs of nucleotides or base pairs.

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Prabir

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