This post was written by James after his successful Radley Scholarship exams.
Genes are the sub-structures of DNA. DNA is a molecule which stores the information for the making of all the proteins that a cell will need. Usually, a single gene only codes for a single protein.
A DNA molecule consists of two strands which spiral, forming the double helix. Every strand of DNA is made up of millions of tiny building blocks, these are called bases. There are four different chemical bases in DNA, these are Adenine, Thymine, Cytosine and Guanine (A, T, C, G).
DNA is kept in the core of a cell’s nucleus (if the cell is eukaryotic ie has a nucleus); however, if a cell is prokaryotic (doesn’t have a nucleus, like bacteria), then the DNA strands are just left free-floating in the cell. In a human cell, there are 46 double strands of DNA. Each molecule is made of 50-250 million bases which are all stored in a chromosome. However, as well as the DNA that actually makes up for a certain characteristic, some of the DNA in a chromosome is inactive, meaning that they do not apply to any characteristic, but can be switched back on (Chickens have genes for teeth, but it is an inactive gene). Chromosomes also contain very large stretches of non-coding DNA, whose uses are unknown; most of these DNA stretches exist because of viruses which have inserted their DNA into a cell during an infection.
Genes are put in the places they are put for a purpose. A gene is put in a certain segment of DNA which has encoded instruction to produce a product, usually a protein such as an enzyme that performs a specific function. Humans have roughly 20,000 genes which are made up of thousands of chemical bases.
A human inherits two sets of chromosomes, one from its father and one from its mother. This is because mature sperm and egg cells only have half the amount of chromosomes. Females inherit an X chromosome from each parent, but a male inherits a Y chromosome from the male parent and an X chromosome from the female parent.
For a cell to make protein, the information from a gene is copied, base by base, from DNA into new strands of messenger RNA (mRNA). Then mRNA travels out of the nucleus into the cytoplasm, to cell organelles called ribosomes. There, mRNA directs the assembly of amino acids that fold into completed protein molecule.
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