Basics of Genetics  

Genetics is the scientific study of how living organisms pass on their features from one generation to the next. This word was ‘invented’ in 1906 by the British biologist William Bateson.  Since the discovery of the genetic code in 1966, research into this view has broadened our understanding of the structure of life, and in controlling protein production in modern biology and biotechnology.

Chromosomes, DNA and Genes

            Every one of us, except identical twins or clones, has a unique set of DNA, or a genome, which in part is what makes us separate individuals.  Inside each of our cells’ nuclei, we have 23 pairs of chromosomes, and one in each pair is inherited from one of our parents.  The thread-like chromosomes contain all our genetic information.  DNA (deoxyribonucleic acid) molecules make up most of a chromosome and are the genetic material for all cellular organisms and most viruses.  They act as the message carriers of chemical sequences governing the production of proteins.  Such patterns are the genes, and all together they make up the blueprint of life.

            DNA has the spiral shape of the famous ‘double helix’.   Like a ladder, it consists of two strands made up of sugars and phosphate groups, connected with base pairs (the rungs).  There are four nucleotide bases, and adenine (A) will only combine with thymine (T); cytosine (C) always with guanine (G).  Such base pairing means that the two strands are complementary.  (e.g. the complementary strand of A-A-G would be T-T-C).  DNA strands has a ‘beginning’ and an ‘end’.  One side has a phosphate, and is called the 5’ end, while the other side without the phosphate is the 3’ end.  Each strand goes in opposite directions, i.e. they are antiparallel. These (the bases) letters of the DNA alphabet arrange themselves in DNA and RNA in three-letter-words, called codons.  Codons instruct the cell into the production of specific amino acids, which form into proteins, the basic material of life. 

Click for a diagram of the DNA structure

            In a human cell, each DNA molecule contains about 3 billion base pairs, or genes, paving the way for countless genetic instruction groups.  Scientists define a gene as ‘the discrete instructions for making a single protein’.  In detail, a gene is the DNA sequence encoding a protein; starting with a ‘start’ codon and ending with a ‘stop’ codon. 

RNA and central dogma

            RNA, another nucleic acid commonly found in the cytoplasm, is a ribonucleic acid sequence created from DNA, and is nearly identical to one of the strands of DNA.  This is the strand of DNA that serves as a template to both its own replication and also the production of messenger RNA (mRNA), the process of which is known as transcription.  The only difference between mRNA and the template DNA is that in kRibonucleic Acid, thymine is replace by uracil.  RNA is produced from DNA by an enzyme called RNA polymerase. 

            The mRNA moves from the nucleus to the ribosome of the cell.  Translation, the synthesis of proteins from mRNA, will then occur in the ribosome.  The transfer RNA (tRNA) binds the specific amino acids to the corresponding codons.  The ribosome helps bind the amino acids into a chain – and a protein is formed.      

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