(a) Transcription
The process of copying genetic information from one strand of DNA into RNA.
It follows the principle of complementarity, except that adenine now pairs with uracil instead of thymine.
Only a segment of the DNA, and only one strand (the template strand, polarity $\displaystyle 3$'→$\displaystyle 5$'), is copied — a transcription unit is defined by a promoter, a structural gene and a terminator.
It is catalysed by DNA-dependent RNA polymerase in three steps — initiation, elongation and termination; in bacteria a single RNA polymerase does all three, associating transiently with the initiation factor (σ) and the termination factor (ρ).
In eukaryotes there are three nuclear RNA polymerases (I for rRNAs, II for hnRNA, III for tRNA, 5srRNA and snRNAs), and the primary transcript must undergo splicing, capping and tailing before it leaves the nucleus as mRNA.
(b) Polymorphism
Variation at the genetic level, arising from mutations in somatic or germ cells.
An allelic sequence variation is formally called a DNA polymorphism if more than one variant (allele) at a locus occurs in the population with a frequency greater than $\displaystyle 0.01$.
Germ-cell mutations that do not impair reproduction spread through the population and keep accumulating generation after generation.
Polymorphism is more likely in non-coding DNA, where a mutation has no immediate effect on an individual's reproductive ability.
It ranges from single nucleotide changes (SNPs) to very large-scale changes, and is the basis of genetic mapping of the human genome, DNA fingerprinting, evolution and speciation.
(c) Translation
The polymerisation of amino acids to form a polypeptide, in the order and sequence dictated by the bases of the mRNA.
Amino acids are first activated using ATP and linked to their cognate tRNA — charging of tRNA (aminoacylation).
The ribosome is the site: the small subunit binds the mRNA, and translation begins at the start codon AUG, recognised only by the initiator tRNA.
During elongation, charged tRNAs bind the appropriate codon by codon–anticodon base pairing, the ribosome moves codon to codon, and peptide bonds form (catalysed by the 23S rRNA ribozyme in bacteria).
A release factor binds the stop codon, terminating translation and releasing the finished polypeptide.
The translational unit lies between the start and stop codons and is flanked by untranslated regions (UTRs) at the $\displaystyle 5$'- and $\displaystyle 3$'-ends, which are needed for efficient translation.
(d) Bioinformatics
A new area of biology whose rapid development was closely associated with the Human Genome Project.
The HGP generated an enormous amount of sequence data, which made high-speed computational devices necessary for its storage, retrieval and analysis.
Specialised computer-based programs were developed for tasks that were humanly impossible — for example, aligning millions of sequenced fragments using their overlapping regions, and annotating the sequence to assign functions to different regions.
In short, it applies computational tools to biological data such as DNA and protein sequences.