The document discusses gene expression and RNA. It describes that gene expression involves two steps - transcription of DNA into mRNA in the nucleus, and translation of mRNA into proteins by ribosomes. There are three main types of RNA - mRNA, rRNA and tRNA. rRNA makes up the majority of RNA and is a component of ribosomes. tRNA helps translate mRNA codons into amino acids during protein synthesis. The genetic code uses three nucleotide mRNA codons to specify the twenty amino acids used to build proteins. Reverse transcriptase was an important discovery as it showed RNA can be converted to DNA, modifying the central dogma that DNA does not influence proteins.
18. An important discovery
Retro viruses (e.g.
HIV) carry RNA as
their genetic
information
When they invade
their host cell they
convert their RNA into
a DNA copy using
reverse
transcriptase
Thus the central dogma is modified:
DNA↔RNAProtein
This has helped to explain an important paradox
in the evolution of life.
Image Credit:
Reverse transcriptase