Question

a) The discovery of ribozymes led to the theory that the evolution of life on Earth began with an “RNA world.” Describe how the current cellular roles of RNA support this theory.

b) Draw a diagram of the transcription and translation of the trp operon under high tryptophan conditions. In addition to the trp operon, show RNA polymerase; the 5` UTR RNA with regions 1, 2, 3, 4, and the string of uracils; and a ribosome.

Answer 1

a.

RNA performs all the activities of proteins synthesis and control of protein synthesis. Proteins are very essential for every bodily activity in the living system. SO RNA by acting as both enzyme and able to synthesise proteins it is considered to have evolved first than the DNA since DNA has only the role of storing genetic information.

RNA can carry the genetic information stored in DNA to the cytoplasm in the form of mRNA. The mRNA gets attached to the ribosomes which are made of rRNA. Ribosomes bind to mRNA at its 5' end start reading the genetic code along with tRNA. The tRNA bring amino acids to ribosomes where protein synthesis is occurring. The amino acids now are joined ot each other to form a protein. The triplet codons are complimentary to the anticodons present in the tRNA. This helps in bringnging an appropriate amino acid to the ribosomes which are bound by peptide bond to form proteins.

An enzyme present in the ribosomes called rhibozyme is also essential during the protein synthesis. So all the jobs of protein synthesis are done by RNA. The role of DNA is only to store the genetic information with out causing any changes. In some viruses RNA also functions as the genetic material storing the genetic codons in the cells.

That is why DNA can't be considered as the molecule that has evolved first. If DNA has evolved first, other jobs of protein synthesis would not be possible with DNA. DNA also does not function as an enzyme like RNA. Protein synthesis also needs some enzymes.

Because the RNA is able to synthesize proteins and also function as enzyme and store genetic information in organisms like viruses, RNA world theory seems right.