Question

Original DNA sequence (coding strand), starting at the beginning of the gene: Normal: 5'-ATGATCTCCTAATACAA... Mutation: 5'-TTGATCTCCTAATACAA... 30. Can a single nucleotide be a conserved sequence? Explain your answer. (4 Points) 31. Explain why self-splicing introns support the RNA world first Hypothesis (life evolved via RNA). (3 Points)

Answer 1

30.

• Mutation is derived from Latin word “Mutare” meaning to change.
• Point mutation may result due to change of one nucleotide with another.

Point mutation may be -

• Transition- conversion of one pair of purine bas to another. Like G-C or A-T or vice versa.

• Transversion- conversion of one pair of purine to pyrimidine. Like A or G to C or T or vice versa.

• In the given sequences, point mutation occurs in the first nucleotide.
• A is converted to T. Thus, it is Transition mutation.
• Thus, converting T back to A will restore the original sequence and mutation may be reversed.

31.

• RNA double-helical structure can slide back to single strand structure, this attributes to flexibility of RNA and the transient structure helps in better modification and allows function as ribozymes.
• Thus, these ribozymes helping in self splicing by which introns are removed, exons are joined to form mature RNA.
• Ribosomes also have catalytic activity as ribozyme.
• During translation, peptidyl transferase activity helps in formation of petide bond.
• 23S rRNA has peptidyl transferase activity.
• Thus, proteins may be created from RNA by ribozyme activity.
• This theory explains the alternate hypothesis of life created from RNA.
• Such concept of RNA world was proposed by Alexander Rich.