Question

1.What is the function of insertion mutations? How can it be harmful?

2. please explain what ORFs are and the role that they play?

3. How does exon shuffling play a role in evolution?

Answer 1

Ques-1.What is the function of insertion mutations? How can it be harmful?

A frame shift mutation is often result in the change in the reading frame either with deletion or insertion of the nucleotide bases and further mutation- induced codons code for different amino acids and truncated protein formation. Insertion of single base pairs in DNA results in frame shift mutations; the reading frame shifts at the point of mutation and results in non-functional proteins with amino acids. Mutagens have the capability to alter the DNA sequences by insertions as a result alterations in nucleic acids. Insertion mutations may produce cell death by producing influential changes in transcription and translation processes, which is harmful to the host body.

Transposon insertion: A few mutagens induced into the coding exon region of gene thereby insertion of new bases or deletion of the bases. Finally result in generation of truncated protein.

DNA rearrangement-insertional mutagenesis: Insertions of nitrogen bases of nucleotide sequences in DNA rearrangement generates cellular oncogenes to cause cancer. These rearrangements are due to exposure of cells to carcinogenic agent

Ques-2. please explain what ORFs are and the role that they play?

A reading frame is defined as the total method of coding sequences associated nucleotides in double helical DNA or single stranded RNA to form a set of constitutive non overlapping triplet codons which code for amino acid. An amino acid can be coded by more than one codon, this strand often possess a 5 prime phosphoryl end and 3’ hydroxyl end (5'→3' direction).

Open reading frame (ORF): It has defined as the reading frame of a gene, which possesses the ability to code for protein (role). It is an open frame, which must start with AUG, or ATG, which further resembles that the chain initiation of peptide started and ends with stop codons, which can be UAA, UAG or UGA.

Role & importance of ORFs in prokaryotes and eukaryotes:

Methionine is starting amino acid coded during translation in both bacteria and animals but N-formyl methionine (f-met) is the initial amino acid in bacteria with ORF and methionine is in eukaryotes.

Prokaryotes and eukaryotes differ with respect to the number of open reading frames that are contained in a typical mRNA in which mainly prokaryotic ORF contains longer than 50 codons (317 codons for Escherichia coli) useful for ORF scanning. Eukaryotic ORF contains approximately more than 400 codons in which majority are CpG islands upstream of many genes with GC content

This difference make sense in view of the translation initiation strategies used by each type of organism. Majority of cis elements in mRNAs are going to “involve in regulating translation” in eukaryotes are AUG codons and these takes place within leader transcript i.e. upstream AUGs. Approximately <10% of eukaryotic mRNA possess “upstream of ORFs” with AUG codons in their leader transcript region (5′ untranslated regions). In case of prokaryotic translation initiation, these ORFs with AUGs are very less and mediate synthesis of N-formymethionine in which no 5′ untranslated regions are existing.

A key regulator turn on a suite of related genes in both prokaryotic and eukaryotes and these genes of mRNA are going to code for peptide products, which potential role in “regulating translation”. For example, in prokaryotes, synthesis of antibiotic resistant enzymes are performed using “short upstream of ORFs” causes ribosome stalling (Shine- Dalnagro’s sequence) at ribosomal peptidyltransferase center once peptide synthesis finished. This sequence is the regulatory sequence in prokaryotic mRNA at 5 prime region. In case of eukaryotes also, similar mechanism of interference occurred due to upstream of ORFs that causes ribosome stalling.