Quiz 14: From Dna to Protein


Following are the steps involved in the conversion of a nucleotide sequence to amino acid sequence. 1. Write the complementary bases for the given nucleotide sequence in order to complete the DNA sequence. 5' GGTTTCTTCAAGAGA 3' 3' CCAAAGAAGTTCTCT 5' (complementary base sequence) 2. Now consider previous half of the DNA sequence and replace its bases as per the bases couples involved in mRNA. (G-C/A-U) 5' GGTTTCTTCAAGAGA 3' 3' CCAAAGAAGUUCUCU 5' (mRNA) 3. Below given mRNA sequence enters the ribosome and then further band into transfer RNA sequence. 5' GGUUUCUUCAAGAGA 3' (mRNA) 3' CCAAAGAAGTTCUCU 5' (tRNA) 4. Through tRNA sequence we can easily decode the amino acid sequence (codon), because it is responsible for carrying the amino acids to the ribosome. Here, each pair of three bases in the tRNA sequence carries an amino acid that codes for a particular amino acid. After pairing them, we make use of a codon table in order to identify the codons and produce an amino acid sequence. 5' GGU UUC UUC AAG AGA 3' (mRNA) 3' CCA AAG AAG TTC UCU 5' (tRNA) img img img img img Amino acids img GFFKR (Amino acid sequence) 5. Therefore, the above sequence represent amino acid sequence and the codons present in the amino acid sequence are glycine (G), phenylalanine (F), phenylalanine (F), lysine (K) and arginine (R).

DNA is neither transcribed to only mRNA nor to proteins. DNA are first transcribed to RNA and then translated to proteins. Therefore, the option (a.) and (b.) both are incorrect. DNA represents the genetic material of organisms that doesn't codes for protein directly, but indirectly through transcription and translation. It contains many different gene regions which are transcribed into different mRNA, tRNA and rRNA. Hence, the correct option is c. mRNAs, tRNAs, rRNAs.

In this case due to wrong base pairing, an error has been caused in the DNA strand by the DNA polymerase. As the DNA strand has already undergone replication, but the error in the DNA strand can also be corrected immediately after replication through a process other than basic repair mechanism, regarded as mismatch repair, which is used when single bases in the DNA are mismatched due to errors during replication as discussed in this case. These alterations are handled by very short patch excision repair. Like in this case, a G-T pair is being produced. Products of the genes MutS and MutL (mutator genes involved in repair system that removes T from G.T and CT mismatches) participate in a very short patch repair system in such a manner that the G-T base pair is restored as G-C base pair. These MutL and MutS system also corrects C-T mismatches.

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