Molecular Basis of Inheritance Test - 87

For cracking the genetic code, different RNA molecules were synthesized Marshall Nirenberg's cell free system for protein synthesis finally helped the protein to be deciphered. A triplet of three nucleotides is read as a codon and an specific amino acid is incorporated against each. For the three stop codons UAA, UAG and UGA no amino acid is incorporated and protein synthesis machinery is terminated.

If a strand of DNA has the following base sequence 3' AAAAGTGACTAGTGA 5', after transcription the mRNA formed will have the sequence 5' UUUUCACUGAUCACU 3'. tRNA are adapter molecules that on one hand read the code and on the other hand would bind to specific amino acids. tRNA has an anticodon loop that has bases complimentary to the code and it binds to codon on the mRNA. The codon anticodon pairing is specific and there are specific tRNAs for each amino acid. There are no tRNAs for stop codons. For initiation, there is another specific tRNA referred to as initiator tRNA. tRNA also has amino acid acceptor end to which it binds to amino acids. The actual structure of tRNA is a compact molecule which looks like an inverted L. But the secondary structure of tRNA looks like a clover leaf. To recognize the third codon of the mRNA produced (as mentioned above in the answer) which is 5' CUG 3' tRNA with a specific anticodon sequence of 3' GAC 5' would be required. Thus, the correct option is C

Heating causes unwinding of dsDNA into a ssDNA molecule by altering the ordered stacking of the bases and breaking their connecting hydrogen bonds. Single stranded DNA do not obey the Chargaff's rule and thus, A : T and G : C ratio can not be taken into consideration. This ssDNA is then studied by comparing the type and number of nucleotides in single strands. Hence, correct option is D.

In the given sequence AUG is the start codon which will initiate the process of translation so it will continue from AUG to CUG because UGA is a stop codon which does not code for any amino acid, other stop codons are UAG & UAA.  

Correct answer: option (B)

Explanation for the correct option: (B)

• A codon is a triplet and encodes a specific amino acid.
  They never overlap.This leads to 4 codons in the mRNA  AUGGCAGUGCCA . the codons are AUG-GCA-GUG-CCA i.e., 4.
• But in the question, it is assumed that they are overlapping. This means that each nucleotide initiates a codon. 
• This leads to a total of 10 codons in the mRNA sequence AUGGCAGUGCCA as AUG, UGG, GGC, GCA, CAG, AGU, GUG, UGC, GCC, CCA. 

Correct Option: C
Explanation:

• The genetic code consists of 64 (4^3) triplets of nucleotides.
• These triplets are called codons. With three exceptions, each codon encodes for one of the 20 amino acids used in the synthesis of proteins.
• That produces some redundancy in the code: most of the amino acids being encoded by more than one codon. 
• So, if evolution on earth has occurred in such a way that there are 96 amino acids instead of 20.
• DNA has 12 different types of bases and DNA synthesis occur in the same way as today.
• The minimum number of bases per DNA codon would be 2 (12^2=144) all the time.

Genome represents the total amount of DNA present in the haploid set of chromosomes. The haploid amount of DNA is also referred to as C-value which is 2.8 picograms or 2.75 X $$10^9$$ basepairs. Since, DNA is a double stranded molecule, the size of genome is given in base pairs which also shows the total number of nucleotides in the genome. Thus, total number of nitrogenous bases in human genome is estimated to be about 3.1 billion. Correct option is "D".

Transcription is when RNA is made from DNA. During transcription, RNA polymerase makes a copy of a gene from the DNA to mRNA as needed. This process is similar in eukaryotes and prokaryotes. One difference, however, is that eukaryotic RNA polymerase associates with mRNA processing enzymes during transcription so that processing can proceed quickly after the start of transcription.

Marshall Nirenberg and Heinrich J. Matthaei were the first to elucidate the nature of a codon in 1961 at the National Institutes of Health. They used a cell-free system to translate a poly-uracil RNA sequence and discovered that the polypeptide that they had synthesized consisted of only the amino acid phenylalanine.They thereby deduced that the codon UUU specified the amino acid phenylalanine.