Question

A gene with 600 nucleotides will code for how many amino acids?
a) 200
b) 600
c) 400
d) 900

Answer 1

Hint:- Once transcription and processing of rRNA, tRNA and snRNA are completed, the RNAs are able to be utilized in the cell assembled into ribosomes and utilized in splicing and protein synthesis. But the mature mRNA isn't yet functional to the cell. It must be translated into the encoded protein and it's called genetic code.

Complete answer:
Experiments testing the results of frameshift mutations showed that the deletion or addition of 1 or 2 nucleotides caused a loss of function, whereas deletion or addition of three nucleotides allowed retention of considerable function. This demonstrated that the coding unit is 3 nucleotides. The nucleotide triplet that encodes an amino acid is named a codon. Each group of three nucleotides encodes one amino alkanoic acid. Since there are 64 combinations of 4 nucleotides taken three at a time and only 20 amino acids, the code is degenerate. The adaptor molecule for translation is tRNA. The machinery for synthesizing proteins under the direction of template mRNA is that the ribosome.
- Size of a codon: 3 nucleotides
- Three is that the minimum number of nucleotides per codon needed to encode 20 amino acids.
20 amino acids are encoded by combinations of 4 nucleotides
With three nucleotides, the set of all combinations can encode
4x4x4 = 64 amino acids
(i.e. 64 different combinations of 4 nucleotides taken three at a time). Of the whole of 64 codons, 61 encode amino acids and three specify termination of translation.
- Degeneracy: The degeneracy of the genetic code refers to the fact that the majority amino acids are specified by quite one codon. The exceptions are methionine (AUG) and tryptophan (UGG).
Degeneracy is found primarily in the third position. Consequently, single nucleotide substitutions at the third position might not result in a change within the organic compound encoded. These are called silent or synonymous nucleotide substitutions. They do not alter the encoded protein.
- There are 13 codon "pairs", within which the nucleotides at the primary two positions are sufficient to specify two amino acids. A purine (R) nucleotide at the third position specifies one amino alkanoic acid, whereas a pyrimidine (Y) nucleotide at the third position specifies the opposite organic compound.

The three codons encoding isoleucine (AUU, AUC and AUA) are half-way between a codon family and a codon pair.
- The codons for leucine and arginine, with both a codon family and a codon pair, provide the few examples of degeneracy within the first position of the codon. For example, both UUA and CUA encode leucine. Degeneracy at the second position of the codon isn't observed for codons encoding amino acids. The sole occurrence of second position degeneracy is for the termination codons UAA and UGA.
- Chemically similar amino acids often have similar codons
- The major codon specifying initiation of translation is AUG: Bacteria may use GUG or UUG, and extremely rarely AUU and possibly CUG.
- Three codons specify termination of translation: UAA, UAG, UGA: of those three codons, UAA is employed most often in E.coli, followed by UGA. UAG is employed much less frequently.
- The genetic code is sort of universal: within the rare exceptions to the current rule, the differences from the genetic code are fairly small. For instance, one exception is RNA from mitochondrial DNA, where both UGG and UGA encode Trp.
Thus, the right option is (a).

Note:- Knowledge of the genetic code allows one to predict the amino acid sequence of any sequenced gene. The entire genome sequences of several organisms have revealed genes coding for several previously unknown proteins.