Answer the following questions about protein synthesis :(a) What is meant by the central dogma ?(b) Explain transcription.(c) What is a codon ?(d) Explain translation.(e) Which type of RNA brings amino acids to the ribosome ?

Answer: (a) DNA → mRNA → protein; (b) formation of mRNA from DNA; (c) a triplet of nitrogen bases on mRNA that codes for one amino acid; (d) formation of a protein on the ribosome as per the codons of mRNA; (e) tRNA.

(a) Central dogma: the genetic information flows from DNA to mRNA (transcription) and from mRNA to protein (translation). Genes in DNA thus control the formation of proteins, which control the characters of the body.

(b) Transcription: in the nucleus, the two strands of the DNA segment carrying the gene separate. One strand acts as a template and an mRNA strand is formed using complementary bases (A pairs with U, T with A, G with C, C with G). The mRNA then leaves the nucleus and reaches the ribosomes in the cytoplasm.

(c) Codon: a group of three consecutive nitrogen bases on mRNA that stands for one particular amino acid, e.g. AUG codes for methionine and is the start codon.

(d) Translation: on the ribosome, the codons of mRNA are read one by one. tRNA molecules, each carrying a specific amino acid, bring the amino acids; the anticodon of tRNA pairs with the codon of mRNA. The ribosome moves along the mRNA codon by codon (translocation), and the amino acids are joined by peptide bonds into a polypeptide chain. The process stops at a stop codon and the protein is released.

(e) Transfer RNA (tRNA).