Question

Describe the process of DNA replication. Include the ingredients needed, the enzymes used, the steps in the process and the final product.

Describe the process by which the information in a gene is transcribed and translated into a protein. Correctly use these words in your description (and highlight them as bold text in your submission):

• tRNA
• amino acid
• start codon
• transcription
• mRNA
• gene
• codon
• RNA polymerase
• ribosome
• translation
• anti-codon
• peptide bond
• stop codon

Answer 1

Nucleic acids constitute the genetic material of all living organisms. They include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). They are built from smaller molecules (monomers) called nucleotides. Each nucleotide contains 3 components - a sugar, and a nitrogenous base and a phosphate group. If the sugar is deoxyribose the polymer is DNA and if the sugar is ribose, the polymer is RNA. A gene is a particular segment of DNA. The sequence of nitrogen bases in DNA determines the sequence of nucleotides along an RNA molecule. A strand of DNA contains a chain of connecting nucleotides. Nitrogen bases of DNA are adenine (A), thymine (T), guanine (G), and cytosine (C). Nitrogen bases of RNA are adenine (A), uracil (U), guanine (G), and cytosine (C)

Proteins are made polymers of amino acids. Protein synthesis occurs in two stages: Transcription and translation.

Transcription is the process of producing a strand of RNA from a strand of DNA. The information that is stored in DNA molecules is rewritten or ‘transcribed’ into a new RNA molecule - the messenger RNA (mRNA). The mRNA then leaves the nucleus and goes to a ribosome in the cytoplasm, where translation occurs.

Transcription begins when the enzyme RNA polymerase separates the two strands of DNA and builds a strand of mRNA by adding the complementary nucleotides (A, U, G, C) to the template strand of DNA.

Translation is the process in which the genetic code in mRNA is read to make a protein. After mRNA reaches the ribosome in the cytoplasm, the ribosome reads the sequence of codons in mRNA, and molecules of tRNA bring amino acids to the ribosome in the correct sequence. Ribosomes provide a platform for mRNA molecules to couple with complimentary transfer RNA (tRNA) molecules. Each tRNA molecule has an anticodon for the amino acid it carries. An anticodon is complementary to the codon for an amino acid.

A protein is formed from many amino acids. Ribosomes catalyse the formation of peptide bonds between adjacent amino acids (via condensation reactions). During translation, the information of the strand of RNA is translated into a sequence of amino acids. Each three-base ‘word’ is called a ‘codon’ and the series of codons holds the information for the production of the polypeptide chain. There are a total of 64 different codons and more than one codon translates into each amino acid. A strand of mRNA has multiple codons which provide the information for multiple amino acids. Each tRNA molecule contains three nitrogenous bases that are complementary to the three bases of a codon on the mRNA strand. The three bases of the tRNA molecule are known as an anticodon. A tRNA molecule reads along one codon of the mRNA strand and collects the necessary amino acid from the cytoplasm.

The coding region of an mRNA sequence always begins with a START codon (AUG) and terminates with a STOP codon. Translation ends when a stop codon on the mRNA site reaches the site where the tRNA molecules bind to the codon of the mRNA strand. The stop codon does not have an anticodon on the tRNA.