Chapter 4.2, Problem 8BYGO

Summary Introduction

Introduction:

In translation, mRNA is converted into amino acid sequences, resulting in protein synthesis. Three important components are involved in translation, mRNA, tRNA, and the ribosome. Protein synthesis occurs in the cytoplasm. mRNA encodes the genetic material that is translated into a specific protein. tRNA binds to free amino acids and transfers them to the ribosome, and the amino acids are added to the growing chain of protein sequence. Ribosome reads mRNA and synthesizes protein based on codons present in the mRNA sequence. It is found in the cytosol, and is attached on the outside of the rough endoplasmic reticulum and nuclear envelope. Inactive ribosomes are found in the cytoplasm as small and large subunits. The two subunits (small subunit and large subunit) join together and become functionally active when they start translation. The ribosome consists of three packets, such as A site (aminoacyl site), P site (peptidyl site), and E site (exit site), where tRNA is used to attach and transfer amino acids. The ribosome binds to the anticodon of a particular tRNA according to mRNA sequence and assembles amino acids corresponding to mRNA codons. Three nucleotides of the mRNA sequence code for a single amino acid of the protein sequence and is known as codon. The twenty amino acids are represented by different patterns of four nitrogenous bases and are called as the genetic code. Sixty-four codons (different patterns of three nucleotides) encode for 20 amino acids. Protein synthesis occurs in three steps, such as initiation, elongation, and termination. AUG is the start codon, which initiates protein synthesis from mRNA sequence, whereas UAG, UGA, and UAA are stop codons that terminate protein synthesis. When a ribosome moves from its place of mRNA sequence, another ribosome will bind and start its translation process. Hence, the single mRNA sequence is translated into several same protein molecules by 10 to 20 ribosomes. The cluster of ribosomes is collectively called as polyribosomes.