Translation Components

Translation Translation Components Identify the following sites on a tRNA molecule and describe their function Acceptor stem - carries the amino acid 1. ………………………………………………………………………………………………………………… 1 2 4 T arm - associates with the ribosome (via E, P, A sites) 2. ………………………………………………………………………………………………………………… Anticodon - associates with mRNA (via complementary codon) 3. ………………………………………………………………………………………………………………… 3 D arm - associates with tRNA-activating enzyme 4. ………………………………………………………………………………………………………………… Describe the process by which amino acids are attached to tRNA molecules Each tRNA molecule carries a specific amino acid (designated by the codon / anticodon) ………………………………………………………………………………………………………………………………………………….......... Hence, different tRNA molecules associate with specific tRNA-activating enzymes ………………………………………………………………………………………………………………………………………………….......... • Enzyme binds ATP to an amino acid (forming a ‘charged’ amino acid-AMP complex) ………………………………………………………………………………………………………………………………………………….......... • The charged complex is then transferred to the tRNA acceptor stem (and AMP is released) ………………………………………………………………………………………………………………………………………………….......... • The purpose of ‘charging’ the molecule is to provide the energy needed in translation for peptide bonds ………………………………………………………………………………………………………………………………………………….......... Outline the structure of ribosomes Ribosomes are composed of a large and a small subunit (made of protein and rRNA) ……………………………………………………………………………………………………………………… The small subunit binds to mRNA ……………………………………………………………………………………………………………………… The large subunit contains three tRNA binding sites (E, P and A) ……………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………… Differentiate between the following types of ribosomes Prokaryotic vs Eukaryotic: Prokaryotic ribosomes are smaller than eukaryotic ribosomes ………………………………………………………………………………………………………………………………………………….......... Prokaryote = 70S ribosomes ; Eukaryote = 80S ribosomes ………………………………………………………………………………………………………………………………………………….......... Bound (ER) vs Free (Cytosolic): Proteins synthesised by bound ribosomes have different destinations to those synthesised by free ribosomes ………………………………………………………………………………………………………………………………………………….......... ER bound ribosomes = Secretory proteins (or lysosome) ; Free ribosomes = Intracellular proteins ………………………………………………………………………………………………………………………………………………….......... Translation Process Explain, with the aid of the following diagram, the process of translation Initiation: Small ribosomal subunit binds to mRNA and moves along it in a 5’ - 3’ direction until the START codon (AUG) ………………………………………………………………………………………………………………………………………………….......... Specific tRNA (carrying Met) binds to the START codon (via complementary anticodon) ………………………………………………………………………………………………………………………………………………….......... Large ribosomal subunit binds to the tRNA molecule (via the P-site), completing the ribosome ………………………………………………………………………………………………………………………………………………….......... Elongation: Another tRNA molecule binds to the next codon in the mRNA sequence (via the ribosomal A-site) ………………………………………………………………………………………………………………………………………………….......... The ribosome transfers the amino acid in the P-site to the amino acid in the A-site (via a peptide bond) ………………………………………………………………………………………………………………………………………………….......... ………………………………………………………………………………………………………………………………………………….......... Translocation: Ribosome moves one codon position along the mRNA sequence (in a 5’ - 3’ direction) ………………………………………………………………………………………………………………………………………………….......... Deacylated tRNA molecule moves to E-site and is released, while tRNA in the A-site moves to the P-site ………………………………………………………………………………………………………………………………………………….......... A new tRNA enters the empty A-site and the elongation and translocation stages are continually repeated ………………………………………………………………………………………………………………………………………………….......... Termination: The ribosome reaches a STOP codon and a releasing factor is recruited ………………………………………………………………………………………………………………………………………………….......... This causes the completed polypeptide chain to dissociate and the ribosome to disassemble ………………………………………………………………………………………………………………………………………………….......... ………………………………………………………………………………………………………………………………………………….......... Define polysome A polysome is a group of ribosomes moving along an mRNA sequence simultaneously ………………………………………………………………………………………………………………………………………………….......... Protein Structure Explain, with the aid of the diagram, the levels of protein structure and indicate their significance Primary Structure: The order / sequence of amino acids within a polypeptide chain ………………………………………………………………………………………………………………………………………………….......... Formed via peptide bonds between the amine and carboxyl groups of adjacent amino acids ………………………………………………………………………………………………………………………………………………….......... Primary structure determines all subsequent levels of protein structure ………………………………………………………………………………………………………………………………………………….......... Secondary Structure: The folding of a polypeptide chain into repeating arrangements (alpha helices or beta-pleated sheets) ………………………………………………………………………………………………………………………………………………….......... Formed via hydrogen bonds between the amine and carboxyl groups of non-adjacent amino acids ………………………………………………………………………………………………………………………………………………….......... ………………………………………………………………………………………………………………………………………………….......... Tertiary Structure: The overall three dimensional shape of the polypeptide chain ………………………………………………………………………………………………………………………………………………….......... Formed via a variety of bonds / interactions between the variable side chains (R groups) ………………………………………………………………………………………………………………………………………………….......... These interactions may include hydrogen bonds, ionic bonds, disulphide bridges or hydrophobic interactions ………………………………………………………………………………………………………………………………………………….......... Quaternary Structure: The presence of multiple polypeptides or prosthetic groups to form a biologically active protein ………………………………………………………………………………………………………………………………………………….......... Not all proteins will have a quaternary structure ………………………………………………………………………………………………………………………………………………….......... …………………………………………………………………………………………………………………………………………………..........