7.3 Translation Understanding: Initiation of translation involves assembly of the components that carry out the process Synthesis of the polypeptide involves a repeated cycle of events Disassembly of the components follows termination of translation Free ribosomes synthesize proteins primarily within the cell Bound ribosomes synthesize proteins primarily for secretion or for use in lysosomes Translation can occur immediately after transcription in prokaryotes The sequence and number of amino acids in the polypeptide is the primary structure The secondary structure is the formation of alpha helixes and beta pleated sheets The tertiary structure is the further folding of the polypeptide The quaternary structure exists in proteins with more than one polypeptide chain Applications: tRNA-activating enzymes illustrate enzyme-substrate specificity and the role of phosphorylation Skills: The use of molecular visualization software to analyse the structure of eukaryotic ribosomes and a tRNA molecule Identification of polysomes in an electron micrograph Nature of science: Developments in scientific research follow improvements in computing

Subunits (one large, one small) Draw and Label… Ribosome Subunits (one large, one small) Three tRNA binding sites and their uses mRNA binding site tRNA CCA base sequence at 3’ end (amino acid attaches) Anticodon loop Bases Hydrogen bonds Skills: The use of molecular visualization software to analyse the structure of eukaryotic ribosomes and a tRNA molecule

Subunits A site: Holds tRNA carrying next amino acid to be added (incoming) P site: Holds tRNA carrying the growing polypeptide chain E site: tRNA has lost its amino acid and is discharged Skills: The use of molecular visualization software to analyse the structure of eukaryotic ribosomes and a tRNA molecule

tRNA Loops created by base pairing Anticodon loop matches codon on mRNA H bonds between bases ACC region carries specific amino acid (depends on anticodon) Skills: The use of molecular visualization software to analyse the structure of eukaryotic ribosomes and a tRNA molecule

Initiation mRNA binds to small ribosomal subunit at mRNA binding site Initiator tRNA molecule carrying methionine (amino acid) binds at start codon ‘AUG’ at the P site Large ribosomal subunit binds to small one Another tRNA binds at the A site Peptide bond forms between amino acids in P and A site and remains on the tRNA molecule at the A site Understanding: Initiation of translation involves assembly of the components that carry out the process

Ribosome moves along the mRNA molecule Elongation Ribosome moves along the mRNA molecule tRNA moves from P site to E site and leaves the ribosome tRNA in the A site moves to the P site Allows next tRNA to bind to the A site Movement of tRNAs from one site to another = translocation Understanding: Synthesis of the polypeptide involves a repeated cycle of events

Process continues until a stop codon is reached Termination Process continues until a stop codon is reached Release factor fills the A site (no amino acid carried) Polypeptide is released Components disassemble Understanding: Disassembly of the components follows termination of translation

Translation Initiation Elongation Termination

Endoplasmic reticulum Ribosomes Different ribosomes used to synthesize proteins bound for different destinations Type of ribosome Proteins used in/at: Free Cytoplasm Mitochondria Chloroplasts Bound to ER Endoplasmic reticulum Golgi apparatus Lysosomes Plasma membrane Outside of cell Understanding: Free ribosomes synthesize proteins primarily within the cell Bound ribosomes synthesize proteins primarily for secretion or for use in lysosomes

Polysomes Many ribosomes attached to a single mRNA molecule Appear as beads on a string Able to see them using an electron microscope Skills: Identification of polysomes in an electron micrograph

Polypeptide Structures Presentations for polypeptide structure Create presentations or videos for the following polypeptide structures. Presentations on Monday: Primary structure and secondary structure Tertiary structure and quaternary structure Fibrous and globular proteins Understanding: The sequence and number of amino acids in the polypeptide is the primary structure The secondary structure is the formation of alpha helixes and beta pleated sheets The tertiary structure is the further folding of the polypeptide The quaternary structure exists in proteins with more than one polypeptide chain

Polypeptide Structures Organizational structure Description Primary Secondary Tertiary Quaternary Fibrous and globular proteins