Translation 2.7 & 7.3

Essential Idea: Genetic information in DNA can be accurately copied and can be translated to make the proteins needed by the cell. 2.7 DNA replication, transcription and translation Understandings: Translation is the synthesis of polypeptides on ribosomes   The amino acid sequence of polypeptides is determined by mRNA according to the Codons of three bases on mRNA correspond to one amino acid in a polypeptide Translation depends on complementary base pairing between codons on mRNA and anticodons on tRNA Applications: Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species Skills: Use a table of the genetic code to deduce which codon(s) corresponds to which amino acid Use a table of mRNA codons and their corresponding amino acids to deduce the sequence of amino acids coded by a short mRNA strand of known base sequence

Essential Idea: Information transferred from DNA to mRNA is translated into an amino acid sequence. 7.3 Translation Understandings: 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 for use primarily within the cell Bound ribosomes synthesize proteins primarily for secretion or for use in lysosomes Translation can occur immediately after transcription in prokaryotes due to the absence of a nuclear membrane The sequence and number of amino acids in the polypeptides is the primary structure The secondary structure is the formation of alpha helices and beta pleated sheets stabilized by hydrogen bonding The tertiary structure is the further folding of the polypeptide stabilized by interactions between R groups The quaternary structure exists in proteins with more than one polypeptide chain Application tRNA – activating enzymes illustrate enzyme – substrate specificity and the role of phosphorylation Skills: Identify polysomes in electron micrographs of prokaryotes and eukaryotes Use molecular visualization software to analyze the structure of eukaryotic ribosomes and a tRNA molecule

I. Types of rna involved RNA Type Function mRNA – messenger Complimentary to a gene, carries message (genetic code) from DNA is nucleus to ribosomes in cytoplasm rRNA – ribosomal Component of the ribosomes (along with proteins) tRNA – transfer Brings amino acids to the ribosome to build the polypeptide

tRNA 1. Forms a t-shape because part of it are complimentary with itself

2. Activation = attachment of an amino acid a 2. Activation = attachment of an amino acid a. Bottom portion contains an anti- codon that is complimentary to a codon (set of 3 bases) on the mRNA b. Anti-codon determines which amino acid to 3’ end c. 20 different enzymes – 1 for each amino acid d. Requires ATP

II. Structure of the ribosome Consists of a large and a small subunit, each made of rRNA (2/3) and proteins (1/3) 1. rRNA constructed in nucleolus and exit nucleus through nuclear pores 2. mRNA will fit in between large and small subunits

3 sites A – holds tRNA carrying next amino acid P – holds tRNA carrying polypeptide E – site where deactivated tRNA exits ribosome

III. The genetic code Bases are read 3 at a time DNA – triplets mRNA – codons tRNA - anticodons Each codon codes for a specific amino acid, but there can be more than one codon for an amino acid Universal – same in all species

V. initiation A. Small subunit attached to mRNA and moves along it until it finds start codon (AUG) B. Activated tRNA hydrogen bonds to codon – anti-codon is UAC, amino acid is methionine

Large subunit joins small subunit/mRNA to form translation initiation complex Initiation factors (proteins that help the process ) join the complex – this requires GTP

VI. elongation tRNAs bring in amino acids 1 at a time Elongation factors – proteins that assist tRNA binding at A site Bond holding amino acid to tRNA in P site breaks and peptide bond forms between that amino acid and the amino acid on the tRNA in the A site

Translocation – tRNA in P site, now deactivated, moves to E site and tRNA in A site moves to P site E. Deactivated tRNA leaves ribosome (goes to be reactivated)

Ribosome moves along mRNA in the 5’ 3’ direction, new activated tRNAs move into the A site, translocation happens repeatedly

VII. Termination Stop codon on mRNA moves into A site Release factor – protein fills the A site – has no amino acid attached 1. Catalyzes hydrolysis between tRNA in the P site and its amino acid (which is holding the polypeptide chain) C. Polypeptide is released and ribosome subunits break apart