MBB topic 8 Translation

stop codons \ UAA UAG UGA;

methanine codon \ AUG;

what is translation \ synthesis of protein from mRNA, takes info from the language of nuclei acids and translates it into language of proteins, takes place in cytosoal;

whats genetic code \ a set of triplet nucleotides (codons) in mRNA that codes for amino acies;

what are codons \ how m RNA is read in non overlapping, consecutive groups of three nucleotides know a scodons, slmost universally code in all present day organisms;

how many codons and amino acids are there \ 64 codons and 20 amino acids;

how are codons redundant \ several different codons encode for the same amino acid;

what is an open reading frame \ a reading frame that has the potential to code for a protein or peptide, first base of the ORF is a start codon, ends with a stop codon;

what are the 4 types of mutations \ 1.missense mutation-a point mutation which a single nucleotide change results in a codon that coes fr a different amino acid 2. nonsense mutation-a point mutation in that reaults in a premature stop codon 3.a silent mutation-doesnt alter the protein sequence encoded by the gene 4. frameshift mutation \ causes a change in the reading frame, this can be caused by insertions or deletions of nucleotides, often generates premature stop codons;

transfer RNA tRNA \ match aino acids to codons in mRNA, composed of single strand of RNA that has formed a double helical structure, each tRNA contains a 3 nuceotide anticodon that recognizes the codons on the RNA the tRNA and mRNA are oriented antiparallel, each tRNA is linked at the 3’ end to a specific amino acid by a specific aminoacyl tRNA synthetas -tRNA linked to an amino acid is charged, some amino acids have more than one tRNA and some can bp w/more than one codon;

how is the mRNA message decoded \ translation is conducted by ribosomes in the cytoplasm, theyre very large complexes of ribosomal RNA (rRNA) and 1/3 protein, each has tyw subunits one large and one small;

ribozymes \ RNA molecules with a catalytic activity, the protein component stabilizes the ribosome and helps it fold, ribosomes are ribozymes, the rRNA in ribozymes dictae the overall structure of the ribosome;

how doe ribosomes choreograph all the movements requried for translation \ ribosomes have 3 binding sites: A=aminoacyltRNA site, P=peptidyl-tRNA site, E=exit site, the mRNA also has a binding site on the small subunit, the ribosome moves along the mRNA in a 5’→3’ direction, translation takes place in a 4 step cycle that repeats over and over again;

steps in initiation of translation in eukaryotes \ 1.initiator tRNA binds to the P site of the small subuit along with the initiation factors 2. mRNA binds to the smalll subunit recognizing the 5’ cap 3. this moves until it encounters the firs AUG 4. initiation factors dissociate, the large ribosomal subunit binds 5.a charged tRNA molecule binds to the A site 6. the methionine in the P site is linked to the amino acid in the A site through a peptide bond;

what are the 4 steps of translation \ 1. charged tRNA carrying the next amino acid bind to the A site by base pairing with the codon in mRNA 2. the carboxyl end of the polypeptide chain (amino acid 3) is uncoupled from the tRNA at the P site and joined by a peptide bond to the free amino group of the amino acid linked to the tRNA at the A site by peptidyl transferase 3. the large subunit shifts relative to the small subunit the tow tRNAs are moved to E and P sites of the large subunit 4. the small subunit moves exactly three nucleotides along mRNA bringing it back to the original position relative to the large subunit, it resets the ribosome on an empty A site (amino acid 4) allowing the binding of the next amino-acyl tRNA (amino acid 5);

differences with translation in bacteria \ in bacteria ….. -mRNA has no 5’ cap so instead the small subunit recognizes a sequence known as the Shine dalgarno sequence which lies upstream of the starte codon this serves as the ribosome binding site, 2. bacteria has polycistronic mRNA several genes are encoded on the same mRNA

transcript

• Each individual gene will have a Shine-Dalgarno sequence so that each product can

be translated independently

• Eukaryotic mRNA is usually monocistronic

steps in termination of bacteria translation \ 1. When a stop codon is encountered, proteins

known as release factors bind

2. The peptide is transferred to a molecule of

water (instead of another amino acid)

causing the peptide chain to be released

3. The ribosome dissociates, ready to be

recycled for another round of translation on

another mRNA;

what are polyribosomes \ a single mRNA transcript can be translated by everal ribosomes simultaneously forming a polyribosome, increases overall rate of protein synthesis, occurs in both eukaryotes and prokaryotes;

what post translation modifications might a peptide have to undergo \ phsophorlyation, glycoslyation, proteolytic cleavages;