7.3 translation

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7.3 Translation

7.3 Translation

Guidance- Names of the tRNA binding sites are expected, as well as their roles.- Examples of stop and start codons are not required.- Polar and non-polar amino acids are relevant to the bonds formed between R-groups.- Quaternary structure may involve the binding of a prosthetic group to form a conjugated proteinUnderstandingsInitiation of translation involves assembly of the components that carry out the process.Synthesis of the polypeptide involves a repeated cycle of the events. Disassembly of the components follows termination of translation.Free ribosomes synthesize proteins for use primarily in 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 polypeptide 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 the R-groups.The quaternary structure exists in proteins with more than one polypeptide chain.Applications/SkillsA: tRNA-activating enzymes illustrate enzyme-substrate specificity and the role of phosphorylation.S: Identification of polysomes in electron micrographs of prokaryotes and eukaryotes.S: The use of molecular visualization software to analyze the structure of eukaryotic ribosomes and a tRNA molecule.

The Ribosome


Composed of rRNA and proteinsHolds the tRNA carrying the next amino acid to be added to the chain Holds the tRNA carrying the growing chainSite from which tRNA that has lost its amino acid is discharged


Adapted from http://classconnection.s3.amazonaws.com/185/flashcards/82185/jpg/6_361320375541451.jpg53CUUCGCGUAGCAThe amino acid attached is determined by a particular enzyme (20 AAs 20 enzymes)Activated Amino Acid

InitiationActivated amino acid (methionine) attaches to a tRNA with the anticodon UACThis combines with an mRNA and small ribosomal subunitSmall subunit moves down the mRNA until it reaches the codon AUGH bonds form between the initiator tRNA and start codonLarge subunit combines with these parts along with initiation factors (proteins) and GTP (similar to ATP)

Elongation tRNAs bring amino acids to the mRNA-ribosomal complex Elongation factors assist in binding the tRNAs to the mRNA codonsInitiator tRNA moves to the P siteRibosomes catalyze the formation of peptide bonds between the amino acids


TranslocationOccurs during elongationMovement of tRNAs from one site to anotherA siteP siteE siteOccurs in the 5 3 directionhttp://www.tokresource.org/tok_classes/biobiobio/biomenu/transcription_translation/translation_1.jpg

TerminationStop codon appears in the A siteA release factor fills the A site and catalyzes hydrolysis of the bond between the tRNA in the P site and the amino acid chainPolypeptide is releasedRibosomal subunits separate from the mRNA





Primary OrganizationSequence of amino acidsDetermines the next 3 levelsChanging one amino acid can result in a dysfunctional protein


Secondary Organization Alpha helix or beta pleated sheet

Results from H bonds between the O from a carboxyl group on one amino acid and the H from the amino group of another amino acid

Does NOT involve R groups


Tertiary OrganizationThree-dimensional configuration as a result of interactions between R-groupsDisulfide bridges: covalent bonds between sulfur atomsH-bonds Van der Waals interactions: hydrophobic R-groups forced inward and hydrophilic R-groups interact with water in aqueous solutionsIonic bonds


Quaternary StructureTwo or more polypeptide chains combine to form a single functional protein

Involves all bonds previously mentioned

Can include a non-polypeptide portion (conjugated protein)http://bio3400.nicerweb.com/Locked/media/ch14/14_20-protein_structure-quaternary.jpg

Fibrous vs Globular ProteinsFibrous GlobularMany polypeptide chains in a long narrow shapeGenerally insoluble in waterEx: CollagenMore three dimensional in shapeGenerally water solubleEx: Insulin