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7.3 Translation

7.3 TranslationBy Darren Aherne

Image from http://www.nobelprize.org/educational/medicine/dna/b/translation/pics/trans_bd.gifEssential Idea: Information transferred from DNA to mRNA is translated into an amino acid sequence.

7.3StatementGuidance7.3 U1Initiation of translation involves assembly of the components that carry out the process.Examples of start codons are not required. Names of the tRNA binding sites are expected as well as their roles. 7.3 U2Synthesis of the polypeptide involves a repeated cycle of events.7.3 U3Disassembly of the components follows termination of translation.Examples of stop codons are not required. 7.3 U4Free ribosomes synthesize proteins for use primarily within the cell.7.3 U5Bound ribosomes synthesize proteins primarily for secretion or for use inlysosomes.7.3 U6Translation can occur immediately after transcription in prokaryotes due to the absence of a nuclear membrane.7.3StatementGuidance7.3 U7The sequence and number of amino acids in the polypeptide is the primary structure.7.3 U8The secondary structure is the formation of alpha helices and beta pleated sheets stabilized by hydrogen bonding.7.3 U9The tertiary structure is the further folding of the polypeptide stabilized by interactions between R groups.Polar and non-polar amino acids are relevant to the bonds formed between R groups. 7.3 U10The quaternary structure exists in proteins with more than one polypeptide chain.Quaternary structure may involve the binding of a prosthetic group to form a conjugated protein. 7.3 A1Application: tRNA-activating enzymes illustrate enzymesubstrate specificityand the role of phosphorylation.7.3 S1Skill: Identification of polysomes in electron micrographs of prokaryotes and eukaryotes.7.3 S2Skill: The use of molecular visualization software to analyse the structure of eukaryotic ribosomes and a tRNA molecule.7.3 S2The use of molecular visualization software to analyse the structure of eukaryotic ribosomes and a tRNA molecule.

Ribosome Structure: Proteins + ribosomal RNA (rRNA)Large subunit & small subunit3 binding sites for tRNA (peptidyl- P site, aminoacyl- A site, exit- E site)2 tRNAs can bind to the surface of the ribosome at a time, 1 mRNA can bind to surface of small subunit

From Biology Course Companion, Allott, A, Oxford University Press, 2014, p. 363

http://www.rcsb.org/pdb/explore/jmol.do?structureId=1GIY&bionumber=1http://www.rcsb.org/pdb/explore/jmol.do?structureId=1JGO&bionumber=1Click the links to view the ribosome imagesImage from textbook removed7.3 S2The use of molecular visualization software to analyse the structure of eukaryotic ribosomes and a tRNA molecule.

tRNA Structure: Double stranded sections by complementary base pairingAnticodon of 3 bases in a loop of 7 bases2 other loopsAmino acid binding site with CCA sequence of unpaired basesFrom Biology Course Companion, Allott, A, Oxford University Press, 2014, p. 363http://www.rcsb.org/pdb/education_discussion/educational_resources/tRNA_jmol.jspClick the link to view the tRNA images

Image from textbook removed7.3 A1Application: tRNA-activating enzymes illustrate enzymesubstrate specificity and the role of phosphorylation.

Every tRNA has a specific enzyme that attaches a specific amino acid, using ATP

An introduction https://www.youtube.com/watch?v=KThCr1XdUGw

http://highered.mheducation.com/sites/9834092339/student_view0/chapter15/aminoacyl_trna_synthetase.htmlFrom Biology Course Companion, Allott, A, Oxford University Press, 2014, p. 364Image from textbook removed

7.3 A1Application: tRNA-activating enzymes illustrate enzymesubstrate specificity and the role of phosphorylation.

http://www.phschool.com/science/biology_place/biocoach/translation/addani.html7.3 U1Initiation of translation involves assembly of the components that carry out the process.

Initiation- assembly of components of translation

mRNA binds to small subunit of the ribosomeInitiator tRNA carrying methionine amino acid with anticodon complementary to AUG binds to start codonLarge subunit of ribosome binds to small subunit

From Purves, Sadava, Orians, & Heller, Life: The Science of Biology, 7th Ed., W.H. Freeman, 2003, p. 2447.3 U1Initiation of translation involves assembly of the components that carry out the process.

Initiation- assembly of components of translationInitiator tRNA is in P-sitetRNA complementary to codon at A-site binds to ribosomePeptide bond is formed between the amino acids at P and A sites through a condensation reaction.From Purves, Sadava, Orians, & Heller, Life: The Science of Biology, 7th Ed., W.H. Freeman, 2003, p. 245

7.3 U2Synthesis of the polypeptide involves a repeated cycle of events.

Elongation- a series of repeated stepsRibosome moves 3 bases along the mRNAtRNA at P-site moves to E-site, allowing it to disengagetRNA complementary to the codon at A-site entersProcess continues many times

From Purves, Sadava, Orians, & Heller, Life: The Science of Biology, 7th Ed., W.H. Freeman, 2003, p. 245

7.3 U3Disassembly of the components follows termination of translation.

Termination- a stop codon ends translationWhen a stop codon is reached the polypeptide is releasedTranslation moves in a 5 > 3 direction

From Purves, Sadava, Orians, & Heller, Life: The Science of Biology, 7th Ed., W.H. Freeman, 2003, p. 246

7.3 U3Disassembly of the components follows termination of translation.

Termination- a stop codon ends translationRibosome breaks apart following translationmRNA may be translated many times to make many copies of its polypeptideFrom Purves, Sadava, Orians, & Heller, Life: The Science of Biology, 7th Ed., W.H. Freeman, 2003, p. 246

http://highered.mheducation.com/sites/0072507470/student_view0/chapter3/animation__how_translation_works.html

http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swfWatch these animations about the process of translation. Can you narrate? Explain the process of translation leading to polypeptide formation. (8 marks)Explain the process of translation leading to polypeptide formation. (8 marks)a. genetic code consists of codons of base triplets;b. mRNA is complementary to the DNA strand;c. mRNA carries information (transcribed) from the DNA gene;d. translation occurs in a ribosome;e. mRNA attaches to the (small subunit of the) ribosome;f. has specific codons;g. each (codon) codes for one amino acid;h. tRNA matches its anticodons with the codons of mRNA;i. by hydrogen bonds between complementary bases;j. each tRNA carries a specific/OWTTE amino acid;k. the amino acids are attached to each other by condensation reactions/peptide bonds;l. the process is repeated;m. forming polypeptides;7.3 U4Free ribosomes synthesize proteins for use primarily within the cell.

Location of protein Synthesis: Cell functions & protein synthesis are compartmentalized (by organelles)Proteins that will be used by the cell in the cytoplasm, mitochondria, and chloroplasts are synthesized on free ribosomes in the cytoplasm.

http://iws.collin.edu/biopage/faculty/mcculloch/1406/outlines/chapter%207/rougher2.jpg7.3 U5 Bound ribosomes synthesize proteins primarily for secretion or for use in lysosomes.

Location of protein Synthesis:Proteins that will be used in the ER, golgi apparatus, lysosomes, plasma membrane, or to be excreted are synthesized on ribosomes bound to the rER. Signal receptor proteins stop translation until the ribosome is bound to the rER.

From Biology Course Companion, Allott, A, Oxford University Press, 2014, p. 366Image from textbook removed7.3 U5 Translation can occur immediately after transcription in prokaryotes due to the absence of a nuclear membrane.

Transcription & translation are coupled in prokaryotes.

http://www.phschool.com/science/biology_place/biocoach/transcription/tctlpreu.html

7.3 S1 Skill: Identification of polysomes in electron micrographs of prokaryotes and eukaryotes.

Polysomes appear as beads on a string in electron micrographs. Beads represent ribosomes attached to a single mRNA moleculePoly = many, some = ribosome

http://www.nature.com/scitable/content/27459/williams_polysome_mid_1.jpg

http://www.nobelprize.org/educational/medicine/dna/a/translation/pics_em/polysome.gifFrom Biology Course Companion, Allott, A, Oxford University Press, 2014, p. 368Image from textbook removed7.3 NOS Developments in scientific research follow improvements in computingthe use of computers has enabled scientists to make advances in bioinformatics applications such as locating genes within genomes and identifying conserved sequences.

Conserved sequence: a homologous sequence of DNA that is identical across all members of a species. Bioinformatics: uses computer databases to store and analyze gene & protein sequences from large amounts of data collected from sequencing genes of various organismsFaster, more powerful computers allow scientist to identify conserved sequences & genes by looking for patterns and homologous sequences within organisms genome. If a sequence is homologous across species or individuals of a species, it usually has a functional role. Eg. It codes for a protein (a gene).

From i-biology.net7.3 U7The sequence and number of amino acids in the polypeptide is the primary structure.

http://www.stolaf.edu/people/giannini/flashanimat/proteins/protein%20structure.swfFrom i-biology.net

From i-biology.net7.3 U8The secondary structure is the formation of alpha helices and beta pleated sheets stabilized by hydrogen bonding.

From i-biology.net

7.3 U9The tertiary structure is the further folding of the polypeptide stabilized by interactions between R groups.

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