7.3 Translation

By Darren AherneImage from http://www.nobelprize.org/educational/medicine/dna/b/translation/pics/trans_bd.gif

Essential Idea: Information transferred from DNA to mRNA is translated into an amino acid sequence.

7.3 Statement Guidance7.3 U1 Initiation 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 U2 Synthesis of the polypeptide involves a repeated cycle of events.

7.3 U3 Disassembly of the components follows termination of translation.

Examples of stop codons are not required.

7.3 U4 Free ribosomes synthesize proteins for use primarily within the cell.

7.3 U5 Bound ribosomes synthesize proteins primarily for secretion or for use inlysosomes.

7.3 U6 Translation can occur immediately after transcription in prokaryotes due to the absence of a nuclear membrane.

7.3 Statement Guidance7.3 U7 The sequence and number of amino acids in the

polypeptide is the primary structure.

7.3 U8 The secondary structure is the formation of alpha helices and beta pleated sheets stabilized by hydrogen bonding.

7.3 U9 The 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 U10

The 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 A1 Application: tRNA-activating enzymes illustrate enzyme–substrate specificityand the role of phosphorylation.

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

7.3 S2 Skill: The use of molecular visualization software to analyse the structure of eukaryotic ribosomes and a tRNA molecule.

7.3 S2 The 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 subunit• 3 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=1

http://www.rcsb.org/pdb/explore/jmol.do?structureId=1JGO&bionumber=1

Click the links to view the ribosome images

Image from textbook removed

7.3 S2 The use of molecular visualization software to analyse the structure of eukaryotic ribosomes and a tRNA molecule.

tRNA Structure: • Double stranded sections by

complementary base pairing• Anticodon of 3 bases in a loop

of 7 bases• 2 other loops• Amino acid binding site with

CCA sequence of unpaired bases

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

http://www.rcsb.org/pdb/education_discussion/educational_resources/tRNA_jmol.jsp

Click the link to view the tRNAimages

Image from textbook removed

7.3 A1 Application: tRNA-activating enzymes illustrate enzyme–substrate 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.html

From Biology Course Companion, Allott, A, Oxford University Press, 2014, p. 364

Image from textbook removed

7.3 A1 Application: tRNA-activating enzymes illustrate enzyme–substrate specificity and the role of phosphorylation.

http://www.phschool.com/science/biology_place/biocoach/translation/addani.html

7.3 U1 Initiation 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 ribosome

• Initiator tRNA carrying methionine amino acid with anticodon complementary to AUG binds to start codon

• Large subunit of ribosome binds to small subunit

From Purves, Sadava, Orians, & Heller, Life: The Science of Biology, 7th Ed., W.H. Freeman, 2003, p. 244

7.3 U1 Initiation of translation involves assembly of the components that carry out the process.

Initiation- assembly of components of translation• Initiator tRNA is in P-site• tRNA complementary to

codon at A-site binds to ribosome

• Peptide 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 U2 Synthesis of the polypeptide involves a repeated cycle of events.

Elongation- a series of repeated steps• Ribosome moves 3 bases

along the mRNA• tRNA at P-site moves to

E-site, allowing it to disengage

• tRNA complementary to the codon at A-site enters

• Process continues many times

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

7.3 U3 Disassembly of the components follows termination of translation.

Termination- a stop codon ends translation• When a stop codon is

reached the polypeptide is released

• Translation 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 U3 Disassembly of the components follows termination of translation.

Termination- a stop codon ends translation• Ribosome breaks apart

following translation• mRNA may be translated

many times to make many copies of its polypeptide

From 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.swf

Watch 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 U4 Free 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.jpg

7.3 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, golgiapparatus, 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. 366

Image from textbook removed

7.3 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 molecule

• Poly = 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.gif

From Biology Course Companion, Allott, A, Oxford University Press, 2014, p. 368

Image from textbook removed

7.3 NOS Developments in scientific research follow improvements in computing—the 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 organisms

Faster, 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.net

7.3 U7 The sequence and number of amino acids in the polypeptide is the primary structure.

http://www.stolaf.edu/people/giannini/flashanimat/proteins/protein%20structure.swf

From i-biology.net

From i-biology.net

7.3 U8 The secondary structure is the formation of alpha helices and beta pleated sheets stabilized by hydrogen bonding.

From i-biology.net

7.3 U9 The tertiary structure is the further folding of the polypeptide stabilized by interactions between R groups.

http://www.wiley.com/college/boyer/0470003790/animations/protein_folding/protein_folding.htm

From i-biology.net

7.3 U10 The quaternary structure exists in proteins with more than one polypeptide chain.

Quaternary Structure• Complex- made of 2 or more

polypeptides folded together• Includes non-polypeptide

parts, such as the heme group in hemoglobin, found in erythrocytes (red blood cells)

• Denature: When a protein is exposed to changes in pH or high temperatures, it can permanently lose its shape and biological activity (shape of active site changes

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Can you identify the different subunits?

From http://www.bio.davidson.edu/Courses/Molbio/MolStudents/spring2010/Hua/Hemoglobin.html

From i-biology.net

From i-biology.net

From i-biology.net

Thanks to these fine folks, and any others that I may have forgotten!