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 protein

Understandings• Initiation 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/Skills

• A: 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

http://melajr.files.wordpress.com/2012/03/ribosome-subunit.jpg

Composed of rRNA and proteins

Holds the tRNA carrying the next amino acid to be added to the chain

Holds the tRNA carrying the growing chain

Site from which tRNA that has lost its amino acid is discharged

tRNA

Adapted from http://classconnection.s3.amazonaws.com/185/flashcards/82185/jpg/6_361320375541451.jpg

5’3’ CUU CGC GUAGCA

The amino acid attached is determined by a particular enzyme (20 AA’s 20 enzymes)

Activated Amino Acid

Initiation• Activated amino acid (methionine) attaches to a

tRNA with the anticodon UAC• This combines with an mRNA and small ribosomal

subunit• Small subunit moves down the mRNA until it

reaches the codon AUG• H bonds form between the initiator tRNA and start

codon• Large subunit combines with these parts along with

initiation factors (proteins) and GTP (similar to ATP)

Elongation • tRNA’s bring amino acids to the mRNA-

ribosomal complex • Elongation factors assist in binding the tRNA’s

to the mRNA codons• Initiator tRNA moves to the P site• Ribosomes catalyze the formation of peptide

bonds between the amino acids

http://www.tokresource.org/tok_classes/biobiobio/biomenu/transcription_translation/translation_1.jpg

Translocation• Occurs during elongation• Movement of tRNA’s from one site to another• A siteP siteE site• Occurs in the 5’ 3’ direction

http://www.tokresource.org/tok_classes/biobiobio/biomenu/transcription_translation/translation_1.jpg

Termination• Stop codon appears in the A site• A release factor fills the A site and catalyzes hydrolysis of the

bond between the tRNA in the P site and the amino acid chain• Polypeptide is released• Ribosomal subunits separate from the mRNA

http://thelessonlocker.com/kvhs/biology/translation_termination.jpg

https://tse1.mm.bing.net/th?id=OIP.kN81dMnIelR1Clg0mXqwJgEsCz&pid=15.1&P=0&w=253&h=152 http://bio3400.nicerweb.com/Locked/media/ch14/14_09-polysomes.jpg

Video

Primary Organization• Sequence of amino acids• Determines the next 3 levels• Changing one amino acid can result in a dysfunctional protein

http://mykelmedia.com/wp-content/uploads/2010/11/sickle-cell.jpg

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

http://www.abcte.org/files/previews/biology/BioMod%203%5B1%5D.3%20secondary%20structure.jpg

Tertiary Organization• Three-dimensional configuration as a result of

interactions between R-groups• Disulfide bridges: covalent bonds between sulfur

atoms• H-bonds • Van der Waals interactions: hydrophobic R-groups

forced inward and hydrophilic R-groups interact with water in aqueous solutions• Ionic bonds

https://bestofbiochemistry.files.wordpress.com/2013/03/tertiary_structure.jpg

Quaternary Structure• Two 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 Globular

- Many polypeptide chains in a long narrow shape- Generally insoluble in water- Ex: Collagen

- More three dimensional in shape- Generally water soluble- Ex: Insulin

http://www.extremepeptides.com/blog/wp-content/uploads/2013/05/2GF1_Insulin-Like_Growth_Factor_Nmr_Minimum_Average_Structure01.pnghttp://www.prevention.com/sites/prevention.com/files/static/comp-3974997-collagen_0.jpg