1 / 7

Translation

Translation. Translation is the process of building a protein from the mRNA transcript. The protein is built as transfer RNA ( tRNA ) bring amino acids (AA), one at a time, to the ribosomal unit holding the mRNA. tRNA.

glynis
Download Presentation

Translation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Translation • Translation is the process of building a protein from the mRNA transcript. The protein is built as transfer RNA (tRNA) bring amino acids (AA), one at a time, to the ribosomal unit holding the mRNA.

  2. tRNA • 3D structure has an attachment site for an AA on one side and the anticodon on the other • anticodon is the complimentary sequence to the mRNA codon • if the mRNA is AAA the tRNA is UUU the AA attached is phe (phenylalanine) • is "L" shaped with a 3' attachment site for an AA and a loop on the other side that carries the anticodon • each tRNA is specific for the AA it attaches to • 45 different versions in the cytoplasm at all times that correspond to the different AAs • should be 61 for the different codons • a few can bind to multiple codons due to a loosely attached 3' site - wobble

  3. tRNA are joined to the correct AA by the enzyme aminoacyl-tRNAsynthetase • each synthetase fits ONLY the tRNA and AA it is specific for • 20 different versions in the cytoplasm at all times • catalyzes the attachment of the AA to the tRNA with the use of ATP • the released tRNA/AA complex is called an activated tRNA or aminoacyltRNA • the activated tRNA delivers its AA to the growing polypeptide chain

  4. Ribosomes • Ribosomes facilitate the binding of the tRNA to the mRNA by aligning the active sites and holding them in place. • Structure • ribosomes are made of mostly ribosomal RNA (rRNA) that is made from DNA that resides in the nucleolus • consists of a large unit and a small unit • each is made of rRNA and proteins imported from the cytoplasm • once assembled the 2 units are exported to the cytoplasm via membrane pores in the nuclear envelope • has 3 binding sites • A - site binds next tRNA with AA atached • P - site binds the tRNA whose AA is being attached to the growing chain • E - site binds the leaving tRNA minus the AA (already attached to the growing chain)

  5. Initiation of translation • Small ribosomal subunit binds with the mRNA and searches for the start codon (AUG) • initiation tRNA (Met) binds to the P-site of the small unit • union of the mRNA & tRNA establishing the reading frame • large unit attaches after the union is made completing the initiation complex - translation begins • proteins called initiation factors bring the units together • energy from GTP is used in the formation of the unit

  6. Elongation of Growing Polypeptide • requires several proteins called elongation factors • 3 GTP are required for each translocation steps (APE) • mRNA moves from 5' to 3' • AAs are added N-terminus to C-terminus with new AAs added to the carboxyl end • elongation ends when a stop is reached - UAG, UAA, UGA • do not code for an AA but binds to a release factor that binds to the adjacent A-site • the release factor binds a water molecule to the end of the polypeptide hydrolyzing the chain • the ribosomal unit comes apart • may be translated by many ribosomes at the same time - ployribosomal unit

  7. Post Translation Modifications • proteins begin to spontaneously fold as they are synthesized • some will require additional proteins (chaperonins) • free ribosomes make proteins destined for the cytosol • bound ribosomes make proteins for the membrane systems of the cell • (NucEnv, ER, Golgi, Lysosomes, Vacuoles, Plasma membrane) as well as secreted proteins (Insulin) • ALL start as free ribosomes and bind to the ER if a signal peptide is present • about 20 peptides that form the signal-recognition particle (SRP) which attaches to the ER • after attachment the SRP is removed by enzymes and translation of the membrane protein continues • each membrane system has its own unique SRP - much like a zip code

More Related