Lecture 5 - Protein Processing

Lecture 5 - Protein Processing - Lecture 5 Background...

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1 Protein Processing Biology 1F25 for Biology Non-Majors Lecture 5 Background Reading Textbook, Chapters 2 and 21 The People Who Prepared This Lecture Harry Peery Jeff Stuart Protein processing: the rest of the story • Once synthesized on the ribosomes, the protein must be processed.
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2 The Endoplasmic Reticulum • It goes first into the endoplasmic reticulum where some of the amino acids are clipped off. • The protein is folded and disulfide bonds are formed. • Once finished, the wall of the endoplasmic reticulum bulges out. • It carries the protein in the bulge. • The bulge is pinched off to form transport vesicles. The transport vesicles join together and become the Golgi Apparatus • Inside the Golgi the protein undergoes additional processing. Transport vesicles from the endoplasmic reticulum Illustration by Russell Knightly Media, Canberra, Australia The finished protein is packaged for export or for use in the cell. Transport vesicles are from the endoplasmic reticulum Camilo Golgi (1843-1926) as he looked in 1898 (age 55), the year of his discovery of the organelle. Secretory granules Insulin is an example of protein processing • Is synthesized on the ribosome as 109 amino acids and called preproinsulin. • Is inactive in this form. • Must be processed during which it is cut down to 51 amino acids – less than half the original peptide
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3 The Processing Sequence of Insulin O 23 amino acids are cut off after preproinsulin enters the endoplasmic reticulum Another 35 are cut off in the secretory granule prior to release to form C-peptide (31 amino acids) and insulin (4 are lost in the cut). 1. Preproinsulin Disulfide bonds joins the A and B chains together – this also occurs in the endoplasmic reticulum Coloured and labeled ovals form insulin which is composed of 51 amino acids 1 3 2 Modified from Porth, Pathophys- iology, 5 th ed. 1998 Lippincott. 2. Proinsulin 3. Insulin is formed just before being released from the cell Insulin • Preproinsulin – synthesized on the ribosomes (inactive) • Proinsulin – formed in the endoplasmic reticulum (Inactive) • Enzymes which will activate insulin are added in the Golgi complex. • Insulin with C-peptide attached are transported in secretory vesicles to the cell membrane where they are stored. • Insulin – formed in the secretory vesicles just before release from the cell membrane (active) along with C- peptide in response to a rise in blood glucose or potassium. • C-peptide has recently been found to be a hormone but
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This note was uploaded on 06/10/2008 for the course BIOL BIOL-1F25 taught by Professor Peery during the Spring '08 term at Brock University, Canada.

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Lecture 5 - Protein Processing - Lecture 5 Background...

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