lec01 - MIT OpenCourseWare http:/ocw.mit.edu 7.88J Protein...

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MIT OpenCourseWare http://ocw.mit.edu 7.88J Protein Folding Problem Fall 2007 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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Lecture Notes - 1 7.24/7.88J/5.48J The Protein Folding Problem Student Review: Side chains of the L amino acids and their pK's L/D difference Planarity of the peptide Bond Lecture Overview: Introduction to the protein folding problem This course and your role in it Peptide Bonds and Polypeptide Chains Fibrous proteins and the Pauling/Corey alpha helices Introduction to the Protein Folding Problem A. The Great Diversity of Protein Functions: Proteins constitute both the building blocks and the machinery of all cells. They carry out an enormous variety of functions that permit cells to grow and reproduce themselves Enzymes –synthetic and degradative Hormones Receptors Membrane structural proteins o Porins o Ion channels o Transporters o Photosynthesis o ATP/energy generators o Photoreceptors Replicases and polymerases Globular Structural proteins –tubulin, flagellin Fibrous structural proteins – collagens, keratins Motor proteins –kinesins, myosin
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B. Properties are determined by Amino Acid Sequences: Prior to World War II, it was generally believed that the properties of proteins were determined by their amino acid composition. However as a result of Frederick Sanger’s (1949-1951) development of methods for determining order of amino acids along the polypeptide chain, followed by the actual complete determination of the insulin sequence, it became clear that properties depended on the sequence of amino acids. Proteins represented: Linear polymers of 20 species of amino acids, without branches. All molecules of a species had exactly specified sequences of amino acids, without permutations. Question for reflection: Why aren’t amino acid sequences branched? For Discussion Next Monday: The combination of the amino acid sequence determination with structural studies led to the emergence of the critical point: However: Unfolded Proteins have few Specific Properties! Scrambled Eggs: Jell-O: Properties of Proteins reflect Interaction of linear sequence of side chains to determine spatial: C. Functions Depend on Sequence operating in highly organized 3- Dimensional structure. Relationship between sequence and structure fundamental question in modern biology and subject of this course! D. How many kinds of proteins do organisms use? Subsequent advances in sequencing of complete genomes have resulted in relatively accurate estimates of the number of kinds of proteins that organisms make use of: Prokaryotes: 1,600 – 5,000 Eukaryotes: 10,000 – 50,000.
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E. Distribution of Lengths of Biological Polypeptide Chains Figure 1.0: Protein Length (Amino Acids) This data shows the distribution of polypeptide chain length for a variety of species: In eight microbial genomes, average length about 340 residues
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lec01 - MIT OpenCourseWare http:/ocw.mit.edu 7.88J Protein...

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