Lecture 3 - Jan. 27

Lecture 3 - Jan. 27 - Cell Biology 341 Last lecture: 4...

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Cell Biology 341 Friday, January 27, 2012 Today: Chapter 3 on protein structure Noncovalent bonds stabilize the three dimensional structure of a protein Go to Molviz.org and view the Hemoglobin and Antibody (parts 1-4) tutorials Next: back to chapter 2 on catalysis Last lecture: 4 types of noncovalent bonds: Ionic bonds Hydrogen bonds-effect on properties of aqueous solutions Hydrophobic forces: amphiphilic molecules such as fatty acids are excluded from water Van der Waals attractions 20 amino acids are the building blocks of proteins
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Chapter 3: Protein Structure and Function Part 1: How proteins fold into the most stable conformation pages 125-152
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Functions of Proteins Proteins most structurally and functionally complex molecules Enzymes catalyze reactions. Some proteins provide support or structure (collagen is a fibrous protein) Receptors and antibodies(immune system) (figure 3-41) bind specific molecules or signals Some proteins act as hormones or regulatory molecules (e.g. insulin, growth hormones, transcription factors(gene expression), testosterone, estrogen) Some proteins transport smaller molecules across the plasma membrane or membranes surrounding organelles. AAs given either one-letter or three-letter abbreviations (e.g. Alanine = A; Ala)
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Proteins are long, linear polymers of amino acids. There are 20 different amino acids commonly found in proteins. (20 common ones + a few more) the side chain (R group) may be acidic, basic, hydrophobic or polar (shown on page 128-129) Only the L-amino optical isomers are found in proteins base acid Alanine, a nonpolar(due to presence of –CH3 side chain) amino acid(19 other AAs differ in side chains.) - Amino acid ionized at pH = 7
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peptide bonds make up polypeptides .) No branching occurs. - No overlapping of atoms and steric interactions between side chains limit 3-D conformations.(Folding occurs, nevertheless.) In a protein, the linear sequence of amino acids linked by covalent peptide bonds is called the primary structure (linear sequence of proteins) Polypeptide bond - planar, rigid, always linear (no free rotation) (Repeating sequence of polypeptide bonds = Polypeptide backbone ) - Always read from the N-terminus C- terminus. The unique sequence of each type of protein, as well as the properties of the 20 different amino acid side chains, determines the overall structure of the folded protein The most stable 3-D structure is largely determined by noncovalent bonds All AAs, except glycine, have D-forms and L-forms(optical isomers). L-forms found in proteins; D-forms found in bacterial cell walls and antibiotics) 5 of 20 AAs have side chains with charges. Figure 2-24
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This note was uploaded on 02/05/2012 for the course BIO 341 taught by Professor Noris during the Spring '09 term at Rhode Island.

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Lecture 3 - Jan. 27 - Cell Biology 341 Last lecture: 4...

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