Proteins. Proteins. Amino Acids. Most diverse and most important molecule in. Functions: Functions (cont d)

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1 Proteins Proteins Most diverse and most important molecule in living i organisms Functions: 1. Structural (keratin in hair, collagen in ligaments) 2. Storage (casein in mother s milk) 3. Transport (HAEMOGLOBIN!) 4. Hormonal (insulin) Proteins Functions (cont d) 5. Receptors (taste buds) 6. Contractile (actin in muscles) 7. Defensive (fibrin for clotting) 8. Enzymatic (lactase) (sophisticated) structure determines function Has its own unique 3D shape/conformation Simplest protein = polymer of amino acids (polypeptides) Amino Acids Amphiprotic (posses both acidic, carboxyl, and basic, amino groups). May be polar, nonpolar or charged depending on the R group Sequence determines the final shape (conformation) of protein. 1

2 Building proteins Polypeptide chains N-terminus = NH 2 end C-terminus = COOH end repeated sequence (N-C-C) is the polypeptide backbone can only grow in one direction Amino Acids There are 20 different R groups, thus different a.a. (amino acids) Of the 20 amino acids that make up proteins, we must consume 8, as we can not make these essential amino acids on our own: trp, met, val, thre, phe, leu, ile, lys. PolypeptideChain Ranges from a few amino acids Amino acids are joined together by peptide bonds (amide bonds) Condensation reaction between amino group and carboxyl group of adjacent amino acid 2

3 Nonpolar amino acids - nonpolar & hydrophobic Polar amino acids - polar or charged & hydrophilic Why are these nonpolar & hydrophobic? Why are these polar & hydrophillic? The Four Levels of Protein Folding Primary Structure: The sequence of amino acids in a polypeptide chain, which is determined by the nucleotide sequence of a particular gene. 3

4 The Four Levels of Protein Folding Secondary Structure: The folding and coiling of the polypeptide chain as it grows into a pleated sheet or helix H bond between C=O group and N-H group every 4 th amino acid to form alpha helix. When 2 parts of the chain lie parallel l forms a beta pleated sheet The Four Levels of Protein Folding Tertiary Structure: The polypeptide chain undergoes additional folding due to side chain interactions. Hydrophobic interaction hydrophobic regions direct themselves into core of protein Hydrogen bonds between polar R grps Ionic bonds - between (+) and (-) charged R grps Disulphide bridges- STRONG covalent bonds between 2 sulfhydryl grps (from cysteine monomers) Quaternary Structure: Two or more polypeptide chains come together, such as in collagen and haemoglobin. Chaperonin proteins Guide protein folding provide shelter for folding polypeptides keep the new protein segregated from cytoplasmic influences 4

5 Protein unfolding Temperature, salinity and ph changes can cause a protein to unravel (denature). A denatured d protein is unable to carry out its biological function. Protein denaturation Uses include: 1. meats cured by denaturing spoilage bacteria 2. Blanching fruits denatures browning enzymes 3. Temporarily curl/straighten hair (w/ heat) 4. Meats easier to chew when heat is used to denature fibrous fb proteins Protein structure (review) Nucleic Acids 1 aa sequence peptide bonds determined by DNA 2 R groups H bonds 3 R groups hydrophobic interactions, disulfide bridges 4 multiple polypeptides hydrophobic interactions Nucleic acids are found in DNA (stores hereditary info.), RNA (ribonucleic acid), ATP and nucleotide coenzymes (NAD +, NADP + and FAD) used in energy transformations. DNA and RNA are nucleotide polymers. Nucleotides consist of a nitrogenous base, a fivecarbon sugar and a phosphate group. The nitrogenous bases are: adenine (A), guanine (G), cytosine (C), thymine (T) and uracil (U). 5

6 Nucleic Acids Cytosine, thymine and uracil are single-ringed pyramidines,, while adenine and guanine are larger double-ringed purines. In DNA, A bonds with T with 2 hydrogen bonds, and G bonds with C with 3 hydrogen bonds. The two strands are antiparallel (one strand is upside down compared to the other). Purines always bond with a pyramidine. Building the polymer 6

7 Nucleic polymer Backbone sugar to PO 4 bond phosphodiester bond new base added to sugar of previous base polymer grows in one direction N bases hang off the sugar-phosphate backbone Information polymer Function series of bases encodes information like the letters of a book stored information is passed from parent to offspring need to copy accurately stored information = genes genetic information Dangling bases? Why is this important? Passing on information? Why is this important? Interesting note ATP Adenosine triphosphate modified nucleotide adenine (AMP) + P i + P i + + 7