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Proteins (aka polypeptides) 3.11-3.14 A. Polymer of amino acid monomers B. 1000s exist each with unique 3D structure that corresponds to its function C. Role in everything a cell /organism does D. Functions: 1. Enzymes- chemical catalyst 2. Structural proteins- hair and fibers of connective tissues 3. Contractile proteins- muscle 4. Defensive proteins- antibodies 5. Signal proteins- chemical messenger communication between cells 6. Receptor proteins- transmit signals into cells 7. Transport protein- help move molecules 8. Storage proteins- source of aa E. Every amino acid (20) has the following structure: Amino group Carboxyl group F. Amino acids are classified as hydrophobic or hydrophilic –nonpolar R group hydrophobic –polar R group hydrophilic Leucine (Leu) Hydrophobic Serine (Ser) Aspartic acid (Asp) Hydrophilic G. Amino acids are linked by dehydration reaction. Carboxyl group Amino acid Amino group Amino acid Carboxyl group Amino acid Amino group Amino acid Peptide bond Dehydration reaction Dipeptide 3.13 A protein’s specific shape determines its function • A polypeptide chain contains hundreds or thousands of amino acids linked by peptide bonds – The amino acid sequence causes the polypeptide to assume a particular shape – The shape of a protein determines its specific function Copyright © 2009 Pearson Education, Inc. Groove Groove 3.14 A protein’s shape depends on four levels of structure • A protein can have four levels of structure – – – – Primary structure Secondary structure Tertiary structure Quaternary structure Copyright © 2009 Pearson Education, Inc. 3.14 A protein’s shape depends on four levels of structure • primary structure- unique amino acid sequence – The correct amino acid sequence is determined by the cell’s genetic information – The slightest change in this sequence affects the protein’s ability to function Copyright © 2009 Pearson Education, Inc. Four Levels of Protein Structure Primary structure Amino acids 3.14 A protein’s shape depends on four levels of structure • secondary structure- coiling or folding of the polypeptide as result of H bonds between areas of polypeptide chain – Coiling results in a helical structure called an alpha helix – Folding may lead to a structure called a pleated sheet Copyright © 2009 Pearson Education, Inc. Four Levels of Protein Structure Primary structure Amino acids Hydrogen bond Secondary structure Alpha helix Pleated sheet 3.14 A protein’s shape depends on four levels of structure • Tertiary structure- overall 3D shape of a protein – results from interactions between the R groups of the various amino acids – Shape stabilized by clustering of hydrophobic R groups, H bonds, and ionic & covalent bonds Copyright © 2009 Pearson Education, Inc. Four Levels of Protein Structure Primary structure Amino acids Hydrogen bond Secondary structure Alpha helix Tertiary structure Polypeptide (single subunit of transthyretin) Pleated sheet 3.14 A protein’s shape depends on four levels of structure Quaternary Structure- occurs in proteins with more than one polypeptide; described as globular or fibrous Four Levels of Protein Structure Primary structure Amino acids Hydrogen bond Secondary structure Alpha helix Tertiary structure Quaternary structure Polypeptide (single subunit of transthyretin) Transthyretin, with four identical polypeptide subunits Pleated sheet 3.13 A protein’s specific shape determines its function • If for some reason a protein’s shape is altered, it can no longer function – Denaturation will cause polypeptide chains to unravel and lose their shape and, thus, their function – Proteins can be denatured by changes in salt concentration and pH Copyright © 2009 Pearson Education, Inc. 3.16 Nucleic acids are information-rich polymers of nucleotides • DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are composed of monomers called nucleotides – Nucleotides have three parts – A five-carbon sugar called ribose in RNA and deoxyribose in DNA – A phosphate group – A nitrogenous base Copyright © 2009 Pearson Education, Inc. Nitrogenous base (adenine) Phosphate group Sugar 3.16 Nucleic acids are information-rich polymers of nucleotides • a polynucleotide forms when the phosphate of one nucleotide bonds to the sugar of the next nucleotide • DNA double helix-two polynucleotide strands wrap around each other – The two strands are associated because particular bases always hydrogen bond to one another – A pairs with T, and C pairs with G, producing base pairs • RNA is usually a single polynucleotide strand Copyright © 2009 Pearson Education, Inc. Base pair 3.16 Nucleic acids are information-rich polymers of nucleotides • A particular nucleotide sequence that can instruct the formation of a polypeptide is called a gene – Most DNA molecules consist of millions of base pairs and, consequently, many genes – These genes, many of which are unique to the species, determine the structure of proteins and, thus, life’s structures and functions Copyright © 2009 Pearson Education, Inc. 3.17 EVOLUTION CONNECTION: Lactose tolerance is a recent event in human evolution • Mutations are alterations in bases or the sequence of bases in DNA – Lactose tolerance is the result of mutations – In many people, the gene that dictates lactose utilization is turned off in adulthood – Apparently, mutations occurred over time that prevented the gene from turning off – This is an excellent example of human evolution Copyright © 2009 Pearson Education, Inc. Amino acids Primary structure Amino acids Hydrogen bond Alpha helix Secondary structure Pleated sheet Polypeptide (single subunit of transthyretin) Tertiary structure Transthyretin, with four identical polypeptide subunits Quaternary structure