Fig. 5-17 Nonpolar Fig. 5-17a Nonpolar Glycine (Gly or G) Alanine (Ala or A) Valine (Val or V) Leucine (Leu or L) Isoleucine (Ile or I) Methionine (Met or M) Phenylalanine (Phe or F) Polar Trypotphan (Trp or W) Proline (Pro or P) Glycine (Gly or G) Alanine (Ala or A) Valine (Val or V) Leucine (Leu or L) Isoleucine (Ile or I) Serine (Ser or S) Threonine (Thr or T) Cysteine (Cys or C) Tyrosine (Tyr or Y) Asparagine (Asn or N) Glutamine (Gln or Q) Acidic Electrically charged Basic Methionine (Met or M) Phenylalanine (Phe or F) Tryptophan (Trp or W) Proline (Pro or P) Aspartic acid (Asp or D) Glutamic acid (Glu or E) Lysine (Lys or K) Arginine (Arg or R) Histidine (His or H) Fig. 5-17b Fig. 5-17c Polar Acidic Electrically charged Basic Serine (Ser or S) Threonine (Thr or T) Cysteine (Cys or C) Tyrosine (Tyr or Y) Asparagine (Asn or N) Glutamine (Gln or Q) Aspartic acid (Asp or D) Glutamic acid (Glu or E) Lysine (Lys or K) Arginine (Arg or R) Histidine (His or H) 1
pep0de bonds Amino Acid Polymers Fig. 5-18 Peptide bond Covalent bond between C and N linking amino acids Polypep8des (a) range in length from a few to more than a thousand monomers Amino acid sequence dictates type of polypep8de and ul8mately type of protein Peptide bond Side chains Backbone (b) Amino end (N-terminus) Carboxyl end (C-terminus) Protein and Func0on Fig. 5-19 func8onal protein consists of one or more polypep8des twisted, folded, and coiled into a unique shape Groove Groove (a) A ribbon model of lysozyme (b) A space-filling model of lysozyme 2
Protein and Func0on Fig. 5-20 Sequence of amino acids determines a protein s three dimensional Protein s determines its func8on Fit substrate in in specific lock and key fashion Antibody protein Protein from flu virus Four Levels of Protein Four Levels of Protein Primary (1 ) sequence of amino acids Secondary (2 ) ini8al folding consists of coils (alpha() helices) and folds (beta() sheets) in the polypep8de chain Ter8ary (3 ) determined by interac8ons among various side chains (R groups) combina8ons of helices and sheets Quaternary (4 ) results when a protein consists of mul8ple polypep8de chains Primary Sequence of amino acids Dictated by sequence of nucleo8des in DNA Codon set of three nucleo8des code for a specific amino acid 3
Fig. 5-21 Four Levels of Protein secondary result from hydrogen bonds between amino acids Primary Tertiary Secondary pleated sheet +H N 3 Amino end Quaternary But between amino acid side chains, but between parts of the backbone helices Examples of amino acid subunits coiled Between every fourth amino acid kera8n hair helix pleated sheet Accordian folds Fibrous proteins Fig. 5-21c Fig. 5-21d Secondary pleated sheet Abdominal glands of the spider secrete silk fibers made of a structural protein containing pleated sheets. Examples of amino acid subunits The radiating strands, made of dry silk fibers, maintain the shape of the web. helix The spiral strands (capture strands) are elastic, stretching in response to wind, rain, and the touch of insects. 4
Ter0ary Four Levels of Protein Combina8ons of helices and pleated sheets determined by interac8ons between R groups, rather than interac8ons between backbone cons8tuents hydrogen bonds ionic bonds hydrophobic interac0ons van der Waals interac8ons Strong covalent bonds called disulfide bridges may reinforce the protein s Quaternary results when two or more polypep8de chains form one macromolecule Collagen fibrous protein consis8ng of three polypep8des coiled like a rope Hemoglobin Four Levels of Protein globular protein consis8ng of four polypep8des: two alpha and two beta chains Fig. 5-21e Fig. 5-21g Polypeptide chain Chains Tertiary Quaternary Iron Heme Collagen Chains Hemoglobin 5
Sickle Cell Disease: A Change in Primary Slight change in primary Fig. 5-22 Primary Secondary and tertiary s Normal hemoglobin Val His Leu Thr Pro Glu Glu 1 2 3 4 5 6 7 subunit Primary Secondary and tertiary s Exposed hydrophobic region Sickle-cell hemoglobin Val His Leu Thr Pro Val Glu 1 2 3 4 5 6 7 subunit can affect a protein s and ability to func8on Sickle cell disease Quaternary Normal hemoglobin (top view) Quaternary Sickle-cell hemoglobin inherited blood disorder results from a single amino acid subs8tu8on in the protein hemoglobin Function Red blood cell shape Molecules do not associate with one another; each carries oxygen. Normal red blood cells are full of individual hemoglobin moledules, each carrying oxygen. 10 µm Function Red blood cell shape Molecules interact with one another and crystallize into a fiber; capacity to carry oxygen is greatly reduced. Fibers of abnormal hemoglobin deform red blood cell into sickle shape. 10 µm What Determines Protein? In addi8on to primary physical and chemical condi8ons can affect ph salt concentra8on Temperature other environmental factors can cause a protein to unravel Denatura0on loss of a protein s na8ve is called biologically inac8ve 6