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Proteins

Proteins. Proteins have many structures , resulting in a wide range of functions Proteins do most of the work in cells and act as enzymes Proteins are made of monomers called amino acids. 1. An overview of protein functions. Table 5.1. 2. Enzymes

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Proteins

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  1. Proteins Proteins have many structures, resulting in a wide range of functions Proteins do most of the work in cells and act as enzymes Proteins are made of monomers called amino acids 1

  2. An overview of protein functions Table 5.1 2

  3. Enzymes Are a type of protein that acts as a catalyst, speeding up chemical reactions Substrate binds to enzyme. 1 Active site is available for a molecule of substrate, the reactant on which the enzyme acts. 2 2 Substrate (sucrose) Glucose Enzyme (sucrase) OH H2O Fructose H O 4 Products are released. 3 Substrate is converted to products. Figure 5.16 3

  4. Polypeptides Polypeptides Are polymers (chains) of amino acids A protein Consists of one or more polypeptides 4

  5. Amino acids Are organic molecules possessing both carboxyl and amino groups Differ in their properties due to differing side chains, called R groups 5

  6. Twenty Amino Acids 20 different amino acids make up proteins CH3 CH3 CH3 CH CH2 CH3 CH3 H CH3 H3C CH3 CH2 CH O O O O O H3N+ H3N+ H3N+ H3N+ C H3N+ C C C C C C C C C O– O– O– O– O– H H H H H Valine (Val) Leucine (Leu) Isoleucine (Ile) Glycine (Gly) Alanine (Ala) Nonpolar CH3 CH2 S H2C CH2 O NH CH2 H2N C C CH2 CH2 O– CH2 O O O H H3N+ H3N+ C C C C H3N+ C C O– O– O– H H H Phenylalanine (Phe) Proline (Pro) Methionine (Met) Tryptophan (Trp) Figure 5.17 6

  7. OH NH2 O C NH2 O C OH SH CH2 CH3 OH Polar CH2 CH CH2 CH2 CH2 CH2 O O O O O O H3N+ H3N+ H3N+ H3N+ H3N+ H3N+ C C C C C C C C C C C C O– O– O– O– O– O– H H H H H H Glutamine (Gln) Tyrosine (Tyr) Asparagine (Asn) Cysteine (Cys) Serine (Ser) Threonine (Thr) Basic Acidic NH3+ NH2 NH+ O– O –O O CH2 C NH2+ C C NH Electrically charged CH2 CH2 CH2 CH2 CH2 O O H3N+ H3N+ CH2 CH2 C CH2 C C C O O– H3N+ O– CH2 C CH2 C H O H H3N+ O– C C CH2 H O O– H3N+ C C H O– H Lysine (Lys) Histidine (His) Arginine (Arg) Glutamic acid (Glu) Aspartic acid (Asp) 7

  8. Amino Acid Polymers Amino acids Are linked by peptide bonds 8

  9. Protein Conformation and Function A protein’s specific conformation (shape) determines how it functions 9

  10. Four Levels of Protein Structure Primary structure Is the unique sequence of amino acids in a polypeptide Amino acid subunits +H3NAmino end Pro Thr Gly Gly Thr Gly Glu Seu Lys Cys Pro Leu Met Val Lys Val Leu Asp Ala Arg Val Gly Ser Pro Ala Glu Lle Asp Thr Lys Ser Tyr Trp Lys Ala Leu Gly lle Ser Pro Phe His Glu His Ala Glu Val Thr Phe Val Ala Asn lle Thr Asp Ala Tyr Arg Ser Ala Arg Pro Gly Leu Leu Ser Pro Tyr Ser Tyr Ser Thr Thr Ala o Val c Val Glu – Lys o Thr Pro Asn Carboxyl end Figure 5.20 10

  11. Secondary structure Is the folding or coiling of the polypeptide into a repeating configuration Includes the  helix and the  pleated sheet H H H H H H O O O O O O O H H H H H H R R R R R R R C C C C C C C C C C C C C N N N N N N N N N N N N N C C C C C C C C C C C C C C R R R R R R H H H H H H H O O O O O O O H H H H H H H  pleated sheet H O H H Amino acidsubunits C C N N N C C C R H O H H H H H H N N N N N N  helix C C O C H H H C C C R R R R R H H C C C C C C O O O O H C R O C C O H C O N N H C C H R H R Figure 5.20 11

  12. Tertiary structure Is the overall three-dimensional shape of a polypeptide Results from interactions between amino acids and R groups Hydrophobic interactions and van der Waalsinteractions CH CH2 CH2 H3C CH3 OH Polypeptidebackbone H3C CH3 Hyrdogenbond CH O HO C CH2 CH2 S S CH2 Disulfide bridge O -O C CH2 CH2 NH3+ Ionic bond 12

  13. Quaternary structure Is the overall protein structure that results from the aggregation of two or more polypeptide subunits Polypeptidechain Collagen  Chains Iron Heme  Chains Hemoglobin 13

  14. Review of Protein Structure +H3N Amino end Amino acid subunits helix 14

  15. Sickle-Cell Disease: A Simple Change in Primary Structure Sickle-cell disease Results from a single amino acid substitution in the protein hemoglobin 15

  16. Normal hemoglobin Sickle-cell hemoglobin Primary structure Primary structure . . . . . . Exposed hydrophobic region Val His Leu Thr Pro Glul Glu Val His Leu Pro Glu Thr Val 5 6 7 3 4 5 6 7 1 2 1 2 3 4 Secondaryand tertiarystructures Secondaryand tertiarystructures  subunit  subunit     Quaternary structure Hemoglobin A Quaternary structure Hemoglobin S     Molecules interact with one another tocrystallize into a fiber, capacity to carry oxygen is greatly reduced. Function Molecules donot associatewith oneanother, eachcarries oxygen. Function 10 m 10 m Normal cells arefull of individualhemoglobinmolecules, eachcarrying oxygen Red bloodcell shape Red bloodcell shape Figure 5.21 Fibers of abnormalhemoglobin deform cell into sickle shape. 16

  17. What Determines Protein Conformation? Protein conformation Depends on the physical and chemical conditions of the protein’s environment Temperature, pH, etc. affect protein structure 17

  18. Denaturation is when a protein unravels and loses its native conformation(shape) Denaturation Normal protein Denatured protein Renaturation Figure 5.22 18

  19. The Protein-Folding Problem Most proteins Probably go through several intermediate states on their way to a stable conformation Denaturated proteins no longer work in their unfolded condition Proteins may be denaturated by extreme changes in pH or temperature 19

  20. Chaperonins Are protein molecules that assist in the proper folding of other proteins Correctlyfoldedprotein Polypeptide Cap Hollowcylinder The cap attaches, causing the cylinder to change shape insuch a way that it creates a hydrophilic environment for the folding of the polypeptide. The cap comesoff, and the properlyfolded protein is released. Steps of ChaperoninAction: An unfolded poly- peptide enters the cylinder from one end. Chaperonin(fully assembled) 2 3 1 Figure 5.23 20

  21. X-ray crystallography Is used to determine a protein’s three-dimensional structure X-raydiffraction pattern Photographic film Diffracted X-rays X-ray beam X-raysource Crystal Nucleic acid Protein (b) 3D computer model (a) X-ray diffraction pattern Figure 5.24 21

  22. Nucleic Acids • Nucleic acids store and transmit hereditary information • There are two types of nucleic acids • Deoxyribonucleic acid (DNA) • Ribonucleic acid (RNA)

  23. Function of DNA and RNA • DNA • Stores information for the synthesis of specific proteins • Found in the nucleus of cells • RNA • Reads information in DNA • Transports information to protein building structures within cell

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