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Chapter 20. Protiens

Chapter 20. Protiens. Sections…. The protein made by spiders to produce a web is a form of silk that can be exceptionally strong. Chapter 20. Proteins.

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Chapter 20. Protiens

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  1. Chapter 20. Protiens Sections… • The protein made by spiders to produce a web is a form of silk that can be exceptionally strong.

  2. Chapter 20. Proteins 20.1 Characteristics of Proteins20.2 Amino Acids: The Building Blocks for Proteins20.3 Chirality and Amino Acids20.4 Acid-Base Properties of Amino Acids20.5 Cysteine: A Chemically Unique Amino Acid20.6 Peptide Formation20.7 Biochemically Important Small Peptides20.8 General Structural Characteristics of Proteins20.9 Primary Structure of Proteins20.10 Secondary Structure of Proteins20.11 Tertiary Structure of Proteins20.12 Quaternary Structure of Proteins20.13 Fibrous and Globular Proteins20.14 Protein Hydrolysis20.15 Protein Denaturation20.16 Glycoproteins20.17 Lipoproteins

  3. Chapter 21. Protein and the Amino Acids These are biopolymers that are constructed from a limited set of amino acids. They are the most plentiful organic substances in the cell. About half of the dry mass of a cell is composed of proteins. They serve a wide range of functions.

  4. Protein function Enzymes biological catalysts. Immuno- antibodies of immune system. globulins Transport move materials around -hemoglobin for O2. Regulatory hormones, control of metabolism. Structural coverings and support - skin, tendons, hair, bone. Movementmuscle, cilia, flagella.

  5. Types of Proteins

  6. Amino acids All proteins are composed of amino acids. Twenty common amino acids. All are -amino acids. Except for proline, primary amino- group is attached to the  carbon - the carbon just after the acid group. General Structure

  7. Handedness/Chirality of Amino Acids

  8. Amino acids Because both acid and base groups are present, an amino acid can form a +/- ion. H H | | R-C-COOH R-C-COO- | | NH2 NH3+ The position of the equilibrium is based on pH and the type of amino acid. Called azwitterion.

  9. H | CH2-C-COO- | +NH3 N H Some amino acid examples H3CH \ | HC-C-COO- / | H3C+NH3 H | CH3-C-COO- | +NH3 alanine valine H | CH3 -S-CH2-CH2-C-COO- | +NH3 methionine tryptophan

  10. Some amino acid examples H | H-C-COO- | +NH3 H | HO-CH2-C-COO- | +NH3 glycine serine O H | || -O-C-CH2-CH2-C-COO- | +NH3 OH | || H2N-C-CH2-C-COO- | +NH3 glutamic acid asparagine

  11. Groups of Amino Acids Hydrophobic Polar, neutral Negatively charged-Acidic positively charged-Basic

  12. Non-polar Amino Acids

  13. Ploar/Neutral Amino Acids

  14. Ploar Acidic/Basic Amino Acids

  15. Abbreviations glycineGly G alanineAla A valineVal V leucineLeu L isoleucineIle I methionineMet M phenylalanine Phe F tryptophan Trp W ProlinePro P

  16. Primary protein structure Proteins are polymers made up of amino acids. Peptide bond - how the amino acids are linked together to make a protein. H | H2NCCOOH | R H | H2NCCOOH | R’ H O | || H2N - C - C - | R H | N - C - COOH | | H R’ + + H2O

  17. Four levels of protein structure Primary structure The sequence of amino acids in a protein. Secondary structure Way that chains of amino acids are coiled or folded - (-helix, -sheet, random coil). Tertiary structure Way -helix, -sheet, random coils fold and coil. Quaternary structure Way that two or more peptide chains pack together.

  18. Three levels of structure: telephone cord

  19. H O | || H2N - C - C | R H O | || - NH - C - C - | R’ H | N - C - COOH | | H R’’ Summary of protein structure primary secondary quaternary tertiary

  20. H O | || H2N - C - C | R H O | || - NH - C - C - | R’ H O | || - NH - C - C - | R’’ H | NH - C - COOH | R’’’ Primary structure All proteins have the same covalent backbone. Part of a protein.

  21. Separation of three amino acids Separation of Lys, Phe, and Glu using electrophoresis after hydrolysis of protein

  22. Secondary structure Long chains of amino acids commonly fold or curl into a regular repeating structure. Structure is a result of hydrogen bonding between amino acids within the protein. Common secondary structures are:  - helix  - pleated sheet Secondary structure adds new properties to a protein like strength, flexibility, ...

  23. -helix Every amide hydrogen and carbonyl oxygen is involved in a hydrogen bond.

  24. Representations of the helix secondary structure

  25. -helix One common type of secondary structure. Properties of an -helix include strength and low solubility in water. Originally proposed by Pauling and Corey in 1951.

  26. The coiled-coil structures The coiled-coil structure of the fibrous protein beta kerotin.

  27. Collagen Family of related proteins. About one third of all protein in humans. Structural protein Provides strength to bones, tendon, skin, blood vessels. Forms triple helix -tropocollagen.

  28. Collagen

  29. R | C R | C O || C O || C H | N H | N N | H C || O C || O N | H C | R C | R C | R R | C R | C O || C H | N O || C H | N N | H C || O C || O N | H C | R C | R C | R -Pleated sheets Another secondary structure for protein. Held together by hydrogen bonding between adjacent sheets of protein. The hydrogen bonding between the carbonyl oxygen atom of one peptide linkage and the amide hydrogen atom of another peptide linkage.

  30. -Pleated sheets Silk fibroin - main protein of silk is an example of a  pleated sheet structure. Composed primarily of glycine and alanine. Stack like corrugated cardboard for extra strength.

  31. -Pleated sheets

  32. Tertiary structure of proteins Fibrous proteins • insoluble in water • form used by connective tissues • silk, collagen, -keratins Globular proteins • soluble in water • form used by cell proteins • 3-D structure - tertiary

  33. Tertiary structure of proteins Results from interaction of side chains. The protein folds into a tertiary structure. Possible side chain interactions: Similar solubilities Ionic attractions Electrostatic attraction between + and -sidechains Covalent bonding

  34. Tertiary Structure

  35. -O \ H -O \ H Tertiary Structure of Proteins Sulfide crosslink Hydrophobic interaction - S - S - -COO- H3N+- Hydrogen bonding Salt bridge

  36. Four types of interactions between amino acid R groups

  37. Quaternary structure of proteins Many proteins are not single peptide strands. They are combinations of several proteins • aggregate of smaller globular proteins. Conjugated protein- incorporate another type of group that performs a specific function. prosthetic group

  38. Quaternary structure of proteins Aggregate structure This example shows four different proteins and two prosthetic groups.

  39. Hemoglobin and Myoglobin Hemoglobin Oxygen transport protein of red blood cells. Myoglobin Oxygen storage protein of skeletal muscles. As with the cytochrome example, both proteins use heme groups. It acts as the binding site for molecular oxygen.

  40. Heme myoglobin 1 heme group hemoglobin 4 heme groups

  41. Myoglobin Heme

  42. Hemoglobin 2 chains 4 heme 2 chains

  43. Oxygen Transport

  44. Example - cytochrome C 550 Heme structure Contains Fe2+ Used in metabolism. Aggregate of proteins and other structures.

  45. Sickle cell anemia Defective gene results in production of mutant hemoglobin. Still transports oxygen but results in deformed blood cells - elongated, sickle shaped. Difficult to pass through capillaries. Causes organ damage, reduced circulation. Affects 0.4 % of African-American.

  46. Comparison of normal and sickle cell hemoglobin Normal Sickle

  47. Denaturation of Proteins The loss of secondary, tertiary, and quaternary structures 1) pH extremes. 2). Heat - 3). Mechanical Agitation (foaming) 4). Detergents 5). Organic Solvents 6). Inorganic Salts -

  48. Heat-Denaturation of Proteins

  49. Permanent for Hair

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