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Protein structure


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Protein structure

  1. 1. Protein Structure Topic 7.5
  2. 2. Proteins- a.k.a.* polypeptides <ul><li>Peptide- short chain of amino acids </li></ul><ul><ul><li>Dipeptides- 2 amino acids bonded together </li></ul></ul><ul><ul><li>Polypeptides- many amino acids bonded together </li></ul></ul><ul><li>Peptide bond between amino acids </li></ul><ul><ul><li>Formed by condensation reaction </li></ul></ul><ul><ul><li>Broken by hydrolysis </li></ul></ul><ul><li>Have up to 4 levels of organization </li></ul><ul><ul><li>All have 3 levels, most have 4 levels </li></ul></ul>* a.k.a.- a lso k nown a s
  3. 3. Primary Structure <ul><li>sequence of amino acids </li></ul><ul><li>precise sequence is determined by genes </li></ul><ul><ul><li>Changing one of the amino acids in a sequence can change entire protein </li></ul></ul><ul><li>Polypeptide chains can be 50 to 1000 amino acids in length </li></ul><ul><li>R groups of the amino acids aid in shaping the protein </li></ul><ul><li>Example: Lysosyme- has 129 amino acids, all in a very specific order. </li></ul>
  4. 4. Secondary Structure <ul><li>Describes the shape of the protein </li></ul><ul><ul><li>2 types: Alpha helices and Beta pleated sheets </li></ul></ul><ul><li>Local folding, short distance interactions </li></ul><ul><li>Can have a mixture of both </li></ul><ul><li>Determined by the Hydrogen bonds across amino acids (the R groups) </li></ul><ul><ul><li>From the carboxyl (C=O) group of one a.a. and the amino group (N-H) of another a.a. </li></ul></ul><ul><ul><li>H-bonds help to stabilize the helices or pleated sheets </li></ul></ul>
  5. 5. Alpha helix Beta pleated sheet Protein with a mixture of both helices and sheets
  6. 6. Tertiary Structure <ul><li>Overall 3-dimensional shape of proteins </li></ul><ul><li>Shape results from further interactions between R groups across that are ‘distant’ </li></ul><ul><ul><li>Also influenced by the aqueous environment- WHY? </li></ul></ul>
  7. 7. Tertiary Structure <ul><li>Interactions include: </li></ul><ul><ul><li>+charged R groups interacting with -charged R groups </li></ul></ul><ul><ul><li>Hydrophobic amino acids orient themselves away from the water, towards the interior to avoid contact </li></ul></ul><ul><ul><li>Hydrophilic amino acids orient themselves towards water (outward) </li></ul></ul><ul><ul><li>Hydrogen bonds between polar R groups </li></ul></ul><ul><ul><li>Disulfide bridges between cysteines (both R groups have sulfur atoms that covalently bond to each other) </li></ul></ul><ul><li>Formed/Maintained by more distant interactions between R groups </li></ul><ul><li>Globular proteins, have a hydrophobic core </li></ul>
  8. 9. Polar and electrically charged amino acids
  9. 10. Non-polar amino acids
  10. 11. With a partner, make a hypothetical chains of at least 25 amino acids (primary structure). Show how the amino acids could potentially interact to make a tertiary structure for a protein.
  11. 12. Quaternary Structure <ul><li>More than 1 chain of polypeptides that fit together . </li></ul><ul><li>Often has a prosthetic group - a non-protein atom or molecule embedded in it. </li></ul><ul><li>Example- hemoglobin has 4 polypeptide chains with 4 iron prosthetic groups . </li></ul>
  12. 13. Lysozyme- an example Primary Structure Secondary Structure Tertiary Structure
  13. 14. 2 main categories of protein shapes <ul><li>Globular Proteins- </li></ul><ul><ul><li>Have hydrophobic amino acids in the interior, hydrophilic on the outside </li></ul></ul><ul><ul><li>Compact and rounded </li></ul></ul><ul><ul><li>Soluble in water </li></ul></ul><ul><ul><li>Example- Enzymes, hemoglobin, insulin, anti-bodies </li></ul></ul><ul><li>Fibrous Proteins- </li></ul><ul><ul><li>Elongated shapes, tough and insoluble </li></ul></ul><ul><ul><li>Example- collagen in skin, keratin in hair </li></ul></ul>
  14. 15. Fibrous protein Globular protein
  15. 16. Structure leads to function <ul><li>Biological activity of the molecule is determined by its structure </li></ul><ul><li>If the structure is changed, the function will change. </li></ul><ul><li>Ability to recognize and bind to some other molecule important to many proteins </li></ul><ul><ul><li>Ex.- antibodies and enzymes </li></ul></ul>
  16. 17. <ul><li>Non-polar amino acids </li></ul><ul><li>-water insoluble </li></ul><ul><li>-stabilize the entire protein when found in the center of water soluble amino acids </li></ul><ul><li>-cause proteins to remain embedded in the cell membrane </li></ul>Polar and Non-polar amino acids
  17. 18. <ul><li>Polar Amino Acids: </li></ul><ul><li>-water soluble (remember water is polar/when considering polarity ‘like attracts like’) </li></ul><ul><li>-In the cell membrane: </li></ul><ul><li>1. create channels in the proteins for hydrophobic substances to pass through </li></ul><ul><li>2. cause parts of membrane proteins to protrude from the cell membrane </li></ul><ul><li>3. Transmembrane proteins have two polar regions (one on surface and one in channel) </li></ul>Polar and Non-polar amino acids
  18. 19. Ways to change the structure of a protein <ul><li>pH </li></ul><ul><li>High temperature </li></ul><ul><li>If the shape of the protein changes, it will no longer be able to function in the same way. </li></ul><ul><li>Denatured- protein is permanently changed </li></ul>
  19. 21. <ul><li>sickle cell anemia- shows how primary sequence affects the quaternary structure. </li></ul>