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Proteins

Proteins. Option B2 IB Chem Text p. 1080-1085 Oxford p. 92-94. 1. Building blocks of proteins. There are 20 different amino acids that make up human proteins. Amino Acids. 2. 3. Alpha Amino Acids. General structure Carboxyl group -COOH Amino group -NH 2 R group

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Proteins

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  1. Proteins Option B2 IB Chem Text p. 1080-1085 Oxford p. 92-94 1

  2. Building blocks of proteins. • There are 20 different amino acids that make up human proteins Amino Acids 2

  3. 3

  4. Alpha Amino Acids General structure Carboxyl group -COOH Amino group -NH2 R group usually a carbon chain other structures possible 4

  5. Depends on the character of the side chain attached. Amino Acids and Proteins 5

  6. In solution, a dipolar ion form is known as a Zwitterion. The Zwitterion Zwitterions are amphoteric in nature (capable of behaving as acids or bases). 6

  7. AA’s as Buffers • The amphoteric nature of amino acids makes it possible for them to act as buffers in aqueous solutions. • When a strong acid, H+, is added to an amino acid, the zwitterion accepts the proton, thus minimizing the effect of the acid added: • If a strong base OH- is added, the zwitterion donates H+ to neutralize the base to form water

  8. Isoelectric Point • The net charge on the zwitterion is affected by pH of its surrounding environment and can become more positively or negatively charged due to the loss or gain of protons (H+). • The isoelectric point is the pH value at which the negative and positive charges are equal. • Used to separate proteins in electrophoresis.

  9. Essential Amino Acids • Of the 20 amino acids that make up proteins 10 of them can be synthesized by the human body • The other 10 amino acids must be acquired from food sources. These amino acids are known as essential amino acids 9

  10. Essential Amino Acids Non-Essential amino acids • Alanine(from pyruvic acid) • Asparagine(from aspartic acid) • Aspartic Acid (from oxaloacetic acid) • Cysteine • Glutamic Acid (from oxoglutaric acid) • Glutamine (from glutamic acid) • Glycine (from serine and threonine) • Proline(from glutamic acid) • Serine (from glucose) • Tyrosine (from phenylalanine) Essential amino acids • Arginine • Histidine • Isoleucine • Leucine • Lysine • Methionine • Phenylalanine • Threonine • Tryptophan • Valine 10

  11. Two amino acids combine • Loss of a water molecule Peptide Bond—Links AA’s + H2O Condensation (Dehydration) Reaction 11

  12. Amino acids can undergo condensation reactions in any order • Possible to form large variety of proteins. • Four levels of structure • Primary • Secondary • Tertiary • Quaternary structure. Proteins- Levels of Structure 12

  13. Primary Structure Defined by the sequence of AA’s in polypeptide chain Determined by the base pair sequence in the DNA Sequence for bovine insulin is shown below 13

  14. Secondary Structure • Describes the way that the chain of AA’s folds itself due to intramolecular hydrogen bonding • Two common secondary structures are • the a-Helix  • and the b- sheet  14

  15. Maintains the three dimensional shape of the protein. • Folding of chains due to interactions between distant AA’s • The AA chain (in the helical, pleated or random coil form) links itself in places to form the unique twisted or folded shape of the protein. Tertiary Structure 15

  16. Four ways in which parts of AA chains interact • Covalent bonding--disulfide bridges formed when two cysteine molecules combine in which the –SH groups are oxidized: • Hydrogen bonding --between polar groups on the side chain • ionic attractions--formed between polar side groups • Van der Waal’s attractions-- between non-polar side groups Tertiary Structure 16

  17. Many proteins are not single strands The diagram below shows the quaternary structure of an enzyme having four interwoven amino acid strands Quaternary Structure 17

  18. What is the level of structure for these? 18

  19. Protein Functions • Structure • Fibrous proteins provide structure and strength • Chief constituents of muscle, cartilage, skin, bones, hair and fingernails. • Transport • Hemoglobin in the red blood cells is vital in carrying oxygen from the lungs to various cells and carbon dioxide from the cells to the lungs • Enzymes/Catalysts • Every reaction that takes place in the human body is catalyzed by enzymes. • Without enzymes, the reactions important for maintaining life would occur much too slowly. • Provide an alternate pathway for the reaction .This lowers the activation energy and speeds up the reaction. • Control • Hormones such as insulin are important proteins in humans and animals. • Immune systems • Antibodies are proteins produced as a result of the presence of foreign materials in the body • Provide immunity to diseases • Energy Storage • Proteins play an important role in the human body as energy storage, • Casein in milk stores nutrients for newborn babies. • Cells contain cytochrome proteins, which extract energy from food via redox reactions.

  20. Gel Electrophoresis • Paper Chromatography • See handout

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