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Amino Acids and Proteins B.2

Amino Acids and Proteins B.2. there are about 20 amino acids that occur naturally they are the basic “building blocks” of life/proteins . Draw the general formula of 2-amino acids (2- because both functional groups are attached to the second carbon). NH 2 CHR COOH.

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Amino Acids and Proteins B.2

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  1. Amino Acids and Proteins B.2

  2. there are about 20 amino acids that occur naturally • they are the basic “building blocks” of life/proteins

  3. Draw the general formula of 2-amino acids (2- because both functional groups are attached to the second carbon) NH2CHRCOOH

  4. Properties of 2-amino acids (B.2.2) • Zwitterion (dipolar) • amino acids contain both acidic and basic groups in the same molecule • therefore, are amphoteric(capable of behaving as acids or bases) in nature • amines can accept a proton • carboxylic acids can donate a proton

  5. Buffers • buffer solution • the pH of the solution is "resistant" to small additions of either a strong acid or strong base • used as a means of keeping pH at a nearly constant value • the amphoteric nature of amino acids makes it possible for them to act as buffers in aqueous solutions • when in a strong acid, H+is added to an amino acid (the zwitterion accepts the proton) thus minimizing the effect of the acid added • if in a strong base, the zwitterion donates H+ to neutralize the base (OH-) to form water

  6. Isoelectric point • Kahn academy video (5:25) • the isoelectric point is the pH value at which the negative and positive charges are equal • this is unique for each a.a. at a certain pH • used to separate proteins in a process called electrophoresis

  7. Condensation Reactions in order to form polypeptides (B.2.3) • amino acids will link together to form polypeptides (proteins) • enzymes are necessary! • the link/bond is between carboxyl group on one a.a. and the amino group on the other • water is formed and remaining N and C link together with a peptide bond • peptide bonds YouTube (1:14)

  8. Primary Structure What is a protein video3:38 Proteins have a complex structure which can be explained by defining four levels of structure (B.2.4) • determined by the number, kind, and order of a.a. in the polypeptide. • held together by simple peptide bonds.

  9. Secondary Structure Two types of spontaneously, regular, repeating structures as the polypeptide is made • alpha helix – a coil or zigzag shape that results from the hydrogen bonds along the strand

  10. beta pleated sheets – back and forth folding of polypeptides because of hydrogen bonds between adjacent polypeptides or in the same strand

  11. Tertiary Structure • highly specific looping and folding of the polypeptide because of the following interactions between their R-groups: • covalent bonding-- disulfide bridges formed when two cysteine amino acids combine due to sulfur in their R groups • 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 • this tertiary level is the final level of organization for proteins containing only a single polypeptide chain

  12. Quaternary Structure • linkage of two or more polypeptides to form a single protein in precise ratios and with a precise 3-D configuration. • some proteins have a prosthetic group (a non-peptide) • these proteins are called conjugated proteins • ex. hemoglobin • John Kyrk protein folding • Protein folding

  13. Quaternary Structureexample

  14. Analysis of Proteins (B.2.5) • there are various analytical techniques that can be used to identify proteins and amino acids • main two are: • paper chromatography • electrophoresis

  15. Paper Chromatography • break peptide bonds in the protein and obtain constituent a.a. • (use 6 M HCl, 110°C) • place sample spot on paper and set paper in solvent • amino acids separate based on polarity • calculate Rf value and compare to amino acids with know values

  16. Electrophoresis • this technique separates charged molecules based on their ability to migrate when an electric field is applied to the system sample is placed in a gel and electricity applied • different a.a. will move at different rates towards a (+) or (-) electrode • will stop at different distances • this is its isoelectric point where a particular a.a. will not move as its charges are balanced • distances can then be compared with known values for identification

  17. Protein Functions (B.2.6) • Structure • fibrous proteins provide structure and strength (muscle, cartilage, skin, bones, hair) • Transport • hemoglobin in the red blood cells is vital in carrying oxygen • Hormones • have a regulatory effect on specific cells/organs in the body • Immunoproteins • play a key role in the fight against infection (antibodies) • Energy Storage • play an important role in the human body as energy storage • Enzymes • catalyze biochemical reactions (1000’s) within the body

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