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Proteins

Proteins. Hannah Barreca Daria Lukasz Ian Reucroft Roshelle Belfer Stephanie Puthumana. B2.1 – Draw the general formula of 2-amino acids. Amino Acids contain a central carbon chain with An amino group NH 2 A carboxyl group COOH A hydrogen Side chain. faculty.irsc.edu. thefullwiki.org.

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Proteins

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  1. Proteins Hannah Barreca Daria Lukasz Ian Reucroft Roshelle Belfer Stephanie Puthumana

  2. B2.1 – Draw the general formula of 2-amino acids • Amino Acids contain a central carbon chain with • An amino group NH2 • A carboxyl group COOH • A hydrogen • Side chain faculty.irsc.edu thefullwiki.org

  3. B2.2 – Describe the characteristic properties of 2-amino acids • Crystalline solids • Very high melting point in excess of 200°C • Very soluble in water, not soluble in organic solutions • Exist as ionic species

  4. Properties of 2-Amino Acids • Contain amine (-NH2) and carboxylic acid (-COOH) functional group • The amine is a base, the acid is an acid • This means that protons (H+) move from the carboxyl group to the amine group • This forms a zwitterion

  5. Properties of 2-Amino Acids • Zwitterions have net charge of zero • Are both positively and negatively charged • This is the form of amino acids even when solid • When dissolved, zwitterion ions are formed • If OH¯ ions added, pH rises • NH3+ loses H+ • Amino acid is negative

  6. Properties of 2-Amino Acids • Lower pH by adding acid • -COO¯ gains H+ • Amino acid is positive • Thus amino acids can be separated by electrophoresis • Positive acids travel to cathode • Negative acids travel to anode

  7. Properties of 2-Amino Acids • If positive amino acid has alkali added to it • Ion has two acidic hydrogens • -COOH hydrogen is more acidic and is removed to make water • We have zwitterion again! • Net charge of zero is restored • Acid wouldn’t go anywhere in electrophoresis

  8. Properties of 2-Amino Acids • pH which results in lack of movement is isoelectric point • Varies from amino acid to amino acid • Not necessarily at pH 7, more often pH 6 • pHI • Buffer action • - COO¯ is proton acceptor: acts as base • NH3+ is proton donor: acts as acid • Amino acids thus are amphiprotic and act as buffers, depending on environment

  9. http://www.ncbi.nlm.nih.gov/books/NBK28418/

  10. B2.3 – Describe the condensation reaction of 2-amino acids to form polypeptides • Amino acids are linked with amide groups, known as peptide bonds • Atoms in the amide group are linked with covalent bonds (Don’t draw peptide bonds as dotted lines, like in bio) • Peptide bonds form during a condensation reaction between the carboxyl group of one amino acid and the amino group of another amino acid • Water is released as a product of this reaction

  11. For example… Condensation reaction between glycine and alanine Image from: http://dl.clackamas.edu/ch106-08/images/68025.jpg

  12. B2.4 – Describe and explain the primary, secondary, tertiary, and quaternary structure of proteins • Primary: • Amino acids link together to form polypeptide chain in a condensation reaction • The order in which amino acids are linked is determined by the genes. Ex: Met is always first. • Peptide bonds link amino acids • Covalent bond  intramolecular

  13. B2.4 – Describe and explain the primary, secondary, tertiary, and quaternary structure of proteins • Secondary: • The polypeptide chain is coiled into either an alpha-helix or beta-pleated sheet • Hydrogen bonds define the structure • Alpha-helix: bonding causes the polypeptide to twist into a helix • Bonds are within a molecule, so could be considered intra-molecular (or intra-chain) forces • Beta-pleated sheets: bonding enables the polypeptide to fold back and forth upon itself like a pleated sheet • Bonds are between chains, so could be called inter-chain forces

  14. B2.4 – Describe and explain the primary, secondary, tertiary, and quaternary structure of proteins • Tertiary: • Alpha-helices and beta-sheets are folded into compact globule • The folding is driven by non-specific hydrophobic interactions • Between non-polar side chains • Ex: Between 2 alkyl side chains in valine. These are attracted by van der Waals forces and create non-polar regions on the interior of the protein • But the structure is stable only when protein parts are locked into place by specific tertiary interactions between the side groups (R groups) of each amino acid

  15. B2.4 – Describe and explain the primary, secondary, tertiary, and quaternary structure of proteins • Tertiary: • Specific interactions between R groups: • Disulfide bonding • Covalent bonds  strongest interactions • Ex: Form between S atoms in cysteine • Hydrogen bonding • Form between polar side chains • Ex: hydrogen bonding is between the R group in serine and aspartic acid • Ionic bonding • Form between charged side chains • Ex: (CH2)4NH3+ in lysine and CH2COO- in aspartic acid

  16. B2.4 – Describe and explain the primary, secondary, tertiary, and quaternary structure of proteins • Quaternary: • Multiple polypeptide chains join together • Subunits are formed • The quaternary structure is stabilized by same non-covalent interactions as tertiary structure • Hydrophobic interactions • Disulfide bonding • Hydrogen bonding • Ionic bonding • Examples: • In hemoglobin, each of 4 subunits have heme group containing iron • Collagen has triple helix structure (3 chains of DNA) consisting of many subunits

  17. B2.6 – List the major functions of proteins in the body

  18. References • http://themedicalbiochemistrypage.org/protein-structure.html • http://www.chemguide.co.uk/organicprops/aminoacids/proteinstruct.html • Amino Acids. (n.d.). Lecture 27. Retrieved August 24, 2011, from http://butane.chem.uiuc.edu/cyerkes/ • the acid base behaviour of amino acids. (n.d.).chemguide: helping you to understand Chemistry. Retrieved August 24, 2011, from http://www.chemguide.co.uk/org

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