CYSTEINE

1. CYSTEINE Vi Do

2. Basic Info & Structure • Nonessential, hydrophobic α-amino acid • Characterized as a non-polar amino acid • Has thiol group containing sulfur • Molecular formula is C3H7NO2S • Cysteine along with glycine and glutamic acid is found in all human tissues • Can form into Cystine when exposed to air due to oxidation • Stabilizes extracellular protein

3. Introduction to D & L Form • Almost every amino acid has 2 forms that are isometric. • It is because the central Carbon atom can have 2 enantiomers (optical isomers) around it. • Enantiomers are chiral molecules. They are mirror images of one another which makes them non-superimposable. • Nomatter how much you rotate or arrange the molecule, they can never be identical.

4. Optical Activity • The structures of D and L amino acids are compared to D-glyceraldehyde and L-glyceraldehyde. • D and L are references to the optical activities of enantiomers (optical isomers). • Optical activity is the interaction of optical isomers with plane-polarized lights. • “When a plane-polarized light beam passes through a pure solution of D-glyceraldehyde the emergent beam will be rotated the light plane to the right, and hence is the enantiomer is considered to be dextrorotatory ("dextra" is Latin for right) and is designated the "D"  enantiomer” (Amino Acid Stereoisomers, 2012). • “However, if beam of plane polarized light passes through a  pure solution of L-glyceraldehyde, the emergent light beam will be rotated in the opposite direction to the left, and hence the enantiomer is considered to be levorotatory (laevus is Latin for left) and is designated the "L"  enantiomer” (Amino Acid Stereoisomers, 2012).

5. D & L Isomers • Only Levorotatory (L) isomers are used for protein formation. • Dextrorotatory (D) isomers are found in nature and on cell walls of bacterial cells. • Since your left and right hands display chiralty, enantiomers are often classified as “left” and “right-handed.” • L is the “left-handed” isomer and D is the “right-handed” isomer. • D-amino acids have a hydrogen atom right below its central carbon atom. The carboxyl, side group, and amine group then follows in a clockwise direction around the carbon. • L-amino acids follow a counterclockwise order around the central carbon atom.

6. L-Cysteine D-Cysteine

7. Zwitterion What does it mean? Zwitterion is a neutral molecule. It has both a negative and positive charge. Though it is neutral, a zwitterion can contain parts with separate positive and negative charges. Amino Acids as Zwitterions An amino acid has an acidic carboxylic acid group as well as a basic amine group. This means the transfer of a hydrogen leaves an ion with both a negative and positive charge.

8. Amine & Carboxylic Acid What are amines? • Amines are compounds that has a single Nitrogen atom with lone pairs (pair of valence electrons that are not shared between the atoms). • These compounds derive from ammonia by replacing one or more hydrogen atoms with an organic group. What is carboxylic acid? • An acid containing a carbonyl (C=O) and a hydroxyl (O-H). • The structure of a carboxylic acid is usually R-COOH • The R represents a univalent atom which has the ability to form one covalent bond.

10. Functions and Uses of Cysteine • Stengthens the lining of the intestines and stomach • Acts as a powerful antioxidant and detoxifier • Can convert to glucose and used as a source of energy • Is believed to have the ability to protect the skin from UV damage • Reduce effect of aging in skin • Prevent cataracts and cancer • L-Cysteine can aid in treatment for diabetes • Breakdown mucous in lungs • Also prevent organ damaged caused by acetaminophen

11. Deficiency & Food Sources Deficiency • Cysteine deficiency is uncommon. • Seen in vegetarians with low intake of food containing cysteine • Deficiency can reduce production of glutathione. • Symptoms of cysteine deficiency include slowed growth in children, loss of pigmentation in hair, liver damage, muscle loss, skin lesions, weakness, fat loss (Cysteine, 2006). Food Sources • Found in high-protein food • Animal Sources: Poultry, egg yolks, dairy, pork • Plant Sources: Garlic, red peppers, broccoli, onions, brussels sprouts

12. Work Cited "Amino Acid Stereoisomers." MCDB. Ed. Duane W. Sears and Holly Rich. N.p., 7 Aug. 2012. Web. 27 Oct. 2013. <http://mcdb-webarchive.mcdb.ucsb.edu/sears/biochemistry/tw-amn/aas-stereo.htm>. Clark, Jim. "The Acid-Base Behavior of Amino Acids." Chem Guide. N.p., 2004. Web. 26 Oct. 2013. <http://www.chemguide.co.uk/organicprops/aminoacids/acidbase.html>. "Cysteine." Birkbeck. N.p., 2009. Web. 26 Oct. 2013. <http://www.cryst.bbk.ac.uk/pps97/assignments/projects/leluk/project.htm#Fig1>. "Cysteine." Vitamins & Health Supplements Guide. Vitamin Supplements Guide, 2005-2006. Web. 26 Oct. 2013. <http://www.vitamins-supplements.org/amino-acids/cysteine.php>. "Cysteine." The World's Healthiest Foods. George Mateljan Foundation, 2001-2013. Web. 26 Oct. 2013. <http://whfoods.org/genpage.php?tname=nutrient&dbid=54>. "Definition of Stereoisomers." Chemicool. Chemicool, 2013. Web. 27 Oct. 2013. <http://www.chemicool.com/definition/stereoisomers.html>. "L- and D-Amino Acids." PhSchool. Pearson Education, n.d. Web. 26 Oct. 2013. <http://www.phschool.com/science/biology_place/biocoach/bioprop/landd.html>. Leluk, Jacek. "WHY CYSTEINE IS SPECIAL?" Birkbeck. N.p., 2009. Web. 26 Oct. 2013. <http://www.cryst.bbk.ac.uk/pps97/assignments/projects/leluk/project.htm#Fig1>. Limbach, Alexander. "Molecule Cysteine L and D." Deposit Photos. Depositphotos, 2013. Web. 27 Oct. 2013. <http://depositphotos.com/9336135/stock-photo-Molecule-Cysteine-L-and-D.html>. "Optical Activity." ChemWiki. UCDavis, n.d. Web. 27 Oct. 2013. <http://chemwiki.ucdavis.edu/Organic_Chemistry/Chirality/Optical_Activity>. "Optical Isomers." Chemicool. Chemicool, 2013. Web. 27 Oct. 2013. <http://www.chemicool.com/definition/stereoisomers.html>. "Sulfur-Containing Amino Acids." The Biology Project. N.p., 25 Aug. 2003. Web. 26 Oct. 2013. <http://www.biology.arizona.edu/biochemistry/problem_sets/aa/sulfur.html>.