Chemistry 100 Chapter 25 Biochemistry

Chiral Molecules  Molecules that have non-superimposable mirror images – chiral molecules Enantiomers  Distinguish using the R and S configuration

Chiral Molecules

Enantiomers  Physical properties are generally identical  Chemical properties are different only in a chiral environment.  Mixture of two enantiomers in equal proportions – racemic mixture.  Some molecules have more than one chiral centre!

Biochemistry  Biomolecules – large and hard to synthesize in the laboratory.  Built up from smaller molecules present in the biosphere – large entropy cost!!  Biologically active polymers – biopolymers. Proteins Polysaccharides Nucleic Acids

Amino Acids and Proteins  Amino Acids Contain the –NH 2 group and the COOH group. Building block of proteins.  Proteins are macromolecules present in all cells.  Physiological pH – present as zwitterions.

Common Amino Acids

The Amino Acids  About 20 common amino acids used to synthesize proteins in biological systems.  These amino acids differ with respect to the R group attached to the  carbon.  The -carbon on all amino acids except glycine is chiral.

Amino Acid Enantiomers  Two enantiomeric forms of amino acids D (dextrorotary) L (levorotary)  L-amino acids are used to synthesize proteins in living systems.

Polypeptides and Proteins  Proteins – polyamides.  The amino acid residues are linked via peptide bonds.  Condensation reaction of amino acids produces peptide sequences.

Polypeptides  Polypeptides are formed when a large number of amino acids are linked together via peptide bonds. Masses are less than  Proteins – linear polypeptides with a molecular weight between 6000 and 50 million amu’s.

Protein Structure  The arrangement or sequence of amino acids along a protein chain Primary structure.  The regular arrangement of segments along the protein chain Secondary structure.

The  -Helix  A common secondary structure type.  Hydrogen bonds and other intermolecular forces hold the helix in place.  Another common type of protein structure is the -pleated sheet.

Tertiary Structure  The three dimensional structure of the protein.  Two broad categories Globular proteins – mainly water soluble. Fibrous Proteins – water-insoluble.  Enzymes – protein catalysts. Largely due to their tertiary structure. Extremely specific with regard to what reactions they catalyze.

Carbohydrates  Have the general formula C n (H 2 O) n  The simple sugars glucose and fructose are the basic building units of many carbohydrates.  These sugar molecules can make rings.

Polysaccharides  Disaccharides like table sugar (sucrose) consists of two rings joined together.  When many rings join we get starch or cellulose.  The difference is in how the rings are joined. We can digest starch but not cellulose.

Simple Sugars  Two common carbohydrates Glucose (an aldehyde sugar or aldose). Fructose (a ketone sugar or ketose).  Glucose is the most common carbohydrate.

Ring Closing  Carbohydrates, containing both aldehyde and alcohol functional groups, can form rings.  These 6-membered rings are not planar.

 and  Glucose  Glucose can form two different six-membered rings, -glucose, and - glucose.  A small difference that can have important biological consequences!!

Mono- and Disaccharaides  Glucose and fructose are both examples of monosaccharides, or simple sugars. monosaccharides  Two monosaccharides can condense to form a disaccharide. Sucrose (table sugar). Lactose (milk sugar).

Polysaccharides  Consist of multiple monosaccharides linked together.  Starch, glycogen, and cellulose are important polysaccharides, and are all made of repeating glucose units.

Nucleic Acids  Nucleic acids carry genetic information.  DNA – deoxyribonucleic acid Molecular mass between 6 – 16 million amu!  RNA - ribonucleic acid Molecular mass between 20 – 40 thousand amu!  Nucleic Acids are made up of monomers called nucleotides.

Nucleotides  A nucleotide consists of three parts. A phosphoric acid unit A five carbon sugar.  DNA – deoxyribose.  RNA – ribose. H 3 PO 4

Nucleic Acids that Make Up Nucleotides  There are five bases found in DNA and in RNA

A Nucleotide  The arrangement of the three components in a nucleotide.  Nucleic acids are formed by the condensation of nucleotides.

Nucleic Acids  A nucleic acid strand is formed by successive condensation of nucleotides.

DNA  DNA consists of two deoxyribonucleic acid strands wound together in a double helix.

Base Pairings  The structure of the double helix is supported by base pairs that optimize hydrogen bonding.  The structures guanine/cytosine and adenine/thymine make them ideal hydrogen bonding partners. Two hydrogen bonds form between A and T. Three H-bonds form between C and G.

Replication  A schematic representation of DNA replication.  The double helix unwinds by separation of the base pairs  Each half serves as a template for the synthesis of a new strand.