Proteins Amino Acids Lesson.pdf

PROTEINS Proteins are extremely diverse macromolecules that are classified based on their function, such as enzymes , structural proteins, transport proteins, and defense proteins Amino Acids Proteins are composed of...

PROTEINS Proteins are extremely diverse macromolecules that are classified based on their function, such as enzymes , structural proteins, transport proteins, and defense proteins Amino Acids Proteins are composed of amino acid monomers Amino acids are composed of an amino group, a carboxyl group, a hydrogen atom, and a side chain (R) To the right is the general formula for an amino acid o The R group is called a side chain , and each amino acid has a different side chain giving it a distinct shape and distinct properties There are 20 amino acids, including 8 essential amino acids that cannot be produced by the human body and must be consumed in our diet o The essential amino acids are isoleucine, leucine, lysine, methionine, phenylalanine, valine, threonine, tryptophan (Note: histidine is an essential amino acid for infants, but not adults) Amino Acid Classification Amino acids are classified into four groups based on the properties of their side chain : ___Non-Polar____ Amino Acids Side chain contains ___hydrocarbon__________ group or ___aromatic______________ group ____Polar_______ Amino Acids Side chain contains __hydroxyl______________, __thiol _________________, or ____amide_______ group __Acidic_____ Amino Acids Side chain contains ___carboxyl______ group The side chain can be __neutral___ or can become ____negatively___ charged at a neutral pH __Basic______ Amino Acids Side chain contains ___amino________ group The side chain can be __neutral___ or can become ____positively____ charged at a neutral pH Amino Acid Isomers The anomeric carbon (α-carbon) at the centre of the amino acid is attached to 4 different groups. There are two enantiomers of amino acids (except for glycine in which the R group is hydrogen , and it is therefore achiral ) D L The structure on the left is the D configuration. All the naturally occurring amino acids have the L configuration, on the right. To determine the D vs L configuration, use the “ CORN ” rule: COOH, R, NH2 and H (where R is a side chain) If the groups are arranged clockwise to spell CORN around the chiral carbon, the amino acid is in the D form. If the groups are arranged counterclockwise , the amino acid is in the L form. Polypeptides Amino acids can join together through a condensation reaction, producing a covalent bond between them called a peptide bond (or amide bond) o 2 amino acids joined together is called a dipeptide o 3 amino acids joined together is called a tripeptide o A polymer made up of many amino acids joined together is called a polypeptide Proteins are composed of one or more polypeptides A polypeptide chain has an amino (N) terminal (where the amino group is unattached) and a carboxyl (C) terminal (where the carboxyl group is unattached) 1 water molecule is PEPTIDE released for each BOND peptide bond formed + 2 H2O PEPTIDE This is a BOND TRIPEPTIDE N terminal C terminal composed of three amino acids joined by peptide bonds Aspartic acid is at the N terminal Valine is in the middle Serine is at the C terminal Four Levels of Protein Structural Organization 1. Primary (1º) Structure o Linear sequence of amino acids connected by peptide bonds 2. Secondary (2º) Structure o Hydrogen bonding occurs between the carboxyl group and amino group of the main chain resulting in: i. alpha (α) helix ( coils ) ii. beta (β) pleated ( folded ) sheets 3. Tertiary (3º) Structure o The three-dimensional structure of a protein due to protein folding, as side chains interact through , hydrogen bonding, bonding, covalent bonding, ionic bonding, disulfide bridges, and hydrophobic interactions 4. Quaternary (4º) Structure o Two or more polypeptides interact to form a functional protein Protein Denaturation Protein denaturation happens when the protein unfolds completely because bonding between side chains (such as hydrogen bonding, ionic bonds, disulfide bridges, and hydrophobic interactions) is disrupted This may occur due to many factors including, hot or cold temperatures, ionic concentration, exposure to chemicals, changes in pH , and changes in pressure