Amino Acids 14.5 – 14.8

Amino Acids 14.5 – 14.8 By: Jean Turber, Kaitlin Clark & KurstynPfleegor

14.5 Uncommon Amino Acids • Occur in some proteins, but not all. • Derived from common amino acids. • Produced in a process called post-translational modification. • This is the process in which protein is synthesized. • Hydroxyproline & Hydroxylysinediffer from their parent amino acids • Their found in connective tissue proteins • collagen • They have hydroxyl groups on their side chains.

14.5 Uncommon Amino Acids Continued • Thyroxine differs from tyrosine. • Has extra iodine-containing aromatic group on the side chain. • Found only in the thyroid gland. • Formed by post-translational modification of tyrosine. • This process produces in the protein thyroglobulin. • Released as a hormone by proteolysis of thyroglobulin.

14.5 Structures • Proline Lysine Tyrosine Thyroxine

14.6 How do Amino Acids Combine to Form Proteins? • Amino Acid has a carboxyl group and an amino group. • The –COO group of one amino acid molecule can combine with the –NH3 group of a second molecule. • this reaction takes place in the cell. • Produces an Amide. • The two Amino Acids are joined together by an peptide bond. (the linking of two amino acids) • Produces dipeptide.

14.6 Example Reaction • Glycine + Alanine = Glycyalanine

14.6 Continued • Dipeptide • Two amino acids combined together. • By adding more amino acids it will turn into a tripeptide, tetrapeptideect. • Chain of hundreds or thousands of amino acids make up protein that serve many functions in living organisms. • The order of chain length goes by peptide (shortest), polypeptide, proteins (longest). • Polypeptides contain 30-50 amino acids • the amino acids in the chain are called residues • One letter or three letter abbreviations are used to represent proteins and peptides ( Ala, Gly, Lys)

14.6 Continued • C-terminal amino acid is the residue with the free –COO group. • The amino acid at the end of a peptide that has a free carboxyl group. • N-terminal amino acid is the residue with the free NH3 group. • Has a free amino group. • Proteins are synthesized from N-terminal to C- terminal.

14.7 What are the Properties of Proteins? • The R group are called the side chains. • The 6 atoms of the peptide backbone lie on the same plane. • 2 adjacent peptide bonds can rotate relative to one another. • The side chains determine the physical and chemical properties of proteins.

14.7 Properties • Proteins behave as zwitterions. • Side chains of glutamic and aspartic acids provide acidic groups. • Lysine and Arginine provide basic groups. • The isoelectric point of a protein occurs at the pH • equal number of positive and negative charges. • Any pH above the isoelectric point the molecules have a negative charge. • Any pH below the isoelectric point the molecules have a positive charge.

14.7 Properties Continued • Hemoglobin has equal numbers of acidic and basic groups. • has a pH of 6.8 • Serum albumin has more acidic groups than basic groups. • pH of 4.9 • Proteins act as buffers in the blood. • Water solubility depends on repulsive forces between like charges.

14.7 Properties Continued • Protein molecules have a charge that causes them to repel one another. • When there are no repulsive forces protein molecules clump together to form two or more molecules, reducing there solubility. • Primary structure describes the linear sequence of amino acids in the polypeptide chain. • Secondary structure refers to repeating patterns. • Tertiary structure describes the overall conformation of the polypeptide chain. • Quarternary structure applies mainly to proteins containing more than one poly peptide chain.

14.8 What is the Primary Structure of Proteins? • The primary structure consists of a sequence of amino acids in a chain • Decarboxylation • Loss of CO2 • Each protein has its own unique sequence of amino • Naming them starts at the N-terminal end • The primary structure determines the native secondary and tertiary structures

14.8 Protein Structures

14.8 Continued • Particular sequences of amino acids allow the whole chain to fold up or curl up • Different sequences may or may not affect the way it functions • Cytochrome • In humans, chimpanzees, sheep, and other animals • Humans and chimpanzees have the same sequence

14.8 Continued • People with diabetes use insulin from cows, sheep, and hogs • The difference in insulin is in the 8,9, and 10 positions of the A-chain and the C-terminal position of the B-chain • Not as affective as human insulin • Human insulin is produced from bacteria • Some people can be allergic to bovine insulin

14.8 Hormones • Two peptide hormones • Oxytocin • Vasopressin • Identical structures • Disulfide bonds • Difference in the amino acids in positions 2 & 7 • Vasopressin increases the amount of water reabsorbed by the kidneys and raises blood pressure

14.8 Hormones Continued • Oxytocin affects the contracts of the uterus at child birth • In the blood protein hemoglobin a change in any one of the 146 amino acids is enough to cause sickle cell anemia • The sequence of an amino acids very important • Sequence of 10,000 protein and peptide molecules have been determined

14.8 Hormone Structures • Oxytocin Vasopressin

Amino Acids 14.5 – 14.8