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

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 & Hydroxylysine differ 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, tetrapeptide ect. 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