UNCOMMON AMINO ACIDS, AMINO ACIDS FORMING PROTEINS, & PRIMARY STRUCTURE OF A PROTEIN

UNCOMMON AMINO ACIDS

Derived from common amino acids

Produced by the parent amino acid being modified after protein is synthesized

Process is called post-translational modification

HYDROXYPROLINE & HYDROXYLYSINE

Both examples of uncommon amino acids

Unlike their parent amino acids, both have hydroxyl groups on their side chains

Found in some proteins in connective tissues

EX: Found in collagen

AMINO ACIDS FORMING PROTEINS

This reaction takes place in the cells by a mechanism

Producing an amide.

Any 2 amino acids can be linked together to form dipeptides

The two amino acids are joined together by a peptide bond Adding another would make it a tripeptide.

Every dipeptide still has a –COO and a –NH3

Amino acids can be linked in different ways to form different dipeptides.

Some protein molecules contain more than 10,000 amino acid units

FORMING PROTEINS

Shorter chains are referred to as peptides while longer chains are referred to as polypeptides

Polypeptides contains a minimum of 30-50 amino acids

Residues are a chain of amino acids

Abbreviations of 1-3 letters are usually used to represent proteins and peptides

SYNTHESIZING

C-terminus- amino acid at the end of a peptide that has a free α-carboxyl group

N-terminus- amino acid at the end of a peptide that has a free α-amino group

Proteins synthesize from the N-terminus to the C-terminus

PROTEINS PROPERTIES

Continuing patterns of peptide bonds form the backbone of peptides and proteins

Side chains- are called an R group

Up to 20 different side chains of the amino acid supply variety and also determine the chemical and physical properties of the protein

The most important property is acid-base behavior

Amino acids behave like zwitterions as do proteins

MORE PROPERTIES

In proteins repulsive forces between like charges on their surfaces determine water solubility

When a protein is at a pH where there is an equal number of positive and negative charges it is at its isoelectric point

When proteins are at their isoelectric point they are least soluble in water and can be precipitated from the solution

PRIMARY STRUCTURE

In a primary structure of a protein the sequence of amino acids form a chain

Most peptides and protein molecules have different sequences of amino acids

Each sequence allows the protein to perform its function

Only a small fraction of all possible protein molecules have been made by biological organisms

PRIMARY STRUCTURE

Like the naming of peptides the assignment of positions of the amino acids starts at the N-terminal end

There are 20 possibilities for the N-terminal amino acid

400 different dipeptides can be formed from 20 amino acids

The primary structure of a protein to a large extent, determines the native, or most frequently reoccurring secondary and tertiary structures

SEQUENCING

A change in sequence may or may not affect the function of a protein depending upon the change

An example of this is how bovine insulin is used for instant injections for humans. Even though the insulin is not identical in structure to human insulin it still performs the same task when introduced into a human. Although it does perform the same task it is not as effective.

An example of where a small change can have a huge effect is in the protein of the blood, hemoglobin. A change in one amino acid can cause the disease sickle cell anemia