1.7 Proteins

Exclusion statement: the molecular structure of amino acids

Protein

molecule consisting of polypeptides folded into a 3D shape

Carbon,hydrogen, oxygen, nitrogen, sulfur

The shape determines the function

the functions can include

antibodies- help protect body from disease

enzyme- carry out chemical reactions or assist in creating new molecules

messenger- transmit signals (ex hormones)

structural- provide structure and support

transport/storage- bind to and carry small atoms and molecules through the body

the formation is amino acid—>peptide—>polypeptide—>protein

Amino acid

molecules that have an amino group and a carboxyl group

monomers of proteins

20 different amino acids

each amino acid has a unique side chain

Unique side chain

each AA has a unique side chain

“R”

unique aspects of the AA are based on the side chain’s physical and chemical properties

can be grouped as non polar(hydrophobic), polar (hydrophilic), or charged/ionic (hydrophilic)

side chains interact, which determine the shape and function of the protein

to locate, look between the n terminus (amino group) and c terminus(carboxyl group) and opposite the side the H is on, below/above the C is the side chain

Polar side chains

tons of oxygen in these side chains

hydrophilic

Nonpolar side chains

tons of carbon and hydrogen

3 special exceptions which are:

cysteine(contains sulfur), methionine(contains sulfur), and tryptophan(contains nitrogen)

hydrophobic

Charged/ionic side chains

have a charge in their side chain indicating if it is positively charged or negatively charged

Peptide bond

link AA

to form a peptide bond, the carboxyl group of one AA must be positioned next to the amino acid group of another AA

they go through a dehydration reaction and form a peptide bond (covalent)

Polypeptides

many AA linked by peptide bonds

each polypeptides has a unique sequence of AAs and directionality (the terminus)

one end is a free amino group (N-terminus)

one end is a free carboxyl group (C-terminus)

the sequence of AAs determines the 3D shape(shape determines function)

when a polypeptide twists and folds(because of R group interaction) it forms a protein

the unique sequence of AAs is determined by genes

Primary structure

linear chain of amino acids

determined by genes

dictates the secondary and tertiary forms

Secondary structure

coils and folds due to hydrogen bonding within the polypeptide backbone

B(beta) pleated sheet-hydrogen bonds between polypeptide chains lying side by side

A(alpha) helix- hydrogen bonding between every 4th AA

Teritiary structure

3D folding due to interactions between the side chains of the AAs

reinforced by hydrophobic interactions, hydrogen bonds, ionic interactions, and disulfide bridges of the side chains

disulfide bridges are the covalent bond formed between sulfer atoms of 2 cysteine monomers

Quaternary structure

association of 2 or more polypeptides, found only in some proteins

some proteins don’t get to this level

all 4 levels of a protein’s structure determine the protein’s function