topic 7: proteins

formations of a protein

amino acid———→ peptide—————→ polypeptide————→ protein

protein: molecule consisting of polypeptides ( polymers of amino acid) folded into a 3D shape.

  • compromised of C,H,O,N, and S

  • shape determines function


amino acids: molecules that have an amino group and a carboxyl group

-20 different amino acids

general structure:

  • amino group

  • carboxyl

  • R= variable side chain


Each amino acid (AA) has a unique side chain

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

side chains can be grouped as:

  • non-polar ( hydrophobic)

  • polar (hydrophilic)

  • charged/ ionic ( hydrophilic)

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


Formation of Peptide bonds

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

-formed through a dehydration reaction


Polypeptides

polypeptides: may AA linked by peptide bonds

-each polypeptide has a unique sequence of AA and directionality

  • each end is chemically unique

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

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

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

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


Funtions of Proteins

  • antibody-help protect the body from disease

  • enzyme-carry out chemical reaction or assist in creating new molecules

  • messenger- transmits signals ( i.e hormones)

  • structural- provides structure and support

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


levels of protein structure

1.primary

  • linear chain of AA

  • determines via genes

  • dictates the secondary and tertiary forms


2.secondary

  • coils and folds due to hydrogen bonding within the polypeptide backbone

  • B pleated sheet- hydrogen bonds between polypeptide chains lying side by side'

  • a helix- hydrogen bonding between every 4th AA.


  1. tertiary

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

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

  • the covalent bond formed between sulfur atoms of two cytosine monomers


4.quaternary

  • association of two or more polypeptides

  • found only in some proteins


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