Protein Review

Protein

• Proteins are polymers (so are nucleic acids)
• Every polymer is a big, complex molecule that is made of many small units (monomers) linked by particular kind of bond.
  • The monomer of the protein is the amino acid
    • There are 20 different commonly used amino acids
    • They differ because of their side chains – each has a different side chain
      • Some side chains are nonpolar (hydrophobic)
      • Some side chains are polar (hydrophilic)
      • Some side chains are charged at pH 7 (hydrophilic)
  • Amino acids are linked together by peptide bonds
    • Peptide bonds are made in the cell by the ribosome
  • So a protein is just a string of lots of amino acids linked together by peptide bonds

Protein structure

- 4 levels of structure

            - primary structure - amino acid sequence of protein

                        - often hundreds of amino acids

- sometimes even a single amino acid change can destroy protein function

- secondary structure - local folding of groups of amino acids

                        - a helix

                                    - in the shape of a helix

                                    - side chains stick out

                        - b sheet

                                    - sort of like a piece of paper crumpled up

                                    - side chains stick up and down

- tertiary structure - 3D structure of the whole polypeptide chain

- quaternary structure - when more than one polypeptide chain interact

                        - hemoglobin is a tetramer – 4 subunits

No one knows how exactly proteins fold into the shape they get in.

- must have correct pH, temp., salt concentration, otherwise they denature (unfold)

- become inactive

Most genes direct the synthesis of a particular protein.  That is, the sequence of nucleotides in DNA directs that amino acids be linked together in a certain sequence.