Protein- Secondary, Tertiary, and Quaternary Structure

Levels of Protein Structure

ProteinsFunctions of Proteins:1. Structural: Muscles, Antibodies2. Hormones: insulin, thyroxin3. Cell Transport Proteins4. Enzymes are Proteins

Central Dogma of Biology

DNA mRNA Protein Transcription Translation

Protein Building BlocksAmino acid structure: NH3 – C - COOH

R Groups Nonpolar Polar Charged

+ Charged - Charged

Nonpolar R Groups

Nonpolar R Groups

Polar, but NOT Charged amino acids

Polar, but NOT Charged amino acids

Polar, Charged (Acidic) amino acids

Basic amino acids

Structure of R-group determines the chemical properties of the amino acid

• The polar uncharged amino acids are hydrophilic and can form hydrogen bonds

• The nonpolar amino acids are hydrophobic and are usually found in the center of the protein; they are also found in proteins which associated with cell membrane

• The electrically charged amino acids have electrical properties that can change depending on the pH

• Cysteine can form disulfide bond• Proline has a unique structure and causes kinks in

the protein chain• When 2 amino acids are joined, the bond formed is

called peptide bond

Building Proteins: The Peptide Bond

Peptide Bond

O H

C N

You must be able to draw this bond, recognize this bond, and the significance of this bond.

Primary Structure of Proteins The sequence of amino acids in

the polypeptide chain The sequence of R groups

determine the properties of the protein

A change of a single amino acid can alter the function of the protein Sickle Cell Anemia- caused by

a change of one amino acid from glutamine to valine

Secondary Structure of Protein Folding and coiling due to hydrogen bond

formation between carboxyl and amino group of non-adjacent amino acid

These bonds occur between the BACKBONE of the strand of amino acids

R groups are NOT involved Folding is due to the disulfide bond Two common examples: alpha helix and beta

pleated sheet

Secondary Structure of Protein

Folding due to Disulfide bond

Tertiary Structure of Protein 3-D structure resulting from the folding of

2o structural elements Stabilized by bonds formed between

amino acid R groups Form many shapes (globular compact

proteins and fibrous elongated proteins)

Tertiary Structure of Proteins

Quaternary Structure of Protein Multiple polypeptide chains bonded

together 3-D structure due to interactions between

polypeptide chains R-group interactions, H bonds, ionic

interactions Assembled after synthesis Only proteins with more than one subunit

can have a quaternary structure

Quaternary Structure of Protein

Denaturation Environment change (increased heat, changes in pH)

proteins can unfold or “denature” Loss of dimensional shape loss of protein function Sometimes able to refold back into it’s original conformation

Nucleic Acids

DNA RNA

Nucleic Acids 3 components to a nucleotide: a pentose

sugar, a phosphate group, and a nucleotide base

Nucleic Acids (2 Common forms): RNA (ribonucleic acid) DNA (deoxyribonucleic acid)

DNA & RNA differ by the presence on an –OH group (RNA) or an H-group (DNA) on the 2’ carbon of the pentose sugar

DNA contains C, T, A, GRNA contains C, U, A, G

DNA: double strandedRNA: single stranded

When a DNA or RNA polymer is created, the bond is formed between 3’ –OH group and 5’ phosphate group phosphodiester bond