# Protein Structure > [!info]- Four Levels of Protein Structure > > **Primary:** A chain of amino acids > ![[Pasted image 20220731122422.png|300]] > --- > **Secondary:** Hydrogen bonding of the peptide backbone causes the amino acids to fold into a repeating pattern > ![[Pasted image 20220731122659.png|300]] > --- > **Tertiary:** A three-dimensional folding pattern of a protein due to side-chain interactions > ![[Pasted image 20220731122711.png|300]] > --- > **Quaternary:** Protein consisting of more than one amino acid chain > ![[Pasted image 20220731122721.png|300]] ![[Pasted image 20240226105734.png|300]] An average protein is between ~100-200 amino acids - Some extreme cases of >1000aa or Amino acids are the building blocks of proteins. They are connected together in **polypeptide chains** through a process known as [[Translation|translation]]. A peptide bond is an amide type of covalent chemical bond linking two consecutive alpha-amino acids from C1 of one alpha-amino acid and N2 of another. - The peptide bond itself is between the nitrogen and the carbonyl carbon atoms and does not involve either alpha carbon A protein's **structure determines its function**. - Like many simple [[Molecules|chemical compounds]], proteins may have similar compositions yet drastically different functions due the folding of their structures. The discrete functional part of a protein is called a **domain**. - The **active site** is the domain where the primary interactions with other molecules occurs at ![[Pasted image 20230126054515.png|400|400]] #### Denaturation Proteins tend to **denature** due to temperature and pH (acidity) - [[Inflammation & Fevers]] are an example of denaturation, as your body is heating up in an attempt to denature the harmful bacteria. The vast majority of pepti ## Primary Protein Structure > See also: > - [[Translation]] > - [[Ribosomes]] ### The Peptide Bond ![[Pasted image 20240226102739.png|300]] A polypeptide chain is The polymer of [[Amino Acids]] is known as a polypeptide chain and is linked together through peptide bonds Similarly to how the sequence of DNA is typically written in 5’→3’, the sequence of amino acids within a chain is written in the N (amino) → C (carboxyl) direction ## Secondary Structure > See also: > - [[Protein Secondary Structure]] ## Tertiary Structure ### Disulfide Bridges 60 kcal/mol, is significantly stronger than the non-covalent weak bonds, but is still on the weaker side of covalent bonds ## Quaternary Structure