L3-The 4 Levels of Protein Structure and Their Significance

Question 1

What are the levels of protein structure?

Answer 1

The four levels of protein structure are:

1. Primary structure
2. Secondary structure
3. Tertiary structure
4. Quaternary structure

Question 2

What are proteins made of, and what is a polypeptide chain?

Answer 2

Proteins are made of** amino acids**, -which are small molecules with a :
1. central carbon,
2. an amino group,
3. a carboxyl group,
4. a hydrogen atom, and
5. a variable side chain (R group).

These amino acids are linked by peptide bonds to form a polypeptide chain — a long chain that looks like beads on a string.

Question 3

What is the primary structure of a protein?

Answer 3

The primary structure is the exact sequence of amino acids in a polypeptide chain, held together by peptide bonds.
1. *This sequence *is determined by DNA and
2. it controls how the protein will fold at all higher levels.

Question 4

What is the secondary structure of a protein?

Answer 4

The secondary structure refers to local folding of the chain into *alpha-helices and beta-pleated sheets.
1. These are** stabilized by hydrogen bonds **between atoms of the protein backbone* (the repeating nitrogen–carbon–carbon chain, excluding side chains(the R groups)).

Question 5

What is the tertiary structure of a protein?

Answer 5

Tertiary structure is the full 3D shape of a single polypeptide chain, formed by interactions between R groups of amino acids.
These include:
1. hydrogen bonds,
2. ionic bonds,
3. hydrophobic interactions,
4. and disulfide bridges.
It creates functional areas called domains.

Question 6

What is the quaternary structure of a protein and why is it important?

Answer 6

Quaternary structure** exists in proteins made of more than one polypeptide chain, called subunits.**
These subunits** interact to form one functional protein**. An example is hemoglobin, which:
1. has four subunits (two alpha and two beta)
2. carries oxygen in the blood.