1.5 Tertiary and Quaternary Protein Structure [HY] Flashcards
Tertiary Structure
- A protein’s three-dimensional shape
- Tertiary structures are mostly determined by hydrophilic and hydrophobic interactions between R groups of amino acids
Where are hydrophobic residues found?
- Interior of proteins
Which bonds found in polypeptide chains form electrostatic interactions and hydrogen bonds?
- N-H (amino) and C=O (carbonyl)
- Stabilize the protein from the inside
Where are hydrophilic residues found?
- On the surface of proteins
- Have polar or charged, R groups
Another way 3-D structure can be determined?
- Hydrogen bonding.
- Acid–base interactions between amino acids with charged R groups, creating salt bridges
Disulfide bonds
- the bonds that form when two cysteine molecules become oxidized to form cystine
- create loops in the protein chain
Protein folding
- 1st secondary structures form first
- 2nd hydrophobic interactions and hydrogen bonds cause the protein to “collapse” into its proper three-dimensional structure
- extremely rapid process; less than a second
Molten Globules
Protein folding intermediate state.
Denaturation
- If a protein loses its tertiary structure
- sometimes reversible, often irreversible
- unfolded proteins cannot catalyze reactions
Solvation layer
- Whenever a solute dissolves in a solvent, the nearby solvent molecules form this
What happens when a hydrophobic side chain (like phenylalanine and leucine) is placed in aqueous solution?
- the water molecules in the solvation layer cannot form hydrogen bonds with the side chain. This forces the nearby water molecules to rearrange themselves into
specific arrangements to maximize hydrogen bonding—which means a negative change in entropy - A -delta S means larger delta G and lack of spontaneity
What happens when a hydrophilic side chain (like serine or lysine ) is placed in aqueous solution?
- allows the nearby water molecules more latitude
in their positioning - increasing their entropy (ΔS > 0), and making the
overall solvation process spontaneous
Quaternary Structure
- not all proteins have quaternary structure
- Quaternary structures only exist for proteins that contain more than one polypeptide chain
- Made of small globular peptides, or subunits, and represents the functional form of the protein
-Ex. hemoglobin and immunoglobulins
Why do quaternary structures form?
- 1st: more stable, by reducing the surface area of the protein complex
- 2nd: they can reduce the amount of DNA needed to encode the protein complex
- 3rd: they can bring catalytic sites close together, allowing
intermediates from one reaction to be directly shuttled to a second reaction - 4th: can induce cooperativity, or allosteric effects (one subunit can undergo conformational or structural changes, which either enhance or reduce the
activity of the other subunits)
Conjugated Proteins
- derive part of their function from covalently attached prosthetic groups
Prosthetic groups
- organic molecules, such as vitamins, or even metal ions, such as iron
- can also direct the protein to be delivered to a certain location, such as the cell membrane, nucleus, lysosome, or endoplasmic reticulum.
Lipoproteins
- Proteins with lipid
Glycoproteins
- Proteins with carbohydrate
Nucleoproteins
- Proteins with nucleic acid prosthetic groups
What is the prosthetic group of hemoglobin?
Heme, hemoglobin is inactive without the heme group
