Protein Denaturation vs. Protein Hydrolysis

Question 1

Conformation and Protein Folding

Answer 1

1)The primary structure of a protein (sequence of amino acids) determines how the protein is folded, hence it’s conformation

2)The conformation of a protein (how it is folded) is important for it’s biological function

3)Disrupting the conformation of a protein means disrupting it’s biological function

Question 2

Protein denaturation

Answer 2

Breaking/disrupting the secondary, tertiary or quaternary structure of a protein

Question 3

Denaturation’s Characteristics

Answer 3

Denaturation changes the conformation (3D structure) of a protein hence causing the protein to lose its biological function

Denaturation occurs when one or more of the forces (Hydrogen bonds, hydrophobic interactions, ionic interaction, disulphide bond) that holds protein in its 3D form are disrupted

Question 4

Process of Denaturation

Answer 4

1)The conformation (3D structure) of protein is held together by hydrogen bonds, hydrophobic interactions, ionic interactions and disulphide bonds. Any forces that break these interactions/bonds cause proteins to denature

2)During denaturation the interactions and bonds that hold the secondary, tertiary, and quarternary structure are broken

3)Protein unfolds and loses it’s 3D structures

Question 5

What happens when protein denatures?

Answer 5

1)Hydrophobic regions are exposed to a hydrophilic environment

2)Therefore they bind randomly to one another cia hydrophobic interactions

3)Regions of opposite charges also bind randomly to each other via ionic interactions

4)Polypeptides bind to each other (coagulate) and become insoluble

Question 6

7 possible ways to denature proteins

Answer 6

Disrupts the non-covalent interactions:
1)Application of heat

2)pH changes

3)Addition of detergents

4)Addition of Organic solvents

5)Addition of salt

6)Mechanical Agitation

Breaking the disulfide bonds:
7)Addition of Reducing Agents

Question 7

1)Application of Heat

Answer 7

Heat energy increases the kinetic energy of the atoms, which allows them to overcome the hydrogen bonds and non-covalent forces

Question 8

2)pH changes

Answer 8

-Extreme pH conditions (highly acidic or highly basic) cause proteins to denature

-The presence of a large quantity of hydrogen ions (acidic) or hydroxide ions disrupts the ionic interactions that holds protein in it’s native conformation

Question 9

4)Addition of organic solvent

Answer 9

1)Alchohol denatures proteins by disrupting it’s hydrogen bonds and hydrophobic interactions

2)The 70% ethanol is widely used as a disinfectant because it penetrates the bacteria cells and denatures the proteins inside of the cells

3)High concentration of alcohol (e.g. 95% ethanol) causes protein to coagulate and form a precipitate

Question 9

3)Addition of Detergent

Answer 9

-Detergents and hydrophobic agents/solvents affect the protein structure by affecting the hydrophobic interaction between molecules

-Detergents interact with the hydrophobic parts of the protein and destabilize the hydrophobic core

-The protein then unfolds and denatures

Question 10

5)Addition of salt
(High salt concentration)

Answer 10

1)When the concentration of salt in solution becomes very high, more and more water molecules will be attracted to the salt ions

2)Thus, less water is available to maintain the hydrophilic interaction of protein dn thus keeping the hydrophobic regions to remain in the core of protein

3)This causes the protein to unfold and the hydrophobic regions become exposed on the protein’s surface

4)The proteins will aggregate by hydrophobic interactions and precipitated from the solution

Question 11

6)Mechanical Agitation

Answer 11

1)Vigorous agitation (e.g. vortex, blending) can break the non-covalent interactions (H-bond, ionic interaction, hydrophobic interaction) on the protein

2)This causes adjacent proteins to bind to one another, leading to precipitation of proteins

Question 12

7)Addition of Reducing Agents

Answer 12

1)Disulfide bonds are formed between 3 thiol (-SH) functional groups located on the side chains of cysteine residues

2)Disulfide bonds are strong covalent bonds

3)They can be broken by adding on a reducing agent (dithiothreitol (DDT) and Beta-mercaptoethanol) and boil

Question 13

Protein Hydrolysis

Answer 13

Breaking/disrupting the peptide bonds
(Breaking the primary structure of a protein)

-Any secondary, tertiary and quaternary structures will also be lost in this process

Question 14

Hydrolysis’s Characteristics

Answer 14

1)Peptide bonds can be broken by acid hydrolysis

2)Once a polypeptide is hydrolyzed into amino acids, it cannot reform back to the polypeptide spontaneously

Question 15

Example of Protein going through hydrolysis and denaturation - A transmembrane receptor protein

Answer 15

A transmembrane receptor protein:
1)The protein is folded such that the middle portion is hydrophobic (containing mostly non-polar side chains pointing out) so that it can be inserted into the phospholipid bilayer

2)The protein is also folded so that the extracellular part has a receptor that can bind to ‘signal’molecules

Question 16

Transmembrane receptor protein - Denaturation

Answer 16

1)Protein unfolds and loses its native conformation

2)The receptor protein can no longer fit properly into the plasma membrane

3)It loses it’s biological function

Question 17

Transmembrane receptor protein - Hydrolysis

Answer 17

1)Breaking of peptide bonds

2)Protein becomes many fragments

3)Lost primary, secondary, tertiary,P and quarternary structures

Question 18

(Protein folding), denaturation, and renaturation

Answer 18

-Protein has only one native conformation

1)There is only one way of folding to give the correct 3D structure for its biological function

2)When an unfolded protein try to fold back by itself, it can give rise to many randomly folded forms, all of which are denatured (no biological function)

Question 19

Protein folding, (denaturation), and renaturation

Answer 19

1)The folding of a protein in the cell is a highly controlled process, so as to ensure that the protein is folded correctly into its native conformation

2)Hence, once a protein is denatured, it is very hard for it to fold back to its native conformation

Question 20

Protein folding, denaturation, and (renaturation)

Answer 20

1)Under carefully controlled conditions and int eh presence of chaperones, renaturation can occur

2)Proteins may be refolded under very carefully controlled conditions to get back its native conformation

Question 21

What are chaperons?

Answer 21

A class of proteins whose main function is to help other proteins fold correctly