Question

Indicate the changes in protein structure for each of the following: a. An egg placed in water at \(100{ }^{\circ} \mathrm{C}\) is soft boiled in about 3 minutes. b. Prior to giving an injection, the skin is wiped with an alcohol swab. c. Surgical instruments are placed in a \(120{ }^{\circ} \mathrm{C}\) autoclave. d. During surgery, a wound is closed by cauterization (heat).

Short answer

Heat and alcohol cause protein denaturation by breaking bonds that maintain structure in situations like boiling eggs, disinfecting skin, sterilizing instruments, and cautery in surgery.

Step-by-step solution

Egg in boiling water

When an egg is placed in water at 100 °C for about 3 minutes, the heat causes the proteins in the egg white and yolk to denature. Denaturation involves the breaking of the hydrogen bonds and other forces that hold the protein's secondary and tertiary structures together, leading to the proteins unfolding and coagulating, which results in the egg becoming soft boiled.

Alcohol swab on skin

When the skin is wiped with an alcohol swab before giving an injection, the alcohol can cause proteins on the skin's surface and on the bacteria to denature. The alcohol disrupts the hydrogen bonds and hydrophobic interactions within the protein structure, effectively killing or disabling the bacteria.

Instruments in autoclave

Placing surgical instruments in a 120 °C autoclave subjects the proteins on any contaminating microorganisms to extreme heat. This high temperature causes the proteins to denature, leading to the death of the microorganisms and sterilizing the instruments. The heat breaks the bonds that maintain the protein structure, causing them to unfold and coagulate.

Cauterization during surgery

During cauterization in surgery, the application of heat to the wound causes the proteins at the site of the wound to denature. This denaturation causes the proteins to unfold and coagulate, which seals the wound and stops bleeding. The bonds stabilizing the protein structures are broken down by the intense heat.

Key concepts

Denaturation of Proteins

Denaturation refers to the process where proteins lose their natural structure. Proteins have complex structures maintained by various bonds and interactions such as hydrogen bonds, disulfide bridges, and hydrophobic interactions. When these bonds are disrupted, the protein structure unfolds, altering its function. This can happen due to changes in pH, temperature, or exposure to chemicals such as alcohol.

For example, when an egg is boiled, the proteins in the egg white and yolk undergo denaturation. The heat breaks the bonds, causing proteins to unfold and aggregate, which changes the egg from a liquid to a semi-solid state.

Heat-Induced Protein Unfolding

Heat-induced protein unfolding is a specific type of denaturation caused by high temperatures. Proteins have a precise structure that is essential for their function. Heat can disrupt this structure by breaking the weak bonds that maintain the protein's folded shape.

A clear example of this process is the boiling of an egg. At approximately 100 °C, the heat causes the egg proteins to unfold and coagulate, transforming the egg's texture.

Another example is the autoclaving of surgical instruments at 120 °C, where the high temperature unfolds and denatures proteins on any contaminating microorganisms, effectively sterilizing the instruments.

Coagulation of Proteins

Coagulation is the process that follows denaturation where unfolded proteins aggregate into a network. This change often results in a semi-solid or solid mass.

In practical terms, coagulation is evident when heat causes the proteins in an egg to solidify. Initially, the heat denatures the proteins, followed by their aggregation, leading to the coagulated state.

During a surgical procedure called cauterization, heat is used to cause denaturation and coagulation at the wound site. This seals the wound, stopping the bleeding and helping to prevent infections.

Sterilization Techniques

Sterilization refers to any process that eliminates all forms of life, including microbial spores. Heat and chemicals are common methods used for sterilization.

Autoclaving, for example, uses steam at temperatures around 120 °C to sterilize surgical instruments. The extreme heat causes microbial proteins to denature and coagulate, effectively killing any potential contaminants.

Alcohol swabs are another common method. When used to clean the skin before an injection, the alcohol disrupts the protein structure of surface bacteria, denaturing their proteins, and thus sterilizing the skin surface.