Proteínas, aminoácidos e desnaturação - Aula 6 - Mód. 1 - Bioquímica e Biologia Celular | Prof. Gui

Summary

This video script covers key concepts in biochemistry, specifically focusing on proteins and their interactions. It explains protein structure, including primary, secondary, tertiary, and quaternary structures, emphasizing the role of bonds like hydrogen, ionic, and disulfide bonds in shaping protein function. The video also addresses protein denaturation—how proteins lose their shape and, consequently, their function due to changes in temperature, pH, or salinity. Through relatable examples like egg whites, fever, and ceviche, the script illustrates how these changes affect protein behavior, providing insights into both biological processes and food preservation.

Takeaways

• 😀 Proteins are formed by amino acids and can have complex structures held together by various types of bonds, such as disulfide bridges.
• 😀 Disulfide bridges are formed between sulfur-containing radicals in proteins and play a critical role in maintaining their shape and function.
• 😀 A protein's shape is directly linked to its function. Altering its shape can lead to a loss of function, which can affect biological processes.
• 😀 Denaturation refers to the process where a protein loses its natural shape and, consequently, its function due to external factors like temperature, pH, or salinity.
• 😀 The loss of protein function due to denaturation can be compared to a chair losing its function when its shape is distorted.
• 😀 An example of denaturation is heating an egg white: it goes from a viscous, transparent state to a solid, opaque one, losing its original function in the process.
• 😀 Fever is a natural defense mechanism where the body increases its temperature to denature the proteins of harmful bacteria or viruses, helping the immune system fight off the infection.
• 😀 However, if the body temperature gets too high (e.g., 39-42°C), it can denature the body's own proteins, leading to complications like convulsions.
• 😀 Changes in pH can also lead to denaturation. For example, when a person takes bicarbonate to neutralize stomach acid, it prevents stomach enzymes from damaging the stomach lining.
• 😀 Ceviche is an example of protein denaturation by acidity, where the fish 'cooks' in lime juice, altering its protein structure without using heat.
• 😀 Salt can also cause denaturation, as seen in salted meats like charque, where the high salinity alters protein structures to preserve the meat and prevent bacterial growth.

Q & A

What are the primary forces responsible for the stability of a protein's structure?

The stability of a protein's structure is mainly determined by non-covalent interactions such as hydrogen bonds, hydrophobic interactions, electrostatic forces, and van der Waals forces. Additionally, covalent bonds like disulfide bridges between sulfur atoms in cysteine residues also play a crucial role in maintaining the protein's 3D shape.

How do disulfide bridges contribute to protein structure?

Disulfide bridges are covalent bonds formed between two sulfur atoms from cysteine residues in a protein. These bridges help stabilize the protein's tertiary structure by holding different parts of the protein together, ensuring its proper folding and shape.

What is meant by the term 'protein denaturation'?

Protein denaturation refers to the process where a protein loses its natural 3D shape, typically due to external factors like changes in temperature, pH, or salinity. This loss of shape leads to a loss of the protein's biological function.

Why is protein denaturation important in biological systems?

Protein denaturation is crucial in biological systems because it can lead to the inactivation of proteins that are harmful or no longer needed. For instance, the body's immune system uses fever to denature bacterial and viral proteins, making them ineffective and easier to eliminate.

What role does temperature play in protein denaturation?

Temperature plays a significant role in protein denaturation. High temperatures can cause the protein's molecules to vibrate too much, disrupting the weak bonds that maintain its structure. This leads to the protein unfolding and losing its functionality, as seen when cooking food or in fever responses.

How does the pH level affect protein structure?

Changes in pH can disrupt the electrostatic interactions and hydrogen bonds that help maintain a protein's structure. Extreme pH values can lead to protein denaturation by altering the charge on amino acid side chains, thereby causing the protein to lose its native shape and function.

Can you provide an example of protein denaturation due to pH changes?

An example of protein denaturation due to pH changes is ceviche, where fish is 'cooked' by marinating it in acidic lime juice. The acid causes the proteins in the fish to unfold and change color and texture, even though no heat is applied.

What happens to a protein when it is exposed to extreme temperatures or pH?

When a protein is exposed to extreme temperatures or pH, it undergoes denaturation, which means the protein loses its specific shape and, consequently, its ability to perform its biological function. For example, an enzyme might stop catalyzing reactions if it denatures.

How does fever act as a defense mechanism in the body?

Fever is a natural defense mechanism where the body raises its temperature to denature the proteins of invading pathogens like bacteria or viruses, rendering them inactive. This helps the immune system fight off infections more effectively.

What is the relationship between salt and protein denaturation?

Salt can affect protein denaturation by altering the ionic environment surrounding the protein. In high concentrations, salt can disrupt the electrostatic interactions and hydrophobic forces that maintain the protein's shape, leading to denaturation. An example is the preservation of meat in salt, which helps prevent bacterial growth by denaturing proteins in microorganisms.