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

Understanding the Importance of Proteins

Introduction to Ora-pro-nóbis

• The plant ora-pro-nóbis, meaning "pray for us" in Latin, contains 20% protein in its leaves, comparable to beef.

• Guilherme, a biology teacher, emphasizes the significance of this lesson on biochemistry and proteins.

The Role of Proteins in Cells

• Proteins are sequences of amino acids linked by peptide bonds; their function is determined by their shape.

• All cellular functions depend on proteins; they are essential for energy production and various cellular activities.

Genetic Influence on Protein Production

• Genetics dictate protein production, influencing physical traits like hair and eye color through specific proteins.

• Melanin (for pigmentation), keratin (in hair), and collagen (in connective tissues) are examples of proteins formed based on genetic information.

Functions of Proteins

• Proteins serve multiple functions: structural support (cytoskeleton), transport (hemoglobin), plasticity (collagen), immune defense (antibodies).

• Hormonal regulation is another key role; insulin regulates blood sugar levels as a protein-based hormone.

Energy Source and Catalysis

• In energy depletion scenarios, proteins can be used as an alternative energy source when carbohydrates and fats are insufficient.

• Enzymes, which are specialized proteins, accelerate chemical reactions acting as biocatalysts within biological systems.

Structure of Proteins

• A single protein can consist of 50 to 5,000 amino acids; these chains form polypeptides through peptide bonds.

Understanding Amino Acids and Their Importance

Structure of Amino Acids

• An amino acid consists of a central carbon atom (chiral carbon) bonded to four different groups, making it unique.

• The central carbon is connected to an amino group (NH2), a hydrogen atom, a carboxylic acid group, and a variable side chain (R group).

• The R group can vary widely, leading to the diversity among amino acids; it can be hydrocarbons, aromatic rings, or chains with sulfur or nitrogen.

Variability Among Amino Acids

• The distinctiveness of each amino acid arises solely from its R group; all other components remain constant across different amino acids.

• Visual representations of amino acids are used to illustrate their structural differences: circles for one type and squares for another.

Peptide Bond Formation

• Peptide bonds form through dehydration synthesis where an -OH from the carboxylic acid and an -H from the amino group combine to release water.

• Each peptide bond connects two amino acids by linking the carbon of one with the nitrogen of another, creating a chain.

Importance of Proteins in Diet

• Consuming proteins is crucial as they provide essential amino acids necessary for synthesizing our own proteins.

• Proteins are broken down into their constituent amino acids during digestion, which are then utilized by cells for various functions.

Essential vs. Non-Essential Amino Acids

• There are 20 different amino acids that make up proteins; 12 can be synthesized by the body (non-essential), while 8 must be obtained through diet (essential).

Understanding Protein Structure

Essential Amino Acids and Their Importance

• The body requires eight essential amino acids from food, as it can only produce 12 out of the 20 total amino acids necessary for survival.

Protein Structure Overview

• The discussion transitions to protein structure, emphasizing that many struggle to understand this topic due to its presentation in textbooks.

• A visual representation of hemoglobin is introduced, illustrating that it consists of four polypeptide chains (two alpha and two beta), which fit together like pieces of a puzzle.

Quaternary and Tertiary Structures

• Proteins with more than one polypeptide chain are classified as having a quaternary structure; hemoglobin serves as a prime example.

• In contrast, proteins made up of a single chain exhibit tertiary structure, which refers to their three-dimensional shape crucial for function.

Importance of Three-Dimensional Shape

• An analogy is drawn using a metal chair heated until deformed; its loss of original shape signifies how proteins must maintain specific forms to function correctly.

• The significance of maintaining the correct three-dimensional structure is highlighted; any alteration can lead to loss of functionality.

Secondary Structures: Alpha Helices and Beta Pleated Sheets

• When examining tertiary structures at a microscopic level, features such as tubes or spirals emerge, representing interactions among amino acids.

• Two types of secondary structures are identified: alpha helices (spiral formations) and beta pleated sheets (folded structures).

Primary Structure and Its Impact on Functionality

• The primary structure refers to the sequence of amino acids in a protein. Mutations affecting this sequence can disrupt higher-level structures and ultimately impair protein function.

• Changes in the primary sequence may alter secondary or tertiary structures, leading to potential dysfunction if the protein cannot interact properly with others.

Conclusion on Amino Acids and Protein Formation

• A brief overview introduces all 20 amino acids relevant for protein formation without requiring memorization but understanding their differences based on radicals.

Hydrogen Bonds and Protein Denaturation

Understanding Hydrogen Bonds

• Hydrogen bonds form between hydroxyl groups (OH) and hydrogen, creating strong interactions with oxygen.

• Weaker hydrophobic interactions and Van der Waals forces exist among non-polar molecules, indicating that even weak interactions can be significant.

Electrostatic Interactions

• Electrostatic interactions occur when charged groups attract each other, such as NH2+ interacting with OH−.

• Disulfide bridges (or sulfide bonds) are formed between sulfur radicals, playing a crucial role in protein structure.

Protein Structure and Function

• The shape of proteins is influenced by their sequence; different sequences lead to various structural forms (e.g., S, N, W).

• Denaturation refers to the loss of a protein's natural structure due to external factors like temperature or pH changes.

Causes of Denaturation

• Denaturation results in the loss of function; for example, heating an egg white transforms it from viscous to solid.

• Factors causing denaturation include temperature variations, pH shifts, and salinity changes.

Examples of Denaturation Effects

• A chair analogy illustrates how losing shape leads to losing function; similarly, proteins lose functionality upon denaturation.

• Cooking an egg demonstrates how heat alters protein structure—egg whites change from transparent to opaque when cooked.

Fever as a Defense Mechanism

• Fever is a body response aimed at increasing temperature to denature bacterial proteins for easier elimination.

• High fevers can be dangerous if they exceed 39°C–40°C due to potential damage to central nervous system proteins.

Impact of pH on Enzymes

• Changes in stomach acidity can affect enzyme activity; taking sodium bicarbonate neutralizes excess acid and alleviates discomfort.

• Enzymes are types of proteins that also undergo denaturation under extreme conditions similar to other proteins.

Culinary Example: Ceviche

Desaturation of Proteins in Fish and Meat

Understanding Protein Denaturation

• The proteins in fish undergo a transformation to a white color due to changes in pH, indicating a process known as denaturation.

• Salinity plays a significant role in altering the texture and appearance of meat, such as charque (dried salted meat), which becomes fibrous and dark due to dehydration effects on microbial cells.

• The original protein structure of the meat is modified by salinity, leading to changes in both its physical form and color, ultimately resulting in loss of function.

• Denaturation is characterized by the loss of protein shape, which directly correlates with the loss of its functional properties.