Chapter 6. Proteins
Chapter Review
IMPORTANT: Key Takeaways
- Proteins are macromolecules composed of amino acids. Similar to carbohydrates and lipids, proteins contain the elements carbon, hydrogen, and oxygen. However, proteins are the only macronutrient that contains nitrogen. Unlike carbohydrates, which have identical repeating units, proteins are made up of unique amino acids.
- In each amino acid, there is a central carbon atom connected to a side chain, a hydrogen, a nitrogen-containing amino group, and a carboxylic acid group. Each amino acid has a unique side chain (R group), which helps us distinguish one amino acid from another. Amino acids join through peptide bonds to form complex polypeptide structures in a process facilitated by ribosomes. These proteins are then organized into four structural levels:
- Primary: the one-dimensional sequence of amino acids held together by peptide bonds.
- Secondary: arises from the chemical interactions between amino acids that cause the protein to fold into a specific shape.
- Tertiary: three-dimensional structure that arises due to the chemical interactions between different amino acid side chains, resulting in a folded structure.
- Quaternary: formed by peptides that join together to form one larger functional protein.
- Non-essential amino acids can be synthesized by the body. On the other hand, essential amino cannot be synthesized in sufficient amounts or at all. Hence essential amino acids must be obtained from the diet.
- Mechanical digestion of proteins begins in the mouth, followed by chemical digestion in the stomach, where hydrochloric acid converts pepsinogen to pepsin, breaking down proteins further. In the small intestine, pancreatic enzymes break polypeptides into amino acids, dipeptides, and tripeptides, which are then transported to the liver via the bloodstream.
- Proteins play crucial roles in wound healing, enzymatic reactions, hormone synthesis, fluid and acid-base balance, molecular transport, and defense against foreign substances. In cases of inadequate carbohydrate and fat intake, amino acids are used for energy, compromising protein synthesis and muscle preservation.
- Protein deficiencies can lead to conditions like marasmus, kwashiorkor, or marasmic kwashiorkor, characterized by poor skin health, growth retardation, edema, fatigue, hunger, and diarrhea. High-protein diets may exacerbate kidney and liver diseases and pose risks of nutrient deficiencies, cardiac, renal, bone, and liver abnormalities.
Practice Questions
- How are over one hundred thousand different proteins produced in the body?
- Describe and explain the basic steps of protein synthesis.
- Describe the four structural levels of proteins.
- What is protein denaturation? How does this process affect the structural and chemical properties of proteins?
- Why do proteins make you feel full for longer than carbohydrates?
- What are the two major pancreatic enzymes that digest proteins?
- How are amino acids recycled to make new proteins?
- How are dietary proteins catabolized for energy production, and what are the overall health implications of protein catabolism?
- How might daily protein recommendations vary among different groups (e.g., the elderly and athletes)?
- What are the health consequences of protein deficiencies and high-protein diets?
- Reflecting on what you’ve learned about protein supplements and their effectiveness, what is your perspective on integrating them into your dietary routine or fitness regimen? How would you weigh the pros and cons of protein supplements?
