24.1|Overview of Metabolic Reactions Pt.2

Introduction to Metabolism and Nutrition

  • Eating is essential to life.

  • Many individuals view eating as a necessity and a pleasure.

  • Starting the day with a good breakfast is often recommended for energy throughout the day.

  • The significance of a balanced diet rich in fruits and vegetables is widely acknowledged.

  • Importance of understanding how dietary choices affect the body and its physiological processes.

Nutrient Absorption and Metabolic Processes

  • The body requires a variety of nutrients for cellular functions including:

    • Building blocks for metabolic processes that release energy.

    • Manufacturing new proteins, cells, and body parts.

    • Recycling materials within cells.

Overview of Metabolism

  • Metabolism defines the chemical reactions essential for life, categorized into:

    • Anabolic Reactions: Synthesis of larger molecules from smaller ones, requiring energy.

    • Catabolic Reactions: Breakdown of large molecules to release energy.

  • Key aspects covered in this chapter include:

    • Importance of oxygen.

    • Function of mitochondria in energy transfer.

    • Role of metabolic hormones and vitamins.

Factors Influencing Metabolism

  • Metabolism varies due to several factors:

    • Age: Decreases approximately 5% per year with aging.

    • Gender: Men typically have a higher basal metabolic rate (BMR) due to greater lean muscle mass.

    • Activity level and lean body mass.

    • Genetic background influencing metabolic rate through proteins and enzymes.

  • Modifications in diet and exercise can positively impact both lean body mass and metabolic rate.

Overview of Metabolic Reactions

  • By the end of the chapter, you should be able to:

    • Describe how polymers are broken down into monomers.

    • Explain how monomers are combined into polymers.

    • Discuss the role of ATP in metabolism.

    • Explain oxidation-reduction reactions.

    • Describe hormones regulating anabolic and catabolic reactions.

Metabolism Defined

  • Metabolism is the sum of all chemical reactions involved in:

    • Catabolism: Breakdown of food to obtain energy.

    • Anabolism: Synthesis of larger molecules from smaller ones.

  • Both sets of reactions are vital for sustaining life.

  • Ideally, energy usage should balance energy produced:

    • Positive Net Energy Change: Catabolism releases more energy than is needed by anabolism, and excess energy is stored as fat (lipid accumulation).

    • Negative Net Energy Change: Catabolism releases less energy than is consumed in anabolism, necessitating usage of stored energy.

Catabolic Reactions

  • Function of catabolic reactions:

    • Break down large organic molecules into smaller ones, releasing energy contained in chemical bonds.

    • Energy release is not 100% efficient; approximately 40% is converted into ATP.

  • ATP (Adenosine Triphosphate):

    • Known as the energy currency of cells.

    • ATP can be used immediately for cellular work (e.g., building new tissue).

    • 60% of energy released during catabolism is lost as heat, absorbed by tissues and fluids.

  • Structure of ATP:

    • Composed of adenine, ribose, and three phosphate groups.

    • High-energy bond is between the second and third phosphate groups, providing the greatest energy source in a cell.

Energy Release from ATP

  • When ATP is utilized, it converts to Adenosine Diphosphate (ADP) and an inorganic phosphate (Pi).

  • ATP cycle involves reactions that build ATP and those that break it down to release energy.

  • Sources of ATP during catabolic reactions:

    • Breakdown of:

    • Proteins to amino acids.

    • Lipids to fatty acids.

    • Polysaccharides to monosaccharides (primarily glucose).

Role of Carbohydrates

  • Carbohydrates are major energy sources, primarily available as:

    • Complex carbohydrates (e.g., starch, glycogen).

    • Simple sugars (monosaccharides) such as glucose and fructose.

  • Glucose is the predominant fuel for ATP production, regulated by endocrine mechanisms.

  • Excess glucose is stored as glycogen in the liver and muscles or converted to fat in adipose cells.

Role of Lipids and Proteins

  • Triglycerides in lipids are often used for energy via β-oxidation.

  • About 50% of excess fat is stored in subcutaneous adipose tissue; the remainder is stored in other body tissues.

  • Proteins broken down into amino acids can be utilized as building blocks or may contribute to ATP production during starvation, leading to muscle wasting.

  • Nucleic acids are metabolized into nucleotides which are used by cells for nucleic acid metabolism.

Anabolic Reactions

  • Anabolic reactions involve:

    • Joining smaller molecules into larger ones (biosynthesis).

    • Combining monomers into polymers such as polysaccharides, triglycerides, proteins, and nucleic acids.

  • These processes require energy derived from ATP generated during catabolic reactions.

  • Anabolic reactions contribute to the generation of new cells and tissues, and aid in the revitalization of organs.

Hormonal Regulation of Metabolism

  • Catabolic and anabolic hormones regulate metabolic processes:

    • Catabolic Hormones: Stimulate breakdown of molecules:

    • Cortisol: Increases blood glucose through gluconeogenesis (break down fats and proteins).

    • Glucagon: Stimulates glycogen breakdown in the liver to raise blood glucose, countering insulin effects in a negative feedback system.

    • Adrenaline/Epinephrine: Activates the sympathetic nervous system, increasing heart rate, bronchodilation, and stimulating gluconeogenesis.

    • Anabolic Hormones: Required for synthesis of molecules:

    • Growth Hormone (GH): Stimulates growth of cells and tissues.

    • Insulin: Essential for carbohydrate and fat metabolism, controls blood glucose levels, promotes glucose uptake in cells.

    • Insulin-like Growth Factor (IGF): Stimulates muscle and bone growth; inhibits apoptosis.

    • Testosterone and Estrogen: Affect muscle mass, strength, and fat deposition in anabolic processes.

Summary of Hormonal Functions

  • Table 24.1: Catabolic Hormones and their Functions

    • Cortisol: Increases blood glucose levels.

    • Glucagon: Promotes glycogen breakdown for energy.

    • Adrenaline/Epinephrine: Prepares body for stress responses.

  • Table 24.2: Anabolic Hormones and their Functions

    • Growth Hormone (GH), Insulin-like Growth Factor (IGF): Promote growth and protect against cell death.

    • Insulin: Regulates blood glucose and promotes energy storage.

    • Testosterone and Estrogen: Promote muscle and bone growth.