Proteins

Functions of Proteins in the Body

Proteins are vital macromolecules that perform a wide range of functions necessary for life and health.

• Structural Support and Movement: Proteins such as collagen and actin provide structure to tissues and enable muscle contraction.

• Catalysts: Enzymes are proteins that accelerate biochemical reactions.

• Chemical Messengers: Some hormones, like insulin, are proteins that regulate physiological processes.

• Fluid and Acid-Base Balance: Proteins help maintain proper fluid distribution and pH in the body.

• Transport: Proteins such as hemoglobin transport substances like oxygen.

• Immune Function: Antibodies are proteins that defend against pathogens.

• Energy Source: Proteins can be metabolized to provide energy (4 kcal/g).

• Satiety: Protein-rich foods promote a feeling of fullness.

Protein Structure and Composition

• Monomers: Proteins are composed of amino acids (20 types).

• Peptide Bonds: Amino acids are linked by peptide bonds to form polypeptides.

• Essential Amino Acids: Nine amino acids must be obtained from the diet.

• Conditionally Essential Amino Acids: Normally nonessential, but become essential under certain conditions (e.g., illness).

Levels of Protein Structure

• Primary: Linear sequence of amino acids.

• Secondary: Local folding into alpha-helices or beta-sheets.

• Tertiary: Three-dimensional folding of a single polypeptide chain.

• Quaternary: Association of multiple polypeptide chains.

Note: Denaturation disrupts secondary, tertiary, and quaternary structures, but not the primary structure.

Protein Digestion and Absorption

• Digestion Begins: In the stomach, with the action of gastrin and pepsin.

• Pancreatic Enzymes: Chymotrypsin and carboxypeptidase further digest proteins in the small intestine.

• Absorption: Amino acids are absorbed in the small intestine.

• Trypsin: Stimulates the pancreas to release proteases.

Protein Metabolism and Balance

• Protein "Wasting": Occurs when amino acids are used for energy rather than protein synthesis.

• Nitrogen Balance: Reflects the balance between nitrogen intake and loss.

Protein Requirements and Quality

• Recommended Intake: 10–35% of daily calories from protein.

• Limiting Amino Acid: The essential amino acid in shortest supply in a food protein.

• Incomplete Proteins: Lack one or more essential amino acids.

Health Implications of Protein Intake

• Excess Protein: May increase risk of heart disease, kidney stones, and displace other nutrients.

• Deficiency: Can lead to protein-energy malnutrition, impairing essential body functions.

Vegetarian Diets

• Pros: Lower risk of heart disease, hypertension, diabetes, cancer, stroke, and obesity.

• Cons: Potential for low intake of essential nutrients (e.g., vitamin B12, iron).

Alcohol

Alcohol Basics

• Beverage Alcohol: Ethanol is the type of alcohol found in drinks.

• Proof: Indicates twice the percentage of alcohol by volume (e.g., 80 proof = 40% alcohol).

• Standard Drink Sizes:

Alcohol Absorption and Metabolism

• Absorption Sites: Stomach and small intestine.

• Factors Affecting Absorption: Food in the stomach (especially fat and carbohydrates) slows absorption.

• Primary Metabolic Organ: The liver metabolizes most alcohol.

• Blood Alcohol Concentration (BAC): The amount of alcohol in the bloodstream before metabolism.

• Influencing Factors: Gender, ethnicity, and genetics affect BAC.

Health Effects of Alcohol

• Short-Term Risks: Alcohol poisoning can impair basic bodily functions.

• Long-Term Risks: Impaired digestion, hormonal disruption, liver disease, depression, cardiovascular disease, increased cancer risk, and pregnancy complications.

• Potential Benefits: Moderate consumption may reduce LDL accumulation, inflammation, and high blood pressure.

• Alcoholism: There is no cure; it is a chronic condition.

Water and Minerals

Water in the Human Body

• Body Composition: Water makes up 45–70% of adult body weight; percentage decreases with age and is higher in males than females.

• Fat Content: Fat tissue contains 10–40% water.

• Polarity: Water is a polar molecule, essential for acid-base balance.

• Universal Solvent: Water dissolves many substances, facilitating biochemical reactions.

Functions of Water

• Assists in digestion and absorption of nutrients.

• Transports oxygen, nutrients, hormones, and waste products.

• Regulates body temperature.

• Lubricates joints and tissues.

• Provides protective cushioning for organs.

• Gives structure to cells.

Water Balance and Distribution

• Sources of Water: Drinking fluids, eating water-rich foods, and metabolic water production.

• Body Compartments: Intracellular (2/3 of body water) and extracellular (1/3 of body water).

• Types of Extracellular Fluid: Includes blood, lymph, interstitial, intraocular, and cerebrospinal fluids.

Electrolytes and Fluid Balance

• Electrolytes: Substances that dissociate in water to form charged ions (cations: positive; anions: negative).

• Major Extracellular Electrolytes: Sodium chloride and sodium bicarbonate.

• Osmosis: Movement of water from areas of low to high solute concentration to balance electrolyte levels.

• Edema: Excess fluid accumulation in tissues.

• Blood Pressure: Increases with excess fluid volume.

• Hyperproteinemia: Excess plasma proteins produced by the liver.

Water Intake and Loss

• Recommended Intake: 80% from beverages, 20% from food.

• Caffeine: Does not cause significant water loss.

• Water Intoxication: Can cause hyponatremia (low blood sodium).

• Dehydration Symptoms: Thirst, low blood pressure, fatigue.

Hormonal Regulation of Water Balance

• Renin: Secreted by kidneys when blood pressure or sodium is low.

• Antidiuretic Hormone (ADH): Released when blood volume is low or osmolality is high, promoting water retention.

Additional Notes

• Water is inorganic (does not contain carbon).

• Sodium-potassium pumps regulate electrolyte balance across cell membranes.

• Proteins help regulate fluid balance by attracting water.

• Aldehyde is a toxic byproduct of ethanol metabolism.

• Gastritis is inflammation of the stomach lining, which can be caused by alcohol.