Ch. 4 – Carbohydrates

Monosaccharides and Disaccharides

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, and are a primary source of energy for living organisms.

• Monosaccharides: The simplest carbohydrates, consisting of single sugar units. Examples include glucose, fructose, and galactose. These are also called simple sugars.

• Disaccharides: Formed when two monosaccharides join together via a glycosidic bond. Examples include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).

• Polysaccharides: Long chains of monosaccharide units. Examples include starch, glycogen, and cellulose.

Equation:

• Food Sources: Disaccharides are found in table sugar (sucrose), milk (lactose), and malted foods (maltose). Polysaccharides are found in grains, potatoes, and legumes.

• Glycogen: The storage form of glucose in animals, primarily stored in the liver and muscles.

• Starch: The storage form of glucose in plants.

Fiber and Digestion

Dietary fiber consists of plant-based carbohydrates that are not digestible by human enzymes.

• Types of Fiber: Soluble (dissolves in water, found in oats, fruits) and insoluble (does not dissolve, found in whole grains, vegetables).

• Functions: Promotes digestive health, regulates blood sugar, and lowers cholesterol.

• Brush Border Enzymes: Enzymes located in the small intestine that aid in carbohydrate digestion, such as maltase, sucrase, and lactase.

Absorption and Metabolism

• After digestion, monosaccharides are absorbed into the bloodstream and transported to the liver.

• Insulin and Glucagon: Hormones that regulate blood glucose levels. Insulin lowers blood sugar by promoting uptake into cells; glucagon raises blood sugar by stimulating glycogen breakdown.

• Fructose and Diabetes: Fructose is metabolized differently than glucose and does not stimulate insulin secretion. Excessive intake may be linked to metabolic disorders.

• Added Sugars: Common sources include soft drinks, candy, and processed foods. Excess intake is associated with health risks.

• Soluble vs. Insoluble Fiber: Soluble fiber can lower cholesterol and regulate blood sugar; insoluble fiber aids in bowel regularity.

Dietary Recommendations

• Dietary guidelines recommend limiting added sugars and increasing fiber intake for heart health.

Ch. 5 – Fats

Types and Functions of Lipids

Lipids are a diverse group of hydrophobic molecules, including fats, oils, and cholesterol, essential for energy storage and cell structure.

• Sources: Animal fats (butter, lard) and plant oils (olive oil, canola oil).

• Triglycerides: The main form of fat in the body and diet, composed of three fatty acids attached to a glycerol backbone.

Equation:

• Saturated Fats: No double bonds; solid at room temperature (e.g., butter).

• Unsaturated Fats: One or more double bonds; liquid at room temperature (e.g., olive oil).

• Trans Fats: Unsaturated fats with trans double bonds; associated with increased health risks.

• Essential Fatty Acids: Linoleic acid (omega-6) and alpha-linolenic acid (omega-3) must be obtained from the diet.

• Functions of Fat: Energy storage, insulation, protection of organs, and absorption of fat-soluble vitamins (A, D, E, K).

Digestion and Absorption

• Fats are emulsified by bile (produced by the liver, stored in the gallbladder) and digested by pancreatic lipase.

• Absorbed fatty acids and monoglycerides enter intestinal cells, are reassembled into triglycerides, and transported via chylomicrons through the lymphatic system.

• Carrier Proteins: Lipoproteins (e.g., LDL, HDL) transport lipids in the blood.

• Short-, Medium-, and Long-Chain Fatty Acids: Differ in absorption and metabolic effects. Short-chain are absorbed directly into the blood; long-chain require chylomicron transport.

Bile and Cholesterol

• Bile: Produced by the liver, stored in the gallbladder, used during digestion of fats.

• Cholesterol: Essential for cell membranes and hormone synthesis; transported by LDL ("bad") and HDL ("good") lipoproteins.

Ch. 6 – Proteins

Structure and Function

Proteins are polymers of amino acids, essential for structure, function, and regulation of the body's tissues and organs.

• Amino Acids: There are 20 amino acids; 9 are essential (must be obtained from diet), and 11 are nonessential (can be synthesized by the body).

• Protein Structure: Composed of one or more polypeptide chains folded into specific shapes.

• Functions: Enzymes, hormones, transport, immune response, and structural support.

Protein Organization

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Alpha helices and beta sheets formed by hydrogen bonding.

• Tertiary Structure: Three-dimensional folding due to interactions among side chains.

• Quaternary Structure: Association of multiple polypeptide chains.

Protein Digestion and Absorption

• Proteins are denatured by stomach acid and digested by enzymes (pepsin, trypsin).

• Amino acids are absorbed in the small intestine and transported to cells for protein synthesis.

• Peptide Bonds: Link amino acids together; formed by dehydration synthesis.

Complementary Proteins and Dietary Considerations

• Complementary Proteins: Combining plant foods to provide all essential amino acids (e.g., rice and beans).

• Protein Quality: Complete proteins contain all essential amino acids; incomplete proteins lack one or more.

• Vegetarian Diets: May require careful planning to ensure adequate protein and nutrient intake.

• Kwashiorkor and Marasmus: Forms of protein-energy malnutrition; kwashiorkor is due to protein deficiency, marasmus is due to overall energy deficiency.

• Nitrogen Balance: Reflects protein intake vs. loss; positive balance indicates growth, negative indicates breakdown.

Gene Expression

• Transcription: DNA is used to make messenger RNA (mRNA).

• Translation: mRNA is used to assemble amino acids into proteins.

Tables

Comparison of Carbohydrate Types

Comparison of Fat Types

Protein Organization Levels

Additional info:

• Some questions reference videos on bile and cholesterol, which are relevant to fat digestion and transport.

• Exam questions may cover topics not listed here; students should review lectures and readings for comprehensive preparation.