Macromolecules and Metabolic Reactions in Anatomy & Physiology

Healthy Eating Recommendations

Canada's Dietary Guidelines

Nutrition is foundational to human health and physiology. Canada's Dietary Guidelines provide evidence-based recommendations for healthy eating, which support optimal body function and disease prevention.

• Eat a variety of vegetables and fruits: These foods supply essential vitamins, minerals, and fiber.

• Choose whole grain and protein foods: Whole grains and plant-based proteins contribute to cardiovascular and metabolic health.

• Limit highly processed foods: Processed foods often contain excess sodium, sugars, and unhealthy fats.

• Replace sugary drinks with water: Water is vital for cellular processes and hydration.

• Be mindful of eating habits: Consider where, why, and how you eat; share meals with others and pay attention to hunger cues.

Example: Eating a balanced meal with vegetables, whole grains, and lean protein supports muscle function and energy metabolism.

Macromolecules: Proteins

Peptide Bonds

Proteins are polymers made of amino acids linked by peptide bonds. The formation of peptide bonds is a dehydration synthesis reaction, which is essential for building polypeptide chains.

• Peptide bond formation: Water is removed when two amino acids join, forming a covalent bond between the carboxyl group of one and the amino group of another.

• Polypeptide chains: Long chains of amino acids require further modifications to become functional proteins.

Equation:

$\text{Amino acid}_1 + \text{Amino acid}_2 \rightarrow \text{Dipeptide} + H_2O$

Example: The enzyme pepsin breaks peptide bonds during protein digestion in the stomach.

Protein Structure

Proteins have complex structures that determine their function. The structure is organized into four levels: primary, secondary, tertiary, and quaternary.

• Primary structure: Sequence of amino acids in a polypeptide chain.

• Secondary structure: Local folding into alpha-helices and beta-sheets due to hydrogen bonding.

• Tertiary structure: Overall 3D shape formed by interactions between R groups (side chains).

• Quaternary structure: Association of multiple polypeptide chains.

• Types of proteins: Fibrous (e.g., collagen), globular (e.g., enzymes), mixed.

• Functions: Hormonal messengers, transport proteins, structural proteins, enzymes.

Example: Hemoglobin is a quaternary protein that transports oxygen in the blood.

Enzymes

Role and Function

Enzymes are biological catalysts that accelerate chemical reactions in cells, essential for metabolism and homeostasis.

• Lower activation energy: Enzymes make reactions occur faster and at lower temperatures.

• Specificity: Each enzyme acts on specific substrates.

• Reusability: Enzymes are not consumed in the reaction.

Equation:

$\text{Enzyme} + \text{Substrate} \rightarrow \text{Enzyme-Substrate Complex} \rightarrow \text{Enzyme} + \text{Product}$

Example: Amylase catalyzes the breakdown of starch into sugars in saliva.

Nucleic Acids

DNA and RNA: Structure and Function

Nucleic acids store and transmit genetic information. DNA and RNA are polymers of nucleotides, each with distinct roles in the cell.

• DNA (Deoxyribonucleic acid): Double helix structure; stores genetic instructions.

• RNA (Ribonucleic acid): Single helix; involved in protein synthesis and gene expression.

• Genetic code analogy: DNA is like an architect's blueprint; RNA is like a tradesperson's instructions for building.

Example: Messenger RNA (mRNA) carries genetic information from DNA to ribosomes for protein synthesis.

Nucleotide Structure

Nucleotides are the building blocks of nucleic acids, each consisting of three components.

• Phosphate group(s)

• Five-carbon sugar: Ribose (RNA) or deoxyribose (DNA)

• Nitrogen-containing base: Purines (adenine, guanine) or pyrimidines (cytosine, thymine, uracil)

Equation:

$\text{Nucleotide} = \text{Phosphate} + \text{Sugar} + \text{Base}$

Example: ATP (adenosine triphosphate) is a nucleotide that stores energy for cellular processes.

Metabolic Reactions

Anabolic and Catabolic Pathways

Metabolism encompasses all chemical reactions in a cell, divided into anabolic (building up) and catabolic (breaking down) pathways.

• Anabolic reactions: Synthesize complex molecules from simpler ones; require energy.

• Catabolic reactions: Break down complex molecules into simpler ones; release energy.

• Reactants and products: Chemical reactions convert substrates (reactants) into products.

• Directionality: Reactions can be forward, reverse, or bidirectional.

Equation:

$A + B \rightarrow C + D$

$A + B \leftrightarrow C + D$

Example: Cellular respiration is a catabolic process that converts glucose and oxygen into carbon dioxide, water, and energy.

Table: Comparison of Macromolecules

Macromolecule	Monomer	Function	Example
Protein	Amino acid	Structure, enzymes, transport	Hemoglobin, collagen
Nucleic Acid	Nucleotide	Genetic information, signaling	DNA, RNA, ATP
Carbohydrate	Monosaccharide	Energy, structure	Glucose, starch
Lipid	Fatty acid, glycerol	Energy storage, membranes	Triglyceride, phospholipid

Additional info: Table expanded to include carbohydrates and lipids for academic completeness.