Introduction to Physiology and Biomolecules: Structure, Function, and Interactions

Physiology: Definition and Scope

What is Physiology?

Physiology is the scientific study of the normal function of living organisms and their component parts, including all chemical and physical processes. It seeks to understand how biological systems work to maintain life.

• Definition: Physiology examines the mechanisms and processes that allow organisms to survive, grow, and reproduce.

• Key Focus: The study includes both the function (why a process occurs) and the mechanism (how a process occurs).

• Example: The function of red blood cells is to carry oxygen to tissues; the mechanism involves haemoglobin molecules binding oxygen.

Teleological vs. Mechanistic Explanations

Physiological processes can be explained in two ways:

• Teleological Explanation: Answers "why" a process occurs, focusing on its purpose or benefit to the organism.

• Mechanistic Explanation: Answers "how" a process occurs, describing the physical and chemical steps involved.

• Example:

  • Teleological: Red blood cells carry oxygen because tissues need oxygen to function.

  • Mechanistic: Oxygen binds to haemoglobin molecules in red blood cells.

Systems of the Human Body and Their Functions

Major Organ Systems

The human body is organized into systems that perform specific functions essential for survival.

• Integumentary System: Composed of the skin, it provides protection and regulates temperature.

• Musculoskeletal System: Supports the body and enables movement.

• Respiratory System: Facilitates gas exchange (oxygen and carbon dioxide).

• Digestive System: Takes in nutrients and eliminates wastes.

• Urinary System: Removes excess water and waste products.

• Reproductive System: Produces eggs and sperm for reproduction.

Integration and Interaction of Systems

Body systems interact to maintain homeostasis and respond to internal and external changes.

• Circulatory System: Pumps blood through vessels, distributing nutrients and oxygen.

• Nervous and Endocrine Systems: Coordinate body functions through electrical and chemical signals.

• Immune System: Protects the body from pathogens and environmental threats.

Biomolecules: Structure and Function

Elements Essential for Life

Although over 100 elements exist on Earth, only a few are essential for life.

• Major Elements: Carbon (C), Oxygen (O), Hydrogen (H), Nitrogen (N) make up most of the body mass.

• Other Important Elements: Sodium (Na), Potassium (K), Calcium (Ca), Magnesium (Mg), Chloride (Cl), Phosphorus (P), Sulfur (S).

Table: Major Ions in Physiology

Cation	Anion
Sodium (Na+)	Chloride (Cl-)
Potassium (K+)	Bicarbonate (HCO3-)
Calcium (Ca2+)	Phosphate (HPO42-)
Hydrogen (H+)	Sulfate (SO42-)
Magnesium (Mg2+)	—

Types of Biomolecules

Biomolecules are compounds essential for life, classified into four major groups:

• Carbohydrates: Provide energy and structural support.

• Lipids: Store energy, form cell membranes, and act as signaling molecules.

• Proteins: Serve as enzymes, structural components, transporters, and regulators.

• Nucleic Acids: Store and transmit genetic information (DNA and RNA).

Lipids: Structure and Function

Lipids are hydrophobic molecules, including fats, oils, steroids, and phospholipids.

• Triglycerides: Composed of glycerol and three fatty acids; main form of stored energy.

• Steroids: Four-ring structure; includes cholesterol, cortisol, and sex hormones.

• Phospholipids: Major component of cell membranes; amphipathic nature allows membrane formation.

Table: Types of Adipocytes

Type	Main Function
White Adipocyte	Energy storage
Brown Adipocyte	Thermogenesis (heat production)
Brite/Beige Adipocyte	Thermogenesis (potentially)

Carbohydrates: Structure and Function

Carbohydrates are the most abundant biomolecules, serving as energy sources and structural materials.

• Monosaccharides: Simple sugars (e.g., glucose).

• Disaccharides: Two monosaccharides linked (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen).

Proteins: Structure and Function

Proteins are polymers of amino acids, performing diverse cellular functions.

• Amino Acids: Building blocks of proteins; each has a central carbon, amino group, carboxyl group, hydrogen, and variable R group.

• Peptides: Short chains of amino acids (oligopeptides: 2-9, polypeptides: 10-100, proteins: >100).

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

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

• Functional Groups: Common groups include amino (-NH2), carboxyl (-COOH), hydroxyl (-OH), phosphate (-H2PO4).

Table: Common Protein Functions

Function	Example
Enzymes	Speed up chemical reactions
Membrane Transporters	Move substances across cell membranes
Signal Molecules	Hormones
Receptors	Bind signaling molecules
Binding Proteins	Hemoglobin
Immunoglobulins	Antibodies
Regulatory Proteins	Transcription factors

Protein-Ligand Interactions

Proteins interact with other molecules (ligands) through reversible binding, forming complexes.

• Equilibrium: The binding reaction is reversible and can be described by the equilibrium constant.

• Equation: $P + L \rightleftharpoons PL$ $K_{eq} = \frac{[PL]}{[P][L]}$

• Affinity: The strength of binding depends on molecular complementarity (key/lock mechanism).

Nucleotides and Nucleic Acids

Nucleotides are the building blocks of nucleic acids, which store and transmit genetic information.

• DNA: Deoxyribonucleic acid; stores genetic information.

• RNA: Ribonucleic acid; involved in protein synthesis and gene regulation.

• Structure: Each nucleotide consists of a phosphate group, a sugar (ribose or deoxyribose), and a nitrogenous base.

Origin of Life: Chemical Foundations

Origin-of-Life Experiments

Experiments such as the Urey-Miller experiment simulated early Earth conditions to investigate the chemical origins of life.

• Findings: Formation of amino acids and other organic molecules from simple precursors.

• Other Hypotheses: Life may have originated near hydrothermal vents or from extraterrestrial sources (meteorites).

Table: Major Theories of Life's Origin

Theory	Main Idea
Urey-Miller Experiment	Organic molecules formed under early Earth conditions
Hydrothermal Vent Hypothesis	Life originated in geochemically reactive underwater environments
Meteorite Hypothesis	Organic molecules delivered to Earth via meteorites

Additional info: Some content was inferred and expanded for clarity and completeness, including the classification of biomolecules, protein structure, and the summary tables.