2P09 cell stucture & Homeostasis 2024

Principles of Human Physiology

• Course Title: HLSC 2P09

• Updated: January 2024

Introduction to Physiology

• Key Topics:

  • Cell Structure and Function: Understanding how cells operate and their various components.

  • Extracellular Fluid (ECF): The fluid outside cells that provides an environment for cellular processes.

  • Intracellular Fluid (ICF): The fluid within cells where biochemical reactions occur.

  • Homeostasis: The maintenance of stable internal conditions necessary for survival.

  • Control Mechanisms: Processes that regulate physiological functions.

• Reading Assignments: Chapters 1 to 4.

Organic Molecules

• Definition: Carbon-containing molecules central to biochemistry.

• Organic Chemistry: The study of organic compounds, primarily found in living organisms.

• Biochemistry: Focuses on the chemical processes within living organisms.

Classification of Organic Molecules

• Core Groups:

  • Carbohydrates: Sugars and starches serving as energy sources.

  • Proteins: Polymers of amino acids that perform a wide range of functions.

  • Lipids: Fats and oils used for energy storage and cell membrane formation.

  • Nucleic Acids: DNA and RNA responsible for genetic information.

Carbohydrates

• Composition: Made of carbon, hydrogen, and oxygen (Cn(H2O)n). Represent approximately 1% of body weight.

• Functions:

  • Central to energy provision for cells.

  • Important in cell-cell communication.

• Types:

  • Monosaccharides: Simple sugars like glucose.

  • Disaccharides: Composed of two monosaccharides, e.g., sucrose.

  • Polysaccharides: Long chains of monosaccharides forming complex carbohydrates.

Proteins

• Composition: Comprised of carbon, hydrogen, oxygen, nitrogen, and sulfur (approximately 17% body weight).

• Functions: Critical for cellular structure and a wide range of cellular functions, including:

  • Enzymes: Catalysts for biochemical reactions.

  • Transporters: Proteins facilitating the movement of substances.

  • Hormones: Signaling molecules that regulate physiological processes.

• Structure: Formed from amino acids linked by peptide bonds, undergoing levels of structural organization (primary to quaternary).

Structural Levels of Protein

1. Primary Structure: Sequence of amino acids.

2. Secondary Structure: Local folding of the polypeptide chain into structures such as alpha helices and beta sheets.

3. Tertiary Structure: Three-dimensional conformation of the protein.

4. Quaternary Structure: Association of multiple polypeptide chains.

Lipids

• Composition: Primarily made of hydrogen and carbon (approximately 15% body weight).

• Characteristics: Non-polar and low solubility in water.

• Types:

  • Fatty Acids: Chains of carbon.

  • Triacylglycerols: Glycerol bonded to three fatty acids.

  • Phospholipids: Similar to triglycerides but with a phosphate group; crucial for cell membranes.

  • Steroids: Structures made of carbon rings, including cholesterol and hormones.

Nucleic Acids

• Types:

  • DNA (Deoxyribonucleic Acid): Carries genetic information.

  • RNA (Ribonucleic Acid): Functions in protein synthesis.

• Importance: Vital for storage, expression, and transmission of genetic info, accounting for about 2% of body weight.

Discovery of DNA Double Helix

• Pioneers:

  • James Watson and Francis Crick proposed the double helix structure of DNA in 1953.

  • Rosalind Franklin contributed through X-ray crystallography, mapping atomic locations in DNA.

Cellular Structure and Function

• Cell: The basic unit of life, characterized by:

  • Oxygen consumption.

  • Nutrient breakdown.

  • Energy requirements for functionality.

Cell Membrane (Plasma Membrane)

• Function: Separates the cell from external environments; functions as a semi-permeable barrier.

• Components:

  • Phospholipid Bilayer: Double layer of phospholipids with hydrophilic heads and hydrophobic tails.

  • Membrane Proteins: Integral and peripheral proteins with various functions.

  • Cholesterol: Modulates membrane fluidity and stability.

Cytoplasm and Organelles

• Cytoplasm: The semifluid portion between the membrane and nucleus containing enzymes and organelles.

• Organelles: Includes structures like ribosomes, endoplasmic reticulum (both smooth and rough), Golgi apparatus, and mitochondria, each with specific functions in cellular metabolism and protein synthesis.

Homeostasis

• Definition: Regulation of internal conditions to maintain stable body functions.

• Control Mechanisms:

  • Negative Feedback: Opposes changes to maintain homeostasis (e.g., body temperature regulation).

  • Positive Feedback: Enhances changes in a process (e.g., labor contractions).

Feedback Control Mechanisms

• Negative Feedback: Reverses changes by inducing responses opposite to disturbances.

• Positive Feedback: Amplifies changes until a specific outcome occurs, typically requiring an external factor to revert.

Organ Systems of the Human Body

• Key Systems:

  • Circulatory: Transports materials throughout the body.

  • Digestive: Breaks down food for nutrient absorption.

  • Nervous: Coordinates body functions through signals.

  • Endocrine: Controls body functions through hormones.

  • Respiratory: Facilitates gas exchange.

  • Urinary: Regulates fluid balance and waste elimination.

  • Reproductive: Ensures species continuation.

Protein Synthesis

• Process Steps:

  1. DNA transcription to mRNA.

  2. mRNA processing and transport to ribosomes.

  3. Translation of mRNA to form proteins.

• Post-Translational Modifications: Folding, cleavage, and addition of functional groups to alter protein functionality.

Recombinant DNA Technology**

• Definition: Utilizes plasmids to clone DNA and express genes in host cells (e.g., bacteria).

• Application: Important for understanding genetic diseases and biotechnology.

• Insulin Gene Cloning: Demonstrates methods for manipulating genes to produce human proteins for therapeutic purposes.