Lecture 1 - Biology Chapter: Key Molecules of Life

Key Molecules of Life

• Prokaryotic cells lack a nucleus (bacteria, archaea)
• Eukaryotic cells contain a nucleus (plants, fungi, animals)
• Plant cells have cell walls and chloroplasts
• Fungi cells have cell walls but no chloroplasts
• Animal cells lack cell walls and chloroplasts

Links Between Molecules, Cells, and Organisms

• Molecules determine phenotypes
• Mutant hemoglobin: Brain cell death, holes in adult brains
• Missing hormone leptin: Loss of cell signaling pathway
• Examples: Sickle cell anemia, Swiss cheese phenotype, obese mouse

Phenotype vs. Genotype

• Phenotype: Observable traits (height, eye color, blood type)
• Genotype: Genetic makeup
• Example: Change in hemoglobin shape causes sickle cell anemia
• Example: Phospholipase is an enzyme

Life's Molecular Building Blocks

• Life is composed of the same molecules in all organisms
• Small molecules form larger molecules
• Building Blocks: Sugars, fatty acids, amino acids, nucleotides
• Larger Molecules and Structures: Polysaccharides, lipids, proteins, nucleic acids

Carbohydrates: Energy and Structure

• Monosaccharides (e.g., glucose): Energy source for cells
• Formula: (CH₂O)ₙ (where n = 3 or more)
• Glucose (n=6), hexose sugar
• α-glucose and β-glucose isomers—interchangeable
• Examples: Glycogen (energy storage in animals, fungi, bacteria), Cellulose (cell walls in plants, algae)

Lipids: Definition and Roles

• Lipids are water-insoluble, but highly soluble in organic solvents
• Diverse structure and functions
• Functions: Energy storage, structure (membrane lipids), signaling (steroid hormones)
• Example: Fatty acids (palmitate), membrane lipids (phospholipids), steroidal hormones (estrogen)

Fatty Acids: Energy Source

• Structure: Carboxylic acid group at one end, methyl group at the other; saturated or unsaturated hydrocarbon chain
• Saturated vs. unsaturated: Differences relate to bonding
• Energy Value: Fatty acids have more energy per gram than glucose

Membrane Lipids: Phospholipids, Glycolipids, and Cholesterol

• Structural components of cell membranes
• Phospholipids have hydrophilic heads and hydrophobic tails
• Phospholipids create a boundary; hydrophobic tails face inward

Steroid Hormones: Signaling

• Function: Control of various bodily functions.
• Examples: Estrogen and progesterone regulate the menstrual cycle
• Steroids have different chemical structures, binding to different receptors, resulting in changes in bodily functions.

Amino Acids

• 20 common amino acids form proteins
• Structure: Central alpha carbon, amino group, carboxyl group, side chain (R group)
• R group variations: Determine the properties of each amino acid
• Examples: Serine (hydrophilic), Valine (hydrophobic)

Proteins: Functions

• Functions: Catalysts (enzymes), communication (receptors), defence (antibodies), transport (hemoglobin), structure (cytoskeleton), control (transcription factors, chaperones)

Nucleotides and Nucleic Acids

• Nucleotides form nucleic acids
• Types of Nucleotides: Adenine, guanine, cytosine, thymine
• Structure: Sugar-phosphate backbone with nitrogenous bases attached.
• The order of bases stores genetic information.

Gene Sequences

• Gene sequences are conserved—shared—across different organisms
• This similarity reflects shared ancestry.
• Implications: The conservation of gene sequences provides evidence of evolutionary relationships

Test your knowledge on the key molecules that form the basis of life and the differences between prokaryotic and eukaryotic cells. Explore phenotypes and genotypes and understand how molecular structures influence cellular function. This quiz includes examples of diseases related to molecular mutations.