Overview
This lecture covers the main concepts in Module 2: Foundations in Biology, including microscopy, cellular ultrastructure, biological molecules, enzymes, membranes, cell division, cellular organization, and stem cells.
Microscopes & Microscopy
- Four microscope types: light/optical, transmission electron (TEM), scanning electron (SEM), and laser scanning confocal.
- Resolution is the minimum distance where two objects are seen as separate; higher in electron microscopes due to shorter wavelengths.
- Magnification is how many times larger an image is compared to the actual specimen.
- Slide preparations: dry mount (thin specimen), wet mount (liquid or live samples), squash slide (thin for light passage), smear slide (spread sample, eg. blood).
- Eyepiece graticule calibration uses a stage micrometer to measure actual specimen size at different magnifications.
- Magnification formula: magnification = image size / actual size (convert units as needed).
Cell Structure & Ultrastructure
- Eukaryotic cells contain membrane-bound organelles: nucleus, mitochondria, ER, Golgi, lysosomes, chloroplasts, etc.
- Prokaryotic cells lack membrane-bound organelles, have circular DNA, plasmids, 70S ribosomes, and peptidoglycan cell wall.
- Key differences: eukaryotes are larger, have nuclei, 80S ribosomes; prokaryotes may have capsules and flagella.
Biological Molecules
- Carbohydrates: monosaccharides (glucose, ribose), disaccharides (maltose, lactose, sucrose), polysaccharides (starch, cellulose, glycogen).
- Condensation reaction joins monomers with water removal, forming glycosidic bonds; hydrolysis splits polymers by adding water.
- Lipids: made of fatty acids and glycerol; triglycerides (energy store), phospholipids (membranes), cholesterol (membrane fluidity).
- Proteins: made from amino acids; structure levels—primary (sequence), secondary (α-helix/β-sheet), tertiary (3D shape), quaternary (multiple chains).
- Fibrous proteins (collagen, keratin, elastin) provide structure; globular proteins (hemoglobin, enzymes, insulin) have metabolic roles.
- Biochemical tests: iodine for starch, Benedict’s for reducing sugars, Biuret for proteins, emulsion test for lipids.
Nucleic Acids & Protein Synthesis
- Nucleotides: monomers of DNA/RNA; DNA has adenine, thymine, cytosine, guanine; RNA contains uracil instead of thymine.
- DNA replication is semiconservative; involves DNA helicase and DNA polymerase.
- Genetic code is degenerate (multiple codons for each amino acid), universal (same in all organisms), and non-overlapping.
- Protein synthesis: transcription (DNA to mRNA), translation (mRNA to polypeptide) at ribosomes; includes roles of mRNA, tRNA, rRNA.
Enzymes
- Enzymes are globular proteins that lower activation energy for reactions; have specific active sites.
- Induced fit model: active site changes shape to fit substrate.
- Factors affecting enzyme activity: temperature, pH, substrate/enzyme concentration, inhibitors (competitive/non-competitive).
- Cofactors (inorganic), coenzymes (organic), and prosthetic groups (permanent) may be needed for enzyme function.
Biological Membranes & Transport
- Plasma membrane: phospholipid bilayer with proteins (channel/carrier), glycoproteins, glycolipids, and cholesterol.
- Transport methods: diffusion, facilitated diffusion, osmosis (water movement), active transport (requires ATP), endocytosis/exocytosis (bulk transport).
- Membrane permeability affected by temperature and solvents.
Cell Division & Cellular Organization
- Cell cycle: interphase (G1, S, G2), mitosis (prophase, metaphase, anaphase, telophase), cytokinesis.
- Mitosis: produces two genetically identical diploid cells; meiosis produces four genetically different haploid cells.
- Genetic variation in meiosis via crossing over and independent assortment.
- Organization: cells → tissues → organs → organ systems → organism; includes examples of specialized cells and tissues.
Stem Cells
- Totipotent: can become any cell type; pluripotent: almost all cell types; multipotent: limited range; unipotent: one type.
- Stem cells used in medicine and research; ethical concerns about embryonic stem cells.
Key Terms & Definitions
- Resolution — Minimum distance to distinguish two points as separate.
- Magnification — Ratio of image size to actual specimen size.
- Glycosidic Bond — Bond formed between carbohydrate monomers.
- Enzyme — Biological catalyst made of protein.
- Osmosis — Movement of water from high to low water potential.
- Plasma Membrane — Phospholipid bilayer controlling entry/exit of substances.
- Totipotent Cell — Stem cell able to form all body cell types.
- Semiconservative Replication — DNA replication where half is original strand.
Action Items / Next Steps
- Create flashcards for ions, cell types, specialized tissues, and protein/globular protein examples.
- Practice scientific drawing rules for microscopy.
- Memorize biochemical test protocols and expected observations.
- Review and diagram cell cycle stages and key events.
- Study properties and functions of water, carbohydrates, proteins, and lipids.
- Complete any assigned textbook readings related to these topics.