Overview
This lecture covers the main structures and functions of cells, focusing on the differences between prokaryotic and eukaryotic cells, organelles, and key concepts such as surface area to volume ratio.
Cell Types and General Concepts
- Cells are three-dimensional and have varied shapes based on tissue and function.
- Two major cell types: prokaryotic ("before nucleus") and eukaryotic ("true nucleus").
- Prokaryotes include bacteria and archaea; eukaryotes include animals, plants, fungi, and protists.
- Cell size is limited by surface area to volume ratio; larger cells have reduced efficiency for diffusion.
- Multicellularity allows organisms to grow larger and develop specialized cells.
Surface Area to Volume Ratio
- As cell size increases, volume grows faster than surface area, reducing diffusion efficiency.
- Small cells have high surface area relative to volume and more efficient material movement.
- Organisms like flatworms rely on diffusion and must remain thin; complex organisms use vascular systems.
Prokaryotic Cell Structure
- No nucleus; DNA is found in the nucleoid region, not protected by a membrane.
- Only internal organelles are ribosomes, which synthesize proteins.
- Surrounded by a plasma membrane and a cell wall (not made of cellulose).
- May have plasmid DNA, flagella for movement, pili for attachment, and sometimes a capsule for added protection.
- All prokaryotes are single-celled.
Eukaryotic Cell Structure: Animal vs. Plant Cells
- Eukaryotic cells have a true nucleus enclosed by a nuclear envelope.
- Both animal and plant cells have organelles: rough/smooth ER, Golgi apparatus, ribosomes, lysosomes, mitochondria.
- Plant cells also have chloroplasts (photosynthesis), vacuole (water regulation), and a cellulose cell wall.
- Animal cells lack cell wall, vacuole, and chloroplasts; some have flagella.
Main Eukaryotic Organelles and Their Functions
- Nucleus: Houses DNA; nuclear envelope contains pores for material exchange.
- Cytoplasm: Cell region outside the nucleus, holds other organelles.
- Ribosomes: Free ribosomes produce proteins for internal use; bound ribosomes (on rough ER) make proteins for export.
- Rough ER: Protein synthesis and export; proteins enter ER, get packaged in vesicles.
- Smooth ER: Detoxification, lipid synthesis, calcium storage (especially in muscle cells).
- Golgi Apparatus: Modifies, sorts, and labels proteins and lipids for export.
- Vesicles: Membranous sacs that transport cell products.
- Lysosomes: Contain hydrolytic enzymes; digest cell debris, food particles, and can trigger apoptosis (cell self-destruction).
- Mitochondria: Site of most ATP production via cellular respiration; own DNA and ribosomes; support endosymbiosis theory.
- Chloroplasts: Only in plants and some protists/bacteria; site of photosynthesis; also support endosymbiosis theory.
- Peroxisomes: Break down hydrogen peroxide into water and oxygen using catalase.
- Cytoskeleton: Provides cell shape, anchors organelles, facilitates intracellular transport, cell movement, and division.
Key Terms & Definitions
- Prokaryote — Cell without a nucleus or membranous organelles.
- Eukaryote — Cell with a true nucleus and internal membranous organelles.
- Organelle — Specialized internal structures within a cell.
- Surface area to volume ratio — The relationship between a cell’s outer surface area and its interior volume.
- Nucleoid — DNA-containing region in prokaryotic cells.
- Ribosome — Organelle for protein synthesis.
- Rough ER — Endoplasmic reticulum with ribosomes, involved in protein export.
- Smooth ER — Endoplasmic reticulum without ribosomes, involved in lipid production and detoxification.
- Golgi apparatus — Organelle for modifying and packaging proteins and lipids.
- Lysosome — Organelle with enzymes for digestion and recycling.
- Mitochondria — Organelle for ATP production; "powerhouse" of the cell.
- Chloroplast — Organelle for photosynthesis in plants and some protists.
- Vesicle — Membrane-bound sac for transport within or outside the cell.
- Exocytosis — Process by which cells export materials via vesicle fusion with the plasma membrane.
- Cytoskeleton — Protein network providing shape, transport, and division functions.
Action Items / Next Steps
- Complete Lab Activity #1: Investigate surface area to volume ratio using potato chunks and iodine diffusion.
- Review organelle functions and differences between prokaryotic and eukaryotic cells.
- Prepare for upcoming lectures on plasma membrane and transport mechanisms.