Cell Organelles Overview

Overview

This lecture explains the structure and function of cell organelles, focusing on how they work together in processes like protein synthesis, energy production, and cell division.

Cell Structure & Membrane

• The cell membrane is a phospholipid bilayer that encloses cell contents and maintains cell integrity.
• Embedded proteins in the membrane function as channels and receptors.
• The cytoplasm is the fluid inside the cell (cyto = cell, plasm = fluid).

Protein Synthesis Process

• The nucleus contains DNA, which is transcribed into messenger RNA (mRNA).
• The nucleolus, within the nucleus, manufactures ribosomes.
• mRNA exits the nucleus and is read by ribosomes, which build proteins from amino acids.
• The rough endoplasmic reticulum (rough ER), covered with ribosomes, modifies proteins (folding, quality control, glycosylation, destination tagging).
• The Golgi apparatus further modifies, sorts, and packages proteins for delivery inside or outside the cell.
• The smooth endoplasmic reticulum (smooth ER) synthesizes lipids and carbohydrates, using enzymes (proteins) delivered to it.

Energy Production

• Mitochondria conduct cellular respiration, converting sugar and oxygen into ATP (usable energy), releasing CO₂ and water.
• Mitochondria have their own DNA, inherited maternally.

Storage & Breakdown

• Lysosomes contain enzymes to digest old organelles, pathogens, or the cell itself (apoptosis).
• Peroxisomes detoxify substances like hydrogen peroxide (perox = peroxide, detox).
• Vacuoles store materials; large in plants, small in most animal cells.

Cell Division

• The nucleus holds genetic material for distribution to daughter cells during mitosis and meiosis.
• The cell membrane divides to form new cells.
• Centrosomes (with centrioles) organize fibers to pull chromosomes apart during cell division.

Structure & Movement

• The cytoskeleton (microtubules and filaments) provides internal structure and organelle support.
• Microvilli increase cell surface area for absorption (e.g., in intestines).
• Cilia are hair-like structures with microtubules for movement (e.g., in respiratory tract).
• Flagella are tail-like structures for cell motility (e.g., sperm cells).

Key Terms & Definitions

• Phospholipid bilayer — double layer forming the cell membrane.
• Cytoplasm — fluid filling the cell interior.
• Nucleus — organelle containing DNA.
• Nucleolus — region in the nucleus that makes ribosomes.
• Ribosome — builds proteins by reading mRNA.
• Rough ER — modifies and processes proteins.
• Smooth ER — synthesizes lipids and carbohydrates.
• Golgi apparatus — modifies, sorts, and packages proteins.
• Mitochondria — produces ATP through cellular respiration.
• Lysosome — breaks down waste/materials in the cell.
• Peroxisome — detoxifies harmful substances.
• Vacuole — stores substances.
• Centrosome/Centriole — organizes cell division.
• Cytoskeleton — protein network for structure and movement.
• Microvilli — membrane folds increasing surface area.
• Cilia/Flagellum — structures for cell movement.

Action Items / Next Steps

• Practice labeling cell diagrams and explaining protein synthesis.
• Review definitions and functions of organelles.
• Reference study resources or guides provided by your instructor.