● Organisms are either: Single-celled, such as most prokaryotes and protists or

1. The Microscopic World of Cells • ● Organisms are either: • Single-celled, such as most prokaryotes and protists or • Multicelled, such as plants, animals, and most fungi

2. The Microscopic World of Cells How do we study cells? Light microscopes can be used to explore the structures and functions of cells.

3. The Microscopic World of Cells ● Electron Microscope 10 m Human height 1 m Length of some nerve and muscle cells 10 cm Unaided eye Chicken egg 1 cm Frog eggs 1 mm 100 mm Plant and animal cells Light microscope 10 mm Nucleus Most bacteria Mitochondrion 1 mm Smallest bacteria Electron microscope 100 nm Viruses Ribosomes 10 nm Proteins Lipids 1 nm Small molecules Atoms 0.1 nm Figure 4.3

4. The Microscopic World of Cells TYPES OF MICROGRAPHS Light Micrograph (LM) (for viewing living cells) Scanning Electron Micrograph (SEM) (for viewing surface features) Transmission Electron Micrograph (TEM) (for viewing internal structures) LM Colorized TEM Colorized SEM Light micrograph of a protist, Paramecium Scanning electron micrograph ofParamecium Transmission electron micrograph ofParamecium

5. The Two Major Categories of Cells ● The countless cells on earth fall into two categories: Prokaryotic cells — Bacteria and Archaea Eukaryotic cells — Eukarya protists, plants, fungi, and animals ● All cells have several basic features. 1. They are all bound by a thin plasma membrane. 2. All cells have DNA. 3. All cells have ribosomes. Cytoplasm-the entire contents of a cell

6. Prokaryotic Cells ● Prokaryotes Are smaller than eukaryotic cells Lack internal structures surrounded by membranes Lack a nucleus Have a rigid cell wall Plasma membrane (encloses cytoplasm) Cell wall (provides Rigidity) Capsule (sticky coating) Prokaryotic flagellum (for propulsion) Ribosomes (synthesize proteins) Nucleoid (contains DNA) Pili (attachment structures) Colorized TEM

7. Eukaryotic Cells ● Eukaryotic cells are fundamentally similar. *Generalized plant cell *Generalized animal cell

8. Membrane Structure ● The plasma membrane separates the living cell from its nonliving surroundings. Proteins Outside of cell Outside of cell Hydrophilic region of protein Hydrophilic head Hydrophobic tail Hydrophilic head Phospholipid bilayer Hydrophobic tail Phospholipid Cytoplasm (inside of cell) (a) Phospholipid bilayer of membrane Hydrophobic regions of protein Cytoplasm (inside of cell) (b) Fluid mosaic model of membrane

9. Membrane Structure ● Phospholipid structure Phospholipids are amphipathic molecules

10. Membrane Structure ● The plasma membrane separates the living cell from its nonliving surroundings. Proteins Outside of cell Outside of cell Hydrophilic region of protein Hydrophilic head Hydrophobic tail Hydrophilic head Phospholipid bilayer Hydrophobic tail Phospholipid Cytoplasm (inside of cell) (a) Phospholipid bilayer of membrane Hydrophobic regions of protein Cytoplasm (inside of cell) (b) Fluid mosaic model of membrane

11. Membrane Structure ● Some functions of membrane proteins Cytoplasm Fibers of extracellular matrix c Enzymatic activity b Cell signaling a Attachment to cytoskeleton and extracellular matrix e Intercellular joining f Cell-cell recognition d Transport Cytoplasm Cytoskeleton ● Cell surface – Extracellular Matrix

12. Nucleus ● The nucleus is an organelle that houses the genetic material of the cell. Nuclear envelope Nucleolus Chromatin Pore Chromatin Nuclear envelope Nucleolus Nuclear Pore TEM TEM Surface of nuclear envelope Nuclear pores

13. Chromatin DNA molecule Proteins Chromatin fiber Chromosome Figure 4.9

14. Ribosomes ● Ribosomes build all the cell’s proteins (protein synthesis) Composed of proteins and Ribosomal RNA Free: proteins for cytosol Membrane-bound: proteins for cell membranes and export

15. How DNA Directs Protein Synthesis ● DNA controls the cell by transferring its coded information into RNA DNA 1 Synthesis of mRNA in the nucleus mRNA • The information in the RNA is used to make proteins Nucleus Cytoplasm mRNA 2 Movement of mRNA into cytoplasm via nuclear pore Ribosome 3 Synthesis of protein in the cytoplasm Protein

16. The Endomembrane System • ● Many of the membranous organelles in the cell belong to the endomembrane system

17. The Endoplasmic Reticulum • Produces an enormous variety of molecules • Is composed of smooth and rough ER Nuclear envelope Ribosomes Rough ER Smooth ER

18. The Endoplasmic Reticulum After the rough ER synthesizes a molecule it packages the molecule into transport vesicles 4 Transport vesicle buds off Secretory protein inside transport vesicle Ribosome 3 Protein 1 Rough ER 2 Polypeptide

19. The Golgi Apparatus • Works in partnership with the ER • Refines, stores, and distributes the products of cells Transport vesicle from ER “Receiving” side of Golgi apparatus Golgi apparatus New vesicle forming Transport vesicle from the Golgi “Shipping” side of Golgi apparatus Plasma membrane

20. Lysosomes • It contains digestive enzymes • The enzymes break down macromolecules • A lysosome is a membrane-enclosed sac • They break down damaged organelles Lysosome Digestion Damaged organelle (b) Lysosome breaking down damaged organelle

21. Vacuoles Vacuoles are membranous sacs

22. Traffic of Large Molecules • Exocytosis is the secretion of large molecules within vesicles. Outside of cell Plasma membrane Cytoplasm

23. Traffic of Large Molecules • Endocytosis takes material into a cell within vesicles that bud inward from the plasma membrane.

24. Transport of large molecules Exocytosis Types of endocytosis found in animal cells: Endocytosis *Phagocytosis *Pinocytosis *Receptor-mediated endocytosis

25. Protein Sorting and Vesicle Transport

26. The Endomembrane System Rough ER Transport vesicle from ER Golgi apparatus Secretory vesicle from Golgi Vacuole Lysosome Secretory protein Plasma membrane