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 1

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

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

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

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

Prokaryotic Cells Are smaller than eukaryotic 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

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

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

Membrane Structure Phospholipids are amphipathic molecules ● Phospholipid structure Phospholipids are amphipathic molecules

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

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

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

Chromatin DNA molecule Chromosome Proteins Chromatin fiber Figure 4.9

Ribosomes Composed of proteins and Ribosomal RNA ● 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

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 2 Movement of mRNA into cytoplasm via nuclear pore mRNA Ribosome 3 Synthesis of protein in the cytoplasm Protein

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

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

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

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