Chapter 3 Cells I. Cells A. History 1. Robert Hooke a. English physicist b. Examined cork slices, used the term "cell" (1665) to describe compartments seen in cork tissue 2. Anton van Leeuwenhoek single celled "animalcules", 1670's 3. Nucleus discovered in 1831 by Robert Brown 4. Matthias Schleiden and Theodor Schwann credited with the cell theory,

5. Rudolf Virchow, 1858, "omnis cellula ecellula", (every cell comes from a preexisting cell), i.e., no spontaneous generation of cells 6. Louis Pasteur's experiments disprove spontaneous generation 7. Discovery of enzymes from dead yeast cells (1897)

B. Modern Microscopes 1. Light microscopes compound and dissecting microscope 2. Electron microscopes a. Useful magnifications of 200,000 b. Transmission (TEM) and scanning electron microscopes (SEM) c. Scanning tunneling microscope (STM) Nobel Prize in Physics (1986) awarded for development of STM

III. Eukaryotic versus Prokaryotic Cells A. Prokaryotic cells (bacteria) lack membrane-bound nuclei and other organelles B. Eukaryotic cells Protists, Plants, Fungi, and Animals have nuclei and other organelles

IV. Cell Size and Structure A. Size and Number 1. Higher plant cells, µm long 2. Bacterial cells, µm long 3. Pear tree leaf contains ~ 50 million cells 4. Full grown pear tree contains ~ 15 trillion cells

B. The Cell Wall 1. Found outside plasma membrane 2. Consists of mostly cellulose cellulose molecules grouped into bundles known as microfibrils 3. Pectins form the middle lamella 4. First formed walls called primary walls, then secondary walls may be formed 5. Lignin may be part of cell wall giving mechanical strength to wall 6. Plasmodesmata interconnect living plant cells

C. Cytoplasm 1. The Nucleus a. Most conspicuous organelle, generally spherical or ellipsoidal in shape b. Control center of the cell, stores hereditary information c. DNA in nucleus makes a copy of itself (RNA) as a blueprint for directing protein synthesis d. Contains 2 membranes (outer and inner), called the nuclear envelope, which contains pores to allow passage of certain molecules e. Outer membrane connected to endoplasmic reticulum f. Nucleoplasm is the granular-appearing fluid inside the nuclear envelope g. Nucleoli are larger bodies noticeable in the nucleoplasm involved in RNA synthesis h. Chromatin is the thread-like DNA strands which shorten and condense into chromosomes when the cell is ready to divide chromatin composed of DNA and protein

2. Plastids a. Types 1) Chloroplasts a) Most common type, green in color b) Stroma, enzyme containing region c) Grana membranes called thylakoids, suspended in the stroma 2) Chromoplasts a) Contain colored pigments such as carotenoids b) Give orange, red, and yellow colors to various plant parts 3) Leucoplasts a) Colorless b) Types i) Amyloplasts, store starch granules ii) Elaioplasts, store oils b. Proplastids all plastids develop from these

3. The Cytoskeleton a. Microtubules 1) Unbranched, thin, hollow tube-like structures 2) Composed of protein 3) nm in diameter and of various lengths 4) Found inside plasma membrane, help control the addition of cellulose to the cell wall 5) Other functions, vesicle transport, motility of flagella and cilia, and component of mitotic spindle b. Microfilaments 1) Long protein filaments approximately 6 nm in diameter 2) Often grouped together in bundles 3) Function in cytoplasmic streaming and as part of the framework of the cell

4. The Plasma Membrane a. Outer boundary of living cell, extremely thin b. Mosaic structure composed of phospholipids and proteins c. Unit membrane structure seen with electron microscope

5. The Endoplasmic Reticulum a. Complex system of membrane channels b. Outer surface of membranes may be covered with ribosomes c. Called "rough" ER because of pebbly appearance d. "Smooth" ER has no ribosomes e. Protein synthesis, secretion and storage associated with rough ER 6. Ribosomes a. Occur free in cytoplasm, mitochondria and chloroplast, or associated with rough ER b. Roughly ellipsoidal in shape, approximately nm in diameter c. Function in protein synthesis by linking amino acids together d. Ribosome composed of two subunits, made up of RNA and proteins

7. The Golgi Apparatus (Dictyosomes) a. Groups of flat, roundish sacs, organized into stacks b. Collecting and packaging centers for proteins and other molecules like carbohydrates 8. Mitochondria a. "Power-houses" of the cell b. Function in generation of ATP, the energy molecule of the cell c. Small organelles, 1-3 µm in length, look like tiny membranes d. Outer and inner membranes present inner membrane has inward extensions or folds called cristae

9. Other Organelles a. Microbodies 1) Small spherical organelles, bounded by a single membrane 2) Contain enzymes which function in photosynthesis, photorespiration, and conversion of fats to carbohydrates b. Lysosomes store digestive enzymes (more typical of animal cells)

10. Vacuoles a. Membrane bound sacs filled with a watery fluid called cell sap vacuolar membrane called the tonoplast b. Cell sap contains salts, sugars, organic acids, and may contain water-soluble pigments called anthocyanins c. Vacuoles are small and numerous in size in newly formed cells but increase in size as cell matures

V. Cyclosis A. Defined cytoplasmic streaming exhibited by all living cells B. Function facilitates exchange and movement of materials within a cell C. Movement microfilaments and microtubules are thought to be responsible for generating the movement of the cytoplasm

VI. Cellular Reproduction A. The Cell Cycle: The dividing cell goes through a cycle of events known as the cell cycle. Such cycle is divided into interphase and mitosis B. Interphase: 1. Period of DNA replication in preparation of nucleus dividing 2. Divided into 3 periods, G1 (1st growth or gap period), S (synthesis), and G2 (2nd growth or gap period)

C. Mitosis: 1. Terms a. Mitosis = division of the nucleus b. Cytokinesis = division of the cytoplasm c. Meristems = regions in plants where mitosis occurs

2. Prophase a. Chromosomes become shorter, thicker (by now they are doubled in DNA content) 1) Chromatids each consist of a DNA double helix. In prophase, each chromosome consists of two chrromatids. 2) Centromeres hold chromatids together 3) Kinetochore near centromere, spindle fibers attach here 4) Other constrictions may occur on individual chromosomes called satellites b. Nucleolus and nuclear envelope disappear c. Centrioles and asters form (only in algae, fungi, and animal cells)

3. Metaphase a. Spindle forms b. Chromosomes become aligned in a plane in the center of the cell (the equator) 4. Anaphase two chromatids of each chromosome separate and move to opposite poles

5. Telophase a. Each group of daughter chromosomes becomes surrounded by a new nuclear envelope b. Daughter chromosomes become longer and thinner c. New nucleoli appear d. Phragmoplast appears e. Cell plate forms vesicles from the Golgi fuse to form the cell plate

VII. Communication Between Cells A. Plasmodesmata fine strands of cytoplasm interconnect plant cells B. Pits discontinuities (gaps) in cell walls create pits

VIII. Higher Plant Cells versus Animal Cells A. Unique Structures of Plant Cells 1. Cell walls 2. Plasmodesmata 3. Cell plate B. Minor Differences 1. Plant cells lack centrioles animal cells have these 2. Plant cells contain plastids animal cells have none 3. Vacuoles, common in plant cells either small or absent in animal cells