Chapter 7 Cells

7.1 Life is Cellular A. The discovery of the cell: since the 1600’s scientists have made many discoveries about the cells of living things. These discoveries lead to the development of the cell theory. Contributions were made from each of the following: a. Robert Hooke: described microscopic cells; coined the term “cell” after viewing a sample of cork and seeing chambers that reminded him of the monk’s chambers in a monastery called cells. b. Anton van Leeuwenhoek: used a single lens microscope to observe a sample of pond water and found swarming little organisms; called them “wild animalcules”; was first to observe living and moving cells. c. Robert Brown: discovered and named the nucleus. d. Matthias Schleiden: concluded that all plants are made of cells. e. Theodor Schwann: concluded that all animals are made of cells; coined the term “metabolism” for all chemical processes in a cell; recognized similarity of plant and animal cells except for animal’s lack of a cell wall. f. Rudolf Virchow: Proposed that all animal and plant cells are produced by the division of existing cells. B. The Cell Theory states: a. All living things are made of cells. b. Cells are the basic units of structure and function in living things. c. New cells are produced from existing cells.

C. Exploring the Cell; cells fall into two broad groups, based on their structure. a. Nucleus: a membrane-enclosed structure that holds the cell’s genetic material (DNA). The nucleus controls many of the cell’s activities. b. Prokaryotes: i. Do Not have a Nucleus ii. Have genetic material that is not contained in a nucleus. iii. Bacteria are prokaryotes. c. Eukaryotes: i. Are cells that have a nucleus in which their genetic material is separated from the rest of the cell. ii. Plants, animals, fungi, and protists are eukaryotes.

7.2 Eukaryotic Cell Structure  Cell biologists divide the eukaryotic cell into two main parts: the nucleus and the cytoplasm. A. In the Nucleus: the nucleus contains most of a cell’s DNA. The DNA contains the coded instructions for making proteins and other important molecules. a. Nuclear envelope: a double membrane that surrounds the nucleus and separates it from the cytoplasm. b. Chromatin: granular material inside the nucleus; made of DNA bound to proteins. During cell division, chromatin condenses into threadlike structures called chromosomes. Chromosomes contain genetic information. c. Nucleolus: small, dense region inside the nucleus where ribosome production begins.

B. In the Cytoplasm: material inside of the cell membrane outside of the nucleus.

a. Cytoplasm is a homogeneous, generally clear jelly-like material that fills cells. The cytoplasm consists of cytosol and the cellular organelles, except the nucleus. The cytosol is made up of water, salts and organic molecules and many enzymes that catalyze reactions. The cytoplasm plays an important role in a cell, serving as a "molecular soup" in which the organelles are suspended and held together by a fatty membrane. It is found within the plasma membrane of a cell and surrounds the nuclear envelope and the cytoplasmic organelles.

The cytoplasm plays a mechanical role, i.e. (example) to maintain the shape, the consistency of the cell and to provide suspension to the organelles.

It is also a storage place for chemical substances indispensable to life. Vital metabolic reactions take place here, for example anaerobic glycolysis and protein synthesis.

b. Organelles: specialized structures that perform important cellular functions within a eukaryotic cell. a. Ribosomes: small particles of RNA and protein spread throughout the cytoplasm. Site for protein synthesis (where proteins are made). b. Endoplasmic reticulum (ER): internal membrane system; site for lipid and protein synthesis. i. Rough ER: has ribosomes on its surface; the part of the ER involved in protein synthesis. ii. Smooth ER: does not have ribosomes on its surface; helps make lipids. c. Golgi Apparatus: closely grouped membranes; the function is to change, sort, and package proteins and other materials from the ER for storage in the cell or secretion outside the cell. d. Lysosome: small organelle filled with enzymes; help break down lipids, carbohydrates, and proteins into small molecules that can be used by the est of the cell. e. Vacuoles: sac-like structures used to store materials. f. Mitochondria: convert the chemical energy stored in food into compounds that are more convenient for the cell to use. g. Chloroplasts: found in plants and some other organisms; capture the energy in sunlight and convert it into chemical energy. h. Cytoskeleton: the structure that helps support the cell; consists of a network of protein filaments; helps cell maintain its shape and is involved in movement.