Chapter 7 Cellular Structure and Function

Section 7.1: Cell Discovery and Theory 1665 – Robert Hooke (U.K.) 1665 – Robert Hooke (U.K.) Made a simple microscope and used it to observe cork. Made a simple microscope and used it to observe cork. He saw small box-like structures and called them cellulae (Latin for small rooms). He saw small box-like structures and called them cellulae (Latin for small rooms). It is from Hooke’s work that we have the term cell. It is from Hooke’s work that we have the term cell.

History of the Cell Theory A cell is the basic structural and functional unit of all living organisms. A cell is the basic structural and functional unit of all living organisms – Anton van Leeuwenhoek (Dutch) 1683 – Anton van Leeuwenhoek (Dutch) Designed his own microscope after reviewing Hooke’s work. Designed his own microscope after reviewing Hooke’s work. Observed single-celled organisms in pond water, milk, and other substances. Observed single-celled organisms in pond water, milk, and other substances.

The Cell Theory 1838 – Scientist discovers plants are made of cells – Scientist discovers plants are made of cells – Scientist discovers that animal tissue also consists of individual cells – Scientist discovers that animal tissue also consists of individual cells – Scientist proposes that all cells are produced from the division of existing cells – Scientist proposes that all cells are produced from the division of existing cells. The Cell Theory – includes three principles: The Cell Theory – includes three principles: 1. All living organisms are composed of one or more cells. 2. Cells are the basic unit of structure and organization of all living organisms. 3. Cells arise only from previously existing cells, with parent cells passing copies of their genetic material on to their daughter cells.

Microscope Technology Developments in microscope technology have given scientists the ability to study cells in great detail. Developments in microscope technology have given scientists the ability to study cells in great detail. Compound Light Microscope – Compound Light Microscope – Consists of a series of glass lenses. Consists of a series of glass lenses. Uses visible light to magnify an image. Uses visible light to magnify an image. Each lens magnifies the image of the previous lens. Each lens magnifies the image of the previous lens. So if we use two 10X lenses, the total magnification will be 100X (10 x 10 = 100). So if we use two 10X lenses, the total magnification will be 100X (10 x 10 = 100). The compound light microscope is limited in that the properties of visible light will always limit the resolution. The compound light microscope is limited in that the properties of visible light will always limit the resolution. Maximum magnification without blurring is 1000X. Maximum magnification without blurring is 1000X.

Microscope Technology (Continued) Electron Microscope (1940s) – Electron Microscope (1940s) – Uses magnets to aim a beam of electrons at a thin slice of a cell. Uses magnets to aim a beam of electrons at a thin slice of a cell. 1. Transmission Electron Microscope (TEM) - Electrons are passed through a specimen to a fluorescent screen. TEMs can magnify up to 500,000X but specimens must be dead, sliced very thin, and stained with heavy metals. TEMs can magnify up to 500,000X but specimens must be dead, sliced very thin, and stained with heavy metals. 2. Scanning Electron Microscope (SEM) – Directs electrons over the surface of the specimen to produce a 3-dimensional image.

Transmission Electron Microscope

Scanning Electron Microscope

Microscope Technology (Continued) 3. Scanning Tunneling Electron Microscope (STM) – produces 3D images of live specimens

Warm-up Question What are the three principles of the cell theory? What are the three principles of the cell theory?

Cells differ in many ways however….. All cells have a plasma membrane – a special boundary that helps control what enters and leaves the cell. All cells have a plasma membrane – a special boundary that helps control what enters and leaves the cell.

Two Broad Categories for Cells Prokaryotic Cells (pro = before; kary = nucleus) Prokaryotic Cells (pro = before; kary = nucleus) Eukaryotic Cells (eu = true; kary = nucleus) Eukaryotic Cells (eu = true; kary = nucleus) Are times larger that prokaryotic cells Are times larger that prokaryotic cells Contain a nucleus and other organelles that are bound by membranes (membrane-bound organelles). Contain a nucleus and other organelles that are bound by membranes (membrane-bound organelles). The nucleus is a distinct central organelle that contains the cell’s genetic material (DNA). The nucleus is a distinct central organelle that contains the cell’s genetic material (DNA). Organelles are specialized structures that carry out specific cell functions. They enable cell functions to take place in different parts of the cell at the same time. Organelles are specialized structures that carry out specific cell functions. They enable cell functions to take place in different parts of the cell at the same time.

Prokaryotic Cells Are defined as cells without a nucleus or other membrane bound organelles. Are defined as cells without a nucleus or other membrane bound organelles. Most unicellular organisms (bacteria) are prokaryotes. Most unicellular organisms (bacteria) are prokaryotes. Are much simpler in structure compared to eukaryotes. Scientists believe eukaryotic cells evolved from prokaryotic cells and that prokaryotes were probably the first form of life on Earth. Are much simpler in structure compared to eukaryotes. Scientists believe eukaryotic cells evolved from prokaryotic cells and that prokaryotes were probably the first form of life on Earth.

The Plasma Membrane helps a cell maintain homeostasis. helps a cell maintain homeostasis. is a thin, flexible boundary that separates a cell from its environment. is a thin, flexible boundary that separates a cell from its environment. allows nutrients to enter and wastes to exit. allows nutrients to enter and wastes to exit. All prokaryotes and eukaryotes have a plasma membrane. All prokaryotes and eukaryotes have a plasma membrane. Selective permeability – allows some substances to pass through and keeps others out. (See fig. 7.5) Selective permeability – allows some substances to pass through and keeps others out. (See fig. 7.5)

Structure of the Plasma Membrane The plasma membrane is composed of a phospholipid bilayer – two layers of phospholipids are arranged tail to tail. The plasma membrane is composed of a phospholipid bilayer – two layers of phospholipids are arranged tail to tail.

Other Components of the Plasma Membrane Transport proteins - create tunnels through which certain substances enter and leave the cell. Transport proteins - create tunnels through which certain substances enter and leave the cell. Needed substances – glucose, water, oxygen Needed substances – glucose, water, oxygen Wastes – carbon dioxide Wastes – carbon dioxide Therefore, transport proteins contribute to the selective permeability of the plasma membrane. Therefore, transport proteins contribute to the selective permeability of the plasma membrane. Cholesterols contribute to the fluidity of the plasma membrane in that they prevent the fatty- acid tails from sticking together. Cholesterols contribute to the fluidity of the plasma membrane in that they prevent the fatty- acid tails from sticking together. Carbohydrates attached to proteins stick out from the plasma membrane. Carbohydrates attached to proteins stick out from the plasma membrane.

Fluid Mosaic Model mb.htm mb.htm mb.htm mb.htm The components of the plasma membrane are in constant motion sliding past each other. The components of the plasma membrane are in constant motion sliding past each other. The phospholipids in the bilayer create a “sea” in which other molecules can float, hence “fluid” and “mosaic” because there are many components which appear as a pattern or a mosaic. The phospholipids in the bilayer create a “sea” in which other molecules can float, hence “fluid” and “mosaic” because there are many components which appear as a pattern or a mosaic.