C2006/F2402 '06 -- Lecture 1 -- Updated 01/16/06

2006  Deborah Mowshowitz, Department of Biological Sciences, Columbia University, New York NY

Handouts: 1A -- Eukaryotic Cell Structure ; 1B -- Cytoskeleton;  1C -- Overview of Course (Brief Description)

Overview is not comprehensive. Be sure to check out 'About C2006' or 'About F2402.'

Optional reading:
"Scientists find smallest form of life", William J. Broad, New York Times, Jan. 18, 2000.
Nanobes. Photos of nanobes, their discover, Dr. Phillipa Uwins, and links to a cool animation.

References to Becker are to 6th ed. (When fig. numbers or pages in 5th edition are different, refs. to 5th ed. follow in parentheses.) Refs to Purves are to 7th ed (6th in parentheses).

Notes for this term will be extensive outlines, not word-for-word. This is partially for practical reasons and partially for educational reasons -- I think it encourages better student note taking and understanding. The outlines will be provided the night before (if not earlier) so you can print them out in advance and annotate them in class. If you like to read ahead, the outlines from last year (2005) are linked to the '05 schedule.

I. The Story So Far -- Summary of last Term

    A. The Major Question: How do Living Things Work? Or how does 1 E.coli make two?

    B. Answer so far has concentrated on

        1. Prokaryotes (mostly) -- 1 intracellular compartment, unicellular

        2. Macromolecular level -- did not discuss larger structures such as organelles, chromosomes, etc.

        3. The "big 5" issues  --  structure, function, manufacture (including energy requirements), regulation, and (evolutionary) origin.

        4. Methods used to figure out how living things work, especially the methods used to get at the "big 5."

    C. Bottom Line: DNA RNA (& more DNA); RNA protein job, say catalyzing X Y. Protein production & activity are regulated.

For some ideas about possible extensions of the central dogma see Scientific American, Nov 2003 p. 46 "The Unseen Genome: Gems among the Junk," by Wayt Gibbs. The author discusses possible regulatory roles of RNA. (A companion article by the same author is in the Dec. issue and discusses chromosome structure and modification, which will be discussed later this term.) To download the article, go to Scientific American, and put the words "unseen genome" in the search box to get the link to the article. You  have to be at a Columbia computer for this to work.

II. Overview of this Term

    A. Similarities: Same Major Question; Same "big-5" issues; same stress on methods.

    B. Differences:

        1. Organisms: This term will concentrate on Eukaryotes (mostly); will look at the two big innovations of eukaryotes and the complications that result. See Becker table 4-1 for comparison of Eukaryotic and Prokaryotic cells. Innovations:

           
a. Intracellular Compartmentalization  

            b. Multicellularity

        2. Topics: Cell Biology, How cells communicate (signaling),  Physiology, & Development. Details below.

    C. Major Subjects of Term

        1. Cell Bio -- study of consequences/implications of compartmentalization within cells (Lectures 1-10)

            a. Macromolecules and bigger things (membranes and organelles -- chromosomes, etc.) Lectures 1-3/

            b. Co-ordination (between different parts of cell) -- how do things get to the right compartment? How do they cross membranes? Lectures 4-8.

            c. Regulation of eukaryotic gene transcription & the cell cycle -- how do things get made at the right time (as well as in the right place)? Lectures 9 & 10.

            d. Note: in this part, we will emphasize generalized features of all eukaryotic cells but discuss some specialized cell types.

        2. Signaling & Cell-Cell communication -- one consequence of multicellularity -- the need for co-ordination between different cells (as vs co-ordination between the different parts of a single cell). Some examples of how specialized cells carry out specialized functions.

            a. How cells communicate chemically (Lectures 11-13); how aberrations in communication may cause cancer.

            b. How cell communicate electrically (Lectures 17 &18 by Dr. Stuart Firestein, & Part of 19) -- structure and function of nerve cells.

        3. Physiology --  study of consequences/implications of multicellularity for maintenance of organism as a whole. How organisms make use of communication, specialization, etc. to maintain a relatively constant internal environment and how all the various functions are co-ordinated. This subject will be divided as follows:

            a. Homeostasis: How the various systems (nervous, hormonal, muscular, respiratory, etc.) work to maintain a constant internal environment of temperature, gas, fluid, salt & water (Lectures 14-16 & 20-22).

            b. Immunology -- The most specialized system; how a multicellular organism fends off invaders (Lecture 22)

        4. Development  -- How to build a multicellular organism. How cells get to the right place in a 3D organism; how the cells specialize and how they stay that way. Lectures 23 & 24 by Dr. Alice Heicklen.

III. Eukaryotes -- a  closer look.

    A. What can you see in the light microscope? Suppose we draw a standard light microscope view of eukaryotic cell -- what can you see?  Can't actually see membranes or details of many organelles. Can see nucleus, nucleolus, chloroplasts and/or mitochondria, Golgi (maybe).

    B. Issues of resolution -- For pictures using the different methods, see Becker fig. 1-3 (5th ed) or Purves 4.4 (4.3.) For more details on microscopy, see Becker appendix (6th & 4th ed.) or Becker's Guide to Microscopy (a supplement included with the 5th ed.) or

  • Types of Microscopes -- Light microscope, SEM (scanning electron microscope) and TEM (transmission electron microscope)

  • Limit of Resolution

    Useful Magnification

    Features

    Eye

    0.1 mm

    1

    Light Microscope

    0.2 micron

    1000X

    Can look at living specimens

    TEM

    1-2 nm (in practice)

    100,000X or 100X light scope

    Detect electrons from source that pass through thin slice of tissue

    SEM

    Larger than TEM but gives 3D picture of surface*

    Less than TEM

    Detect secondary electrons emitted from surface of sample

    * For a nice picture see Becker fig. 1-3 (1-4).

    1/1000

    1/1000

    1/1000

    1/10

    m (meter)

    mm

    micron

    nm (nano)

    Angstrom

    Cell Type  Diameter
    Typical eukaryotic animal cell  50 microns (mu) = 50,000 nm.  
    Typical bacterium 1-5 microns = 1-5000 nm
    Smallest known bacterium 0.2 microns = 200 nm 
    nanobe (for Times article see; for more info see) 20-150 nm
    ribosome 50-60 nm

    For more examples and tables of relative sizes see Becker fig.1-2  & box 1A or Purves 4.1 (4.2) . 

        C. What you can see in the EM? See handout 1A and fig. 4-5 of Becker or 4.7 of Purves for pictures of whole cells. Some specific references to pictures of organelles are given below, but all pictures in Ch. 4 of both texts are well worth it. Methods used to characterize the various parts are described below in IV, but will be discussed as they come up.

            1. Membranes. In the EM you can actually see membranes (6-9 nm across); Membrane = bilayer of lipid plus associated proteins. Detailed structure of membranes will be covered next time.

            2. Nuclear details  -- See figs. 4-4 & 4-10 of Becker or 4.9 (4.8) of Purves.

    3. Endomembrane system (See Purves figs. 4.11 to 4.13 or Becker fig. 4-15 to 4-18)

    a. Rough ER, Golgi, most vesicles: Involved in processing, sorting, packaging and transporting proteins to their proper destination -- to right part of EMS or outside the cell. 
    b. Lysosomes: contain acid hydrolases -- used to degrade/recycle macromolecules from the outside of the cell.
    c. Smooth ER: lipid synthesis, Ca++ storage, detoxification of drugs & toxins, etc.

              4. Peroxisomes  (See Becker fig. 4-19 & 4-20 or Purves 4.19)

    5.  Mitochondria and chloroplasts

  • Structures -- see handout 1A & texts (Becker fig. 4-11 & 4-14; Purves 4-14 & 4-15.) Note double membranes (2 bilayers), prokaryotic style ribosomes, circular DNA, overall size similar to that of bacteria.

  • Have own genetic systems (DNA, ribosomes etc. -- everything needed for DNA replication, transcription & translation.) Mitochondrial DNA is often used for identifications (when nuclear DNA is not available) or for tracing inheritance of the female line. For a recent example, click here.

  • Most proteins of mito and chloro are NOT made inside the organelle -- most are encoded in the nucleus, made in the cytoplasm, and transported into the organelle after synthesis.

  • There are strong similarities between  mito &. chloro -- electron transport in membrane used to pump protons, H+ gradient used to make ATP; carbon rearrangements carried out in matrix or equivalent, etc. Exergonic process that drives electron transport is different -- light absorption (in chloro) vs oxidation of reduced carbon compounds (in mito).

  • Origins -- probably endosymbionts.  Mito. and chloro. were once probably free living bacteria. [See Purves 4.18 or Becker Box  11A (15A)]

  • Q's to ask yourself: (1) What are the major similarities and differences between peroxisomes, lysosomes and mitochondria? How can you tell them apart? It is a good idea to make a table that compares and contrasts the three organelles. (2) How are new organelles made? The answers are different for the 3 types of organelles and will be discussed in a few lectures.

            6. Location/function of ribosomes.

            7. Cytoskeleton (see handout 1B & Becker figs. 4-23 & 4-24 or Purves 4.21) -- we will probably not get to this until next time.

  • Three components -- IF, MT & MF

  • Structure & properties of each type are summarized in table on 1B (see texts for pictures)

  • Functions

  • a. Support/strength -- weight bearing, shape determining.

    b. Movement (MF & MT)-- can change shape of cell (as in muscle or amoeba) and/or  help move organelles within cells.

    c. Localization of other factors -- act as peg board or framework for attachment of organelles, enzymes, etc. (Cytoplasm is not simply a "bag of enzymes.")

    IV. Methods -- these will be discussed in Lecture #1 or #2 as we get to them. How do you find out which components are in each cell part?

    Reminder: Becker has a guide to all techniques and methods described in the book -- see  inside front cover in 5th or 6th ed. (pp. xiii -xv in 4th).

        A. "Grind and Find" (Biochemical separations and assays). See Becker Box 4B (4A)  and Box12A, pp. 322 - 326 (326-330); Purves 4.8.

    1. Grind: Break up cell into parts, and separate (fractionate) parts by ultracentrifugation.

    2. Find: Assay (test) each cell fraction for enzymes of interest. Find the cell part associated with each particular enzyme.

        B. In situ labeling (Localization of enzymes "in situ" = in place).

    1. Substrate: Provide solution of substrate. Enzyme substrate is soluble, so it diffuses to site of enzyme.

    2. Product: Product of enzyme catalyzed reaction is insoluble, so it stays in the place where it is made. If cells are washed, unused substrate will be removed, but product will stay put.

    3. Localization: Insoluble product is produced and precipitates only at location of enzyme -- pin points position of enzyme.

    4. Detection of product: Can be colored (for detection in light microscope) or electron dense (for detection in EM). For an example, see Becker fig. 12-20.

        C. Immunofluorescence -- Use of labeled antibodies as tags -- direct (one step) and indirect (two step). See Becker table 15-2 (22-2). For more details, see Appendix, A-8  to A-11 (or Guide to Microscopy pp 8-11). For a picture of a typical result, see Becker 15-1 (22-1) or Purves 4.3. A handout detailing the procedure will be provided next time. Allows you to visualize location(s) of particular proteins.

    Next time: More on the cytoskeleton, and the structure of cell membranes.