C2006/F2402 '04 -- Lecture 1 -- Updated 01/19/04

2004  Deborah Mowshowitz, Department of Biological Sciences, Columbia University, New York NY

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

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 5th ed. (When fig. numbers or pages in 4th edition are different, refs. to 4th ed. follow in parentheses.) Refs to Purves are to 6th ed.

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.

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

    A. The Major Question: How do Living Things Work?

    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. Looked at "big 5" issues = structure, function, manufacture (including energy requirements), regulation, and (evolutionary) origin

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

For recent developments on extensions of the central dogma see Scientific American, Nov 2003 p. 46 "The Unseen Genome: Gems among the Junk," by Wayt Gibbs. (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 may 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.

    B. Differences: Will concentrate on Eukaryotes (mostly); will look at the two big innovations of eukaryotes. -- Intracellular Compartmentalization & Multicellularity -- and the complications that result. See Becker table 4-1 for comparison of Eukaryotic and Prokaryotic cells.

    C. Major Subjects of Term

        1. Cell Bio -- study of consequences/implications of compartmentalization within cells (Lectures 1-9)

            a. Macromolecules and bigger things (membranes and organelles -- chromosomes, etc.)

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

            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)?

            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

    a. How cells communicate chemically (Lectures 10-13); how aberrations in communication may cause cancer.

    b. How cell communicate electrically (Lectures 16-18 by Dr. Stuart Firestein)

        3. Physiology --  study of consequences/implications of multicellularity for maintenance of homeostasis, movement & defense.
How specialized cells in a multicellular organism work to maintain a relatively constant internal environment and how their functions are co-ordinated. This subject will be divided as follows:

            a. How the various systems (nervous, muscular, respiratory, etc.) work to maintain homeostasis of temperature, gas, fluid, salt & water (Lectures 14, 15 & 19-21

            b. Immunology -- The most specialized system; how a multicellular organism fends off invaders (Lectures 22-23)

        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 24-25.

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.

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

  • 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

    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 4.2 . 

        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. In the EM you can actually see membranes; structure of membranes will be covered next time. What else can you see in a typical animal cell?

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

    2. 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.
    c. Smooth ER: lipid synthesis, Ca++ storage, detoxification, etc.

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

    4. Location/function of ribosomes.

    5.  Mitochondria and chloroplasts

  • Structures -- see handout 1A & texts (Becker fig. 4-11 & 4-14; Purves 4-14 & 4-15.) Note double membranes, 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.)

  • 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 cmpds (in mito).

  • Origins -- probably endosymbionts.  Mito. and chloro. were once probably free living bacteria. (See Purves 4.15 or Becker Box 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.

           5. Cytoskeleton (see handout 1B & Becker figs. 4-23 & 4-24 or Purves 4.21) -- we may 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)-- most movement involving MF & MT occurs by sliding of one fiber or organelle relative to another. (Changes in length due to polymerization and depolymerization do occur.) 

    c. Localization of other factors -- act as peg board or framework for attachment of organelles, enzymes, etc. 


    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 ed. (pp. xiii -xv in 4th).

        A. "Grind and Find" (Biochemical separations and assays). See Becker Box 12A pp. 326-330 (332-336).

    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: 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..

            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 Guide to Microscopy pp 8-11 (Appendix, pp. 824-827) and table 22-2. For a picture of a typical result, see Becker 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.