Lecture #2 Outline – Introduction to Cell Biology (cont.)

 

  1. Units of measure & common cell sizes
    1. 1 m = 1X 103 mm = 1 X 106 mm = 1 X 109 nm
    2. Approximate size of some common cell types

                                                               i.      Single celled organisms

1.       Algae (Euglene gracilis)       50 mm

2.       Yeast                                     5 mm

3.       E. coli                                     1 um

                                                             ii.      Single cells from multi-cellular organisms

1.       Red blood cell                        7 mm

2.       chicken egg yolk                     cms

3.       axon                                       up to 1m or more

    1. As a general rule, most cells are 1-30 mm

                                                               i.      Size is generally limited by diffusion

                                                             ii.      There are, of course, exceptions to this rule

 

  1. Diffusion
    1. The spontaneous movement of molecules from a region of high concentration to low concentration
    2. Rate of diffusion is dependant on:

                                                               i.      Size of molecule – inverse relationship

                                                             ii.      Environment through which the substance is diffusing

1.       temperature – proportional relationship

2.       viscosity – inverse relationship

3.       distance – proportional to sq. rt. of time

    1. effective for moving small molecules relatively short distances

                                                               i.      ATP, sugars, amino acids, etc.

                                                             ii.      10 mm traveled / ~0.2 sec

    1. example of 2nd law of thermodynamics

                                                               i.      entropy

                                                             ii.      the degree of disorder in a system only increases

    1. rate of diffusion for various biologically relevant molecules limits most cells to a maximum of 30-50 mm in diameter

                                                               i.      if cells were larger, then metabolic pathways would be compromised

                                                             ii.      specialized mechanisms exist to deal with this in large/long cells and multi-cellular settings

1.       circulatory systems

2.       capillary networks

3.       molecular transport (cytoplasmic streaming)

 

  1. Ratio of surface area (SA) to volume (V)
    1. Related to diffusion
    2. As a cell grows SA increases more slowly than V
    3. Graphical illustration (in-class)
    4. As SA/V ratio drops insufficient material is able to cross at a rate high enough to meet metabolic needs and waste cannot be eliminated at an adequate rate
    5. Some cells can partially overcome this problem by increasing the SA of the plasma membrane

                                                               i.      Microvilli

                                                             ii.      Projections of membrane to increase SA and maximize diffusion

 

  1. Lower limits to cell size

 

  1. Common characteristics of cells

 

    1. Take in raw materials
    2. Produce energy
    3. Synthesize molecules
    4. Organized growth
    5. Ability to respond to internal and external stimuli
    6. Reproduce (although there are many exceptions to this)

 

  1. Common structural characteristics
    1. Plasma membrane

                                                               i.      Selectively permeable

                                                             ii.      Thin, outer membrane

    1. Heredity information in DNA

                                                               i.      Genetic code is basically the same

                                                             ii.      Conserved molecular heritage across phyla

    1. Information flow is similar

                                                               i.      DNA -> RNA -> Protein

                                                             ii.      Protein sysnthesis at ribosomes

    1. Proteins govern structure and function

 

  1. Virus: living or not?
    1. in-class discussion
    2. reproduces only with assistance
    3. borrows/enslaves protein synthesis machinery
    4. release

 

  1. Prokaryotes VS Eukaryotes
    1. Inspite of similarities, there are significant fundamental differences between some cell types
    2. Super-kingdoms of life – division made based on morphology, cytology and molecular characteristics

                                                               i.      Prokaryotes

1.       Eubacteria – two major groups

a.       Common bacteria

b.       Cyanobacteria

2.       Archaebacteria - exploit and thrive in harsh environmental conditions

a.       Extreme halophoiles

b.       Extreme thermophiles

c.       Methanogens

d.       Sulfobacteria

e.       Common features (in-class)

                                                             ii.      Eukaryotes – at least 4 common linages

1.       Protists (Protozoans and Algae)

2.       Fungi

3.       Plant

4.       Animal

 

  1.  Major differences between prokaryotes and eukaryotes
    1. Table presented in-class
    2. Discussion in-class

 

  1. Other distinguishing characteristics
    1. Prokaryotes

                                                               i.      More direct transcription/translation

                                                             ii.      More efficient replication

                                                            iii.      Minimal capacity for specialization

                                                            iv.      Generally more compact in size

                                                              v.      Generally less complex

    1. Eukaryotes

                                                               i.      More elaborate transcription systems

                                                             ii.      Non-coding DNA

                                                            iii.      Cell specialization more common

                                                            iv.      Generally express only part of genome

                                                              v.      More limited capacity for replication

                                                            vi.      Ability to produce large amounts of specific components

 

  1. Common techniques for looking at living cells (details and discussion of each in-class)
    1. Phase-contrast microscopy
    2. Fluorescent microscopy 
    3. Transmission electron microscopy
    4. Scanning electron microscopy