Transcript Biol 178 Lecture 6

Bio 178 Lecture 6
Cell Structure
Sui Huang and Donald E. Ingber, http://w3.mit.edu/i-m/image2big.htm
Reading
•
Chapter 5
Quiz Material
•
Questions on P 104
•
Chapter 5 Quiz on Text Website
(www.mhhe.com/raven7)
Outline
• Characteristics of cells
• Microscopy
Characteristics of All Cells
1. Hereditary Material
• Prokaryotes
Nucleoid - DNA not surrounded by a membrane.
• Eukaryotes
Nucleus - DNA is surrounded by the nuclear envelope.
2. Cytoplasm
Cell matrix.
Characteristics of All Cells
3. Phosopholipid Bilayer boundary
Plasma membrane is 5-10 nm thick and contains
embedded proteins.
Modern Cell Theory
1. All organisms are composed of one or more cells.
2. A cell is the smallest living entity.
3. New cells arise only via division of pre-existing
cells.
Schleiden
Schwann
Cell Size
Most eukaryotic cells are 5-20 µm
Reasons
• Surface to Volume Ratio
1. Cells need a large a S:V to allow transport of nutrients,
gases, & waste across the plasma membrane.
2. Much easier to achieve if an organism is made of
numerous small cells rather than few large cells.
• One Command Center per Cell
The nucleus can more easily provide for the cell if the cell
is small.
Cell Size
How do large cells overcome these problems?
• Syncytium
Skeletal Muscle
http://www8.nos.noaa.gov/coris_glossary/index.aspx?letter=s
Cell Size
How do large cells overcome these problems?
• Syncytium (cntd.)
Soybeet syncytium induced by nematode parasite Heterodera
glycines.
http://www.apsnet.org/education/IllustratedGlossary/PhotosSV/syncytium.htm
Cell Size
How do large cells overcome these problems?
• Cell Shape
http://www.nature.com/news/2004/040531/images/nerve_180.jpg
http://web.sfn.org/content/Publications/BrainBackgrounders/communicat
ion.htm
Cell Size
How do large cells overcome these problems?
• Large Nuclei
ES gland of Otostrongylus circumlitus (copyright J. Elson-Riggins)
Microscopy
Resolution
The minimum distance between 2 points at which they can
be distinguished as separate objects.
Human Eye:
~ 100 µm
Light Microscope:
0.2 µm (in theory)
Electron Microscope:
0.1 nm
Microscopy
Resolution (R)
R = 0.61 
n sin 
 = 1/2 angular width cone of light rays collected by objective lens
n = refractive index of medium separating object from objective and condenser lenses
 = wavelength
What limits the resolution of the
light microscope?
William H. Heidcamp, http://homepages.gac.edu/~cellab/chpts/chpt1/figure1-3.html
LM of O. circumlitus Anterior End
Copyright J. Elson-Riggins
Electron Microscope
Transmission Electron Microscope (TEM)
Electrons are transmitted through the specimen (thin section).
http://euch3i.chem.emory.edu/~nmr/apk/inst
rumentation.html
 (light) = 0.53 µm
http://www.barrettresearch.ca/teaching/
nanotechnology/nano02.htm
 (electrons) = 0.004 nm
TEM (O. circumlitus ES Gland)
Copyright J. Elson-Riggins
Scanning Electron Microscope (SEM)
Electrons are reflected off the surface of the specimen gives 3D images.
Ant head
http://www.ucmp.berkeley.edu/esem/gallery.html
Staining Specimens for Microscopy
Staining increases contrast (cells are 70% water  little to
impede passage of light rays/electrons).
O. Circumlitus ES gland
stained with PAS and
aniline blue-black.
Specific stains are
used to visualize
structures.
Copyright J. Elson-Riggins
Staining Specimens for Microscopy
Immunocytochemistry
Antibodies are labeled with fluorescent molecules (or other
substances) and used to stain specific structures.
Squamous carcinoma cells.
Blue = Nuclei,
Red = Cytoplasm,
Green = Plasma
membrane
NANCY KEDERSHA / IMMUNOGEN / SCIENCE PHOTO, LIBRARY
http://www.sciencephoto.com/images/imagePopUpDetails.html?id=771320363
Characteristics of Principle Cell Types
2 structurally different types of cells:
PROKARYOTE
True Nucleus?
Membrane
bound
organelles?
Kingdoms
EUKARYOTE