Bio 178 Lecture 6Cell 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 SizeMost 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 SizeHow do large cells overcome these problems?• Syncytium (cntd.)

Soybeet syncytium induced by nematode parasite Heterodera glycines.

http://www.apsnet.org/education/IllustratedGlossary/PhotosS-V/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/communication.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

MicroscopyResolution (R)R = 0.61 = 1/2 angular width cone of light rays collected by objective lens

n sin n = refractive index of medium separating object from objective and condenser lenses = wavelength

William H. Heidcamp, http://homepages.gac.edu/~cellab/chpts/chpt1/figure1-3.html

What limits the resolution of the light microscope?

LM of O. circumlitus Anterior End

Copyright J. Elson-Riggins

Electron MicroscopeTransmission Electron Microscope (TEM)Electrons are transmitted through the specimen (thin section).

http://euch3i.chem.emory.edu/~nmr/apk/instrumentation.html http://www.barrettresearch.ca/

teaching/nanotechnology/nano02.htm

(light) = 0.53 µm (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.

Copyright J. Elson-Riggins

Specific stains are used to visualize structures.

Staining Specimens for Microscopy

Immunocytochemistry

Antibodies are labeled with fluorescent molecules (or other substances) and used to stain specific structures.

NANCY KEDERSHA / IMMUNOGEN / SCIENCE PHOTO, LIBRARY

http://www.sciencephoto.com/images/imagePopUpDetails.html?id=771320363

Squamous carcinoma cells. Blue = Nuclei,

Red = Cytoplasm,

Green = Plasma membrane

Characteristics of Principle Cell Types

2 structurally different types of cells:

PROKARYOTE EUKARYOTE

True Nucleus?

Membrane bound

organelles?

Kingdoms