Cell Structure and Function

1. Cell Structure and Function

2. Cell Theory • Based upon work of Theodor Schwann, Matthais Schleiden and Rudolph Virchow. • All organisms are composed of cells • Cells are the basic units of structure and function in organisms • Cells come only from preexisting cells because cells are self-reproducing.

3. Why are most cells microscopic? • Cells need a large surface area to adequately exchange nutrients and wastes • surface-area-to-volume ratio • Total surface area (HxWxSxC) divided by total volume (HxWxLxC) • Some organelles have microvilli, villi and rugae to increase surface area

4. Microscopes • 17th century – Leewenhooke • Compound Light Microscope • Uses light rays and glass lenses to focus

5. Transmission Electron Microscope • Electrons pass through the specimen • Focus by magnetic lenses • Image projected on fluorescent screen

6. Scanning electron microscope • Narrow beam of electrons scan surface of specimen • Specimen is coated with metal layer • Secondary electrons given off by metal produce an image on a screen

7. Magnification and Resolution • Light microscope = approx. 1000x • TEM = hundreds of thousands • Difference is in illumination – wavelength of electrons is shorter than wavelength of light. • Greater resolution=greater detail • Resolution – minimum distance between 2 objects at which they can still be seen as two separate objects. • If humans eyes are set at 1.0, LM=500, EM = 100,000 resolving power.

8. Viewing advancements • To increase the contrast of a specimen, different types of light, staining and optical methods can be used. • Confocal microscopy – 3-D using laser beam. • Video enhanced contrast microscopy

9. Prokaryotic Cells • Lack nucleus and membrane bound organelles • Can cause disease, decompose and help to make foods/chemicals • Classified into 2 Domains

10. Structure • Bacillus – rod shaped • Coccus – sphere shaped • Spirilla – rigid twisted rods • (called spirochetes if flexible)

11. Cell envelope • Plasma membrane – phospholipid bilayer embedded with proteins • Regulates materials into and out of the cytoplasm • Internal pouches – mesosomes – increase surface area for enzymes Cell wall – contains peptidoglycan – maintains shape Glycocalyx – layer of polysaccharides outside of cell wall, aids in protection from immune system and attachment capsule – if organized and hard to remove slime layer – if unorganized and easy to remove

12. Cytoplasm • Nucleoid region – houses the single circular strand of DNA • Plasmid – extrachromosomal piece of circular DNA used as vector in GE • Ribosomes • Inclusion body – stored nutrients

13. Cyanobacteria • Photosynthetic bacteria • Contain thylakoids in cytoplasm that contain chlorophyll that absorb solar energy to produce carbs. • Release oxygen

14. Appendages – made of protein • Flagella – locomotion, made of filament, hook and basal body • Fimbriae – small, bristlelike fibers on surface of cell, attachment • Sex Pili – rigid tubular structures, exchanging DNA - conjugation

15. Domain: Archaea • No peptidoglycan in cell wall • More diverse in shape • May be more closely related to eukaryotes because of biochemical make-up. • Live in extreme habitats, like those of long ago…