Cell Structure and Function

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.

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

Microscopes

17th century – Leewenhooke Compound Light Microscope Uses light rays and glass lenses to

focus

Transmission Electron Microscope

Electrons pass through the specimen Focus by magnetic lenses Image projected on fluorescent screen

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

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.

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

Prokaryotic Cells

Lack nucleus and membrane bound organelles

Can cause disease, decompose and help to make foods/chemicals

Classified into 2 Domains

Structure

Bacillus – rod shaped Coccus – sphere shaped Spirilla – rigid twisted rods

(called spirochetes if flexible)

Cell envelope Plasma membrane – phospholipid bilayer

embedded with proteins Regulates materials into and out of the

cytoplasm Internal pouches – mesosomes – increase

surface area for enzymesCell wall – contains peptidoglycan – maintains

shapeGlycocalyx – layer of polysaccharides outside of

cell wall, aids in protection from immune system and attachmentcapsule – if organized and hard to removeslime layer – if unorganized and easy to remove

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

Cyanobacteria

Photosynthetic bacteria Contain thylakoids in cytoplasm that

contain chlorophyll that absorb solar energy to produce carbs.

Release oxygen

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

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…