1. AP BIOLOGY Cell Structure INTRO
Chapter 6
Slide shows combined and modified from:

2. CELL THEORY All organisms are made of one or more cells.
Cells are the basic unit of structure and function in living things
Cells arise only by division of a pre- existing cell.

4. Anton van Leeuwenhoek 1st to see
1665- Robert Hooke
saw “little boxes”
in cork and
called them cells
1673-
Anton van Leeuwenhoek 1st to see
living cells
Microscope image: Cork image:
Hooke image:
Microscope/Leeuwenhoek image: Animation from:

5. 1838- Matthias Schleiden concluded that
ALL PLANTS
are made of cells
1839- Theodor Schwann
concluded that ALL ANIMALS are made of cells
Plant image: Schleiden image:
Schwann image:
Animals image:

6. Rudolph Virchow saw dividing cells in the microscope and reasoned that
1855-
Rudolph Virchow saw dividing cells
in the microscope
and reasoned that
cells come from
other cells
Virchow:
Mitosis:

7. How do we study cells? Microscopes Light microscopes
Electron microscopes
Transmission (TEM)
Scanning electron microscope (SEM)

8. LIGHT MICROSCOPES 0.2 µm resolution (10-6 m) ~ size of bacterium
Visible light passes through specimen
Can be used to
study LIVE cells

10. TRANSMISSION ELECTRON MICROSCOPY (TEM)
Aims an electron beam through thin sections of specimens
Used mainly to study internal structure of cells
Uses heavy metals to stain
Image called a “micrograph”

11. SCANNING ELECTRON MICROSCOPE (SEM)
Used to study surface structures
Sample covered with thin film of gold
Beam excites electrons on surface
Great depth of field ~ appears 3D

12. Differential centrifugation
Cell Fractionation
Tissue
cells
Homogenization
Homogenate
1000 g
(1000 times the
force of gravity)
10 min
Differential centrifugation
Supernatant poured
into next tube
20,000 g
20 min
Pellet rich in
nuclei and
cellular debris
mitochondria
(and chloro-
plasts if cells
are from a
plant)
“microsomes”
(pieces of
plasma mem-
branes and
cells’ internal
membranes)
ribosomes
150,000 g
3 hr
80,000 g
60 min
ULTRACENTRIFUGE used to separate organelles from cell
Variable density of organelles

13. EXAMPLE: RIBOSOMES PROKARYOTIC vs EUKARYOTIC
S = Svedberg unit
Measure of sedimentation rate (how fast it settles)

17. Cell Size As size increases,
volume increases much more rapidly than surface area.

23. PROKARYOTES EUKARYOTES
DNA in nucleoid Chromosomes in
region, without a nucleus
nuclear membrane surrounded by a nuclear membrane

24. Nucleus Nucleolus – ribosome sub-units are made here;
Repository for genetic material
Directs activities of the cell
Usually single, some cells several, RBC none
Nucleolus – ribosome sub-units are made here;
Surface of nucleus bound by two phospholipid bilayer membranes
nuclear membrane (envelope)
Nuclear pores – protein gatekeepers
Usually proteins going in and RNA going out

25. Chromosomes DNA of eukaryotes is divided into linear chromosomes.
exist as strands of chromatin, except during cell division
associated with packaging histones, packaging proteins
Nucleosomes-
beadlike unit of DNA packaging (histones help)