1. Tour of the Cell

2. I. Why do cells have organelles (little organs)?
mitochondria
I. Why do cells have organelles (little organs)?
Specialized structures
specialized functions
cilia or flagella for locomotion
Containers
partition cell into compartments
create different local environments
separate pH, or concentration of materials
distinct & incompatible functions
lysosome & its digestive enzymes
Membranes as sites for chemical reactions
unique combinations of lipids & proteins
embedded enzymes & reaction centers
chloroplasts & mitochondria
chloroplast
Golgi
Why organelles?
There are several reasons why cells evolved organelles. First, organelles can perform specialized functions. Second, membrane bound organelles can act as containers, separating parts of the cell from other parts of the cell. Third, the membranes of organelles can act as sites for chemical reactions.
Organelles as specialized structures
An example of the first type of organelle is cilia, these short filaments act as "paddles" to help some cells move.
Organelles as Containers
Nothing ever invented by man is as complex as a living cell. At any one time hundreds of incompatible chemical reactions may be occurring in a cell. If the cell contained a uniform mixture of all the chemicals it would not be able to survive. Organelles surrounded by membranes act as individual compartments for these chemical reactions. An example of the second type of organelle is the lysosome. This structure contains digestive enzymes, these enzymes if allowed to float free in the cell would kill it.
Organelle membranes as sites for chemical reactions
An example of the third type of organelle is the chloroplast. The molecules that conduct the light reactions of photosynthesis are found embedded in the membranes of the chloroplast. ER

3. II. Isolation of organelles A. Occurs by process of cell fractionation
II. Isolation of organelles A. Occurs by process of cell fractionation. B. Based on various densities of organelles. C. Begins with breaking open cell membranes without damaging organelles; Called homogenization.

5. Homogenate is spun in a centrifuge to separate the pellet of organelles from the liquid (supernatant).
Pellet is removed, and the supernatant is spun again at
higher speed to cause heaviest of
remaining organelles to settle out.

7. Heaviest to lightest cell fractions are nuclei, mitochondria/chloroplasts,
parts of membranes, then ribosomes.
G. Specific metabolic processes are
identified with certain cell fractions, and then tied to specific organelles.

8. (Show “Cell Fractionation Animation” from microbiology web site.)

9. Prokaryote bacteria cells Eukaryote animal cells
Types of cells
Prokaryote bacteria cells
Eukaryote animal cells
Eukaryote plant cells

10. II. General Types of cells
Basic cell structures
1. Plasma membrane
2. Cytosol (jelly-like substance)
3. Ribosomes
4. DNA
B. Prokaryotic cells have DNA in nucleiod region; No membrane around
DNA.

12. C. Eukaryotic cells have DNA in
membrane-bound nucleus.
D. Eukaryotes also have membrane-bound
organelles floating in cytoplasm (region
between nucleus and cell membrane).
E. Eukaryotes are bigger than prokaryotes.

13. F. Eukaryotes have many internal membranes that divide internal space into compartments.
G. Compartmentalization allows for multiple metabolic processes to occur at the same time.

14. Limits to cell size Lower limit Upper limit smallest bacteria
mycoplasmas
0.1 to 1.0 micron (µm = micrometer)
most bacteria
1-10 microns
Upper limit
eukaryotic cells
microns
micron = micrometer = 1/1,000,000 meter
diameter of human hair = ~20 microns

15. Why is a huge single-celled creature not possible?
What limits cell size?
Surface to volume ratio
as cell gets bigger its volume increases faster than its surface area
smaller objects have greater ratio of surface area to volume
Why is a huge single-celled creature not possible?
square - cube law
As cell gets larger, volume increases cubically, but surface area only increases by the square.
The volume of the cell is demanding… it needs exchange. The surface area is the exchange system… as cell gets larger, the surface area cannot keep up with demand.
Instead of getting bigger, cell divides -- mitosis.
s:v
6:1
~1:1
6:1

16. Limits to cell size Metabolic requirements set upper limit
in large cell, cannot move material in & out of cell fast enough to support life O2 aa
CHO CH
CO2
NH3 aa O2 CH
CHO
CO2
What process is this?
diffusion
What’s the solution?
cell divides
make a multi-celled creature = lots of little cell, rather than one BIG cell aa
NH3
CHO CH O2 aa
What’s the solution?

17. How to get bigger? Become multicellular (cell divides) aa O2 aa aa aa
But what challenges do you have to solve now? aa
CO2
NH3 O2 CH
CHO aa O2 CH
CHO
CO2
Larger organisms do not generally have larger cells than smaller organisms — simply more cells
What’s challenges do you have to solve now?
how to bathe all cells in fluid that brings nutrients to each & removes wastes from each aa
NH3
CHO CH O2 aa

18. Cells gotta live! What jobs do cells have to do? building proteins
proteins control every cell function
make energy
for daily life
for growth
build more cells
growth
reproduction
repair

19. Why study protein production?
proteins
DNA
cells
organism
Repeat after me…
DNA gets the glory, but
Proteins do all the work!

20. Building Proteins Organelles involved nucleus ribosomes
endoplasmic reticulum (ER)
Golgi apparatus
vesicles
The Protein Assembly Line
Golgi apparatus
nucleus
ribosome ER
vesicles

21. Making proteins Putting it together… cytoplasm nucleus cell membrane
transport
vesicle
Golgi
apparatus
smooth ER
rough ER
nuclear pore
nucleus
ribosome
cell
membrane
protein secreted
cytoplasm

22. endoplasmic reticulum
TO:
nucleus
protein on its way!
TO:
DNA
RNA
vesicle
TO:
TO:
vesicle
ribosomes
TO:
protein
finished protein
Golgi apparatus
Making Proteins

23. ATP Cells gotta live! What jobs do cells have to do? make proteins
proteins control every cell function
make energy
for daily life
for growth
build more cells
growth
reproduction
repair
ATP

24. ATP Cells need power! Making energy take in food & digest it
take in oxygen (O2)
make ATP
remove waste
ATP

25. Where old organelles go to die!
1960 | 1974
Lysosomes
Christian de Duve
Function
little “stomach” of the cell
digests macromolecules
“clean up crew” of the cell
cleans up broken down organelles
Structure
vesicles of digestive enzymes
Where old organelles go to die!
only in animal cells

26. Lysosomal enzymes Lysosomal enzymes work best at pH 5
organelle creates custom pH
how?
proteins in lysosomal membrane pump H+ ions from the cytosol into lysosome
why?
enzymes are very sensitive to pH
enzymes are proteins — pH affects structure
why is this an adaptation: digestive enzymes which function at pH different from cytosol?
digestive enzymes won’t function well if some leak into cytosol = don’t want to digest yourself!
lysosomes create a space where cell can digest macromolecules safely
rupturing a few lysosomes has little impact on a cell (pH of cytosol affects functionality of the lysosomal enzymes), but massive leakage from lysosomes can destroy cell
why evolve digestive enzymes which function at pH so different from cytosol?
digestive enzymes won’t function well if leak into cytosol = most times don’t want to digest yourself!
low pH = acid environment cause oxidation (removing electrons) & promotes hydrolysis

27. But sometimes cells need to die…
Lysosomes can be used to kill cells when they are supposed to be destroyed
some cells have to die for proper development in an organism
apoptosis
“auto-destruct” process
lysosomes break open & kill cell
ex: tadpole tail gets re-absorbed when it turns into a frog
ex: loss of webbing between your fingers during fetal development
ex: self-destruct of cancerous cell
Feedback mechanism
There are sensors in the cell that monitor growth. They trigger self-destruct when they sense processes.
Brown spots on leaves too.
Virus infected plant cell auto-destructs and even cells around it to wall off virus.

28. syndactyly
Fetal development
6 weeks
15 weeks

29. When things go wrong… Diseases of lysosomes are often fatal
digestive enzyme not working in lysosome
picks up biomolecules, but can’t digest one
lysosomes fill up with undigested material
grow larger & larger until disrupts cell & organ function
lysosomal storage diseases
more than 40 known diseases
example: Tay-Sachs disease build up undigested fat in brain cells

30. From food to making Energy
Cells must convert incoming energy to forms that they can use for work
mitochondria: from glucose to ATP
chloroplasts: from sunlight to ATP & carbohydrates
ATP = immediate energy
carbohydrates = stored energy
ATP
ATP +

31. Mitochondria & Chloroplasts
Lynn Margulis
U of M, Amherst
Mitochondria & Chloroplasts
Important to see the similarities
transform energy
generate ATP
double membranes = 2 membranes
semi-autonomous organelles
move, change shape, divide
internal ribosomes, DNA & enzymes

32. Membrane-bound Enzymes
glucose + oxygen  carbon + water + energy
dioxide
C6H12O6
6O2
6CO2
6H2O
ATP  +

33. Membrane-bound Enzymes
+ water + energy  glucose + oxygen
carbon
dioxide
6CO2
6H2O
C6H12O6
6O2
light
energy  +

34. Mitochondria are everywhere!!
animal cells
plant cells

35. Cells gotta live! What jobs do cells have to do? building proteins
proteins control every cell function
make energy
for daily life
for growth
build more cells
growth
reproduction
repair

36. Cytoskeleton Function structural support motility regulation
maintains shape of cell
provides anchorage for organelles
protein fibers
microfilaments, intermediate filaments, microtubules
motility
cell locomotion
cilia, flagella, etc.
regulation
organizes structures & activities of cell

37. Cytoskeleton
actin
microtubule
nuclei

38. Centrioles Cell division
in animal cells, pair of centrioles organize microtubules
guide chromosomes in mitosis

39. Cell Size

40. Limits to cell size Lower limit Upper limit smallest bacteria
mycoplasmas
0.1 to 1.0 micron (µm = micrometer)
most bacteria
1-10 microns
Upper limit
eukaryotic cells
microns
micron = micrometer = 1/1,000,000 meter
diameter of human hair = ~20 microns

41. Why is a huge single-celled creature not possible?
What limits cell size?
Surface to volume ratio
as cell gets bigger its volume increases faster than its surface area
smaller objects have greater ratio of surface area to volume
Why is a huge single-celled creature not possible?
square - cube law
As cell gets larger, volume increases cubically, but surface area only increases by the square.
The volume of the cell is demanding… it needs exchange. The surface area is the exchange system… as cell gets larger, the surface area cannot keep up with demand.
Instead of getting bigger, cell divides -- mitosis.
s:v
6:1
~1:1
6:1

42. Limits to cell size Metabolic requirements set upper limit
in large cell, cannot move material in & out of cell fast enough to support life O2 aa
CHO CH
What process is this?
CO2
NH3 aa O2 CH
CHO
CO2
What process is this?
diffusion
What’s the solution?
cell divides
make a multi-celled creature = lots of little cell, rather than one BIG cell aa
NH3
CHO CH O2 aa
What’s the solution?

43. How to get bigger? Become multicellular (cell divides) aa O2 aa aa aa
But what challenges do you have to solve now? aa
CO2
NH3 O2 CH
CHO aa O2 CH
CHO
CO2
Larger organisms do not generally have larger cells than smaller organisms — simply more cells
What’s challenges do you have to solve now?
how to bathe all cells in fluid that brings nutrients to each & removes wastes from each aa
NH3
CHO CH O2 aa

44. Cell membrane Exchange structure
plasma membrane functions as selective barrier
allows passage of O2 & nutrients IN
allows passage of products & wastes OUT
Phospholipid
Cholesterol
Membrane
proteins

45. Any Questions??