1. The Cell

2. Why are cells so small? Why can’t they be as huge as an hippo?

3. Overview: The Fundamental Units of Life
All organisms are made of cells
The cell is the simplest collection of matter that can be alive
Cell structure is correlated to cellular function
For the Discovery Video Cells, go to Animation and Video Files.

4. -Lenses refract (bend) the light, so that the image is magnified
Concept 6.1: Biologists use microscopes and the tools of biochemistry to study cells
In a light microscope (LM), visible light is passed through a specimen and then through glass lenses
-Lenses refract (bend) the light, so that the image is magnified
Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3-D
Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3-D

5. Figure 6.2 The size range of cells.
Human height
1 m
Length of some nerve and muscle cells
0.1 m
Unaided eye
Chicken egg
1 cm
Frog egg
1 mm
Human egg
100 m
Most plant and animal cells
Light microscopy
10 m
Nucleus
Most bacteria
Mitochondrion
1 m
Figure 6.2 The size range of cells.
Smallest bacteria
Super- resolution microscopy
Electron microscopy
100 nm
Viruses
Ribosomes
10 nm
Proteins
Lipids
1 nm
Small molecules
0.1 nm
Atoms

6. Cell Fractionation
Cell fractionation takes cells apart and separates the major organelles from one another

7. Figure 6.4 Research Method: Cell Fractionation
TECHNIQUE
Homogenization
Tissue cells
Homogenate
Centrifuged at 1,000 g (1,000 times the force of gravity) for 10 min
Centrifugation
Supernatant poured into next tube
Differential centrifugation
20,000 g
20 min
80,000 g
60 min
Pellet rich in nuclei and cellular debris
Figure 6.4 Research Method: Cell Fractionation
150,000 g
3 hr
Pellet rich in mitochondria (and chloro- plasts if cells are from a plant)
Pellet rich in “microsomes” (pieces of plasma membranes and cells’ internal membranes)
Pellet rich in ribosomes

8. 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
Alka-seltzer Demo
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

9. Cell characteristics All cells: surrounded by a plasma membrane
have cytosol
semi-fluid substance within the membrane
cytoplasm = cytosol + organelles
contain chromosomes which have genes in the form of DNA
have ribosomes
tiny “organelles” that make proteins using instructions contained in genes

10. Prokaryote bacteria cells Eukaryote animal cells
Types of cells
- no organelles
- organelles
Eukaryote animal cells
Eukaryote plant cells

11. Types of cells Prokaryotic vs. eukaryotic cells Prokaryotic cell
DNA in nucleoid region, without a membrane separating it from rest of cell
Cell wall present in all (type differs)
Eukaryotic cell
chromosomes in nucleus, membrane-enclosed organelle
Cell walls present in fungi and plants only
More complex
Membrane bound organelles present

12. The prokaryotic cell is much simpler in structure, lacking a nucleus and the other membrane-enclosed organelles of the eukaryotic cell.

13. Why organelles? mitochondria chloroplast Golgi ER
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

14. Cells gotta work to live!
What jobs do cells have to do?
make proteins
proteins control every cell function
make energy
for daily life
for growth
make more cells
growth
repair
renewal

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

16. Synthesizing proteins
cytoplasm
cisternal
space
mRNA
ribosome
membrane of
endoplasmic reticulum
polypeptide
signal
sequence
ribosome

17. Nucleolus Function ribosome production
build ribosome subunits from rRNA & proteins
exit through nuclear pores to cytoplasm & combine to form functional ribosomes
small
subunit
large subunit
ribosome
rRNA &
proteins
nucleolus

18. Types of Ribosomes Free ribosomes Bound ribosomes suspended in cytosol
synthesize proteins that function in cytosol
Bound ribosomes
attached to endoplasmic reticulum
synthesize proteins for export or for membranes
membrane proteins

19. Rough ER function
Finalize protein formation and prepare for export out of cell (protein folding)
protein secreting cells will have lots
packaged into transport vesicles to golgi
Which cells have a lot of ER?
protein production cells like pancreas = production of digestive enzymes (rough endoplasmic reticulum from a cell of exocrine pancreas (88000X))

20. Golgi Apparatus Function finishes, sorts, tags & ships cell products
like “UPS shipping department”
ships products in vesicles
membrane sacs
“UPS trucks”
transport vesicles
secretory
vesicles
Cells specialized for secretion?
endocrine glands: produce hormones
pituitary, pancreas, adrenal, testes, ovaries
exocrine glands: produce digestive enzymes & other products
pancreas, mammary glands, sweat glands

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. Smooth ER function Membrane production Many metabolic processes
synthesis
synthesize lipids
oils, phospholipids, steroids & sex hormones
hydrolysis
hydrolyze glycogen into glucose
in liver
detoxify drugs & poisons
ex. alcohol & barbiturates

23. Lysosomes Function Structure little “stomach” of the cell
digests macromolecules
“clean up crew” of the cell
cleans up broken down organelles
Structure
vesicles of digestive enzymes
synthesized by rER, transferred to Golgi
only in
animal cells

24. Cellular digestion Lysosomes fuse with food vacuoles
polymers digested into monomers
pass to cytosol to become nutrients of cell
vacuole
lyso– = breaking things apart
–some = body

25. When 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
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.

26. 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 = active energy
carbohydrates = stored energy
ATP
ATP +

27. 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

28. Mitochondria Function cellular respiration generate ATP
from breakdown of sugars, fats & other fuels
in the presence of oxygen
break down larger molecules into smaller to generate energy = catabolism
generate energy in presence of O2 = aerobic respiration

29. Mitochondria Almost all eukaryotic cells have mitochondria
there may be 1 very large mitochondrion or 100s to 1000s of individual mitochondria
number of mitochondria is correlated with aerobic metabolic activity
more activity = more energy needed = more mitochondria
What cells would have a lot of mitochondria?
active cells:
• muscle cells
• nerve cells

30. Chloroplasts Chloroplasts are plant organelles
class of plant structures = plastids
amyloplasts
store starch in roots & tubers
chromoplasts
store pigments for fruits & flowers
chloroplasts
store chlorophyll & function in photosynthesis
in leaves, other green structures of plants & in eukaryotic algae

31. Who else divides like that?
Chloroplasts
Function
photosynthesis
generate ATP & synthesize sugars
transform solar energy into chemical energy
produce sugars from CO2 & H2O
Semi-autonomous
moving, changing shape & dividing
can reproduce by pinching in two
Who else divides like that?
bacteria!

32. Mitochondria & chloroplasts are different
Organelles not part of endomembrane system
Grow & reproduce
semi-autonomous organelles
Proteins primarily from free ribosomes in cytosol & a few from their own ribosomes
Own circular chromosome
directs synthesis of proteins produced by own internal ribosomes
ribosomes like bacterial ribosomes
Who else has a circular chromosome not bound within a nucleus?
bacteria

33. Endosymbiosis theory
Mitochondria & chloroplasts were once free living bacteria
engulfed by ancestral eukaryote
Endosymbiont
cell that lives within another cell (host)
as a partnership
evolutionary advantage for both
one supplies energy
the other supplies raw materials & protection
Lynn Margulis
From hypothesis to theory!
Paradigm shifting ideas in evolutionary biology.
Lynn Margulis
U of M, Amherst

34. Evolution of eukaryotes
Endosymbiosis theory
Evolution of eukaryotes

35. Food & water storage plant cells animal cells food vacuoles
central vacuole
animal cells
contractile vacuole

36. Vacuoles & vesicles Function little “transfer ships” Food vacuoles
phagocytosis, fuse with lysosomes
Contractile vacuoles
in freshwater protists, pump excess H2O out of cell
Central vacuoles
in many mature plant cells

37. Vacuoles in plants Functions storage
stockpiling proteins or inorganic ions
depositing metabolic byproducts
storing pigments
storing defensive compounds against herbivores
selective membrane
control what comes in or goes out

38. Putting it all together, try labeling..
animal cells
plant cells