1. The Cell

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

3. 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
What cell organelle governs this?
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.
Why is a huge single-celled creature not possible?
s:v
6:1
1.2:1
6:1

4. Limits to cell size Metabolic requirements set upper limit
in large cell, cannot move material in & out of cell fast enough to support life aa aa
What process is this? CH
NH3 aa
CHO O2 CH
CHO
CO2
CHO
CO2
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 O2
NH3 O2
CHO
NH3 aa
CO2 CH aa CH O2 aa O2
What’s the solution?

5. How to get bigger? Become multi-cellular (cell divides) aa aa aa O2 aa
But what challenges do you have to solve now?
CO2
CO2 O2
NH3 aa
NH3 aa
CO2
NH3 O2
CO2
CO2 CH
CHO
CO2
NH3
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 O2
NH3
NH3
CO2
CO2
CO2
CHO aa
NH3
NH3
NH3 CH
CHO
CO2
CO2 O2 aa aa CH

6. 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

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

8. 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

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

10. 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

11. 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

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

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

14. 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

15. 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

16. Which cells have lot of rough ER?
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 lot of rough ER?
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))

17. Which cells have lots of Golgi?
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
Which cells have lots of Golgi?
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

18. 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

19. 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

20. Where old organelles go to die!
Lysosomes
Function
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

21. 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

22. 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.

23. syndactyly
Fetal development
6 weeks
15 weeks

24. 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 +

25. 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

26. 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

27. 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

28. 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

29. 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!

30. 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

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

32. 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

33. 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