Tour of the Cell 1(Ch. 6)
Dead White Men Who Discovered (and were made of) Cells:
Anton Van Leeuwenhoek Robert Hooke
Where the Magic Happened
The size range of cells
Nucleus
Most bacteria
Measurements1 centimeter (cm) = 102 meter (m) = 0.4 inch
1 millimeter (mm) = 10–3 m1 micrometer (µm) = 10–3 mm = 106 m1 nanometer (nm) = 10–3 µm = 10 9 m
10 m
1 m
0.1 m
1 cm
1 mm
100 µm
10 µm
1 µm
100 nm
10 nm
1 nm
0.1 nm
Human height
Length of somenerve and
muscle cells
Chicken egg
Frog egg
Most plant andanimal cells
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
Proteins
Lipids
Small molecules
Atoms
Un
aid
ed
ey
e
Lig
ht
mic
rosc
op
e
Ele
ctr
on
mic
ros
co
pe
nucleus
Most bacteria
Comparing the size of a virus, a bacterium, and an animal cell
0.25 m
Virus
Animalcell
Bacterium
Animal cell nucleus
While we’re on the topic of
size...
Why Cells Are So Small: The SA:V Ratio
Surface area increases while total volume remains constant
5
11
Total surface area (height width
number of sides number of boxes)
Total volume (height width length
number of boxes)
Surface-to-volume ratio
(surface area volume)
6
1
6
150
125
12
750
125
6
Diffusion: The movement of molecules from an area of high concentration to low concentration.
Cell FractionationAPPLICATION
Cell fractionation is used to isolate (fractionate) cell components, based on size and density.
TECHNIQUE
First, cells are homogenized in a blender tobreak them up. The resulting mixture (cell homogenate) is then centrifuged at various speeds and durations to fractionate the cellcomponents, forming a series of pellets.
Tissuecells
Homogenization
Homogenate1000 g(1000 times theforce of gravity)
10 min Differential centrifugationSupernatant poured
into next tube
20,000 g20 min
Pellet rich innuclei and
cellular debris
Pellet rich inmitochondria(and chloro-plasts if cellsare from a
plant)Pellet rich in
“microsomes”(pieces of
plasma mem-branes and
cells’ internalmembranes)
Pellet rich inribosomes
150,000 g3 hr
80,000 g60 min
RESULTS
In the original experiments, the researchers used microscopy to identify the organelles in each pellet, establishing a baseline for further experiments. In the next series of experiments, researchers used biochemical methods to determine the metabolic functions associated with each type of organelle. Researchers currently use cell fractionation to isolate particular organelles in order to study further details of their function.
Prokaryotebacteria cells
Types of cells
Eukaryoteanimal cells
- no organelles
- organelles
Eukaryoteplant cells
Why organelles?• Specialized structures
– specialized functions• Containers
– Compartments = different local environments• pH, concentration differences
– distinct & incompatible functions• lysosome & its digestive enzymes
• Membranes as sites for chemical reactions– Unique lipids & proteins – embedded enzymes & reaction centers
• chloroplasts & mitochondria
Cells gotta work to live! – make proteins
• proteins control every cell function
– make energy• for daily life• for growth
– make more cells• growth• repair• renewal
Proteins do all the work!
cellsDNA
proteins
organismRepeat after me…
Proteins do all the work!
Cell functions • Building proteins
– copy DNA– DNA -> RNA– build proteins– process proteins
• Folding, modifying–Remove amino acids–Add molecules (e.g. glycoproteins)
– address & transport proteins
Protein Synthesis• Organelles involved
– nucleus– ribosomes– endoplasmic reticulum
(ER)– Golgi apparatus– vesicles
nucleus ribosome ERGolgi
apparatusvesicles
The Protein Assembly Line
The Endomembrane System
nuclearpores
nuclearpore
nuclear envelopenucleolus
histone protein
chromosome
DNA
• Function– protects DNA
• Structure– nuclear envelope
• double membrane• membrane fused in spots to create pores
Nucleus
What kind of molecules need to
pass through?
DNA
NucleusmRNA
nuclearmembrane
smallribosomal
subunit
largeribosomal
subunit
cytoplasm
mRNA
nuclear pore
production of mRNA from DNA in nucleus
mRNA travels from nucleus to ribosome in cytoplasm through nuclear pore
1
2
Nucleolus• Function
– ribosome production• build ribosome subunits from rRNA & proteins• Ribosome assembly is completed in cytoplasm
smallsubunit
large subunit
ribosome
rRNA &proteins
nucleolus
smallsubunit
largesubunit
Ribosomes • Function
– protein production• Structure
– rRNA & protein– 2 subunits combine 0.08mm
RibosomesRough
ER
SmoothER
membrane proteins
Types of Ribosomes• Free ribosomes
– suspended in cytosol– synthesize proteins that stay in
cytosol• Bound ribosomes
– attached to endoplasmic reticulum
– synthesize proteins for export or membranes
Endoplasmic Reticulum
• Function – processes proteins– manufactures membrane– synthesis & hydrolysis of
many compounds• Structure
– membrane connected to nuclear envelope & extends throughout cell
Types of ER
rough smooth
Smooth ER function• Membrane production• Metabolic processes
– Lipid Synthesis– Glycogen hydrolysis (in liver)– Drug detoxification (in liver)
Membrane Factory
• Build new membrane– synthesize
phospholipids– ER membrane expands
• buds off & transfers to other parts of cell.
Rough ER function• Produces proteins for export out of cell
– protein secreting cells– packaged into transport vesicles for export
Which cellshave lot of rough ER?
Synthesizing proteins
cytoplasm
cisternalspace
mRNA
ribosome
membrane ofendoplasmic reticulum
polypeptide
signalsequence
ribosome
Golgi Apparatus
Which cellshave lots of Golgi?
transport vesicles
secretoryvesicles
• Function– finishes, sorts, tags & ships products
• like “UPS shipping department”
– ships products in vesicles• membrane sacs• “UPS trucks”
Golgi Apparatus
Vesicle transport
vesiclebuddingfrom roughER
fusionof vesiclewith Golgiapparatus
migratingtransportvesicle
protein
ribosome
proteins
transportvesicle
Golgiapparatus
vesicle
smooth ER
rough ER
nuclear porenucleus
ribosome
cellmembrane protein secreted
cytoplasm
The Endomembrane SystemPutting it together…
Any Questions!!
Review Questions
1.. In which cell would you expect to find the most smooth endoplasmic reticulum?A. Muscle cell in the thigh muscle of a long-distance
runnerB. Pancreatic cell that manufactures digestive
enzymesC. Macrophage (white blood cell) that engulfs
bacteriaD. Epithelial cells lining the digestive tractE. Ovarian cell that produces estrogen (a steroid
hormone)
2. In which cell would you expect to find the most bound ribosomes?A. Muscle cell in the thigh muscle of a long-distance
runnerB. Pancreatic cell that manufactures digestive
enzymesC. Macrophage (white blood cell) that engulfs
bacteriaD. Epithelial cells lining the digestive tractE. Ovarian cell that produces estrogen (a steroid
hormone)
3. Of the following, which is probably the most common route for membrane flow in the endomembrane system? A. Golgi → lysosome → ER → plasma membrane B. tonoplast → plasma membrane → nuclear envelope
→ smooth ER C. nuclear envelope → lysosome → Golgi → plasma
membrane D. rough ER → vesicles → Golgi → plasma membrane E. ER → chloroplasts → mitochondrion → cell
membrane