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The Cell
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Why are cells so small?
Why can’t they be as huge as an hippo?
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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
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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
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0.1 m
Length of some
nerve and
muscle cells
Chicken egg
Unaided eye
Human height
1m
1 cm
Frog egg
Human egg
Most plant and
animal cells
10 m
1 m
100 nm
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
10 nm
Proteins
Lipids
1 nm
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0.1 nm
Small molecules
Atoms
Superresolution
microscopy
Electron microscopy
100 m
Light microscopy
1 mm
Cell Fractionation
 Cell fractionation takes cells apart and
separates the major organelles from one
another
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Figure 6.4
TECHNIQUE
Homogenization
Tissue
cells
Homogenate
Centrifuged at
1,000 g
(1,000 times the
force of gravity)
for 10 min Supernatant
Centrifugation
poured into
next tube
Differential
centrifugation
20,000 g
20 min
80,000 g
60 min
Pellet rich in
nuclei and
cellular debris
150,000 g
3 hr
Pellet rich in
mitochondria
(and chloroplasts if cells
are from a plant)
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Pellet rich in
“microsomes”
(pieces of plasma
membranes and
cells’ internal
Pellet rich in
membranes)
ribosomes
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
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s:v
6:1
2005-2006 6:1
~1:1
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
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Types of cells
Prokaryote
bacteria cells
- no organelles
- organelles
Eukaryote
animal cells
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Eukaryote
plant cells
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)
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Eukaryotic cell
 chromosomes in
nucleus, membraneenclosed organelle
 Cell walls present in
fungi and plants
only
 More complex
 Membrane bound
organelles present
The prokaryotic cell is much simpler in structure, lacking a nucleus and
the other
2005-2006
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membrane-enclosed
organelles of the eukaryotic cell.
Why organelles?
 Specialized structures

specialized functions
mitochondria
 cilia or flagella for locomotion
 Containers


partition cell into compartments
create different local environments
chloroplast
 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
Golgi
 chloroplasts & mitochondria
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ER
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
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Building Proteins
 Organelles involved
nucleus
 ribosomes
 endoplasmic reticulum
(ER)
 Golgi apparatus
 vesicles

The Protein Assembly Line
nucleus
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ribosome
ER
Golgi
apparatus
vesicles
Synthesizing proteins
cisternal
space
polypeptide
signal
sequence
ribosome
ribosome
mRNA
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membrane of
endoplasmic reticulum
cytoplasm
Nucleolus
 Function

ribosome production
 build ribosome subunits from rRNA & proteins
 exit through nuclear pores to cytoplasm &
combine to form functional ribosomes
large subunit
small
subunit
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rRNA &
proteins
ribosome
nucleolus
Types of Ribosomes
 Free ribosomes


suspended in cytosol
synthesize proteins that
function in cytosol
 Bound ribosomes


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attached to endoplasmic
reticulum
synthesize proteins
for export or
for membranes
membrane proteins
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
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Golgi Apparatus
 Function

finishes, sorts, tags & ships cell products
 like “UPS shipping department”

ships products in vesicles
 membrane sacs
 “UPS trucks”
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secretory
vesicles
transport vesicles
Putting it together…
nucleus
nuclear pore
Making proteins
cell
membrane
protein secreted
rough ER
ribosome
vesicle
proteins
smooth ER
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transport
vesicle
cytoplasm
Golgi
apparatus
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
 in liver
 ex. alcohol & barbiturates
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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
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only in
animal cells
Cellular digestion
 Lysosomes fuse with food vacuoles

polymers
digested into
monomers
 pass to cytosol
to become
nutrients of
cell
vacuole
 lyso– = breaking things apart
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 –some
= body
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
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Making Energy
 Cells must convert incoming energy to
forms that they can use for work
mitochondria:
ATP
from glucose to ATP
 chloroplasts:
from sunlight to ATP & carbohydrates

 ATP = active energy
 carbohydrates = stored energy
ATP
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+
Mitochondria & Chloroplasts
 Important to see the similarities

transform energy
 generate ATP
double membranes = 2 membranes
 semi-autonomous organelles

 move, change shape, divide

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internal ribosomes, DNA & enzymes
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
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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
AP
Biology cells
• nerve
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
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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?
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bacteria!
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?
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bacteria
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
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Lynn Margulis
U of M, Amherst
Endosymbiosis theory
Evolution of eukaryotes
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food vacuoles
Food & water storage
plant cells
central vacuole
animal cells
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contractile
vacuole
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
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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
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Putting it all together, try labeling..
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animal cells
plant cells