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Cell Size is Limited
• Surface to Volume Ratio limits upper size
• Larger cells have less surface area relative to volume
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A Generic Animal Cell
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• An idealized plant cell
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Cell Membrane
Function
1. Separates cytoplasm from external
environment
2. Regulates what enters and leaves cell
3. Cell identification
4. Cell-cell communication
Plasma membrane
regulates movement of
materials due to its
chemical composition:
Phospholipids
Cholesterol
Proteins
Phospholipids
• Phospholipids Bilayer
Phospholipids have:
1. Hydrophilic head
2. Nonpolar
hydrophobic tail
Hydrophilic "heads" faces the watery
environment inside and outside cell
Hydrophobic tail forced to face inward –
away from water.
The phospholipids are not
bound together – gives the
membrane a fluid nature
CHOLESTEROL
• Function:
1. Stabilizes membrane (structural support)
2. Cell communication (cell-cell and cellhormone)
Some interesting facts
• Most common molecule in membrane (>50%)
• Due small size and weight – only 20% of
membrane mass
• Is an amphipathic molecule Homework – find
out what this means
Proteins
• Are embedded in membrane
• Serve different functions
Functions
• 1. Channel Proteins - small openings for molecules to
diffuse through
•
2. Carrier Proteins- binding site on protein "grabs”
molecules, pulls them into cell
•
3. Receptor Proteins – act as triggers that set off cell
responses (such as release of hormones or opening of
channel proteins)
•
4. Cell Recognition Proteins - ID tags, identify cell to
immune system
•
5. Enzymatic Proteins - carry out metabolic reactions
LABEL YOUR DIAGRAM WITH THE FOLLOWING DETAILS
Task: Due Tuesday Oct. 4, 2011
• Read pages 47 -49 in your text
• Answer questions 1 – 5 in practice section
• Explain the structure and function of
glycoproteins.
• How are liposomes used in cancer treatment and
gene therapy?
• What role might receptor proteins have in medical
disorders such as Hypertension?
Structure and Function of the Nucleus
• Occurs only in eukaryotic cells
• Surrounded by a double membrane called the
nuclear envelope
– It contains
– chromatin -a DNA-protein structure
– a nucleolus - which produces ribosomal parts
– Nucleoplasm
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• Animation of nuclear membrane system
• http://users.uma.maine.edu/SBaker/nucleus_end
o.html
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Nuclear Pore Complex
Allows movement of material into and out of nucleus
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Ribosomes
• Ribosomes build all the cell’s proteins
– Are not membrane bound
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How DNA Controls the Cell
• DNA controls the
cell by transferring
its coded
information into
RNA
– The information in
the RNA is used to
make proteins
DNA
1 Synthesis of
mRNA in the
nucleus
Nucleus
Cytoplasm
2 Movement of
mRNA into
cytoplasm via
nuclear pore
3 Synthesis of
protein in the
cytoplasm
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mRNA
mRNA
Ribosome
Protein
THE ENDOMEMBRANE SYSTEM:
MANUFACTURING AND DISTRIBUTING
CELLULAR PRODUCTS
• Many of the membranous organelles in the cell
belong to the endomembrane system
– Endoplasmic reticulum - rough and smooth
– Golgi Apparatus
– Lysosomes
– Vacuoles
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The Endoplasmic Reticulum
• The endoplasmic
reticulum (ER)
Nuclear
envelope
– Greek for
‘network within
a cell’
– Produces an
enormous variety
of molecules
– Is composed of
smooth and
rough ER
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Ribosomes
Rough ER
Smooth ER
Rough ER
• The “roughness” of the rough ER is due to
ribosomes that stud the outside of the ER
membrane
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• The functions of the rough ER include
– Producing proteins
– Producing new membrane
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• After the
rough ER
synthesizes a
molecule it
packages the
molecule
into
transport
vesicles
1
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Smooth ER
• The smooth ER lacks
the surface
ribosomes of ER
• Produces lipids,
including steroids
and sex hormones
• Regulates sugar
• Detoxifies drugs
• Stores calcium
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
The Golgi Apparatus
• The Golgi apparatus
– Works in partnership with the ER
– Refines, stores, and distributes the products of cells
Transport
vesicle
from ER
“Receiving” side of
Golgi apparatus
Golgi apparatus
New vesicle forming
Transport vesicle
from the Golgi
“Shipping” side of
Golgi apparatus
Plasma membrane
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Lysosomes
• A lysosome is a membrane-enclosed sac
– Greek for ‘breakdown body’
– It contains digestive enzymes
• Isolated by membrane
– The enzymes break down
• Macromolecules
• Old organelles
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• Lysosomes have several
types of digestive
functions
• They exit the Golgi
apparatus
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– They fuse
with food
vacuoles to
digest the
food
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– They fuse with
old organelles
to recycle parts
– Digest bacteria
in white blood
cells
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Lysosomal diseases
Genetic disorders
Recipe is messed up
Enzyme doesn’t work
what should get broken down doesn’t
Tay-Sachs
lipids aren’t broken down
build up occurs
death by age 5
Pompe’s disease
glycogen builds up
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Vacuoles
• Vacuoles are membranous sacs
– Two types are the contractile vacuoles of protists
and the central vacuoles of plants
Central
vacuole
Contractile
vacuoles
(a) Contractile vacuoles in a protist
(b) Central vacuole in a plant cell
Figure 4.15
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• A review of the endomembrane system
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CHLOROPLASTS AND MITOCHONDRIA:
ENERGY CONVERSION
• Cells require a constant energy supply to do all
the work of life
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CHLOROPLASTS
• Chloroplasts are
the sites of
photosynthesis,
the conversion
of light energy
to chemical
energy
Figure 4.17
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Inner and outer
membranes of
envelope
Granum
Space between
membranes
Stroma (fluid in
chloroplast)
Chloroplasts
• Double membrane
• Grana
– Stacks of thylakoids
• Hollow disks
• Sunlight energy is coverted to chemical
energy
• Stroma- fluid filling chloroplast
• Contains some DNA
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Mitochondria
• Mitochondria are the sites of cellular respiration,
which involves the production of ATP from food
molecules
Outer
membrane
Inner
membrane
Cristae
Matrix
Space between
membranes
Figure 4.18
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Mitochondria
• Double membrane
– Big bag stuffed into smaller bag
– Folds of inner bag called cristae
• Matrix -space inside inner bag
• Contains some DNA
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THE CYTOSKELETON:
CELL SHAPE AND MOVEMENT
• The cytoskeleton is an infrastructure of the cell
consisting of a network of fibers
– Microfilaments - small threads
– Intermediate filaments - ropelike
– Microtubules - small tubes
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Maintaining Cell Shape
• One function of
the cytoskeleton
– Provide
mechanical
support to
the cell and
maintain its
shape
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Figure4.9x
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• The cytoskeleton can
change the shape of a cell
– This allows cells like
amoebae to move
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Cilia and Flagella
• Cilia and flagella are motile appendages
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• Flagella propel the cell
in a whiplike motion
• Cilia move in a
coordinated back-andforth motion
Figure 4.20A, B
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• Some cilia or flagella
extend from nonmoving
cells
– The human windpipe is
lined with cilia
– Smoking damages the
cilia
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Cilia and Flagella
• Same
structure and
function
• 9+2
arrangement
of
microtubules
• Wrapped in
plasma
membrane
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Mechanism of Movement
• Dynein arms use ATP for energy to ‘walk’ up adjoining
microtubule, causing them to bend
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CELL SURFACES:
PROTECTION, SUPPORT, AND CELL-CELL
INTERACTIONS
• Most cells secrete materials that are external to
the plasma membrane
• This extra cellular matrix
– Regulates
– Protects
– Supports
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Plant Cell Walls and Cell Junctions
• Plant cells are encased by cell walls
– These provide support for the plant cells
Walls of two adjacent
plant cells
Vacuole
Plasmodesmata
(channels between cells)
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Figure 4.21
Animal Cell Surfaces and Cell Junctions
• Animal cells lack cell walls
– They secrete a sticky covering called the
extracellular matrix
– This layer helps hold cells together
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• Animal cells connect by various types of
junctions
– Tight junctions – leakproof – fuses membranes of cells –
found in intestinal epithelium (lining of intestine). Made of
filaments (type of cytoskeleton material made from
glycoprotein)
– Anchoring junctions - Desmosomes - hold cells together
– Communicating junctions - gap junctions. Provides a
channel between cells for passage of small ions and
molecules. Gap junctions are found in embryos, cardiac
muscles and endocrine glands
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Extracellular matrix
(a) Tight junctions
(b) Anchoring
junctions
(c) Communicating
junctions
Plasma membranes
of adjacent cells
Extracellular matrix
Figure 4.22
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings