1. Cell Transport
Ch 3

2. 3.3: Movements Into and Out of the Cell
Passive (Physical) Processes
Require no cellular energy and include:
Simple diffusion
Facilitated diffusion
Osmosis
Filtration
Active (Physiological) Processes
Require cellular energy and include:
Active transport
Endocytosis
Exocytosis
Transcytosis

3. Simple Diffusion
Movement of substances from regions of higher concentration to regions of lower concentration
Oxygen, carbon dioxide and lipid-soluble substances
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Permeable membrane
Solute molecule W
ater molecule A B A B A B
(1)
(2)
(3) T
ime

4. Facilitated Diffusion
Diffusion across a membrane with the help of a channel or carrier molecule
Glucose and amino acids
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Region of higher
concentration
Transported
substance
Region of lower
concentration
Protein carrier
molecule
Cell
membrane

5. Osmosis
Movement of water through a selectively permeable membrane from regions of higher concentration to regions of lower concentration
Water moves toward a higher concentration of solutes
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Selectively
permeable
membrane
Protein molecule W
ater molecule A A B B
(1)
(2) T
ime

6. Osmosis and Osmotic Pressure
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Osmotic Pressure – ability of osmosis to generate enough pressure to move a volume of water
Osmotic pressure increases as the concentration of nonpermeable solutes increases
(a)
Isotonic – same osmotic pressure
Hypertonic – higher osmotic pressure (water loss)
Hypotonic – lower osmotic pressure (water gain)
(b)
(c)
© David M. Phillips/Visuals Unlimited

7. Filtration Smaller molecules are forced through porous membranes
Hydrostatic pressure important in the body
Molecules leaving blood capillaries
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Capillary wall
Tissue fluid
Blood
pressure
Blood
flow
Larger molecules
Smaller molecules

8. Active Transport
Carrier molecules transport substances across a membrane from regions of lower concentration to regions of higher concentration
Sugars, amino acids, sodium ions, potassium ions, etc.
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Carrier protein
Binding site
Region of higher
concentration
Cell membrane
Region of lower
concentration
Phospholipid
molecules
Transported
particle
(a)
Carrier protein
with altered shape
Cellular
energy
(b)

9. Active Transport: Sodium-Potassium Pump
Active transport mechanism
Creates balance by “pumping” three (3) sodium (Na+) OUT and two (2) potassium (K+) INTO the cell
3:2 ratio

10. Endocytosis
Cell engulfs a substance by forming a vesicle around the substance
Three types:
Pinocytosis – substance is mostly water
Phagocytosis – substance is a solid
Receptor-mediated endocytosis – requires the substance to bind to a membrane-bound receptor
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Cell
membrane
Particle
Phagocytized
particle V
esicle
Nucleus
Nucleolus

11. Endocytosis Cell membrane Particle Phagocytized particle Vesicle
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Cell
membrane
Particle
Phagocytized
particle
Vesicle
Nucleus
Nucleolus
Molecules
outside cell
Receptor-ligand
combination V
esicle
Receptor
protein
Cell
membrane
Cell
membrane
indenting
Cytoplasm
(a)
(b)
(c)
(d)

12. Exocytosis Reverse of endocytosis
Substances in a vesicle fuse with cell membrane
Contents released outside the cell
Release of neurotransmitters from nerve cells
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Endoplasmic
reticulum
Golgi
apparatus
Nucleus

13. Receptor-mediated endocytosis
Transcytosis
Endocytosis followed by exocytosis
Transports a substance rapidly through a cell
HIV crossing a cell layer
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HIV-infected
white blood cells
Anal or
vaginal canal V
iruses bud
HIV
Receptor-mediated endocytosis
Lining of anus
or vagina
(epithelial cells)
Exocytosis
Cell
membrane
Receptor-mediated
endocytosis
Virus infects
white blood cells on
other side of lining

14. 3.4: The Cell Cycle
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Series of changes a cell undergoes from the time it forms until the time it divide
Stages:
Interphase
Mitosis
Cytokinesis
G2 phase
Interphase
Prophase
Mitosis
S phase:
genetic
material
replicates
Metaphase
Anaphase
Telophase
G1 phase
cell growth
Cytokinesis
Proceed
to division
Remain
specialized
Restriction
checkpoint
Apoptosis

15. Interphase Very active period Cell grows
Cell maintains routine functions
Cell replicates genetic material to prepare for nuclear division
Cell synthesizes new organelles to prepare for cytoplasmic division
Phases:
G phases – cell grows and synthesizes structures other than DNA
S phase – cell replicates DNA

16. Mitosis Produces two daughter cells from an original somatic cell
Nucleus divides – karyokinesis
Cytoplasm divides – cytokinesis
Phases of nuclear division:
Prophase – chromosomes form; nuclear envelope disappears
Metaphase – chromosomes align midway between centrioles
Anaphase – chromosomes separate and move to centrioles
Telophase – chromatin forms; nuclear envelope forms

17. Mitosis Late Interphase Cell has passed the restriction checkpoint
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Late Interphase
Cell has passed the
restriction checkpoint
and completed DNA
replication, as well as
replication of centrioles
and mitochondria, and
synthesis of extra
membrane.
Early Interphase
of daughter cells—
a time of normal cell
growth and function.
(a)
Restriction
checkpoint
Nuclear
envelope
Chromatin
fibers
Centrioles
Cleavage
furrow
Aster
Prophase
Chromosomes condense and
become visible. Nuclear
envelope and nucleolus
disperse. Spindle apparatus
forms.
Microtubules
(e)
(b)
Centromere
Spindle fiber
Late prophase
Chromosomes
Sister
chromatids
Nuclear
envelopes
Telophase and Cytokinesis
Nuclear envelopes begin to
reassemble around two daughter
nuclei. Chromosomes decondense.
Spindle disappears. Division of
the cytoplasm into two cells.
(d)
(c)
Mitosis
Cytokinesis
G1 phase
Anaphase
Sister chromatids separate to
opposite poles of cell. Events
begin which lead to cytokinesis.
Metaphase
Chromosomes align along
equator, or metaphase plate
of cell.
S phase
Interphase
G2 phase
© Ed Reschke

18. Cytoplasmic Division Also known as cytokinesis Begins during anaphase
Continues through telophase
Contractile ring pinches cytoplasm in half

19. 3.5: Control of Cell Division
Cell division capacities vary greatly among cell types
Skin and blood cells divide often and continually
Neuron cells divide a specific number of times then cease
Chromosome tips (telomeres) that shorten with each mitosis provide a mitotic clock
Cells divide to provide a more favorable surface area to volume relationship
Growth factors and hormones stimulate cell division
Hormones stimulate mitosis of smooth muscle cells in uterus
Epidermal growth factor stimulates growth of new skin
Contact (density dependent) inhibition
Tumors are the consequence of a loss of cell cycle control

20. © Tony Brain/Photo Researchers, Inc.;
Tumors
Two types of tumors:
Benign – usually remains localized
Malignant – invasive and can metastasize; cancerous
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Normal cells
(with hairlike cilia)
Two major types of genes cause cancer:
Oncogenes – activate other genes that increase cell division
Tumor suppressor genes – normally regulate mitosis; if inactivated they are unable to regulate mitosis
Cells are now known as “immortal”
Cancer cells
© Tony Brain/Photo Researchers, Inc.;

21. 3.6: Stem and Progenitor Cells
Stem cell:
Can divide to form two new stem cells
Self-renewal
Can divide to form a stem cell and a progenitor cell
Totipotent – can give rise to every cell type
Pluripotent – can give rise to a restricted number of cell types
Progenitor cell:
Committed cell
Can divide to become any of a restricted number of cells
Pluripotent

22. Stem and Progenitor Cells
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Sperm
Egg
Sebaceous
gland cell
Progenitor
cell
Fertilized
egg
Progenitor cell
Skin cell
Stem cell
Progenitor
cell
Progenitor
cell
Stem cell
Neuron
Progenitor
cell
Progenitor
cell
Progenitor
cell
Astrocyte
Progenitor
cell
Progenitor
cell
Progenitor
cell
Bone cells
one or more steps
Fibroblasts (a connective tissue cells)
produces another stem cell
(self-renewal)
Blood cells and platelets

23. 3.7: Cell Death Apoptosis: Programmed cell death
Acts as a protective mechanism
Is a continuous process