Transcript Cell Membrane

Chapter 3
Lecture
PowerPoint
Cells
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3.1: Introduction
• The basic organizational
structure of the human body is
the cell.
• There are 50-100 trillion cells
in the human body.
• Differentiation is when cells
specialize.
• As a result of differentiation,
cells vary in size and shape
due to their unique function.
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3.2: A Composite Cell
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Phospholipid bilayer
• Major parts include:
• Nucleus
• contains DNA
• Cytoplasm
• cellular contents
between plasma
membrane &
nucleus
• Cell membrane
• selective barrier
Flagellum
Nucleus
Chromatin
Nuclear envelope
Nucleolus
Ribosomes
Cell membrane
Basal body
Microtubules
Rough
Endoplasmic
reticulum
Centrioles
Mitochondrion
Smooth
Endoplasmic
reticulum
Microvilli
Secretory
vesicles
Cilia
Golgi
apparatus
Microtubule
Microtubules
Lysosomes
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Cell Membrane
(aka Plasma Membrane)
•
•
•
•
Outer limit of the cell
Controls what moves in and out of the cell
Selectively permeable
Phospholipid bilayer
•
•
•
•
Water-soluble “heads” form surfaces (hydrophilic)
Water-insoluble “tails” form interior (hydrophobic)
Permeable to lipid-soluble substances
Cholesterol stabilizes the membrane
4
Cell Membrane
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Extracellular side
of membrane
Fibrous protein
Glycolipid Carbohydrate
Glycoprotein
“Heads” of
phospholipid
Double
layer of
Phospholipid
molecules
“Tails” of
phospholipid
Cell membrane
(a)
Cell membrane
(b)
a: © Biophoto Associates/Photo Researchers, Inc.
Cholesterol Globular
molecules protein
Cytoplasmic side
of membrane
Hydrophobic
fatty acid
“tail”
Hydrophilic
Phosphate
“head”
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Cytoplasm
• Cytosol = water
• Organelles = solids
Cytoplasm is really like a Jello fruit
salad where the Jello is the cytosol and
the fruits (oranges, grapes, bananas,
maybe walnuts, etc.) are the
organelles.
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Organelles
Endoplasmic Reticulum (ER)
• Connected, membrane-bound
sacs, canals, and vesicles
• Transport system
• Rough ER
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Membranes
Membranes
• Studded with ribosomes
• Smooth ER
• Lipid synthesis
• Added to proteins
arriving from rough ER
• Break down of drugs
Ribosomes
(b)
(c)
Ribosomes
• Free floating or connected to ER
• Provide structural support and enzyme activity
to amino acids to form protein (protein synthesis)
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Organelles
Golgi apparatus
• Stack of flattened,
membranous sacs
• Modifies, packages
and delivers proteins
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Vesicles
• Membranous sacs
• Store substances
Mitochondria
• Membranous sacs with
inner partitions
• Generate energy
Inner membrane
Cristae
Outer membrane
(a)
(b)
a: © Bill Longcore/Photo Researchers, Inc.
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Organelles
Lysosomes
• Enzyme-containing
sacs
• Digest worn out cell
parts or unwanted
substances
Centrosome
• Two rod-like centrioles
• Used to produce cilia
and flagella
• Distributes
chromosomes during cell
division
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Peroxisomes
• Enzyme-containing
sacs
• Break down organic
molecules
•Detoxifies alcohol
Centriole
(cross-section)
Centriole
(longitudinal section)
(a)
(b)
a: © Don W. Fawcett/Visuals Unlimited
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Organelles
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Cilia
• Short hair-like projections
• Propel substances on cell
surface
Flagellum
• Long tail-like projection
• Provides motility to sperm
(a)
a: © Oliver Meckes/Photo Researchers, Inc.
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© Colin Anderson/Brand X/CORBIS
Organelles
Microfilaments and microtubules
• Thin rods and tubules
• Support cytoplasm
• Allows for movement of
organelles
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Microtubules
Microfilaments
© M. Schliwa/Visuals Unlimited
11
Cell Nucleus
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• Is the control center of the cell
• Nuclear envelope
• Porous double membrane
• Separates nucleoplasm from
cytoplasm
• Nucleolus
• Dense collection of RNA and
proteins
• Site of ribosome production
Nucleus
Nuclear
envelope
Nucleolus
• Chromatin
• Fibers of DNA and proteins
• Stores information for synthesis of
proteins
Chromatin
Nuclear
pores
(a)
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3.3: Movements Into
and Out of the Cell
There are 2 ways substances move through the cell
membrane.
•Passive mechanisms do
not require energy.
• Simple diffusion
• Facilitated diffusion
• Osmosis
• Filtration
Active mechanisms require cell
energy
• Active transport
• Endocytosis
• Exocytosis
• Transcytosis
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Simple Diffusion
•The process by which molecules or ions scatter or spread
spontaneously from a higher concentration to a lower
concentration
• Oxygen and carbon dioxide can diffuse readily through the cell
membrane
•Equilibrium is reached.
Solute molecule
Permeable
membrane
A
Water molecule
B
(1)
A
B
(2)
Time
A
B
(3)
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Animation:
How Diffusion Works
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Facilitated Diffusion
• Substances that are not able to pass through the lipid
bilayer need the help of membrane proteins to get across,
this is called Facilitated Diffusion
•Carrier molecules “revolving doors” are used to carry large
molecules (transported substance) across the membrane.
• Ex. Glucose and amino acids
Region of higher
concentration
Transported
substance
Region of lower
concentration
Protein carrier
molecule
Cell
membrane
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Animation:
How Facilitated Diffusion
Works
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Osmosis
• The diffusion of water
• Water moves toward a higher concentration of
solutes
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Selectively
permeable
membrane
Protein molecule
Water molecule
A
A
B
B
(1)
(2)
Time
18
Animation:
How Osmosis Works
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19
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
• Isotonic – same osmotic
pressure
• Hypertonic – higher osmotic
pressure (water loss)
• Hypotonic – lower osmotic
pressure (water gain)
(a)
(b)
(c)
© David M. Phillips/Visuals Unlimited
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Filtration
• Smaller molecules are forced through porous membranes
• Hydrostatic pressure important in the body
• Molecules leaving blood capillaries
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Capillary wall
Blood
pressure
Tissue fluid
Blood
flow
Larger molecules
Smaller molecules
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Active Transport
• The process that moves particles through membranes from regions of
lower concentration to regions of higher concentration
• Equilibrium is never reached.
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Carrier protein
Binding site
Cell membrane
Region of higher
concentration
Region of lower
concentration
Phospholipid
molecules
Transported
particle
(a)
Carrier protein
with altered shape
Cellular
energy
(b)
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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
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QuickTime™ and a
decompressor
are needed to see this picture.
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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
Particle
membrane
Nucleus Nucleolus
Phagocytized
particle
Vesicle
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Endocytosis
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Cell
Particle
membrane
Phagocytized
particle
Vesicle
Nucleus Nucleolus
Receptor-ligand
combination
Molecules
outside cell
Vesicle
Receptor
protein
Cell
membrane
Cell
membrane
indenting
Cytoplasm
(a)
(b)
(c)
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(d)
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
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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
Viruses bud
HIV
Receptor-mediated endocytosis
Lining of anus
or vagina
(epithelial cells)
Cell
membrane
Exocytosis
Receptor-mediated
endocytosis
Virus infects
white blood cells on
other side of lining
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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
S phase:
genetic
material
replicates
G1 phase
cell growth
Proceed
to division
Remain
specialized
Apoptosis
Cytokinesis
Restriction
checkpoint
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Interphase
• Very active period
• 3 Phases are involved
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• During the G1 phase,
the cell grows
• During the S phase,
the cell replicates DNA
• During the G2 phase, Proceed
to division
the cell is in
preparation for cell
Remain
specialized
division
G2 phase
S phase:
genetic
material
replicates
Apoptosis
G1 phase
cell growth
Cytokinesis
Restriction
checkpoint
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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 31
forms
Mitosis
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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.
(a)
Early Interphase
of daughter cells—
a time of normal cell
growth and function.
Restriction
checkpoint
Nuclear
envelope
Chromatin
fibers
Centrioles
Cleavage
furrow
Prophase
Chromosomes condense and
become visible. Nuclear
envelope and nucleolus
disperse. Spindle apparatus
forms.
Aster
Microtubules
(e)
(b)
Centromere
Late prophase
Spindle fiber
Sister
chromatids
Chromosomes
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.
© Ed Reschke
S phase
G2 phase
Interphase
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Animation:
Mitosis and Cytokinesis
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33
Cytoplasmic Division
• Also known as cytokinesis
• Begins during anaphase
• Continues through telophase
• Contractile ring pinches cytoplasm in half
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Animation:
Control of the Cell Cycle
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35
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
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Tumors
• Two types of tumors:
• Benign – usually remains
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localized
• Malignant – invasive and
Normal cells
(with hairlike cilia)
can metastasize; cancerous
• Two major types of genes
cause cancer:
• Oncogenes – activate
other genes that increase cell
division
Cancer cells
• Tumor suppressor
genes – normally regulate
mitosis; if inactivated they are
unable to regulate mitosis
• Cells are now known as
“immortal”
© Tony Brain/Photo Researchers, Inc.;
37
Animation:
How Tumor Suppressor Genes
Block Cell Division
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38
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
39
Stem and Progenitor Cells
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Sperm
Sebaceous
gland cell
Egg
Progenitor
cell
Progenitor cell
Fertilized
egg
Skin cell
Stem cell
Progenitor
cell
Progenitor
cell
Stem cell
Neuron
Progenitor
cell
Progenitor
cell
Astrocyte
Progenitor
cell
Progenitor
cell
Progenitor
cell
Bone cells
Progenitor
cell
one or more steps
Fibroblasts (a connective tissue cells)
Blood cells and platelets
produces another stem cell
(self-renewal)
40
3.7: Cell Death
Apoptosis:
• Programmed cell death
• Acts as a protective mechanism
• Is a continuous process
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