Transcript 3 - Brazosport College

PowerPoint® Lecture Slides
prepared by
Barbara Heard,
Atlantic Cape Community
College
CHAPTER
3
Cells: The
Living Units:
© Annie Leibovitz/Contact Press Images
© 2013 Pearson Education, Inc.
Cell Theory
• Cell - structural and functional unit of life
• Organismal functions depend on individual
and collective cell functions
• Biochemical activities of cells dictated by
their shapes or forms, and specific
subcellular structures
• Continuity of life has cellular basis
© 2013 Pearson Education, Inc.
Figure 3.1 Cell diversity.
Erythrocytes
Fibroblasts
Epithelial cells
Cells that connect body parts, form linings, or transport
gases
Skeletal
muscle
cell
Smooth
muscle cells
Cells that move organs and body parts
Macrophage
Fat cell
Cell that stores nutrients
Cell that fights disease
Nerve cell
Cell that gathers information and controls body functions
Sperm
Cell of reproduction
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Figure 3.3 The plasma membrane.
Extracellular fluid
(watery environment
outside cell)
Polar head of
phospholipid
molecule
Nonpolar tail
of phospholipid
molecule
Cholesterol Glycolipid
Glycocalyx
(carbohydrates)
Lipid bilayer
containing
proteins
Outward-facing
layer of
phospholipids
Inward-facing
layer of
phospholipids
Cytoplasm
(watery environment
inside cell)
Integral Filament of Peripheral
proteins cytoskeleton proteins
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Glycoprotein
Membrane Lipids
• 75% phospholipids (lipid bilayer)
– Phosphate heads: polar and hydrophilic
– Fatty acid tails: nonpolar and hydrophobic
(Review Fig. 2.16b)
• 5% glycolipids
– Lipids with polar sugar groups on outer
membrane surface
• 20% cholesterol
– Increases membrane stability
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Membrane Proteins
•
•
•
•
•
•
Allow communication with environment
½ mass of plasma membrane
Most specialized membrane functions
Some float freely
Some tethered to intracellular structures
Two types:
– Integral proteins; peripheral proteins
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Membrane Proteins
• Integral proteins
– Firmly inserted into membrane (most are
transmembrane)
– Have hydrophobic and hydrophilic regions
• Can interact with lipid tails and water
– Functions?
PLAY
Animation: Transport Proteins
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Membrane Proteins
• Peripheral proteins
– Loosely attached to integral proteins
– Include filaments on intracellular surface for
membrane support
– Functionss? enzymes; motor proteins for
shape change during cell division and muscle
contraction; cell-to-cell connections
PLAY
Animation: Structural Proteins
PLAY
Animation: Receptor Proteins
© 2013 Pearson Education, Inc.
Figure 3.3 The plasma membrane.
Extracellular fluid
(watery environment
outside cell)
Polar head of
phospholipid
molecule
Nonpolar tail
of phospholipid
molecule
Cholesterol Glycolipid
Glycocalyx
(carbohydrates)
Lipid bilayer
containing
proteins
Outward-facing
layer of
phospholipids
Inward-facing
layer of
phospholipids
Cytoplasm
(watery environment
inside cell)
Integral Filament of Peripheral
proteins cytoskeleton proteins
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Glycoprotein
Six Functions of Membrane Proteins
1. Transport
2. Receptors for signal transduction
3. Attachment to cytoskeleton and
extracellular matrix
© 2013 Pearson Education, Inc.
Figure 3.4a Membrane proteins perform many tasks.
Transport
• A protein (left) that spans the membrane
may provide a hydrophilic channel across
the membrane that is selective for a
particular solute.
• Some transport proteins (right) hydrolyze
ATP as an energy source to actively pump
substances across the membrane.
PLAY
Animation: Transport Proteins
© 2013 Pearson Education, Inc.
Figure 3.4b Membrane proteins perform many tasks.
Signal
• A membrane protein exposed to the
outside of the cell may have a binding site
that fits the shape of a specific chemical
messenger, such as a hormone.
• When bound, the chemical messenger may
cause a change in shape in the protein that
initiates a chain of chemical reactions in the
cell.
Receptor
PLAY
Receptors for signal transduction
Animation: Receptor Proteins
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Figure 3.4c Membrane proteins perform many tasks.
Attachment to the cytoskeleton and
extracellular matrix
• Elements of the cytoskeleton (cell's internal
supports) and the extracellular matrix
(fibers and other substances outside the
cell) may anchor to membrane proteins,
which helps maintain cell shape and fix the
location of certain membrane proteins.
• Others play a role in cell movement or bind
adjacent cells together.
PLAY
Animation: Structural Proteins
© 2013 Pearson Education, Inc.
Six Functions of Membrane Proteins
4. Enzymatic activity
5. Intercellular joining
6. Cell-cell recognition
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Figure 3.4d Membrane proteins perform many tasks.
Enzymatic activity
Enzymes
PLAY
• A membrane protein may be an enzyme
with its active site exposed to substances in
the adjacent solution.
• A team of several enzymes in a membrane
may catalyze sequential steps of a metabolic
pathway as indicated (left to right) here.
Animation: Enzymes
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Figure 3.4d
Figure 3.4e Membrane proteins perform many tasks.
Intercellular joining
• Membrane proteins of adjacent cells may
be hooked together in various kinds of
intercellular junctions.
• Some membrane proteins (cell adhesion
molecules or CAMs) of this group provide
temporary binding sites that guide cell
migration and other cell-to-cell interactions.
CAMs
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Figure 3.4f Membrane proteins perform many tasks.
Cell-cell recognition
• Some glycoproteins (proteins bonded to
short chains of sugars) serve as
identification tags that are specifically
recognized by other cells.
Glycoprotein
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Membrane Transport
• Concentration = grams of solutes/100 ml
water
= % or osmoles
• Concentration gradient – difference in
concentration
• Equilibrium – no difference in
concentration
9/1/09
Mickey Dufilho
Types of Membrane Transport
• Passive processes
– No cellular energy (ATP) required
– Substance moves down its concentration
gradient
• Active processes
– Energy (ATP) required
– Occurs only in living cell membranes
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Passive Processes
• Two types of passive transport
– Diffusion
• Simple diffusion
• Carrier- and channel-mediated facilitated diffusion
• Osmosis
– Filtration
• Usually across capillary walls
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Passive Processes: Diffusion
• Collisions cause molecules to move down or
with their concentration gradient
– Difference in concentration between two
areas
• Speed influenced by molecule size and
temperature
• Molecule will passively diffuse through
membrane if
– It is lipid soluble, small enough to pass
through membrane channels, or assisted by
carrier molecule
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Passive Processes: Simple Diffusion
• Nonpolar lipid-soluble
(hydrophobic)
substances diffuse
directly through the
phospholipid bilayer
Mickey Dufilho
9/1/09
22
Passive Processes: Facilitated Diffusion
• Certain lipophobic molecules (e.g.,
glucose, amino acids, and ions)
transported passively by
– Binding to protein carriers
– Moving through water-filled channels
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Passive Processes: Facilitated Diffusion
Mickey Dufilho
9/1/09
24
Passive Processes: Osmosis
• Movement of solvent (e.g., water) across
selectively permeable membrane
• Water diffuses through plasma
membranes
– Through lipid bilayer
– Through specific water channels called
aquaporins (AQPs)
• Occurs when water concentration different
on the two sides of a membrane
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Figure 3.7d Diffusion through the plasma membrane.
Water
molecules
Lipid
bilayer
Aquaporin
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Osmosis, diffusion of a
solvent such as water
through a specific
channel protein
(aquaporin) or through
the lipid bilayer
Passive Processes: Osmosis
• Water concentration varies with number of
solute particles because solute particles
displace water molecules
• Osmolarity - Measure of total
concentration of solute particles
• Water moves by osmosis until hydrostatic
pressure (back pressure of water on
membrane) and osmotic pressure
(tendency of water to move into cell by
osmosis) equalize
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Figure 3.8a Influence of membrane permeability on diffusion and osmosis.
Membrane permeable to both solutes and water
Solute and water molecules move down their concentration gradients
in opposite directions. Fluid volume remains the same in both compartments.
Left
compartment:
Right
compartment:
Solution with
Solution with
lower osmolarity greater osmolarity
Solute
Freely
permeable
membrane
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Solute
molecules
(sugar)
Both solutions have the
same osmolarity: volume
unchanged
Figure 3.8b Influence of membrane permeability on diffusion and osmosis.
Membrane permeable to water, impermeable to solutes
Solute molecules are prevented from moving but water moves by osmosis.
Volume increases in the compartment with the higher osmolarity.
Left
compartment
Selectively
permeable
membrane
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Right
compartment
Solute
molecules
(sugar)
Both solutions have identical
osmolarity, but volume of the
solution on the right is greater
because only water is
free to move
Tonicity
• Tonicity: Ability of solution to alter cell's
water volume
– Isotonic: Solution with same non-penetrating
solute concentration as cytosol
– Hypertonic: Solution with higher nonpenetrating solute concentration than cytosol
– Hypotonic: Solution with lower nonpenetrating solute concentration than cytosol
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Figure 3.9 The effect of solutions of varying tonicities on living red blood cells.
Isotonic solutions
Cells retain their normal size and
shape in isotonic solutions (same
solute/water concentration as inside
cells; water moves in and out).
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Hypertonic solutions
Cells lose water by osmosis and shrink
in a hypertonic solution (contains a
higher concentration of solutes
than are present inside the cells).
Hypotonic solutions
Cells take on water by osmosis until they
become bloated and burst (lyse) in a
hypotonic solution (contains a lower
concentration of solutes than are
present inside cells).
Table 3.1 Passive Membrane Transport Processes
© 2013 Pearson Education, Inc.
Passive Membrane Transport: Filtration
• The passage of water and solutes through
a membrane by hydrostatic pressure
• Pressure gradient pushes solutecontaining fluid from a higher-pressure
area to a lower-pressure area
• Does not occur into or out of cell, but
through filtration membrane made of rows
of cells.
Mickey Dufilho
9/1/09
33
Membrane Transport: Active Processes
• Two types of active processes
– Active transport
– Vesicular transport
• Both require ATP to move solutes across
a living plasma membrane because
– Solute too large for channels
– Solute not lipid soluble
– Solute not able to move down concentration
gradient
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Active Transport
• Requires carrier proteins (solute pumps)
– Bind specifically and reversibly with
substance
• Moves solutes against concentration
gradient
– Requires energy
• Two types
– Primary active transport
– Secondary active transport
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Primary Active Transport
• Energy from hydrolysis of ATP causes
shape change in transport protein that
"pumps" solutes (ions) across membrane
• E.g., calcium, hydrogen, Na+-K+ pumps
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Figure 3.10 Primary active transport is the process in which solutes are moved across cell
membranes against electrochemical gradients using energy supplied directly by ATP.
Extracellular fluid
Na+
Na+–K+ pump
K+
Na+ bound
ATP-binding site
Cytoplasm
1 Three cytoplasmic Na+ bind to pump
protein.
P
K+ released
2 Na+ binding promotes hydrolysis of ATP.
The energy released during this reaction
phosphorylates the pump.
6 Pump protein binds ATP; releases K+ to
the inside, and Na+ sites are ready to bind
Na+ again. The cycle repeats.
Na+ released
K+ bound
P
Pi
K+
5 K+ binding triggers release of the
phosphate. The dephosphorylated pump
resumes its original conformation.
3 Phosphorylation causes the pump to
change shape, expelling Na+ to the outside.
P
4 Two extracellular K+ bind to pump.
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Slide 1
Secondary Active Transport
• Depends on ion gradient created by
primary active transport
• Energy stored in ionic gradients used
indirectly to drive transport of other solutes
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Secondary Active Transport
• Cotransport—always transports more
than one substance at a time
– Symport system: Substances transported in
same direction
– Antiport system: Substances transported in
opposite directions
© 2013 Pearson Education, Inc.
Figure 3.11 Secondary active transport is driven by the concentration gradient created by primary active
transport.
Extracellular fluid
Slide 1
Glucose
Na+-K+
pump
Na+-glucose
symport
transporter
loads glucose
from extracellular
fluid
Na+-glucose
symport transporter
releases glucose
into the cytoplasm
Cytoplasm
1 Primary active transport
The ATP-driven Na+-K+ pump
stores energy by creating a
steep concentration gradient for
Na+ entry into the cell.
© 2013 Pearson Education, Inc.
2 Secondary active transport
As Na+ diffuses back across the membrane
through a membrane cotransporter protein, it
drives glucose against its concentration gradient
into the cell.
Vesicular Transport
• Transport of large particles, macromolecules, and fluids
across membrane in membranous sacs called vesicles
• Requires cellular energy (e.g., ATP)
• Functions:
– Exocytosis—transport out of cell
– Endocytosis—transport into cell
• Phagocytosis, pinocytosis, receptor-mediated
endocytosis
– Transcytosis—transport into, across, and then out of
cell
– Vesicular trafficking—transport from one area or
organelle in cell to another
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Figure 3.12 Events of endocytosis mediated by protein-coated pits.
1 Coated pit ingests
substance.
Protein coat
(typically
clathrin)
2 Protein-coated
vesicle detaches.
Extracellular fluid
Plasma
membrane
Cytoplasm
3 Coat proteins are
recycled to plasma
membrane.
Transport
vesicle
Uncoated endocytic
vesicle
Endosome
4 Uncoated vesicle
fuses with a sorting
vesicle called an
endosome.
Lysosome
5 Transport
vesicle containing
membrane compone
-nts moves to the plasma
membrane for recycling.
6 Fused vesicle may (a)
fuse with lysosome for
digestion of its contents,
or (b) deliver its contents
to the plasma membrane
on the opposite side of the
cell (transcytosis).
© 2013 Pearson Education, Inc.
Slide 1
Endocytosis
• Phagocytosis
– Pseudopods engulf solids and bring them into
cell's interior
– Form vesicle called phagosome
• Used by macrophages and some white
blood cells
– Move by amoeboid motion
• Cytoplasm flows into temporary extensions
• Allows creeping
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Figure 3.13a Comparison of three types of endocytosis.
Receptors
Phagosome
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Phagocytosis
The cell engulfs a large particle
by forming projecting pseudopods
("false feet") around it and enclosing
it within a membrane sac called a
phagosome. The phagosome is
combined with a lysosome.
Undigested contents remain in
the vesicle (now called a residual
body) or are ejected by exocytosis.
Vesicle may or may not be protein
coated but has receptors capable of
binding to microorganisms or solid
particles.
Endocytosis
• Pinocytosis (fluid-phase endocytosis)
– Plasma membrane infolds, bringing
extracellular fluid and dissolved solutes inside
cell
• Fuses with endosome
– Most cells utilize to "sample" environment
– Nutrient absorption in the small intestine
– Membrane components recycled back to
membrane
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Figure 3.13b Comparison of three types of endocytosis.
Pinocytosis
The cell "gulps" a drop of
extracellular fluid containing solutes
into tiny vesicles. No receptors are
used, so the process is nonspecific.
Most vesicles are protein-coated.
Vesicle
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Endocytosis
• Receptor-mediated endocytosis
– Allows specific endocytosis and transcytosis
• Cells use to concentrate materials in limited supply
– Clathrin-coated pits provide main route for
endocytosis and transcytosis
• Uptake of enzymes, low-density lipoproteins, iron,
insulin, and, unfortunately, viruses, diphtheria, and
cholera toxins
© 2013 Pearson Education, Inc.
Figure 3.13c Comparison of three types of endocytosis.
Vesicle
© 2013 Pearson Education, Inc.
Receptor-mediated endocytosis
Extracellular substances bind to
specific receptor proteins, enabling
the cell to ingest and concentrate
specific substances (ligands) in
protein-coated vesicles. Ligands
may simply be released inside the
cell, or combined with a lysosome to
digest contents. Receptors are
recycled to the plasma membrane in
vesicles.
Exocytosis
• Usually activated by cell-surface signal or
change in membrane voltage
• Substance enclosed in secretory vesicle
• v-SNAREs ("v" = vesicle) on vesicle find
t-SNAREs ("t" = target) on membrane and
bind
• Functions
– Hormone secretion, neurotransmitter release,
mucus secretion, ejection of wastes
© 2013 Pearson Education, Inc.
Figure 3.14 Exocytosis.
Slide 1
The process of exocytosis
Plasma membrane
Extracellular
SNARE (t-SNARE)
fluid
Secretory
vesicle
Vesicle
SNARE
(v-SNARE)
Molecule to
be secreted
Cytoplasm
Fused
v- and
t-SNAREs
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Fusion pore formed
1 The membranebound vesicle
migrates to the
plasma membrane.
2 There, proteins at
the vesicle surface
(v-SNAREs) bind
with t-SNAREs
(plasma membrane
proteins).
3 The vesicle
and plasma
membrane
fuse and a pore
opens up.
4 Vesicle
contents are
released to the
cell exterior.
Figure 3.14b Exocytosis.
Photomicrograph
of a secretory
vesicle releasing
its contents
by exocytosis
(100,000x)
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Mediated transport
•
•
•
•
Specificity
Competition
Saturation
Transport maximum
Mickey Dufilho
9/1/09
52
Table 3.2 Active Membrane Transport Processes (1 of 2)
© 2013 Pearson Education, Inc.
Table 3.2 Active Membrane Transport Processes (2 of 2)
© 2013 Pearson Education, Inc.