Transcript Inquiry into Life, Eleventh Edition

Inquiry into Life
Eleventh Edition
Sylvia S. Mader
Chapter 4
Lecture Outline
1-1
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
4.1 Plasma membrane structure
and function
• Membrane structure
– Fluid-mosaic model
– Phospholipid bilayer
• Hydrophobic tails face inward
• Hydrophilic heads face surfaces
– Proteins
• Integral proteins-embedded
• Peripheral proteins- surface
– Glycoproteins, glycolipids, cholesterol
1-2
The plasma membrane separates the
internal environment of the cell from its
surroundings.
The plasma membrane is a
phospholipid bilayer with embedded
proteins.
The plasma membrane has a fluid
consistency and a mosaic pattern of
embedded proteins.
1-3
Fluid-mosaic model of membrane
structure
• Fig. 4.1
1-4
Membrane structure and function,
cont’d.
• Functions of membrane proteins
– Channel proteins
• Form channels for substances can move across membrane
– Receptor proteins
• Bind to substances in the environment and trigger cell
responses
– Carrier proteins
• Transport specific substances across cell membrane
– Enzymes
• Catalyze chemical reactions for cell metabolism
1-5
Membrane protein diversity
• Fig 4.2
1-6
When lipids have carbohydrate
chains attached, they are called
glycolipids
When proteins have
carbohydrate chains attached,
they are called glycoproteins
1-7
Channel protein
1-8
Carrier protein
1-9
Enzymatic protein
1-10
Cell recognition protein
1-11
Membrane structure and function, cont’d.
• Carbohydrate chains
– Bound to only outer surface of cell recognition
proteins
– Form a “sugar coat”-glycocalyx
– Diversity of this Glycocalyx produces individual
“fingerprint”
• Recognition of self vs. nonself
• Immune responses
Glycocalyx is only on the outer surfaces,
so the inner and outer surfaces of the
Cell Membrane are not identical.
1-12
In animal cells, the carbohydrate chains
of cell recognition proteins are
collectively called the glycocalyx.
The glycocalyx can function in cell-to-cell
recognition, adhesion between cells, and
reception of signal molecules.
The diversity of carbohydrate chains is
enormous, providing each individual with
a unique cellular “fingerprint”.
1-13
4.2 Permeability of plasma membrane
• Plasma membrane is referred to as selectively
permeable or differentially permeable
– Some substances pass through freely while others do
not. Small, uncharged molecules pass through the
cell membrane, following their concentration gradient.
• Passive transport-no cellular energy required
– Kinetic energy drives passive mechanisms
– Movement is always from high concentration to low
– Diffusion, facilitated diffusion (carrier-mediated)
1-14
The plasma membrane is differentially
permeable.
Macromolecules cannot pass through
because of size, and tiny charged
molecules do not pass through the
nonpolar interior of the membrane.
Small, uncharged molecules pass through
the membrane, following their
concentration gradient.
1-15
Passage of molecules into and out of
cells
• Table 4.1
1-16
Permeability of plasma membrane, cont’d.
• Active transport mechanisms-require ATP,
can transport against a concentration
gradient
– Active transport
• Requires a carrier protein
• Transports molecules from low concentration to high
– Exocytosis-vesicle mediated transport – Uses Energy
• Transports cell products and wastes out of the cell by vesicle
formation. The release of digestive enzymes from cells of the
pancreas, or secretion of the hormone insulin in response to
rising blood glucose levels are examples.
– Endocytosis-vesicle mediated transport–Uses Energy
• Transports substances into the cell by vesicle formation
• Pinocytosis-”cell drinking”, takes in small particles or liquids
• Phagocytosis-”cell eating”, takes in larger particles
1-17
Movement of materials across a
membrane may be passive or active.
Passive transport does not use chemical
energy; diffusion and facilitated transport
are both passive.
Active transport requires chemical
energy and usually a carrier protein.
Exocytosis and endocytosis transport
macromolecules across plasma
membranes using vesicle formation,
which requires energy.
1-18
Crossing the plasma membrane
• Fig. 4.3
1-19
4.3 Diffusion and osmosis
• Diffusion
– Movement of molecules from an area of
high concentration to an area of low
concentration
– Random kinetic energy drives diffusion
– Lipid soluble molecules, gases, and
some small water soluble molecules
may diffuse freely across cell membrane
1-20
Process of diffusion
• Fig. 4.4
1-21
Osmosis in cells
A solution contains a solute (solid)
and a solvent (liquid).
Cells are normally isotonic to their
surroundings, and the solute
concentration is the same inside and
out of the cell.
“Iso” means the same as, and
“tonocity” refers to the strength of the
solution.
1-22
4.3 Diffusion and osmosis, cont’d.
• Osmosis-diffusion of water across a semi
permeable membrane
– Osmotic pressure-force that causes
water to move in a direction
– Osmotic pressure is due to the number of
nondiffusable particles in solution
– Hypotonic solutions-cause cells to swell and burst,
called lysis in animal cells, increased turgor pressure
in plant cells since cell walls resist rupture.
– Hypertonic solutions-cause cells to shrink, called
crenation in animal cells, plasmolysis in plant cells.
– Isotonic solutions-no change
1-23
Osmosis demonstration
• Fig. 4.6
1-24
Osmosis in animal and plant cells
• Fig 4.7
1-25
4.4 Transport by carrier proteins
• Transport by carrier proteins
– Carrier proteins are specific for the molecules they
transport
• Facilitated transport
– Passive mechanism
– Transports from high concentration to low
• Active transport
– Requires cellular energy
– Transports against the concentration gradient
– The sodium-potassium pump moves sodium ions
to the outside of the cell and potassium ions to
the inside.
1-26
Facilitated transport and active
transport
• Fig. 4.8
• Fig. 4.9
1-27
The sodium-potassium pump
• Fig 4.10
1-28
4.5 Exocytosis and endocytosis
• Exocytosis
– Vesicles containing cell products fuse
with plasma membrane
– Products are released and vesicle
membrane becomes part of the plasma
membrane
1-29
Exocytosis
• Fig 4.11
1-30
Exocytosis and endocytosis,
cont’d.
• Endocytosis-an area of cell membrane
invaginates and surrounds a substance,
then pinches off to form a vesicle
– Phagocytosis-material taken in is large; ex:
bacteria, cell debris
– Pinocytosis-material is liquid or small
– Receptor-mediated-specific type of
pinocytosis which occurs in response to
receptor stimulation, often with a coated pit,
an area with a high concentration of receptors
1-31
Three methods of endocytosis
• Fig 4.12
1-32