Download Plasma Membrane

Ch. 3
CELLS AND TISSUES
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Generalized Cell
• All cells:
• Human cells have three basic parts:
• Plasma membrane—flexible outer boundary
• Cytoplasm—intracellular fluid containing
organelles
• Nucleus—control center
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Chromatin
Nucleolus
Nuclear envelope
Nucleus
Smooth endoplasmic
reticulum
Mitochondrion
Cytosol
Lysosome
Centrioles
Centrosome
matrix
Cytoskeletal
elements
• Microtubule
• Intermediate
filaments
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Plasma
membrane
Rough
endoplasmic
reticulum
Ribosomes
Golgi apparatus
Secretion being
released from cell
by exocytosis
Peroxisome
Figure 3.2
Plasma Membrane
• The plasma membrane separates the
intracellular fluid (ICF) from extracellular fluid
(ECF)
• The plasma membrane is semi-permeable
which means that some things can cross the
membrane and some things cannot
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Extracellular fluid
Intracellular fluid
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Figure 3.3
Types of Membrane Transport
• A concentration gradient is:
• Passive Transport
• No cellular energy (ATP) required
• Substance moves down its concentration
gradient
• Active Transport
• Energy (ATP) required
• Substances are moved or“pumped” against
their gradient
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Passive Transport
•What determines whether or not a substance
can passively cross the plasma membrane?
1. Is the substance a lipid (Lipid solubility of
substance)
2. Size of substance passing
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Three Types of Passive Transport Across
Cellular membranes
• Simple diffusion
• Facilitated diffusion
• Osmosis
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Passive Transport: Simple Diffusion
• What types of substances use simple diffusion
to cross the plasma membrane?
• Small, nonpolar, hydrophobic substances
diffuse directly through phospholipid bilayer
(O2, CO2)
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Extracellular fluid
Lipidsoluble
solutes
Cytoplasm
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Figure 3.7a
Passive Transport: Facilitated Diffusion
• What types of substances use facilitated
diffusion to cross the plasma membrane?
• Larger, hydrophilic molecules (glucose, amino
acids)
• Can pass through carriers or channels
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A Carrier Protein
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Hydrophilic
molecules
Figure 3.7b
Passive Transport: Osmosis
• Movement of solvent (water) across a
selectively permeable membrane from where
it is most concentrated to where it is less
concentrated
• Water diffuses through plasma membranes:
• mainly through channels
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A Channel Protein
Water
molecules
Lipid
billayer
Aquaporin
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Figure 3.7d
(a)
Membrane permeable to both solutes and water
Solute and water molecules move down their concentration gradients
in opposite directions.
Both solutions have the
same osmolarity: volume
unchanged
H2O
Solute
Membrane
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Solute
(sugar)
Figure 3.8a
(b)
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
Right
compartment
Both solutions have identical
osmolarity, increases on the right
because only water is
free to move
H2O
Membrane
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Solute
(sugar)
Figure 3.8b
Importance of Osmosis
• When osmosis occurs, water enters or leaves
a cell
• A change in cell volume disrupts cell function
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Tonicity
• Defined as: The ability of a solution to cause a
cell to shrink or swell
• Isotonic: A solution that does not cause a
change in cell volume
• Hypertonic: A solution that causes a cell to
shrink
• Hypotonic: A solution that causes a cell to
swell.
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(a)
Isotonic solutions
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(b)
Hypertonic solutions
(c)
Hypotonic solutions
Figure 3.9
Active Transport
• Defined as:
• The Sodium-potassium pump (Na+-K+ ATPase) is a
specific example of active transport
• Located in all plasma membranes
• Maintains electrochemical gradients essential for
muscle and nerve functions
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Other Cellular Organelles
• Membranous structures
• Nucleus with chromatin• Mitochondria –
• Endoplasmic Reticulum (ER) (rough and
smooth) –
• Golgi Apparatus-
• Lysosomes-
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Nucleus
Nuclear envelope
Smooth ER
Rough ER
Vesicle
Plasma
membrane
Lysosome
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Golgi
apparatus
Transport
vesicle
Smooth ER
Nuclear
envelope
Rough ER
Ribosomes
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Rough ER
Phagosome
ER
membrane
Plasma
membrane
Vesicle becomes
lysosome
Golgi
apparatus
Secretory
vesicle
Secretion by
exocytosis
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Extracellular fluid
Mitochondria
• Organelle with shelflike
folds called cristae
• Provide most of cell’s
ATP (enzymes for this
process are located on
cristae)
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Other Organelles
• Non-Membranous structures
• Centrioles- involved in cell division
• Cytoskeleton- protein filaments that help
maintain cell shape, cell movement and in cell
division (microtubules)
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Centrosome matrix
Centrioles
(a)
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Microtubules
Extensions of the plasma membrane
• Cilia are: short, hairlike structures; move
substances across cell surfaces
• Flagella are: Whiplike, tails that move the
entire cell
• Microvilli are: fingerlike extensions found on
absorptive cells
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Microvillus
Actin
filaments
Terminal
web
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The Cell Cycle
• Includes:
• Interphase
• Period from cell formation to cell division
• Three sub phases of Interphase:
• G1 (gap 1)—growth and metabolism
• S (synthetic)—DNA replication
• G2 (gap 2)—preparation for division
• Cell division (mitotic phase or mitosis)
• Consists of four sub phases of mitosis
(PMAT) and cytokinesis
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Mitosis (Cell Division)
• Purpose:
• Does not occur in:
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S
Growth and DNA
synthesis
G1
Growth
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M
G2
Growth and final
preparations for
division
During the S-phase of Interphase DNA is
Replicated
• Helicase untwists the double helix and
exposes complementary chains
• Each nucleotide strand serves as a template
for building a new complementary strand
• DNA polymerase forms new DNA strand
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DNA Replication
• End result: two DNA molecules formed from
the original
• This process is called semiconservative
replication
• After DNA has been replicated the cell
progresses into mitosis and cytokinesis
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Chromosome
Free nucleotides
DNA polymerase
Template for synthesis
of new strand
Leading strand
Old DNA
Helicase unwinds
the double helix and
Exposes bases
Replication
fork
Adenine
Thymine
Cytosine
Guanine
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Lleading and lagging strands are
synthesized in opposite directions
Lagging
strand
DNA polymerase Old (template) strand
Mitosis and Cytokinesis
• Mitosis—four stages of nuclear division:
• Prophase-
• Metaphase• Anaphase-
• Telophase-
• Cytokinesis—division of cytoplasm by
cleavage furrow
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S
Growth and DNA
synthesis
G1
Growth
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M
G2
Growth
Early Prophase
Early mitotic
spindle
Aster
Early Prophase
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Chromosome
consisting of two
sister chromatids
Centromere
Microtubule
Late Prophase
Late Prophase
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Fragments
of nuclear
envelope
Microtubule
Metaphase
Spindle
Metaphase
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Metaphase
plate
Anaphase
Anaphase
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Daughter
chromosomes
Cytokinesis
• Begins during late anaphase
• Ring of actin microfilaments contracts to form
a cleavage furrow
• Two daughter cells are pinched apart, each
containing a nucleus identical to the original
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Nuclear
envelope
forming
Telophase and Cytokinesis
Telophase
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Nucleolus
forming
Contractile
ring at
cleavage
furrow