Download Plasma Membrane

Generalized Cell
• 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
•Two main factors determine 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- Small, nonpolar, hydrophobic substances
diffuse directly through plasma membrane (O2, CO2)
• Facilitated diffusion-Larger, hydrophilic molecules (glucose,
amino acids)
• Use membrane proteins to cross
• Osmosis-Movement of solvent (water) across a selectively
permeable membrane from where it is most concentrated to
where it is less concentrated
• Water mainly diffuses through channels (AQP) in the plasma
membrane
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Extracellular fluid
Lipidsoluble
solutes
Cytoplasm
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Figure 3.7a
A Carrier Protein
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Hydrophilic
molecules
Figure 3.7b
A Channel Protein
Water
molecules
Lipid
billayer
Aquaporin
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Figure 3.7d
Importance of Osmosis
• When osmosis occurs, water enters or leaves
a cell
• A change in cell volume disrupts cell function
• Tonicity is the ability of a solution to change a
cell’s volume
• Hypertonic, Hypotonic and Isotonic solutions
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(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
(a)
Isotonic solutions
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(b)
Hypertonic solutions
(c)
Hypotonic solutions
Figure 3.9
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
Figure 3.22
Smooth ER
Nuclear
envelope
Rough ER
Ribosomes
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Figure 3.18a
Other Organelles
• Non-Membranous structures
• Cytoskeleton- protein filaments that help
maintain cell shape, cell movement and in cell
division (microtubules)
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Extensions of the plasma membrane
• Cilia are: short, hairlike structures; move
substances across cell surfaces
• Flagella are: Whiplike, tails that move the
entire cell
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THE CELL CYCLE
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The Cell Cycle
• Includes:
• Interphase
• Period from cell formation to cell division
• Three sub phases of Interphase:
• G1, S, G2
• Cell division (mitotic phase or mitosis)
• Consists of four sub phases of mitosis
(PMAT) and cytokinesis
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Mitosis (Cell Division)
• Mitosis increases the # of
cells for growth/tissue
repair
S
Growth and DNA
synthesis
G1
Growth
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M
G2
Growth and final
preparations for
division
Figure 3.31
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 in a process called
semiconservative replication
• After DNA has been replicated the cell
progresses into mitosis and cytokinesis
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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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G2
Growth
M
Figure 3.31
Early Prophase
Early mitotic
spindle
Aster
Early Prophase
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Chromosome
consisting of two
sister chromatids
Centromere
Figure 3.33
Microtubule
Late Prophase
Late Prophase
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Fragments
of nuclear
envelope
Microtubule
Figure 3.33
Metaphase
Spindle
Metaphase
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Metaphase
plate
Figure 3.33
Anaphase
Anaphase
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Daughter
chromosomes
Figure 3.33
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
Nucleolus
forming
Contractile
ring at
cleavage
furrow
Telophase and Cytokinesis
Telophase
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Figure 3.33