unit_1_cell
TRANSCRIPT
The Cell
Dr. S. Francis
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Typical Cell
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Cytoplasm
• Portion of cell interior not occupied by the nucleus
• Consists of– Organelles
• “little organs”• Distinct, highly organized, membrane-enclosed
structures– Cytosol
• Complex, gel-like mass in which the cytoskeleton is found
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Cytosol
• Occupies about 55% of total cell volume• Semi-liquid portion of cytoplasm that surrounds
the organelles• Contains cytoskeleton and cell nutrients• Activities associated with gelatinous portion of
cytoplasm– Enzymatic regulation of intermediary metabolism– Ribosomal protein synthesis– Storage of fat, carbohydrate, and secretory vesicles
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Cytoskeleton
• Complex protein network protein of cytosol that acts as “bone and muscle” of cell
• Three distinct elements– Microtubules– Microfilaments– Intermediate filaments
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Element FunctionMicrotubules •Transport secretory vesicles
•Movement of specialized cell projections•Form mitotic spindle during cell division
Microfilaments •Contractile systems•Mechanical stiffeners
Intermediate filaments
•Help resist mechanical stress
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Examples of Organelles• Endoplasmic reticulum• Golgi complex• Lysosome• Peroxisome• Ribosomes• Mitochondrion• Vault
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Endoplasmic Reticulum (ER)• Elaborate fluid-filled membranous system
distributed throughout the cytosol• Primary function
– Protein and lipid manufacture• Two types
– Smooth ER (lipid synthesis)• Mesh of tiny interconnected tubules
– Rough ER (protein synthesis)• Projects outward from smooth ER as stacks of relatively
flattened sacs• Surface has attached ribosomes
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Endoplasmic Reticulum (ER)
Ribosomes
• Consist of two subunits– Large and a small subunit
• Involved in Protein Synthesis
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Golgi Complex
• Closely associated with ER• Consists of a stack of flattened, slightly curved,
membrane-enclosed sacs called cisternae• Number of Golgi complexes per cell varies
with the cell type• Functions
– Processes raw materials into finished products– Sorts and directs finished products to their final
destinations
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Golgi Complex
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Lysosomes
• Membranous sacs containing hydrolytic enzymes
• Serve as intracellular digestive system• Extracellular material attacked by lysosomes
enters cell by endocytosis– Pinocytosis– Receptor-mediated endocytosis– phagocytosis
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Peroxisomes
• Membranous sacs that house oxidative enzymes that detoxify various waste products
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Vaults• Shaped like octagonal barrels• May serve as extracellular transport vehicles• May contribute to multi-drug resistance
sometimes displayed in cancer cells• Exact function is not clear
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Mitochondria
• Energy organelle– Major site of ATP
production– Contains enzymes for citric
acid cycle and electron transport chain
• Enclosed by a double membrane– Inner infolded membrane
is called the cristae
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Nucleus
• Typically largest single organized cell component
• Enclosed by a double-layered nuclear envelope
• Contains cell’s genetic material, DNA– DNA functions
• Directs protein synthesis• Serves as genetic blueprint during cell replication
Chapter 2 Cellular PhysiologyHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Plasma Membrane
• Also called the cell membrane• Surrounds every cell• Separates cell contents from its surroundings
– Separates ICF and ECF• Controls movement of molecules into and out
of cell
Chapter 3 The Plasma Membrane and Membrane PotentialHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Plasma Membrane Structure• Most abundant are the lipids (phospholipids)
• Polar end of phospholipid is hydrophilic• Nonpolar end of phospholipid is hydrophobic .
• Fluid lipid bilayer embedded with proteins• Also has small amount of carbohydrates
– On outer surface only• Cholesterol
– Tucked between phospholipid molecules– Contributes to fluidity and stability of cell
membrane
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Plasma Membrane• Functions of the Plasma Membrane
– Physical isolation• Barrier
– Regulates exchange with environment• Ions and nutrients enter• Wastes eliminated and cellular products released
– Monitors the environment• Extracellular fluid composition• Chemical signals
– Structural support • Anchors cells and tissues
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Plasma Membrane
• Membrane Lipids
– Double layer of phospholipid molecules
• Hydrophilic heads—toward watery environment, both
sides
• Hydrophobic fatty-acid tails—inside membrane
• Barrier to ions and water—soluble compounds
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Plasma Membrane• Membrane Carbohydrates
– Proteoglycans, glycoproteins, and glycolipids• Extend outside cell membrane
• Form sticky “sugar coat” (glycocalyx)
– Functions of the glycocalyx• Lubrication and protection
• Anchoring and locomotion
• Specificity in binding (receptors)
• Recognition (immune response)
Chapter 3 The Plasma Membrane and Membrane PotentialHuman Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Plasma Membrane Structure
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Plasma Membrane
• Membrane Proteins
– Integral proteins
• Within the membrane
– Peripheral proteins
• Bound to inner or outer surface of the membrane
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Plasma Membrane• Membrane Proteins
– Anchoring proteins (stabilizers)• Attach to inside or outside structures
– Recognition proteins (identifiers) • Label cells as normal or abnormal
– Enzymes • Catalyze reactions
– Receptor proteins• Bind and respond to ligands (ions, hormones)
– Carrier proteins • Transport specific solutes through membrane
– Channels • Regulate water flow and solutes through membrane
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Membrane Transport• The plasma (cell) membrane is a barrier, but
– Nutrients must get in
– Products and wastes must get out
• Permeability determines what moves in and out of a cell, and
a membrane that
– Lets nothing in or out is impermeable
– Lets anything pass is freely permeable
– Restricts movement is selectively permeable
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Membrane Transport• Plasma membrane is selectively permeable
– Allows some materials to move freely– Restricts other materials
• Selective permeability restricts materials based on– Size– Electrical charge– Molecular shape– Lipid solubility
Membrane Transport: Fat-and Water-Soluble Molecules
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Membrane Transport• Transport through a plasma membrane can
be– Active (requiring energy and ATP)– Passive (no energy required)
• Diffusion (passive)• Carrier-mediated transport (passive or active)• Vesicular transport (active)
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Membrane Transport• All molecules are constantly in motion • Molecules in solution move randomly• Random motion causes mixing• Concentration is the amount of solute in a
solvent• Concentration gradient
– More solute in one part of a solvent than another
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Diffusion• Diffusion is a Function of the Concentration
Gradient– Diffusion
• Molecules mix randomly
• Solute spreads through solvent
• Eliminates concentration gradient
• Solutes move down a concentration gradient
Membrane Transport: Diffusion
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Diffusion
Figure 3–14 Diffusion.
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Diffusion• Factors Affecting Diffusion
– Distance the particle has to move
– Molecule size • Smaller is faster
– Temperature • More heat, faster motion
– Gradient size • The difference between high and low concentrations
– Electrical forces • Opposites attract, like charges repel
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Diffusion• Diffusion Across Plasma Membranes
– Can be simple or channel mediated• Materials that diffuse through plasma membrane by
simple diffusion:– lipid-soluble compounds (alcohols, fatty acids, and steroids)– dissolved gases (oxygen and carbon dioxide)
• Materials that pass through transmembrane proteins (channels):
– are water–soluble compounds– are ions
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Diffusion
• Diffusion across Plasma Membranes
– Factors in channel-mediated diffusion
• Passage depends on:
– size
– charge
– interaction with the channel
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Diffusion
Figure 3–15 Diffusion across the Plasma Membrane
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Diffusion• Osmosis: A Special Case of Diffusion
– Osmosis is the diffusion of water across the cell membrane
• More solute molecules, lower concentration of water molecules
• Membrane must be freely permeable to water, selectively permeable to solutes
• Water molecules diffuse across membrane toward solution with more solutes
• Volume increases on the side with more solutes
Membrane Transport
• Osmosis – Net diffusion of water down its own concentration gradient
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Diffusion
• Osmosis: A Special Case of Diffusion
– Osmotic Pressure
• Is the force of a concentration gradient of water
• Equals the force (hydrostatic pressure) needed to block
osmosis
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Diffusion
FIGURE 3–16 Osmosis.
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Diffusion• Tonicity
– The osmotic effect of a solute on a cell:
– Isotonic (iso- = same, tonos = tension)• A solution that does not cause osmotic flow of water in or out of a
cell
– Hypotonic (hypo- = below)• Has less solutes and loses water through osmosis
– Hypertonic (hyper- = above) • Has more solutes and gains water by osmosis
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Diffusion• Osmolarity and Tonicity
– A cell in a hypotonic solution:
• Gains water
• Ruptures (hemolysis of red blood cells)
– A cell in a hypertonic solution:
• Loses water
• Shrinks (crenation of red blood cells)
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Carriers and Vesicles• Carrier-Mediated Transport
– Carrier-mediated transport of ions and organic substrates• Facilitated diffusion • Active transport
– Characteristics• Specificity:
– one transport protein, one set of substrates
• Saturation limits: – rate depends on transport proteins, not substrate
• Regulation: – cofactors such as hormones
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Carriers and Vesicles
• Carrier-Mediated Transport
– Cotransport• Two substances move in the same direction at the
same time
– Countertransport• One substance moves in while another moves out
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Carriers and Vesicles• Carrier-Mediated Transport
– Facilitated diffusion• Passive
• Carrier proteins transport molecules too large to fit through channel proteins (glucose, amino acids):
– molecule binds to receptor site on carrier protein
– protein changes shape, molecules pass through
– receptor site is specific to certain molecules
Membrane Transport: Facilitated Diffusion
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Carriers and Vesicles
FIGURE 3–18 Facilitated Diffusion.
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Carriers and Vesicles• Carrier-Mediated Transport
– Active transport• Active transport proteins:
– move substrates against concentration gradient
– require energy, such as ATP
– ion pumps move ions (Na+, K+, Ca2+, Mg2+)
– exchange pump countertransports two ions at the same time
Membrane Transport: Active Transport
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Carriers and Vesicles
• Carrier-Mediated Transport
– Active transport
• Sodium-potassium exchange pump
– active transport, carrier mediated:
» sodium ions (Na+) out, potassium ions (K+) in
» 1 ATP moves 3 Na+ and 2 K+
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Carriers and Vesicles
Figure 3–19 The Sodium–Potassium Exchange Pump
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Carriers and Vesicles
• Carrier-Mediated Transport
– Active transport
• Secondary active transport
– Na+ concentration gradient drives glucose transport
– ATP energy pumps Na+ back out
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Carriers and Vesicles
Figure 3–20 Secondary Active Transport.
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Carriers and Vesicles• Vesicular Transport (or bulk transport)
– Materials move into or out of cell in vesicles
• Endocytosis (endo- = inside) is active transport using ATP:
– receptor mediated
– pinocytosis
– phagocytosis
• Exocytosis (exo- = outside)
– Granules or droplets are released from the cell
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Carriers and Vesicles
• Endocytosis
– Receptor-mediated endocytosis:
• Receptors (glycoproteins) bind target molecules (ligands)
• Coated vesicle (endosome) carries ligands and receptors into the
cell
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Carriers and Vesicles
Figure 3–21 Receptor-Mediated Endocytosis.
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Carriers and Vesicles• Endocytosis
– Pinocytosis
• Endosomes “drink” extracellular fluid
– Phagocytosis
• Pseudopodia (psuedo- = false, pod- = foot)
• Engulf large objects in phagosomes
– Exocytosis
• Is the reverse of endocytosis
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Organelles and the Cytoplasm
• Membranous Organelles
– Membrane flow
• A continuous exchange of membrane parts by vesicles:
– all membranous organelles (except mitochondria)
– allow adaptation and change