BIOLOGY 240

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CHAPTER 3

• CELLULAR LEVEL OF ORGANIZATION

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Cell Overview

• Plasma Membrane phospholipid bilayer
• Cytoplasm
• Cytosol intracellular fluid
• Organelles cells organs
• Nucleus contains chromatin

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TYPICAL EUKARYOTIC CELL
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PLASMA MEMBRANEFluid Mosaic Model
ECF
ICF
Figure 3.2
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PLASMA MEMBRANEFluid Mosaic Model

• Plasma membrane is about as viscous as olive oil
• Molecules move freely in two dimensions
• Phospholipids
• Proteins
• Cholesterol
• Glycolipids
• Components naturally reorient themselves when
  disturbed, torn or punctured

Fluid
Mosaic
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PLASMA MEMBRANEStructural Components

• LIPIDS
• 50 lipid molecules for each protein molecule
• PROTEINS

ECF
ICF
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PLASMA MEMBRANEStructural Components

• LIPIDS barrier to exit and entry of most polar
  substances
• Phospholipids 75 of membrane lipids
• Amphipathic having both polar and nonpolar
  regions
• Cholesterol Hydroxyl groups H-bond with polar
  heads of other lipids
• Imparts some rigidity (but too much makes cells
  too stiff)
• Glycolipids on extracellular surface

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Figure 2.18
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PLASMA MEMBRANEStructural Components

• PROTEINS Integral Peripheral
• Integral proteins are amphipathic

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PLASMA MEMBRANE Structural Components

• PROTEINS Integral Peripheral
• Mostly gatekeepers (regulate solute passage)
• Functions
• Channels transmembrane pores
• Transporters facilitate solute crossing
• Receptors bind with specific ligands, initiate
  cellular response

Fig 3.3
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• PROTEINS
• Functions, cont.
• Enzymes embedded for metabolic action on PM
• Identity Markers glycoproteins
• Linkers add strength to cell or cell connection

Fig 3.3
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PLASMA MEMBRANESelective Permeability

• PM permits passage only of select molecules
• Molecules that can pass through the PM
• Nonpolar Uncharged Substances
• O2, other gases, lipids
• Special Case H2O
• Can pass through spaces formed as phospholipids
  move

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PLASMA MEMBRANESelective Permeability

• Molecules that can not pass through the PM
• Polar and/or charged substances
• Ions, glucose, amino acids, some vitamins
• To cross the PM, they rely on other mechanisms
• Channels, transporters, endocytosis/exocytosis

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PLASMA MEMBRANEGradients
Figure 3.4
ECF
ICF
ECF
ICF
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TRANSPORT MECHANISMS Movement Across the Plasma
Membrane

• Passive transport
• No ATP input involved
• Substance moves down its gradient
• Diffusion
• Osmosis
• Facilitated diffusion (requires a transporter
  protein)

• Active transport
• Cellular energy (ATP) input required
• Substance moves up (against) its gradient

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PASSIVE TRANSPORT MECHANISMSDiffusion

• Diffusion
• Simple diffusion through the Phospholipid Bilayer
  
• Diffusion through Protein Channels
• Open channels
• Gated channels (typically for ions flowing down
  electrical gradient)

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Gated Ion Channel
Figure 3.9
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PASSIVE TRANSPORT MECHANISMSDiffusion

• Diffusion
• Simple diffusion
• Diffusion through protein channels
• Facilitated Diffusion - protein changes shape to
  allow molecular access (glucose)

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Figure 3.10
Facilitated Diffusion
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Figure 3.5
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Passive Transport ProcessesFactors Affecting
Diffusion Rate

• Steepness of gradient
• Temperature
• Size of the molecule
• Surface area
• Diffusion distance

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PASSIVE TRANSPORT MECHANISMSOsmosis

• Osmosis Diffusion of water down its own
  concentration gradient

Figure 3.6
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PASSIVE TRANSPORT MECHANISMSOsmosis

• Effects of H2O concentration on cells
• Isotonic solution No effect
• Hypotonic solution (Osmotic) Lysis
• Hypertonic solution Crenation

Figure 3.7
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ACTIVE TRANSPORT MECHANISMS

• Moves molecules against their concentration
  gradient
• Uses transport proteins
• Requires energy
• Two Types
• Primary Active Transport
• Secondary Active Transport

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ACTIVE TRANSPORT MECHANISMS Primary Active
Transport

• Primary Active Transport fueled by ATP
  hydrolysis
• Example Na/K Pump - keeps intracellular
  concentrations of Na low

Figure 3.8
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ACTIVE TRANSPORT MECHANISMS Secondary Active
Transport

• Secondary active transport takes advantage of
  stored (potential) energy of steep ionic
  gradients
• Often Na gradient
• Stored energy is released as Na leaks back into
  the cell (i.e. down its concentration gradient)
• Another substance travels against its own
  gradient by using this released energy
• Takes advantage of Na gradient
• Established by 1E Active Transport
• Symporters vs. Antiporters

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SECONDARY ACTIVE TRANSPORTSymporters vs.
Antiporters
Move in opposite directions
Move in same direction
Figure 3.9
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ACTIVE TRANSPORT MECHANISMSVesicle Transport

• Vesicles small membrane-enclosed sacs
• Two types of vesicle transport
• Exocytosis (substances exit the cell)
• Endocytosis (substances enter the cell)
• Both require ATP ? Active transport

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VESICLE TRANSPORTExocytosis
Exocytosis

• Bulk removal of cellular contents
• Vesicle attaches to inside of PM
• Vesicle bilayer fuses with PM
• Contents are released into interstitial
  fluid/space

http//www.biology.washington.edu/bsa/IonTransport
/exocytosis.html
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VESICLE TRANSPORTEndocytosis

• Intake of substances by the cell
• Invagination of the PM
• Extracellular contents brought into the cell by
  means of vesicle formation
• Specific types
• Pinocytosis (bulk-phase endocytosis)
  endocytosis of extracellular fluid (H20 plus
  solutes)
• Phagocytosis endocytosis of large extracellular
  particles (microbes, debris, dead self cells)
• Receptor-mediated endocytosis endocytosis of
  receptor-specific ligands

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Figure 3.15
Pinocytosis
Figure 3.12
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Figure 3.14
Phagocytosis
Figure 3.11
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Figure 3.13
Receptor- mediated endocytosis
Figure 3.10
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Examples of Ligands for Receptor-Mediated
Endocytosis

• Toxins
• Diptheria Toxin Pseudomonas toxin Cholera
  toxin
• Viruses
• Rous sarcoma virus Semliki forest virus
  Vesicular stomatitis virus Adenovirus
• Serum transport proteins and antibodies
• Transferrin Low density lipoprotein

• Hormones and Growth Factors
• Insulin Epidermal
• Growth Factor Growth Hormone Thyroid
  stimulating hormone Nerve Growth Factor
  Calcitonin Glucagon Prolactin Luteinizing
  Hormone Thyroid hormone Platelet Derived
  Growth Factor Interferon

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Cell Overview

• Plasma Membrane phospholipid bilayer
• Cytoplasm
• Cytosol intracellular fluid
• Organelles cells organs
• Nucleus contains chromatin

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CYTOPLASM

• CYTOSOL
• Liquid component of cytoplasm
• 75-90 Water - depending on cell type
• Other contents various ions molecules
• Many chemical reactions occur here

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CYTOPLASM

• ORGANELLES (Cells organs)
• Intracellular structures with specific purposes
• Possess a recognizable shape
• Membrane bound or non-membrane bound
• Different concentrations in different cells
• Same organelles can make different products in
  different cells

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Figure 3.1
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ORGANELLESCYTOSKELETON

• Fibrous framework of the cell
• Composed of various protein fiber types
• Microfilament - movement/support
• Intermediate filament -support
• Microtubule - movement/transport

Figure 3.16