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Cells and Tissues. Cell Physiology: Membrane Transport. Membrane transport—movement of substances into and out of the cell Two basic methods of transport Passive transport No energy is required Active transport Cell must provide metabolic energy (ATP). Solutions and Transport.

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Cells and Tissues

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Cells and Tissues


Cell Physiology: Membrane Transport

  • Membrane transport—movement of substances into and out of the cell

  • Two basic methods of transport

    • Passive transport

      • No energy is required

    • Active transport

      • Cell must provide metabolic energy (ATP)


Solutions and Transport

  • Solution—homogeneous mixture of two or more components

    • Solvent—dissolving medium; typically water in the body

    • Solutes—components in smaller quantities within a solution

  • Intracellular fluid—nucleoplasm and cytosol

  • Interstitial fluid—fluid on the exterior of the cell


Selective Permeability

  • The plasma membrane allows some materials to pass while excluding others

  • This permeability influences movement both into and out of the cell


Passive Transport Processes

  • Diffusion

    • Particles tend to distribute themselves evenly within a solution

    • Movement is from high concentration to low concentration, or down a concentration gradient

Figure 3.9


Passive Transport Processes

  • Types of diffusion

    • Simple diffusion

      • An unassisted process

      • Solutes are lipid-soluble materials or small enough to pass through membrane pores


Passive Transport Processes

Figure 3.10a


Passive Transport Processes

  • Types of diffusion (continued)

    • Osmosis—simple diffusion of water

      • Highly polar water molecules easily cross the plasma membrane through aquaporins


Passive Transport Processes

Figure 3.10d


Passive Transport Processes

  • Facilitated diffusion

    • Substances require a protein carrier for passive transport

    • Transports lipid-insoluble and large substances


Passive Transport Processes

Figure 3.10b–c


Passive Transport Processes

  • Filtration

    • Water and solutes are forced through a membrane by fluid, or hydrostatic pressure

    • A pressure gradient must exist

      • Solute-containing fluid is pushed from a high-pressure area to a lower pressure area


Active Transport Processes

  • Substances are transported that are unable to pass by diffusion

    • Substances may be too large

    • Substances may not be able to dissolve in the fat core of the membrane

    • Substances may have to move against a concentration gradient

  • ATP is used for transport


Active Transport Processes

  • Two common forms of active transport

    • Active transport (solute pumping)

    • Vesicular transport

      • Exocytosis

      • Endocytosis

        • Phagocytosis

        • Pinocytosis


Active Transport Processes

  • Active transport (solute pumping)

    • Amino acids, some sugars, and ions are transported by protein carriers called solute pumps

    • ATP energizes protein carriers

    • In most cases, substances are moved against concentration gradients


Extracellular fluid

Na+

K+

Na+

P

Na+

P

Na+

Na+

K+

K+

Na+

P

K+

ATP

ADP

Loss of phosphate restoresthe original conformation ofthe pump protein. K+ isreleased to the cytoplasm andNa+ sites are ready to bind Na+again; the cycle repeats.

Binding of cytoplasmic Na+to the pump proteinstimulates phosphorylationby ATP, which causes thepump protein to change itsshape.

The shape change expelsNa+ to the outside.Extracellular K+ binds,causing release of thephosphate group.

Cytoplasm

Figure 3.11


Extracellular fluid

Na+

Na+

Na+

P

ATP

ADP

Binding of cytoplasmic Na+to the pump proteinstimulates phosphorylationby ATP, which causes thepump protein to change itsshape.

Cytoplasm

Figure 3.11, step 1


Extracellular fluid

Na+

K+

Na+

P

Na+

P

Na+

Na+

K+

Na+

P

ATP

ADP

Binding of cytoplasmic Na+to the pump proteinstimulates phosphorylationby ATP, which causes thepump protein to change itsshape.

The shape change expelsNa+ to the outside.Extracellular K+ binds,causing release of thephosphate group.

Cytoplasm

Figure 3.11, step 2


Extracellular fluid

Na+

K+

Na+

P

Na+

P

Na+

Na+

K+

K+

Na+

P

K+

ATP

ADP

Loss of phosphate restoresthe original conformation ofthe pump protein. K+ isreleased to the cytoplasm andNa+ sites are ready to bind Na+again; the cycle repeats.

Binding of cytoplasmic Na+to the pump proteinstimulates phosphorylationby ATP, which causes thepump protein to change itsshape.

The shape change expelsNa+ to the outside.Extracellular K+ binds,causing release of thephosphate group.

Cytoplasm

Figure 3.11, step 3


Active Transport Processes

  • Vesicular transport

    • Exocytosis

      • Moves materials out of the cell

      • Material is carried in a membranous vesicle

      • Vesicle migrates to plasma membrane

      • Vesicle combines with plasma membrane

      • Material is emptied to the outside


Active Transport Processes: Exocytosis

Figure 3.12a


Active Transport Processes: Exocytosis

Figure 3.12b


Active Transport Processes

  • Vesicular transport (continued)

    • Endocytosis

      • Extracellular substances are engulfed by being enclosed in a membranous vescicle

    • Types of endocytosis

      • Phagocytosis—“cell eating”

      • Pinocytosis—“cell drinking”


Extracellularfluid

Extracellularfluid

Cytoplasm

Plasmamembrane

Pit

Recycling of membraneand receptors (if present)to plasma membrane

Transport to plasmamembrane andexocytosis ofvesicle contents

Ingestedsubstance

Vesicle

Lysosome

Detachmentof vesicle

Release ofcontents tocytoplasm

Vesicle containingingested material

Plasmamembrane

Vesicle fusingwith lysosomefor digestion

(a)

Active Transport Processes: Endocytosis

Figure 3.13a


Extracellularfluid

Extracellularfluid

Plasmamembrane

Cytoplasm

Pit

Ingestedsubstance

Plasmamembrane

(a)

Active Transport Processes: Endocytosis

Figure 3.13a, step 1


Extracellularfluid

Extracellularfluid

Plasmamembrane

Cytoplasm

Pit

Ingestedsubstance

Detachmentof vesicle

Vesicle containingingested material

Plasmamembrane

(a)

Active Transport Processes: Endocytosis

Figure 3.13a, step 2


Extracellularfluid

Extracellularfluid

Plasmamembrane

Cytoplasm

Pit

Ingestedsubstance

Vesicle

Lysosome

Detachmentof vesicle

Vesicle containingingested material

Plasmamembrane

Vesicle fusingwith lysosomefor digestion

(a)

Active Transport Processes: Endocytosis

Figure 3.13a, step 3


Extracellularfluid

Extracellularfluid

Plasmamembrane

Cytoplasm

Pit

Ingestedsubstance

Vesicle

Lysosome

Detachmentof vesicle

Release ofcontents tocytoplasm

Vesicle containingingested material

Plasmamembrane

Vesicle fusingwith lysosomefor digestion

(a)

Active Transport Processes: Endocytosis

Figure 3.13a, step 4


Extracellularfluid

Extracellularfluid

Plasmamembrane

Cytoplasm

Pit

Transport to plasmamembrane andexocytosis ofvesicle contents

Ingestedsubstance

Vesicle

Lysosome

Detachmentof vesicle

Release ofcontents tocytoplasm

Vesicle containingingested material

Plasmamembrane

Vesicle fusingwith lysosomefor digestion

(a)

Active Transport Processes: Endocytosis

Figure 3.13a, step 5


Extracellularfluid

Extracellularfluid

Plasmamembrane

Cytoplasm

Pit

Recycling of membraneand receptors (if present)to plasma membrane

Transport to plasmamembrane andexocytosis ofvesicle contents

Ingestedsubstance

Vesicle

Lysosome

Detachmentof vesicle

Release ofcontents tocytoplasm

Vesicle containingingested material

Plasmamembrane

Vesicle fusingwith lysosomefor digestion

(a)

Active Transport Processes: Endocytosis

Figure 3.13a, step 6


Active Transport Processes: Endocytosis

Figure 3.13b–c


Active Transport Processes


Cell Life Cycle

  • Cells have two major periods

    • Interphase

      • Cell grows

      • Cell carries on metabolic processes

    • Cell division

      • Cell replicates itself

      • Function is to produce more cells for growth and repair processes


DNA Replication

  • Genetic material is duplicated and readies a cell for division into two cells

  • Occurs toward the end of interphase

  • DNA uncoils and each side serves as a template


DNA Replication

Figure 3.14


Events of Cell Division

  • Mitosis—division of the nucleus

    • Results in the formation of two daughter nuclei

  • Cytokinesis—division of the cytoplasm

    • Begins when mitosis is near completion

    • Results in the formation of two daughter cells


Stages of Mitosis

  • Prophase

    • First part of cell division

    • Centrioles migrate to the poles to direct assembly of mitotic spindle fibers

    • DNA appears as double-stranded chromosomes

    • Nuclear envelope breaks down and disappears


Stages of Mitosis

  • Metaphase

    • Chromosomes are aligned in the center of the cell on the metaphase plate


Stages of Mitosis

  • Anaphase

    • Chromosomes are pulled apart and toward the opposite ends of the cell

    • Cell begins to elongate


Stages of Mitosis

  • Telophase

    • Chromosomes uncoil to become chromatin

    • Nuclear envelope reforms around chromatin

    • Spindles break down and disappear


Stages of Mitosis

  • Cytokinesis

    • Begins during late anaphase and completes during telophase

    • A cleavage furrow forms to pinch the cells into two parts


Centrioles

Spindlemicrotubules

Centrioles

Chromatin

Centromere

Centromere

Formingmitoticspindle

Plasmamembrane

Chromosome,consisting of twosister chromatids

Fragments ofnuclear envelope

Spindlepole

Nuclearenvelope

Nucleolus

Early prophase

Interphase

Late prophase

Nucleolusforming

Metaphaseplate

Spindle

Cleavagefurrow

Nuclearenvelopeforming

Sisterchromatids

Daughterchromosomes

Telophase and cytokinesis

Metaphase

Anaphase

Stages of Mitosis

Figure 3.15


Centrioles

Chromatin

Plasmamembrane

Nuclearenvelope

Nucleolus

Interphase

Stages of Mitosis

Figure 3.15, step 1


Centrioles

Centrioles

Chromatin

Centromere

Formingmitoticspindle

Plasmamembrane

Chromosome,consisting of twosister chromatids

Nuclearenvelope

Nucleolus

Interphase

Early prophase

Stages of Mitosis

Figure 3.15, step 2


Centrioles

Spindlemicrotubules

Centrioles

Chromatin

Centromere

Centromere

Formingmitoticspindle

Plasmamembrane

Chromosome,consisting of twosister chromatids

Fragments ofnuclear envelope

Spindlepole

Nuclearenvelope

Nucleolus

Interphase

Early prophase

Late prophase

Stages of Mitosis

Figure 3.15, step 3


Metaphaseplate

Spindle

Sisterchromatids

Metaphase

Stages of Mitosis

Figure 3.15, step 4


Metaphaseplate

Spindle

Daughterchromosomes

Sisterchromatids

Metaphase

Anaphase

Stages of Mitosis

Figure 3.15, step 5


Nucleolusforming

Metaphaseplate

Spindle

Cleavagefurrow

Nuclearenvelopeforming

Daughterchromosomes

Sisterchromatids

Metaphase

Anaphase

Telophase and cytokinesis

Stages of Mitosis

Figure 3.15, step 6


Centrioles

Spindlemicrotubules

Centrioles

Chromatin

Centromere

Centromere

Formingmitoticspindle

Plasmamembrane

Chromosome,consisting of twosister chromatids

Fragments ofnuclear envelope

Spindlepole

Nuclearenvelope

Nucleolus

Early prophase

Interphase

Late prophase

Nucleolusforming

Metaphaseplate

Spindle

Cleavagefurrow

Nuclearenvelopeforming

Sisterchromatids

Daughterchromosomes

Telophase and cytokinesis

Metaphase

Anaphase

Stages of Mitosis

Figure 3.15, step 7


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