Cells and Tissues. Cell Physiology: Membrane Transport Membrane transport—movement of substances...
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Transcript of Cells and Tissues. Cell Physiology: Membrane Transport Membrane transport—movement of substances...
Cells and Tissues
Cell Physiology: Membrane TransportMembrane transport—movement of
substances into and out of the cellTwo basic methods of transport
Passive transportNo energy is required
Active transportCell must provide metabolic energy (ATP)
Solutions and TransportSolution—homogeneous mixture of two or
more componentsSolvent—dissolving medium; typically water
in the bodySolutes—components in smaller quantities
within a solutionIntracellular fluid—nucleoplasm and cytosolInterstitial fluid—fluid on the exterior of the
cell
Selective PermeabilityThe plasma membrane allows some
materials to pass while excluding othersThis permeability influences movement
both into and out of the cell
Passive Transport ProcessesDiffusion
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 ProcessesTypes of diffusion
Simple diffusionAn unassisted processSolutes are lipid-soluble materials or small enough
to pass through membrane pores
Passive Transport Processes
Figure 3.10a
Passive Transport ProcessesTypes of diffusion (continued)
Osmosis—simple diffusion of waterHighly polar water molecules easily cross the
plasma membrane through aquaporins
Passive Transport Processes
Figure 3.10d
Passive Transport ProcessesFacilitated diffusion
Substances require a protein carrier for passive transport
Transports lipid-insoluble and large substances
Passive Transport Processes
Figure 3.10b–c
Passive Transport ProcessesFiltration
Water and solutes are forced through a membrane by fluid, or hydrostatic pressure
A pressure gradient must existSolute-containing fluid is pushed from a high-
pressure area to a lower pressure area
Active Transport ProcessesSubstances are transported that are unable
to pass by diffusion Substances may be too largeSubstances may not be able to dissolve in
the fat core of the membraneSubstances may have to move against a
concentration gradientATP is used for transport
Active Transport ProcessesTwo common forms of active transport
Active transport (solute pumping)Vesicular transport
Exocytosis Endocytosis
PhagocytosisPinocytosis
Active Transport ProcessesActive transport (solute pumping)
Amino acids, some sugars, and ions are transported by protein carriers called solute pumps
ATP energizes protein carriersIn most cases, substances are moved against
concentration gradients
Figure 3.11, step 1
Extracellular fluid
Cytoplasm
Binding of cytoplasmic Na+
to the pump proteinstimulates phosphorylationby ATP, which causes thepump protein to change itsshape.
ADP
Na+
Na+
Na+ P
ATP
Figure 3.11, step 2
Extracellular fluid
Cytoplasm
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.
ADP
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
P
PP
ATP
Figure 3.11, step 3
Extracellular fluid
Cytoplasm
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.
ADP
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
K+
K+
P
PP
ATP
Active Transport ProcessesVesicular transport
ExocytosisMoves materials out of the cellMaterial is carried in a membranous vesicleVesicle migrates to plasma membraneVesicle combines with plasma membraneMaterial is emptied to the outside
Active Transport Processes: Exocytosis
Figure 3.12a
Active Transport Processes: Exocytosis
Figure 3.12b
Active Transport ProcessesVesicular transport (continued)
EndocytosisExtracellular substances are engulfed by being
enclosed in a membranous vescicleTypes of endocytosis
Phagocytosis—“cell eating”Pinocytosis—“cell drinking”
Active Transport Processes: Endocytosis
Figure 3.13a
CytoplasmExtracellularfluid
Extracellularfluid
Plasmamembrane
Plasmamembrane
Ingestedsubstance
Pit
(a)
Active Transport Processes: Endocytosis
CytoplasmExtracellularfluid
Extracellularfluid
Plasmamembrane
Detachmentof vesicle
Vesicle containingingested material
Plasmamembrane
Ingestedsubstance
Pit
(a)
Active Transport Processes: Endocytosis
CytoplasmExtracellularfluid
Extracellularfluid
Plasmamembrane
Detachmentof vesicle
Vesicle containingingested material
Vesicle
Vesicle fusingwith lysosomefor digestion
Lysosome
Plasmamembrane
Ingestedsubstance
Pit
(a)
Active Transport Processes: Endocytosis
CytoplasmExtracellularfluid
Extracellularfluid
Plasmamembrane
Detachmentof vesicle
Vesicle containingingested material
Vesicle
Vesicle fusingwith lysosomefor digestion
Release ofcontents tocytoplasm
Lysosome
Plasmamembrane
Ingestedsubstance
Pit
(a)
Active Transport Processes: Endocytosis
CytoplasmExtracellularfluid
Extracellularfluid
Plasmamembrane
Detachmentof vesicle
Vesicle containingingested material
Vesicle
Vesicle fusingwith lysosomefor digestion
Release ofcontents tocytoplasm
Lysosome
Transport to plasmamembrane andexocytosis ofvesicle contents
Plasmamembrane
Ingestedsubstance
Pit
(a)
Active Transport Processes: Endocytosis
Recycling of membraneand receptors (if present)to plasma membrane
CytoplasmExtracellularfluid
Extracellularfluid
Plasmamembrane
Detachmentof vesicle
Vesicle containingingested material
Vesicle
Vesicle fusingwith lysosomefor digestion
Release ofcontents tocytoplasm
Lysosome
Transport to plasmamembrane andexocytosis ofvesicle contents
Plasmamembrane
Ingestedsubstance
Pit
(a)
Active Transport Processes: Endocytosis
Figure 3.13b–c
Cell Life CycleCells have two major periods
InterphaseCell growsCell carries on metabolic processes
Cell division Cell replicates itselfFunction is to produce more cells for growth and
repair processes
DNA ReplicationGenetic material is duplicated and readies
a cell for division into two cellsOccurs toward the end of interphaseDNA uncoils and each side serves as a
template
DNA Replication
Figure 3.14
Events of Cell DivisionMitosis—division of the nucleus
Results in the formation of two daughter nuclei
Cytokinesis—division of the cytoplasmBegins when mitosis is near completionResults in the formation of two daughter cells
Stages of MitosisProphase
First part of cell divisionCentrioles migrate to the poles to direct
assembly of mitotic spindle fibersDNA appears as double-stranded
chromosomesNuclear envelope breaks down and
disappears
Stages of MitosisMetaphase
Chromosomes are aligned in the center of the cell on the metaphase plate
Stages of MitosisAnaphase
Chromosomes are pulled apart and toward the opposite ends of the cell
Cell begins to elongate
Stages of MitosisTelophase
Chromosomes uncoil to become chromatinNuclear envelope reforms around chromatin Spindles break down and disappear
Stages of MitosisCytokinesis
Begins during late anaphase and completes during telophase
A cleavage furrow forms to pinch the cells into two parts
Stages of Mitosis
Figure 3.15
Centrioles
Plasmamembrane
Interphase Early prophase Late prophase
Nucleolus
Nuclearenvelope
Spindlepole
Chromatin
Centrioles
Formingmitoticspindle
Centromere
Chromosome,consisting of twosister chromatids
Fragments ofnuclear envelope
CentromereSpindlemicrotubules
Metaphase Anaphase Telophase and cytokinesis
Daughterchromosomes
Sisterchromatids
Nuclearenvelopeforming
NucleolusformingSpindle Metaphase
plate
Cleavagefurrow
Stages of Mitosis
Figure 3.15, step 1
Centrioles
Plasmamembrane
Interphase
Nucleolus
Nuclearenvelope
Chromatin
Stages of Mitosis
Figure 3.15, step 2
Centrioles
Plasmamembrane
Interphase Early prophase
Nucleolus
Nuclearenvelope
Chromatin
Centrioles
Formingmitoticspindle
Centromere
Chromosome,consisting of twosister chromatids
Stages of Mitosis
Figure 3.15, step 3
Centrioles
Plasmamembrane
Interphase Early prophase Late prophase
Nucleolus
Nuclearenvelope
Spindlepole
Chromatin
Centrioles
Formingmitoticspindle
Centromere
Chromosome,consisting of twosister chromatids
Fragments ofnuclear envelope
CentromereSpindlemicrotubules
Stages of Mitosis
Figure 3.15, step 4
Metaphase
Sisterchromatids
Spindle Metaphaseplate
Stages of Mitosis
Figure 3.15, step 5
Metaphase Anaphase
Daughterchromosomes
Sisterchromatids
Spindle Metaphaseplate
Stages of Mitosis
Figure 3.15, step 6
Metaphase Anaphase Telophase and cytokinesis
Daughterchromosomes
Sisterchromatids
Nuclearenvelopeforming
Nucleolusforming
Spindle Metaphaseplate
Cleavagefurrow
Stages of Mitosis
Figure 3.15, step 7
Centrioles
Plasmamembrane
Interphase Early prophase Late prophase
Nucleolus
Nuclearenvelope
Spindlepole
Chromatin
Centrioles
Formingmitoticspindle
Centromere
Chromosome,consisting of twosister chromatids
Fragments ofnuclear envelope
CentromereSpindlemicrotubules
Metaphase Anaphase Telophase and cytokinesis
Daughterchromosomes
Sisterchromatids
Nuclearenvelopeforming
NucleolusformingSpindle Metaphase
plate
Cleavagefurrow