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