Essentials of Anatomy and PhysiologyEssentials of Anatomy and PhysiologyFifth editionFifth edition

Seeley, Stephens and TateSeeley, Stephens and Tate

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Chapter 3: Cell Structures and their Functions

Selective PermeabilitySelective Permeability

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Membrane permeability is ‘selective’

Some materials pass while others are excluded

Permeability includes movement into the cell and out of the cell

Cellular Physiology:Cellular Physiology:Membrane TransportMembrane Transport

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Membrane Transport – movement of substance into and out of the cell

Transport is by two basic methods Passive transport

No energy (ATP) is required

Active transport

The cell must provide ATP

Solutions and TransportSolutions and Transport

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Solution – homogeneous mixture of two or more components

Solvent – dissolving medium (fluid, usually water)

Solutes – components in smaller quantities within a solution (“dissolved particles”)

Solutions and TransportSolutions and Transport

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In living systems:

Intracellular fluid – nucleoplasm and cytosol (cytoplasm)

Interstitial fluid – fluid on the exterior of the cell interstitial = “in spaces” or…

extracellular = “outside cells”

Passive Transport ProcessesPassive Transport Processes

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Diffusion Particles tend to distribute themselves

evenly within a solution Movement is

from high concentration to low concentration, or down a concentration gradient

Figure 3.8

Passive Transport ProcessesPassive Transport Processes

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Types of diffusion

Simple diffusion

Unassisted process

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

Passive Transport ProcessesPassive Transport Processes

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Types of diffusion, con’t.

Osmosis – simple diffusion of water

Highly polar water easily crosses

Movement of water depends on solute concentrations

“more concentrated” solutions attract water (“salt draws water”)

Passive Transport ProcessesPassive Transport Processes

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Types of diffusion, con’t.

Facilitated diffusion

Substances require a protein carrier for passive transport

Example: glucose movement into cells

Diffusion through the Plasma Diffusion through the Plasma MembraneMembrane

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Figure 3.9

Passive Transport ProcessesPassive Transport Processes

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Filtration

Water and solutes are forced through a membrane by hydrostatic pressure

A pressure gradient must exist

Solute-containing fluid moves from a high pressure area to a lower pressure area

Active Transport ProcessesActive Transport Processes

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Moves substances that are unable to pass by diffusion because…

They may be too large

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

They may have to move against a concentration gradient

Active Transport ProcessesActive Transport Processes

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Two types of active transport:

Solute pumping

Amino acids, some sugars and ions are transported

ATP moves substances against concentration gradients

Active Transport ProcessesActive Transport Processes

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Figure 3.10

Active Transport ProcessesActive Transport Processes

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Bulk transport Exocytosis

Moves materials out of the cell

Material is carried in a membranous vesicle

Vesicle migrates to plasma membrane

Vesicle fuses with plasma membrane

Material is emptied to the outside

Active Transport ProcessesActive Transport Processes

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Figure 3.11

Active Transport ProcessesActive Transport Processes

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Bulk transport

Endocytosis

Extracellular substances are engulfed by being enclosed in a membranous vesicle

Material is moved into the cell for “processing”

Active Transport ProcessesActive Transport Processes

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Types of endocytosis

Phagocytosis – cell eating

Pinocytosis – cell drinking

Active Transport ProcessesActive Transport Processes

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Figure 3.12

Phagocytosis

Pinocytosis

Cell Life CycleCell Life Cycle

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Cycle has two major periods

Interphase

Cell grows

Cell carries on metabolic processes

DNA replicates

Cell Life CycleCell Life Cycle

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Cell Division

Cell replicates itself

Function is to produce more cells for growth and repair processes

Cell Life CycleCell Life Cycle

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Interphase

Longest phase

Averages 96% of cell life cycle

Cell “does” what it is specialized to do

Toward end, DNA replicates

Cell prepares for division

DNA ReplicationDNA Replication

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Genetic material duplicates

Occurs toward end of interphase

DNA uncoils, each strand serves as a template for a new strand

Requires enzymes and ATP

Figure 3.13

DNA ReplicationDNA Replication

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Utilizes stored nucleotides

From nucleolus

Enzymes are used to add complementary DNA nucleotides

A=T

C=G

Figure 3.13

DNA ReplicationDNA Replication

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Produces two identical strands of DNA

Half of each is from the “parent” strand

Half of each is “new” DNA

Called “semiconservative” replication

Figure 3.13

Events of Cell DivisionEvents of Cell Division

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Mitosis Division of the nuclear material

Results in the formation of two daughter nuclei Identical to parent nucleus

Identical to each other

Events of Cell DivisionEvents of Cell Division

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Cytokinesis Division of the cytoplasm

Begins when mitosis is near completion

Results in the formation of two daughter cells

Stages of MitosisStages of Mitosis

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Interphase

No cell division occurs

The cell carries out normal metabolic activity and growth

Long, complex phase

Toward end, DNA replicates

Stages of Mitosis: InterphaseStages of Mitosis: Interphase

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Figure 3.14; 1

Stages of MitosisStages of Mitosis

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Prophase

First part of cell division

Centrioles migrate to the poles

Nuclear membrane, nucleolus “disappear”

Chromosomes become visible

Stages of Mitosis: ProphaseStages of Mitosis: Prophase

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Figure 3.14; 1

Stages of MitosisStages of Mitosis

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Metaphase

Spindles attach to chromosomes

Chromosomes align around “equator” of the cell

Stages of Mitosis: MetaphaseStages of Mitosis: Metaphase

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Figure 3.14; 2

Sister Chromatids

Stages of MitosisStages of Mitosis

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Anaphase

Daughter chromosomes are pulled toward the poles

By spindle fibers

The cell begins to elongate

Stages of Mitosis: AnaphaseStages of Mitosis: Anaphase

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Figure 3.14; 2

Stages of MitosisStages of Mitosis

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Telophase

Daughter nuclei begin forming

A cleavage furrow (for cell division) begins to form

Stages of Mitosis: TelophaseStages of Mitosis: Telophase

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Figure 3.14; 2

Cell Life CycleCell Life Cycle

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Cytokinesis

Division of the cytoplasm and organelles

Functions to distribute material to new daughter cells

Each receives ~1/2 the “stuff”

Cell can now begin to grow and function