cell

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Review of normal cellular

structure and function

2

Introduction• The basic organizational structure of the human body is the cell.

• There are 50-100 trillion cells in the human body.

• Differentiation is when cells specialize.

• As a result of differentiation, cells vary in size and shape due to their unique function.

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A Composite Cell

• Also called a ‘typical’ cell• Major parts include:

• Nucleus• contains DNA

• Cytoplasm• cellular contents

between plasma membrane &nucleus

• Cell membrane• selective barrier

Microtubules

Flagellum

Nuclear envelope

Basal body

Chromatin

Ribosomes

Cell membrane

Mitochondrion

Cilia

Microtubules

Microtubule

Centrioles

Microvilli

Lysosomes

Nucleolus

Nucleus

Phospholipid bilayer

SmoothEndoplasmicreticulum

RoughEndoplasmicreticulum


Golgiapparatus

Secretoryvesicles

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Cell Membrane(aka Plasma Membrane)

• Outer limit of the cell• Controls what moves in and out of the cell• Selectively permeable• Phospholipid bilayer

• Water-soluble “heads” form surfaces (hydrophilic)• Water-insoluble “tails” form interior (hydrophobic)• Permeable to lipid-soluble substances

• Cholesterol stabilizes the membrane• Proteins:

• Receptors• Pores, channels and carriers• Enzymes• Self-markers

5

Cell Membrane

Cell membraneCell membrane

(b)(a)

“Heads” ofphospholipid

“Tails” ofphospholipid


a: © Biophoto Associates/Photo Researchers, Inc.

Fibrous proteinCarbohydrateGlycolipidGlycoprotein

Extracellular sideof membrane

Cytoplasmic sideof membrane

Cholesterolmolecules

Globularprotein

Doublelayer ofPhospholipidmolecules

Hydrophobicfatty acid“tail”

HydrophilicPhosphate“head”


Cell MembraneElectrochemical Gradient

• due to selective permeability

• difference in concentration of chemicals across membrane

• difference in distribution of charges across the membrane

• difference is the membrane potential

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Cell Adhesion Molecules (CAMs)

• Guide cells on the move

• Selectin – allows white blood cells to “anchor”

• Integrin – guides white blood cells through capillary walls

• Important for growth ofembryonic tissue

• Important for growth of nerve cells

Adhesion

White blood cell

Integrin

Selectin

Exit

Splinter

Attachment(rolling)

Blood vessellining cell

Carbohydrateson capillary wall

Adhesionreceptor proteins


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Cytoplasm

• Cytosol = water

• Organelles = solids

Cytoplasm is really like a Jello fruit salad where the Jello is the cytosol and the fruits (oranges, grapes, bananas,

maybe walnuts, etc.) are the organelles.

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OrganellesEndoplasmic Reticulum (ER)

• Connected, membrane-bound sacs, canals, and vesicles• Transport system• Rough ER

• Studded with ribosomes• Smooth ER

• Lipid synthesis• Added to proteinsarriving from rough ER

• Break down of drugsRibosomes

• Free floating or connected to ER• Provide structural support and enzyme activityto amino acids to form protein (protein synthesis)

Membranes

Ribosomes

Membranes

(b) (c)


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OrganellesGolgi apparatus• Stack of flattened, membranous sacs• Modifies, packagesand delivers proteins

Vesicles• Membranous sacs• Store substances

Inner membrane

Outer membrane

Cristae

(a) (b)


a: © Bill Longcore/Photo Researchers, Inc.

Mitochondria• Membranous sacs with inner partitions• Generate energy

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Organelles

Lysosomes• Enzyme-containing sacs• Digest worn out cell parts or unwanted substances

Peroxisomes• Enzyme-containing sacs• Break down organic molecules

Centrosome• Two rod-like centrioles• Used to produce cilia and flagella• Distributes chromosomes during cell division

(a) (b)

Centriole(cross-section)

Centriole(longitudinal section)


a: © Don W. Fawcett/Visuals Unlimited

12

Organelles

Cilia• Short hair-like projections• Propel substances on cell surface

Flagellum• Long tail-like projection• Provides motility to sperm

(a)


a: © Oliver Meckes/Photo Researchers, Inc.

© Colin Anderson/Brand X/CORBIS

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Microfilaments and microtubules• Thin rods and tubules• Support cytoplasm• Allows for movement of organelles

Organelles

Inclusions

• Temporary nutrients and pigments

Microtubules

Microfilaments


© M. Schliwa/Visuals Unlimited

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Cell Nucleus

• Is the control center of the cell

• Nuclear envelope• Porous double membrane• Separates nucleoplasm from cytoplasm

• Nucleolus• Dense collection of RNA and proteins• Site of ribosome production

• Chromatin• Fibers of DNA and proteins• Stores information for synthesis of proteins


Nucleus

Nucleolus

Chromatin

(a)

Nuclearpores

Nuclearenvelope

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Movements Into and Out of the Cell

Passive (Physical) Processes

• Require no cellular energy and include:

• Simple diffusion• Facilitated diffusion• Osmosis• Filtration

Active (Physiological) Processes• Require cellular energy and include:

• Active transport• Endocytosis• Exocytosis• Transcytosis

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Simple Diffusion

• Movement of substances from regions of higher concentration to regions of lower concentration• Oxygen, carbon dioxide and lipid-soluble substances

Time

Solute molecule

Water molecule

A B A B

(2) (3)

Permeablemembrane

A B

(1)


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Animation:How Diffusion Works

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Facilitated Diffusion• Diffusion across a membrane with the help of a channel or carrier molecule• Glucose and amino acids

Region of higherconcentration

Transportedsubstance

Region of lowerconcentration

Protein carriermolecule

Cellmembrane


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Animation:How Facilitated Diffusion

Works


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Osmosis• Movement of water through a selectively permeable membrane from regions of higher concentration to regions of lower concentration• Water moves toward a higher concentration of solutes

Time

Protein molecule

Water molecule

A

B

A B

(1) (2)

Selectivelypermeablemembrane


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Animation:How Osmosis Works


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Osmosis and Osmotic Pressure

• Osmotic Pressure – ability of osmosis to generateenough pressure to move a volume of water

• Osmotic pressure increases as the concentrationof nonpermeable solutes increases

• Isotonic – same osmotic pressure• Hypertonic – higher osmotic pressure (water loss)• Hypotonic – lower osmotic pressure (water gain)


© David M. Phillips/Visuals Unlimited

(b)

(a)

(c)

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Filtration

• Smaller molecules are forced through porous membranes• Hydrostatic pressure important in the body• Molecules leaving blood capillaries


Capillary wall

Larger molecules

Smaller molecules

Bloodpressure Blood

flow

Tissue fluid

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Active Transport

• Carrier molecules transport substances across a membrane from regions of lower concentration to regions of higher concentration• Sugars, amino acids, sodium ions, potassium ions, etc.


Carrier protein Binding site

(a)

(b)

Cel

l mem

bra

ne

Carrier proteinwith altered shape

Phospholipidmolecules Transported

particle

Cellularenergy

Region of higherconcentration

Region of lowerconcentration

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Active Transport:Sodium-Potassium Pump

• Active transport mechanism• Creates balance by “pumping” three (3) sodium (Na+) OUT and two (2) potassium (K+) INTO the cell• 3:2 ratio

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Animation:How the Sodium-Potassium

Pump Works


Secondary Active Transport• uses the energy stored in a concentration gradient

– the gradient is established through active transport• symporters move substances in the same direction while

antiporters move substances in opposite directions

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Endocytosis• Cell engulfs a substance by forming a vesicle around the substance• Three types:

• Pinocytosis – substance is mostly water• Phagocytosis – substance is a solid• Receptor-mediated endocytosis – requires the substance to bind to a membrane-bound receptor

Nucleus Nucleolus

Particle VesiclePhagocytizedparticle

Cellmembrane


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Endocytosis

Cytoplasm

Vesicle

(a) (b) (c) (d)

Receptorprotein

Cellmembrane

Moleculesoutside cell

Cellmembraneindenting

Receptor-ligandcombination

Nucleus Nucleolus

Particle VesiclePhagocytizedparticle

Cellmembrane


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Exocytosis• Reverse of endocytosis• Substances in a vesicle fuse with cell membrane• Contents released outside the cell• Release of neurotransmitters from nerve cells

Nucleus

Endoplasmicreticulum

Golgiapparatus


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The Cell Cycle

• Series of changes a cell undergoes from the time it forms until the time it divide• Stages:

• Interphase• Mitosis• Cytokinesis

Apoptosis

G2 phase

Prophase

Metaphase

AnaphaseTelophase

Cytokinesis

Restrictioncheckpoint

Remainspecialized

Proceedto division

S phase:geneticmaterialreplicates

G1 phasecell growth


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Interphase

• Very active period• Cell grows• Cell maintains routine functions• Cell replicates genetic material to prepare for nuclear division• Cell synthesizes new organelles to prepare for cytoplasmic division• Phases:

• G phases – cell grows and synthesizes structures other than DNA• S phase – cell replicates DNA

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Mitosis

• Produces two daughter cells from an original somatic cell• Nucleus divides – karyokinesis• Cytoplasm divides – cytokinesis • Phases of nuclear division:

• Prophase – chromosomes form; nuclear envelope disappears• Metaphase – chromosomes align midway between centrioles• Anaphase – chromosomes separate and move to centrioles• Telophase – chromatin forms; nuclear envelope forms

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Mitosis

Telophase and CytokinesisNuclear envelopes begin toreassemble around two daughternuclei. Chromosomes decondense.Spindle disappears. Division ofthe cytoplasm into two cells.

AnaphaseSister chromatids separate toopposite poles of cell. Eventsbegin which lead to cytokinesis.

MetaphaseChromosomes align alongequator, or metaphase plateof cell.

ProphaseChromosomes condense andbecome visible. Nuclearenvelope and nucleolusdisperse. Spindle apparatusforms.

Late InterphaseCell has passed therestriction checkpointand completed DNAreplication, as well asreplication of centriolesand mitochondria, andsynthesis of extramembrane.

Early Interphaseof daughter cells—a time of normal cellgrowth and function.

Cleavagefurrow

Nuclearenvelopes

Nuclearenvelope

Chromatinfibers

Chromosomes

Spindle fiber

Centromere

Aster

Centrioles

Late prophase

Sisterchromatids

Microtubules

Mitosis

Cytokinesis

S phase

G1 phase

Interphase

Restrictioncheckpoint

(a)

(b)

(c)(d)

(e)


© Ed Reschke

G2 phase

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Animation:Mitosis and Cytokinesis


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Cytoplasmic Division

• Also known as cytokinesis • Begins during anaphase• Continues through telophase• Contractile ring pinches cytoplasm in half

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Animation:Control of the Cell Cycle


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3.5: Control of Cell Division• Cell division capacities vary greatly among cell types

• Skin and blood cells divide often and continually• Neuron cells divide a specific number of times then cease

• Chromosome tips (telomeres) that shorten with each mitosis provide a mitotic clock

• Cells divide to provide a more favorable surface area to volume relationship

• Growth factors and hormones stimulate cell division• Hormones stimulate mitosis of smooth muscle cells in uterus• Epidermal growth factor stimulates growth of new skin

• Tumors are the consequence of a loss of cell cycle control

• Contact (density dependent) inhibition

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Tumors• Two types of tumors:

• Benign – usually remains localized• Malignant – invasive and can metastasize; cancerous

• Two major types of genes cause cancer:

• Oncogenes – activate other genes that increase cell division• Tumor suppressor genes – normally regulate mitosis; if inactivated they are unable to regulate mitosis

• Cells are now known as “immortal”

Normal cells(with hairlike cilia)

Cancer cells


© Tony Brain/Photo Researchers, Inc.;

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Animation:How Tumor Suppressor Genes

Block Cell Division


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3.6: Stem and Progenitor Cells

• Stem cell:• Can divide to form two new stem cells

• Self-renewal• Can divide to form a stem cell and a progenitor cell• Totipotent – can give rise to every cell type• Pluripotent – can give rise to a restricted number of cell types

• Progenitor cell:• Committed cell• Can divide to become any of a restricted number of cells • Pluripotent

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Stem and Progenitor Cells

one or more steps

Sperm

Egg

Fertilizedegg

Stem cell

Stem cell

Progenitor cell

Progenitorcell

Progenitorcell

Blood cells and platelets

Fibroblasts (a connective tissue cells)

Bone cells

Progenitorcell

Astrocyte

Neuron

Skin cell

Sebaceousgland cell

produces another stem cell(self-renewal)

Progenitorcell

Progenitorcell

Progenitorcell

Progenitorcell

Progenitorcell

Progenitorcell


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3.7: Cell Death

Apoptosis:

• Programmed cell death

• Acts as a protective mechanism

• Is a continuous process

cell

Technology

membrane proteins

cell nucleus

membrane difference

cell parts

cell division

cell controls

composite cell

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