Cells Cells

August 28August 28thth, 2007, 2007

Cell HistoryCell History• Robert Hooke (1635-Robert Hooke (1635-

1703)1703)

• Viewed slices of cork Viewed slices of cork under a crude under a crude compound compound microscopemicroscope

• He saw boxes which He saw boxes which reminded him of cells reminded him of cells that monks lived inthat monks lived in– Hence the name “cell”Hence the name “cell”

Cell HistoryCell History

• Anton van Leeuwenhoek Anton van Leeuwenhoek (1632-1723)(1632-1723)

• Designed an early Designed an early microscopemicroscope

• First to see living First to see living organisms in a drop of organisms in a drop of waterwater

Cell HistoryCell History

• Robert Brown (1773-1858)Robert Brown (1773-1858)

• Used special stains and Used special stains and dye to view nucleusdye to view nucleus

Cell HistoryCell History

Mathias Schleiden, Mathias Schleiden, botanist (1804-1881)botanist (1804-1881)

Theodor Schwann, Theodor Schwann, zoologist, (1810-zoologist, (1810-1882)1882)

Rudolph Rudolph Virchow, Virchow, physician (1821-physician (1821-1902)1902)

Cell TheoryCell Theory

• Schleiden, Schwann and Virchow Schleiden, Schwann and Virchow each contributed to the cell theory each contributed to the cell theory (1838-1839):(1838-1839):

1.1. Cells are the basic unit of structure Cells are the basic unit of structure and function of all living thingsand function of all living things

2.2. All living things are composed of one All living things are composed of one or more cellsor more cells

3.3. New cells are produced from existing New cells are produced from existing cellscells

Cell TypesCell Types• ProkaryoticProkaryotic

– First appear in fossil First appear in fossil record 3.5 BYArecord 3.5 BYA

– No membrane bound No membrane bound organellesorganelles

– No NucleusNo Nucleus– BacteriaBacteria

• EukaryoticEukaryotic– Evolved 1.5 BYAEvolved 1.5 BYA– Have membrane bound Have membrane bound

organellesorganelles– Have NucleusHave Nucleus– Protists, fungi, animals, Protists, fungi, animals,

plantsplants

Cell StructuresCell Structures• Cell Membrane Cell Membrane

(AKA: Plasma Membrane)(AKA: Plasma Membrane)– Selectively permeable Selectively permeable

• Regulates what goes in Regulates what goes in and outand out

– FlexibleFlexible– Provides protection Provides protection

and supportand support– Made of a lipid bilayerMade of a lipid bilayer

PhospholipidsPhospholipids• Fatty acid tails are Fatty acid tails are

non-polarnon-polar

• Heads are polarHeads are polar

• Tails don’t want to Tails don’t want to be near water be near water because water is because water is polar so they are polar so they are inside the bilayer.inside the bilayer.

Cell MembraneCell Membrane

• Lipid BilayerLipid Bilayer

Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel

Lipid bilayer

Carbohydratechains

Cellular TransportationCellular Transportation

The cell membrane is selectively The cell membrane is selectively permeable and allows some particles permeable and allows some particles come into the cell and keeps some of come into the cell and keeps some of

them out.them out.

2 Types of Transportation2 Types of Transportation

Passive TransportPassive Transport * The cell does not * The cell does not

use any energy.use any energy.

** Materials flow Materials flow down the down the concentration concentration gradient from gradient from High High concentration to concentration to low concentrationlow concentration

Active TransportActive Transport* Requires that the * Requires that the

cell use energy.cell use energy.

* Movement of * Movement of solutes against a solutes against a concentration concentration gradient from gradient from Low Low concentration to concentration to High High concentration.concentration.

The 3 most common The 3 most common types of types of Passive Transport: Passive Transport:

1. Diffusion 1. Diffusion

2. Osmosis2. Osmosis

3. Facilitated Diffusion3. Facilitated Diffusion

DiffusionDiffusion • The overall direction of the movement The overall direction of the movement

is referred to as the is referred to as the GradientGradient. .

• In diffusion molecules usually move In diffusion molecules usually move “down the concentration gradient”..... “down the concentration gradient”..... flow from high concentration to low flow from high concentration to low concentration. concentration.

• A state of “A state of “equilibriumequilibrium”” is reached is reached where molecules are uniformly where molecules are uniformly distributed but continue to move distributed but continue to move randomly.randomly.

Simple DiffusionSimple Diffusion

High Concentration Low Concentration

Direction of Diffusion

Molecules

Selectively Permeable Membrane

OsmosisOsmosis•The diffusion of The diffusion of WATERWATER across across

a selectively permeable a selectively permeable membrane is called OSMOSIS. membrane is called OSMOSIS.

•Osmotic environments are Osmotic environments are classified by the concentration classified by the concentration of the solutes in the solution.of the solutes in the solution.

Osmotic Osmotic environments are environments are classified as:classified as:

1. Isotonic1. Isotonic

2. Hypertonic 2. Hypertonic

3. Hypotonic3. Hypotonic

Isotonic Isotonic EnvironmentEnvironment• In an In an Isotonic solutionIsotonic solution, the concentration of , the concentration of

solutes outside and inside the cell are equal. solutes outside and inside the cell are equal.

• Water is moving in and out at an equal rate.Water is moving in and out at an equal rate.

95% Water

5% Solutes95% Water

5% Solutes

Hypertonic EnvironmentHypertonic Environment

• Concentration of solutes is greater outside Concentration of solutes is greater outside the cell than inside the cell.the cell than inside the cell.

• Water will move outside the cell… the cell Water will move outside the cell… the cell will shrink and die.will shrink and die.

95% Water

5% solute

97% Water

3% solute

Hypotonic EnvironmentHypotonic Environment

• Concentration of solutes is greater inside Concentration of solutes is greater inside the cell than outside the cell.the cell than outside the cell.

• Water will move inside the cell… the cell Water will move inside the cell… the cell will swell, or burst, and die.will swell, or burst, and die.

97% Water

3% solute

95% Water

5% solute

Facilitated DiffusionFacilitated Diffusion• The The diffusiondiffusion of large particles of large particles through through

channel proteinschannel proteins in the plasma membrane. in the plasma membrane.• Example:Example: Glucose moves in and out of Glucose moves in and out of

cells through cells through Facilitated DiffusionFacilitated Diffusion..

Active TransportActive Transport*Solutes flow against the concentration *Solutes flow against the concentration gradient.gradient. * The cell uses energy… usually ATP. * The cell uses energy… usually ATP.*Requires Transport Proteins*Requires Transport Proteins

Types of Active Transport are:Types of Active Transport are:

1. Exocytosis1. Exocytosis2. Endocytosis2. Endocytosis

(Phagocytosis & Pinocytosis)(Phagocytosis & Pinocytosis)

ExocytosisExocytosis (exo = outside, Cyto = cell)(exo = outside, Cyto = cell)Moving substances outside the cellMoving substances outside the cell

Process of vesicles fusing with the plasma Process of vesicles fusing with the plasma membrane and releasing their content to membrane and releasing their content to

the outside of the cell.the outside of the cell.

EndocytosisEndocytosis (endo = inside, cyto = cell)(endo = inside, cyto = cell)

The capture of substances The capture of substances outside the cell when the outside the cell when the plasma membrane merges plasma membrane merges

to engulf it.to engulf it.

PhagocytosisPhagocytosis (phago = to eat, cyto = cell)(phago = to eat, cyto = cell) Phagocytosis occurs when undissolved solids enter a cell.

•The plasma membrane wraps around the solid material and engulfs it, forming a vesicle.

•Phagocytic cells, such as white blood cells, attack and engulf bacteria in this manner.

PinocytosisPinocytosis (pino = to drink, cyto = cell)(pino = to drink, cyto = cell)

Pinocytosis occurs when dissolved materials enter a

cell.

•The plasma membrane folds inward to form a channel allowing the liquid to enter.

• The plasma membrane closes off the channel, encircling the liquid inside a vesicle.

Cell StructuresCell StructuresThe cytoplasm is a jelly-like substance that holds many other The cytoplasm is a jelly-like substance that holds many other

organelles such as:organelles such as:

• Endoplasmic Reticulum – transports lipids and proteinsEndoplasmic Reticulum – transports lipids and proteins

• Ribosomes – produce proteinsRibosomes – produce proteins

• Golgi Apparatus – packages and delivers proteinsGolgi Apparatus – packages and delivers proteins

• Mitochondria – Transform energy into a chemical form that Mitochondria – Transform energy into a chemical form that can be used by the cell.can be used by the cell.

• Lysosomes – Help with cell digestionLysosomes – Help with cell digestion

• Peroxisomes – House enzymes that speed up chemical Peroxisomes – House enzymes that speed up chemical reactions. reactions.

Cell Structures Cell Structures (cont.)(cont.)

• Microfilaments/Microtubules – form Microfilaments/Microtubules – form cytoskeleton to help with cell movement.cytoskeleton to help with cell movement.

• Centrosome – Contains centrioles that help Centrosome – Contains centrioles that help during Mitosis.during Mitosis.

• Cilia/Flagella – Cellular extensions that aid in Cilia/Flagella – Cellular extensions that aid in cell movement.cell movement.

• Vesicles – sacs that form to help particles come Vesicles – sacs that form to help particles come into and out of the cell.into and out of the cell.

Why are cells so small?Why are cells so small?

•Surface Area vs. VolumeSurface Area vs. Volume– As a cell grows larger, the volume As a cell grows larger, the volume

increases faster than the SAincreases faster than the SA– A bigger cell needs more A bigger cell needs more

nutrients, but has relatively less nutrients, but has relatively less SA to take in those nutrientsSA to take in those nutrients

Surface Area vs. VolumeSurface Area vs. Volume

Cell SizeCell Size 5 cm5 cm 10 cm10 cm

Surface Surface Area Area (l×w×6)(l×w×6)

150 cm150 cm22 600 cm600 cm22

Volume Volume (l×w×h)(l×w×h)

125 cm125 cm33 1000 cm1000 cm33

SA to SA to Volume Volume RatioRatio

150/125 150/125 = 6:5= 6:5

600/1000 600/1000 = 6:10= 6:10

Cell CycleCell Cycle

• Cells divide before growing too largeCells divide before growing too large• Before dividing, cells must prepareBefore dividing, cells must prepare• Preparation = InterphasePreparation = Interphase

– GG11 phase: Cell grows larger phase: Cell grows larger– S phase: Cell makes new DNA for S phase: Cell makes new DNA for

daughter celldaughter cell– GG2 2 phase: Cell makes new organelles for phase: Cell makes new organelles for

daughter celldaughter cell

Cell CycleCell Cycle

ChromosomesChromosomes

• Each chromosome is Each chromosome is replicated during the S replicated during the S phasephase

• A replicated A replicated chromosome has two chromosome has two identical sister identical sister chromatids connected chromatids connected by a centromereby a centromere

CentromereCentromere

Sister ChromatidsSister Chromatids

MitosisMitosis

• Four Stages:Four Stages:– PProphase (pro- means first)rophase (pro- means first)– MMetaphase (meta- means middle/after)etaphase (meta- means middle/after)– AAnaphase (ana- means apart)naphase (ana- means apart)– TTelophase (telo- means far away/end)elophase (telo- means far away/end)

ProphaseProphase

• Chromatin condenses Chromatin condenses into chromosomesinto chromosomes

• Nuclear envelope and Nuclear envelope and nucleolus disintegratenucleolus disintegrate

• Centrioles migrate to Centrioles migrate to opposite ends of the opposite ends of the cell cell

• Spindle fibers form in Spindle fibers form in foot ball shape across foot ball shape across cellcell Chromosomes

condensing

ProphaseProphase

MetaphaseMetaphase

• Chromosomes Chromosomes line up in the line up in the middle (equator) middle (equator) of the cellof the cell

• Spindle fibers Spindle fibers attach to attach to centromerescentromeres

Metaphase

Metaphase

AnaphaseAnaphase

• Sister chromatids Sister chromatids separateseparate

• Spindle fibers shorten, Spindle fibers shorten, pulling chromatids to pulling chromatids to opposite ends of cellopposite ends of cell

• Animal cells begin to Animal cells begin to pinch inpinch in

• Plant cells begin to Plant cells begin to form cell plate in the form cell plate in the middlemiddle

AnaphaseAnaphase

TelophaseTelophase

• Nuclear membrane Nuclear membrane built from ER built from ER around each set of around each set of chromosomeschromosomes

• Nucleolus reforms Nucleolus reforms in each nucleusin each nucleus

• Chromosomes Chromosomes become mass of become mass of chromatinchromatin

TelophasTelophasee

Two cells dividing into four

CytokinesisCytokinesis

• Final division of cytoplasm resulting Final division of cytoplasm resulting in two daughter cellsin two daughter cells

• Animals – Cell Membrane pinches Animals – Cell Membrane pinches togethertogether

• Plants – Cell plate forms new Cell Plants – Cell plate forms new Cell Membrane dividing into the daughter Membrane dividing into the daughter cellscells

Which phases can you see?Which phases can you see?

ProphaseMetaphase

Anaphase

TelophaseInterphase

Knowing when to divideKnowing when to divide

• CyclinsCyclins– Protein that regulates the cell cycle in Protein that regulates the cell cycle in

eukaryoteseukaryotes

• Internal regulators – tell the cell Internal regulators – tell the cell when to enter mitosiswhen to enter mitosis

• External regulators – control the rate External regulators – control the rate of the cell cycleof the cell cycle

Cellular Response to InjuryCellular Response to Injury

Effect of CyclinsEffect of Cyclins

Cytoplasm isremoved fromcell in mitosis

Cytoplasm is injectedinto a second cell in G2 phase

Second cell enters mitosis

CancerCancer

• Cancer results when cells do not Cancer results when cells do not respond to cell cycle regulatorsrespond to cell cycle regulators

• Cells grow unregulated, forming a Cells grow unregulated, forming a tumortumor

• Tumor damages surrounding tissueTumor damages surrounding tissue

Leukemia – Blood cancerLeukemia – Blood cancer

Mammary (Breast) CancerMammary (Breast) Cancer

Skin CancerSkin Cancer