CellsCells

The Units of LifeThe Units of Life

Mid 1600s - Robert Hooke observed Mid 1600s - Robert Hooke observed

and described cells in corkand described cells in cork

Late 1600s - Antony van Leeuwenhoek Late 1600s - Antony van Leeuwenhoek

observed sperm, microorganismsobserved sperm, microorganisms

1820s - Robert Brown observed and 1820s - Robert Brown observed and

named nucleus in plant cellsnamed nucleus in plant cells

Early DiscoveriesEarly Discoveries

Cell TheoryCell Theory

Schleiden and SchwannSchleiden and Schwann Every organism is composed of one or more Every organism is composed of one or more

cellscells

Cell is smallest unit having properties of lifeCell is smallest unit having properties of life

VirchowVirchow All exisiting cells arise from pre-existing All exisiting cells arise from pre-existing

cells.cells.

Smallest unit of lifeSmallest unit of life

Can survive on its own or has Can survive on its own or has

potential to do sopotential to do so

Is highly organized for metabolismIs highly organized for metabolism

Senses and responds to environmentSenses and responds to environment

Has potential to reproduceHas potential to reproduce

CellCell

Measuring Measuring

Cells Vary in SizeCells Vary in Size

Why Are Cells So Small?Why Are Cells So Small?

Surface-to-volume ratioSurface-to-volume ratio

The bigger a cell is, the less surface The bigger a cell is, the less surface

area there is per unit volumearea there is per unit volume

Above a certain size, material cannot be Above a certain size, material cannot be

moved in or out of cell fast enoughmoved in or out of cell fast enough

Size is Limited Size is Limited

Create detailed images of something Create detailed images of something

that is otherwise too small to seethat is otherwise too small to see

Light microscopesLight microscopes Simple or compoundSimple or compound

Electron microscopesElectron microscopes Transmission EM or Scanning EMTransmission EM or Scanning EM

Ways to Study Cells:Ways to Study Cells:MicroscopesMicroscopes

Different Types of Light Microscopy: A Different Types of Light Microscopy: A ComparisonComparison

Limitations of Light Limitations of Light MicroscopyMicroscopy

Wavelengths of light are 400-750 nmWavelengths of light are 400-750 nm

If a structure is less than one-half of a If a structure is less than one-half of a wavelength long, it will not be visiblewavelength long, it will not be visible

Light microscopes can resolve objects Light microscopes can resolve objects down to about 200 nm in sizedown to about 200 nm in size

Electron MicroscopyElectron Microscopy

Uses streams of accelerated Uses streams of accelerated electrons rather than lightelectrons rather than light

Electrons are focused by magnets Electrons are focused by magnets rather than glass lensesrather than glass lenses

Can resolve structures down to 0.5 Can resolve structures down to 0.5 nm nm

Elecrton MicroscopesElecrton Microscopes

Electron micrographsElectron micrographs

Ways to Study Cells:Ways to Study Cells:Cell FractionationCell Fractionation

Structure of CellsStructure of Cells

Two types of cellsTwo types of cells ProkaryoticProkaryotic EukaryoticEukaryotic

All cells have:All cells have: Plasma membrane Plasma membrane Region where DNA is storedRegion where DNA is stored Cytoplasm Cytoplasm

Prokaryotic CellsProkaryotic Cells No nucleusNo nucleus

Nucleoid area where DNA residesNucleoid area where DNA resides No membrane bound organelles.No membrane bound organelles. 70s ribosomes70s ribosomes Cell walls contain petidoglycan or Cell walls contain petidoglycan or

pseudomureinpseudomurein Prokaryotic OrganismsProkaryotic Organisms

ArchaeobacteriaArchaeobacteria EubacteriaEubacteria CyanobacteriaCyanobacteria

A prokaryotic cellA prokaryotic cell

E. coliE. coli

Eukaryotic CellsEukaryotic Cells

Have a nucleus and Have a nucleus and other organellesother organelles

Eukaryotic organismsEukaryotic organisms ProtistansProtistans Fungi Fungi PlantsPlants AnimalsAnimals

Overview of an animal cellOverview of an animal cell

The nucleus and its envelope The nucleus and its envelope 

Keeps the DNA molecules of Keeps the DNA molecules of eukaryotic cells separated from eukaryotic cells separated from metabolic machinery of cytoplasmmetabolic machinery of cytoplasm

Makes it easier to organize DNA and Makes it easier to organize DNA and to copy it before parent cells divide to copy it before parent cells divide into daughter cells into daughter cells

Functions of NucleusFunctions of Nucleus

Group of related organelles in which lipids Group of related organelles in which lipids are assembled and new polypeptide are assembled and new polypeptide chains are modifiedchains are modified

Products are sorted and shipped to various Products are sorted and shipped to various destinationsdestinations

Components of the cytomembrane systemComponents of the cytomembrane system Endoplasmic reticulumEndoplasmic reticulum Golgi apparatusGolgi apparatus vesiclesvesicles

Cytomembrane SystemCytomembrane System

Endoplasmic ReticulumEndoplasmic Reticulum

In animal cells, continuous with In animal cells, continuous with

nuclear membranenuclear membrane

Extends throughout cytoplasmExtends throughout cytoplasm

Two regions - rough and smoothTwo regions - rough and smooth

Rough ERRough ER

Arranged into flattened sacsArranged into flattened sacs Ribosomes on surface give it a rough Ribosomes on surface give it a rough

appearanceappearance Some polypeptide chains enter rough Some polypeptide chains enter rough

ER and are modifiedER and are modified Cells that specialize in secreting Cells that specialize in secreting

proteins have lots of rough ERproteins have lots of rough ER

Smooth ERSmooth ER

A series of interconnected tubules A series of interconnected tubules No ribosomes on surfaceNo ribosomes on surface Lipids assembled inside tubulesLipids assembled inside tubules Smooth ER of liver inactivates Smooth ER of liver inactivates

wastes, drugswastes, drugs Sarcoplasmic reticulum of muscle is Sarcoplasmic reticulum of muscle is

a specialized forma specialized form

Endoplasmic reticulum (ER)Endoplasmic reticulum (ER)

Golgi BodiesGolgi Bodies

Put finishing touches on proteins and Put finishing touches on proteins and lipids that arrive from ERlipids that arrive from ER

Package finished material for Package finished material for shipment to final destinationsshipment to final destinations

Material arrives and leaves in vesiclesMaterial arrives and leaves in vesicles

The Golgi apparatusThe Golgi apparatus

VesiclesVesicles

Membranous sacs that Membranous sacs that

move through the move through the

cytoplasmcytoplasm

LysosomesLysosomes

PeroxisomesPeroxisomes

LysosomesLysosomes

Review: relationships among organelles of the Review: relationships among organelles of the endomembrane systemendomembrane system  

The mitochondrion, site of cellular The mitochondrion, site of cellular respirationrespiration

Organelles with no Organelles with no MembranesMembranes

RibosomesRibosomes Function in protein synthesisFunction in protein synthesis

CytoskeletonCytoskeleton Function in maintenance of cell shape Function in maintenance of cell shape

and positioning of organellesand positioning of organelles Centrioles (animals only)Centrioles (animals only)

Function during cell divisionFunction during cell division

RibosomesRibosomes

Present in all eukaryotic cellsPresent in all eukaryotic cells

Basis for cell shape and internal Basis for cell shape and internal organizationorganization

Allows organelle movement within Allows organelle movement within cells and, in some cases, cell motilitycells and, in some cases, cell motility

CytoskeletonCytoskeleton

Cytoskeletal ElementsCytoskeletal Elements

microtubule

microfilament

intermediatefilament

MicrotubulesMicrotubules

Largest elementsLargest elements

Composed of the protein tubulinComposed of the protein tubulin

Arise from microtubule organizing Arise from microtubule organizing

centers (MTOCs)centers (MTOCs)

Polar and dynamicPolar and dynamic

Involved in shape, motility, cell Involved in shape, motility, cell

divisiondivision

MicrotubulesMicrotubules

Largest elementsLargest elements

Composed of the protein tubulinComposed of the protein tubulin

Arise from microtubule organizing Arise from microtubule organizing

centers (MTOCs)centers (MTOCs)

Polar and dynamicPolar and dynamic

Involved in shape, motility, cell Involved in shape, motility, cell

divisiondivision

MicrofilamentsMicrofilaments

Thinnest cytoskeletal elementsThinnest cytoskeletal elements

Composed of the protein actin Composed of the protein actin

Polar and dynamicPolar and dynamic

Take part in movement, formation Take part in movement, formation

and maintenance of cell shapeand maintenance of cell shape

Intermediate FilamentsIntermediate Filaments

Present only in animal cells of certain Present only in animal cells of certain tissuestissues

Most stable cytoskeletal elementsMost stable cytoskeletal elements Six known groupsSix known groups Different cell types usually have 1-2 Different cell types usually have 1-2

different kindsdifferent kinds

Cell JunctionsCell Junctions

tightjunctions

adhering junction

gapjunction

Cell MembranesCell Membranes

Structure and FunctionStructure and Function

Fig. 4.3, p. 52

one layerof lipids

one layerof lipids

lipid bilayer

fluid

fluid

Main component Main component of cell membranesof cell membranes

Gives the Gives the membrane its fluid membrane its fluid propertiesproperties

Two layers of Two layers of phospholipidsphospholipids

Lipid BilayerLipid Bilayer

Figure 8.2 Two generations of membrane modelsFigure 8.2 Two generations of membrane models

The detailed structure of an animal cell’s plasma membrane, in The detailed structure of an animal cell’s plasma membrane, in cross sectioncross section

Functions of Membrane Functions of Membrane ProteinsProteins

TransportTransport Enzymatic Enzymatic

activityactivity Receptors for Receptors for

signal signal transductiontransduction

Figure 3.4.1

Functions of Membrane Functions of Membrane ProteinsProteins

Figure 3.4.2

Intercellular Intercellular adhesionadhesion

Cell-cell Cell-cell recognitionrecognition

Attachment to Attachment to cytoskeleton cytoskeleton and and extracellular extracellular matrixmatrix

Fig. 4.4, p. 53

EXTRACELLULAR ENVIRONMENT

(cytoskeletal pro-teins beneatch the plasma membrane)

ADHESION PROTEIN

oligosaccharide groups

phospholipid

cholesterol

LIPID BILAYER

RECOGNITION PROTEIN

RECEPTOR PROTEIN

CYTOPLASM

PLASMA MEMBRANE

(area of enlargment)

TRANSPORT PROTEINS

open channel protein

gated channel proten (open)

active transport protein

gated channel proten (closed)

The fluidity of membranesThe fluidity of membranes

Cell Membranes Show Cell Membranes Show Selective PermeabilitySelective Permeability

O2, CO2, and other smallnonpolar molecules;and H2O

C6H12O6, and other large, polar(water-soluble) molecules; ions such as H+, Na+, CI-, Ca++; plus H2O hydrogen-bonded to them

X

Membrane Crossing Membrane Crossing MechanismsMechanisms

Diffusion across lipid bilayerDiffusion across lipid bilayer

Passive transportPassive transport

Active transportActive transport

EndocytosisEndocytosis

ExocytosisExocytosis

DiffusionDiffusion

The net movement of like molecules The net movement of like molecules or ions down a concentration or ions down a concentration gradientgradient

Although molecules collide randomly, Although molecules collide randomly, the net movement is away from the the net movement is away from the place with the most collisions (down place with the most collisions (down gradient)gradient)

Concentration Gradient Concentration Gradient

Means the number of molecules or Means the number of molecules or ions in one region is different than ions in one region is different than the number in another regionthe number in another region

In the absence of other forces, a In the absence of other forces, a substance moves from a region substance moves from a region where it is more concentrated to one where it is more concentrated to one one where it’s less concentrated - one where it’s less concentrated - “down” gradient“down” gradient

Factors Affecting Factors Affecting Diffusion RateDiffusion Rate

Steepness of concentration gradientSteepness of concentration gradient Steeper gradient, faster diffusionSteeper gradient, faster diffusion

Molecular sizeMolecular size Smaller molecules, faster diffusionSmaller molecules, faster diffusion

TemperatureTemperature Higher temperature, faster diffusionHigher temperature, faster diffusion

Electrical or pressure gradientsElectrical or pressure gradients

The diffusion of solutes across membranesThe diffusion of solutes across membranes

Osmosis Osmosis A Special Case of Simple DiffusionA Special Case of Simple Diffusion

Diffusion of water molecules across a Diffusion of water molecules across a selectively permeable membraneselectively permeable membrane

Direction of net flow is determined by Direction of net flow is determined by water concentration gradientwater concentration gradient

Side with the most solute molecules Side with the most solute molecules has the lowest water concentrationhas the lowest water concentration

Tonicity Tonicity

Refers to Refers to relativerelative solute solute concentration of two fluidsconcentration of two fluids

Hypertonic - having more solutes Hypertonic - having more solutes

Isotonic - having same amountIsotonic - having same amount

Hypotonic - having fewer solutesHypotonic - having fewer solutes

Tonicity and OsmosisTonicity and Osmosis

2% sucrose

water 10% sucrose 2% sucrose

The water balance of living cellsThe water balance of living cells

The contractile vacuole of The contractile vacuole of ParameciumParamecium: an evolutionary : an evolutionary adaptation for osmoregulationadaptation for osmoregulation

Increase in Fluid VolumeIncrease in Fluid Volume

compartment1

HYPOTONIC SOLUTION

membrane permeable towater but not to solutes

HYPERTONICSOLUTION

compartment2

fluid volume increasesIn compartment 2

Passive Transport Passive Transport

Faciltiated DiffusionFaciltiated Diffusion Flow of solutes through the interior of Flow of solutes through the interior of

passive transport proteins down their passive transport proteins down their concentration gradientsconcentration gradients

Passive transport proteins allow Passive transport proteins allow solutes to move both wayssolutes to move both ways

Does not require any energy inputDoes not require any energy input

Span the lipid bilayerSpan the lipid bilayer Interior is able to open to both sidesInterior is able to open to both sides Change shape when they interact Change shape when they interact

with solute with solute Play roles in active and passive Play roles in active and passive

transport transport

Transport ProteinsTransport Proteins

Two models for facilitated diffusionTwo models for facilitated diffusion

Facilitated DiffusionFacilitated Diffusion

solute

Active TransportActive Transport

Net diffusion of solute is against Net diffusion of solute is against concentration gradientconcentration gradient

Transport protein must be activatedTransport protein must be activated ATP gives up phosphate to activate ATP gives up phosphate to activate

proteinprotein Binding of ATP changes protein Binding of ATP changes protein

shape and affinity for soluteshape and affinity for solute

Active Active TransportTransport

ATP gives up ATP gives up phosphate to phosphate to activate proteinactivate protein

Binding of ATP Binding of ATP changes protein changes protein shape and affinity shape and affinity for solutefor solute

P

P

P

P

High solute concentration

Low solute concentration

ATP ADP

The sodium-potassium pump: a specific case of active The sodium-potassium pump: a specific case of active transporttransport

Review: passive and active transport comparedReview: passive and active transport compared

Bulk Transport – Another Bulk Transport – Another form of Active Transportform of Active Transport

Exocytosis

Endocytosis

The three types of endocytosis in animal cellsThe three types of endocytosis in animal cells

MitosisMitosis

How to clone a nucleusHow to clone a nucleus

Roles of MitosisRoles of Mitosis

Multicelled organismsMulticelled organisms

GrowthGrowth

Cell replacementCell replacement

Some protistans, fungi, plants, Some protistans, fungi, plants,

animalsanimals

Asexual reproductionAsexual reproduction

ChromosomeChromosome

A DNA molecule & attached proteinsA DNA molecule & attached proteins Duplicated in preparation for mitosisDuplicated in preparation for mitosis

one chromosome (unduplicated)

one chromosome (duplicated)

Cell Cycle Cell Cycle

Cycle starts when a new cell formsCycle starts when a new cell forms

During cycle, cell increases in mass During cycle, cell increases in mass and duplicates its chromosomesand duplicates its chromosomes

Cycle ends when the new cell dividesCycle ends when the new cell divides

InterphaseInterphase

Usually longest part of the cycleUsually longest part of the cycle

Cell increases in massCell increases in mass

Number of cytoplasmic components Number of cytoplasmic components

doublesdoubles

DNA is duplicatedDNA is duplicated

Mitosis Mitosis

Period of nuclear divisionPeriod of nuclear division Usually followed by cytoplasmic Usually followed by cytoplasmic

divisiondivision Four stages:Four stages:

ProphaseProphase

MetaphaseMetaphase

AnaphaseAnaphase

TelophaseTelophase

Control of the CycleControl of the Cycle

Once S begins, the cycle automatically Once S begins, the cycle automatically

runs through G2 and mitosisruns through G2 and mitosis

The cycle has a built-in molecular brake The cycle has a built-in molecular brake

in G1in G1

Cancer involves a loss of control over Cancer involves a loss of control over

the cycle, malfunction of the “brakes”the cycle, malfunction of the “brakes”

Stopping the CycleStopping the Cycle

Some cells normally stop in interphaseSome cells normally stop in interphase

Neurons in human brainNeurons in human brain

Arrested cells do not divideArrested cells do not divide

Adverse conditions can stop cycleAdverse conditions can stop cycle

Nutrient-deprived amoebas get stuck in Nutrient-deprived amoebas get stuck in

interphaseinterphase

Stages of Mitosis Stages of Mitosis

ProphaseProphase

MetaphaseMetaphase

AnaphaseAnaphase

TelophaseTelophase

Early Prophase - Early Prophase - Mitosis BeginsMitosis Begins

Duplicated chromosomes begin to Duplicated chromosomes begin to condensecondense

Late ProphaseLate Prophase

New microtubules New microtubules are assembledare assembled

One centriole pair One centriole pair is moved toward is moved toward opposite pole of opposite pole of spindlespindle

Nuclear envelope Nuclear envelope starts to break upstarts to break up

Transition to MetaphaseTransition to Metaphase

Spindle formsSpindle forms Spindle Spindle

microtubules microtubules become attached become attached to the two sister to the two sister chromatids of each chromatids of each chromosomechromosome

MetaphaseMetaphase

All chromosomes All chromosomes are lined up at are lined up at the spindle the spindle equatorequator

Chromosomes Chromosomes are maximally are maximally condensedcondensed

AnaphaseAnaphase

Sister chromatids Sister chromatids of each of each chromosome are chromosome are pulled apartpulled apart

Once separated, Once separated, each chromatid each chromatid is a chromosome is a chromosome

TelophaseTelophase

Chromosomes Chromosomes decondensedecondense

Two nuclear Two nuclear membranes form, membranes form, one around each one around each set of set of unduplicated unduplicated chromosomeschromosomes

Results of MitosisResults of Mitosis

Two daughter Two daughter nuclei nuclei

Each with same Each with same chromosome chromosome number as parent number as parent cellcell

Chromosomes in Chromosomes in unduplicated formunduplicated form

Cytoplasmic Division Cytoplasmic Division

Usually occurs between late Usually occurs between late

anaphase and end of telophaseanaphase and end of telophase

Two mechanisms Two mechanisms

Cell plate formation (plants)Cell plate formation (plants)

Cleavage (animals)Cleavage (animals)

Animal Cell DivisionAnimal Cell Division