This document provides an overview of cell structure and function. It begins with a brief history of cell theory and outlines the key points of cell theory. It then describes the basic structures found in both prokaryotic and eukaryotic cells, including the plasma membrane, genetic material, cytoplasm, and organelles. Specific organelles like the nucleus, endoplasmic reticulum, Golgi apparatus, vesicles, lysosomes and mitochondria are explained in more detail. The roles of these structures and organelles in protein modification and transport are summarized. The document also addresses why cells are typically small in size.

1. Cell Structure andCell Structure and
FunctionFunction

2. Chapter OutlineChapter Outline
 Cell theoryCell theory
 Properties common to all cellsProperties common to all cells
 Cell size and shape –Cell size and shape – why are cells so small?why are cells so small?
 Prokaryotic cellsProkaryotic cells
 Eukaryotic cellsEukaryotic cells

Organelles and structure in all eukaryotic cellOrganelles and structure in all eukaryotic cell

Organelles in plant cells but not animalOrganelles in plant cells but not animal
 Cell junctionsCell junctions

3. History of Cell TheoryHistory of Cell Theory
 mid 1600s – Anton van Leeuwenhoekmid 1600s – Anton van Leeuwenhoek

Improved microscope, observed many living cellsImproved microscope, observed many living cells
 mid 1600s – Robert Hookemid 1600s – Robert Hooke

Observed many cells including cork cellsObserved many cells including cork cells
1850 – Rudolf Virchow1850 – Rudolf Virchow

Proposed that all cells come from existingProposed that all cells come from existing
cellscells

4. Cell TheoryCell Theory
1.1. All organisms consist of 1 or moreAll organisms consist of 1 or more
cells.cells.
2.2. Cell is the smallest unit of life.Cell is the smallest unit of life.
3.3. All cells come from pre-existingAll cells come from pre-existing
cells.cells.

5. Observing CellsObserving Cells (4.1)(4.1)
 Light microscopeLight microscope

Can observe living cells in true colorCan observe living cells in true color

Magnification of up to ~1000xMagnification of up to ~1000x

Resolution ~ 0.2 microns – 0.5 micronsResolution ~ 0.2 microns – 0.5 microns

6. Observing CellsObserving Cells (4.1)(4.1)
 Electron MicroscopesElectron Microscopes

Preparation needed kills the cellsPreparation needed kills the cells

Images are black and white – may beImages are black and white – may be
colorizedcolorized

Magnifcation up to ~100,000Magnifcation up to ~100,000
• Transmission electron microscope (TEM)Transmission electron microscope (TEM)

2-D image2-D image
• Scanning electron microscope (SEM)Scanning electron microscope (SEM)

3-D image3-D image

7. SEM
TEM

8. Cell StructureCell Structure
 All Cells have:All Cells have:

an outermost plasma membranean outermost plasma membrane

genetic material in the form of DNAgenetic material in the form of DNA

cytoplasm with ribosomescytoplasm with ribosomes

9. Cell StructureCell Structure
 All Cells have:All Cells have:

an outermost plasma membranean outermost plasma membrane
• Structure – phospholipid bilayer withStructure – phospholipid bilayer with
embedded proteinsembedded proteins
• Function – isolates cell contents,Function – isolates cell contents,
controls what gets in and out of thecontrols what gets in and out of the
cell, receives signalscell, receives signals

10. Cell StructureCell Structure
 All Cells have:All Cells have:

genetic material in the form of DNAgenetic material in the form of DNA
• Eukaryotes – DNA is within aEukaryotes – DNA is within a
membrane (nucleus)membrane (nucleus)
• Prokaryotes – no membrane aroundProkaryotes – no membrane around
the DNA (DNA region called nucleoid)the DNA (DNA region called nucleoid)

11. Cell StructureCell Structure
 All Cells have:All Cells have:

cytoplasm with ribosomescytoplasm with ribosomes
• Cytoplasm – fluid area inside outerCytoplasm – fluid area inside outer
plasma membrane and outside DNAplasma membrane and outside DNA
regionregion
• Ribosome – site of protein synthesisRibosome – site of protein synthesis

12. Why Are Cells So Small?Why Are Cells So Small? (4.2)(4.2)
 Cells need sufficient surface area to allowCells need sufficient surface area to allow
adequate transport of nutrients in andadequate transport of nutrients in and
wastes out.wastes out.
 As cell volume increases, so does theAs cell volume increases, so does the
need for the transporting of nutrients andneed for the transporting of nutrients and
wastes.wastes.

13. Why Are Cells So Small?Why Are Cells So Small?
 However, as cell volume increases theHowever, as cell volume increases the
surface area of the cell does not expandsurface area of the cell does not expand
as quickly.as quickly.

If the cell’s volume gets too large it cannotIf the cell’s volume gets too large it cannot
transport enough wastes out or nutrients in.transport enough wastes out or nutrients in.
 Thus, surface area limits cell volume/size.Thus, surface area limits cell volume/size.

14. Why Are Cells So Small?Why Are Cells So Small?
 Strategies for increasing surfaceStrategies for increasing surface
area, so cell can be larger:area, so cell can be larger:

““Frilly” edged…….Frilly” edged…….

Long and narrow…..Long and narrow…..
 Round cells will always be small.Round cells will always be small.

15. Prokaryotic Cell StructureProkaryotic Cell Structure
 Prokaryotic Cells are smaller andProkaryotic Cells are smaller and
simpler in structure than eukaryoticsimpler in structure than eukaryotic
cells.cells.

Typical prokaryotic cell is __________Typical prokaryotic cell is __________

Prokaryotic cells do NOT have:Prokaryotic cells do NOT have:
• NucleusNucleus
• Membrane bound organellesMembrane bound organelles

16. Prokaryotic Cell StructureProkaryotic Cell Structure
 StructuresStructures

Plasma membranePlasma membrane

Cell wallCell wall

Cytoplasm with ribosomesCytoplasm with ribosomes

NucleoidNucleoid

Capsule*Capsule*

Flagella* and pili*Flagella* and pili*
*present in some, but not all prokaryotic cells*present in some, but not all prokaryotic cells

17. Prokaryotic CellProkaryotic Cell

19. TEM Prokaryotic Cell

20. Eukaryotic CellsEukaryotic Cells
 Structures in all eukaryotic cellsStructures in all eukaryotic cells

NucleusNucleus

RibosomesRibosomes

Endomembrane SystemEndomembrane System
• Endoplasmic reticulum – smooth and roughEndoplasmic reticulum – smooth and rough
• Golgi apparatusGolgi apparatus
• VesiclesVesicles

MitochondriaMitochondria

CytoskeletonCytoskeleton

21. CYTOSKELETON
MITOCHONDRION
CENTRIOLES
LYSOSOME
GOLGI BODY
SMOOTH ER
ROUGH ER
RIBOSOMES
NUCLEUS
PLASMA
MEMBRANE
Fig. 4-15b, p.59

22. NucleusNucleus (4.5)(4.5)
 FunctionFunction – isolates the cell’s genetic– isolates the cell’s genetic
material, DNAmaterial, DNA

DNA directs/controls the activities of the cellDNA directs/controls the activities of the cell
• DNA determines which types of RNA are madeDNA determines which types of RNA are made
• The RNA leaves the nucleus and directs theThe RNA leaves the nucleus and directs the
synthesis of proteins in the cytoplasmsynthesis of proteins in the cytoplasm

23. NucleusNucleus
 StructureStructure

Nuclear envelopeNuclear envelope
• Two Phospholipid bilayers withTwo Phospholipid bilayers with
protein lined poresprotein lined pores

Each pore is a ring of 8 proteins with anEach pore is a ring of 8 proteins with an
opening in the center of the ringopening in the center of the ring

Nucleoplasm – fluid of the nucleusNucleoplasm – fluid of the nucleus

24. Nuclear pore bilayer facing cytoplasm Nuclear envelope
bilayer facing
nucleoplasm
Fig. 4-17, p.61

25. NucleusNucleus
 DNA is arranged in chromosomesDNA is arranged in chromosomes

Chromosome – fiber of DNA and theChromosome – fiber of DNA and the
proteins attached to the DNAproteins attached to the DNA

Chromatin – all of the cell’s DNA andChromatin – all of the cell’s DNA and
the associated proteinsthe associated proteins

26. NucleusNucleus
 Structure,Structure, continuedcontinued

NucleolusNucleolus
• Area of condensed DNAArea of condensed DNA
• Where ribosomal subunits are madeWhere ribosomal subunits are made

Subunits exit the nucleus via nuclear poresSubunits exit the nucleus via nuclear pores

28. Endomembrane SystemEndomembrane System (4.6 – 4.9)(4.6 – 4.9)
 Series of organelles responsible for:Series of organelles responsible for:

Modifying protein chains into their finalModifying protein chains into their final
formform

Synthesizing of lipidsSynthesizing of lipids

Packaging of fully modified proteins andPackaging of fully modified proteins and
lipids into vesicles for export or use inlipids into vesicles for export or use in
the cellthe cell

29. Endomembrane SystemEndomembrane System
 Endoplasmic Reticulum (ER)Endoplasmic Reticulum (ER)

Continuous with the outer membrane ofContinuous with the outer membrane of
the nuclear envelopethe nuclear envelope

Two forms - smooth and roughTwo forms - smooth and rough
 Transport vesiclesTransport vesicles
 Golgi apparatusGolgi apparatus

30. Endoplasmic ReticulumEndoplasmic Reticulum
 Rough Endoplasmic Reticulum (RER)Rough Endoplasmic Reticulum (RER)
• Network of flattened membrane sacs createNetwork of flattened membrane sacs create
a “maze”a “maze”
• Ribosomes attached to the outside of theRibosomes attached to the outside of the
RER make it appear roughRER make it appear rough

31. Endoplasmic ReticulumEndoplasmic Reticulum
 Function RERFunction RER
• Where proteins are modified and packagedWhere proteins are modified and packaged
in transport vesicles for transport to thein transport vesicles for transport to the
Golgi bodyGolgi body

32. Endomembrane SystemEndomembrane System
 Smooth ER (SER)Smooth ER (SER)

Tubular membrane structureTubular membrane structure

Continuous with RERContinuous with RER

No ribosomes attachedNo ribosomes attached
 Function SERFunction SER

Synthesis of lipids (fatty acids, phospholipids,Synthesis of lipids (fatty acids, phospholipids,
sterols..)sterols..)

33. Endomembrane SystemEndomembrane System
 Additional functions of the SERAdditional functions of the SER

In muscle cells, the SER stores calcium ionsIn muscle cells, the SER stores calcium ions
and releases them during muscle contractionsand releases them during muscle contractions

In liver cells, the SER detoxifies medicationsIn liver cells, the SER detoxifies medications
and alcoholand alcohol

34. Golgi ApparatusGolgi Apparatus
 Golgi ApparatusGolgi Apparatus

Stack of flattened membrane sacsStack of flattened membrane sacs
 Function Golgi apparatusFunction Golgi apparatus

Completes the processing substancesCompletes the processing substances
received from the ERreceived from the ER

Sorts, tags and packages fully processedSorts, tags and packages fully processed
proteins and lipids in vesiclesproteins and lipids in vesicles

35. Golgi ApparatusGolgi Apparatus
 Golgi apparatus receives transportGolgi apparatus receives transport
vesicles from the ER on one side of thevesicles from the ER on one side of the
organelleorganelle

Vesicle binds to the first layer of the Golgi andVesicle binds to the first layer of the Golgi and
its contents enter the Golgiits contents enter the Golgi

36. Golgi ApparatusGolgi Apparatus

The proteins and lipids are modified as theyThe proteins and lipids are modified as they
pass through layers of the Golgipass through layers of the Golgi

Molecular tags are added to the fully modifiedMolecular tags are added to the fully modified
substancessubstances
• These tags allow the substances to be sorted andThese tags allow the substances to be sorted and
packaged appropriately.packaged appropriately.
• Tags also indicate where the substance is to beTags also indicate where the substance is to be
shipped.shipped.

37. Golgi ApparatusGolgi Apparatus

38. Transport VesiclesTransport Vesicles
 Transport VesiclesTransport Vesicles

Vesicle = small membrane bound sacVesicle = small membrane bound sac

Transport modified proteins and lipids fromTransport modified proteins and lipids from
the ER to the Golgi apparatus (and from Golgithe ER to the Golgi apparatus (and from Golgi
to final destination)to final destination)

39. Endomembrane SystemEndomembrane System
 Putting it all togetherPutting it all together

DNA directs RNA synthesisDNA directs RNA synthesis  RNARNA
exits nucleus through a nuclear poreexits nucleus through a nuclear pore 
ribosomeribosome  protein is madeprotein is made  proteinsproteins
with proper code enter RERwith proper code enter RER  proteinsproteins
are modified in RER and lipids areare modified in RER and lipids are
made in SERmade in SER  vesicles containing thevesicles containing the
proteins and lipids bud off from the ERproteins and lipids bud off from the ER

40. Endomembrane SystemEndomembrane System
 Putting it all togetherPutting it all together
ER vesicles merge with Golgi bodyER vesicles merge with Golgi body 
proteins and lipids enter Golgiproteins and lipids enter Golgi  eacheach
is fully modified as it passes throughis fully modified as it passes through
layers of Golgilayers of Golgi  modified products aremodified products are
tagged, sorted and bud off in Golgitagged, sorted and bud off in Golgi
vesiclesvesicles  ……

41. Endomembrane SystemEndomembrane System
 Putting it all togetherPutting it all together
 Golgi vesicles either merge with theGolgi vesicles either merge with the
plasma membrane and release theirplasma membrane and release their
contents OR remain in the cell andcontents OR remain in the cell and
serve a purposeserve a purpose

42. VesiclesVesicles
 Vesicles - small membrane bound sacsVesicles - small membrane bound sacs

ExamplesExamples
• Golgi and ER transport vesiclesGolgi and ER transport vesicles
• PeroxisomePeroxisome

Where fatty acids are metabolizedWhere fatty acids are metabolized

Where hydrogen peroxide is detoxifiedWhere hydrogen peroxide is detoxified
• LysosomeLysosome

43. LysosomesLysosomes (4.10)(4.10)
 The lysosome is an example of anThe lysosome is an example of an
organelle made at the Golgi apparatus.organelle made at the Golgi apparatus.

Golgi packages digestive enzymes in aGolgi packages digestive enzymes in a
vesicle. The vesicle remains in the cell and:vesicle. The vesicle remains in the cell and:
• Digests unwanted or damaged cell partsDigests unwanted or damaged cell parts
• Merges with food vacuoles and digest the contentsMerges with food vacuoles and digest the contents
• Figure 4.10AFigure 4.10A

44. LysosomesLysosomes (4.11)(4.11)
 Tay-Sachs disease occurs when theTay-Sachs disease occurs when the
lysosome is missing the enzyme neededlysosome is missing the enzyme needed
to digest a lipid found in nerve cells.to digest a lipid found in nerve cells.

As a result the lipid accumulates and nerveAs a result the lipid accumulates and nerve
cells are damaged as the lysosome swellscells are damaged as the lysosome swells
with undigested lipid.with undigested lipid.

45. MitochondriaMitochondria (4.15)(4.15)
 Function – synthesis of ATPFunction – synthesis of ATP

3 major pathways involved in ATP3 major pathways involved in ATP
productionproduction
1.1. GlycolysisGlycolysis
2.2. Krebs CycleKrebs Cycle
3.3. Electron transport system (ETS)Electron transport system (ETS)

46. MitochondriaMitochondria
 Structure:Structure:

~1-5 microns~1-5 microns

Outer membraneOuter membrane

Inner membrane - Highly foldedInner membrane - Highly folded
• Folds called cristaeFolds called cristae

Intermembrane space (or outer compartment)Intermembrane space (or outer compartment)

MatrixMatrix
• DNA and ribosomes in matrixDNA and ribosomes in matrix

47. MitochondriaMitochondria

48. MitochondriaMitochondria (4.15)(4.15)
 Function – synthesis of ATPFunction – synthesis of ATP

3 major pathways involved in ATP3 major pathways involved in ATP
productionproduction
1.1. Glycolysis - cytoplasmGlycolysis - cytoplasm
2.2. Krebs Cycle - matrixKrebs Cycle - matrix
3.3. Electron transport system (ETS) -Electron transport system (ETS) -
intermembrane spaceintermembrane space

49. MitochondriaMitochondria
TEMTEM

51. VacuolesVacuoles (4.12)(4.12)
 Vacuoles are membrane sacs that areVacuoles are membrane sacs that are
generally larger than vesicles.generally larger than vesicles.

Examples:Examples:
• Food vacuole - formed when protists bring foodFood vacuole - formed when protists bring food
into the cell by endocytosisinto the cell by endocytosis
• Contractile vacuole – collect and pump excessContractile vacuole – collect and pump excess
water out of some freshwater protistswater out of some freshwater protists
• Central vacuole – covered laterCentral vacuole – covered later

52. CytoskeletonCytoskeleton (4.16, 4.17)(4.16, 4.17)
 FunctionFunction

gives cells internal organization, shape, andgives cells internal organization, shape, and
ability to moveability to move
 StructureStructure

Interconnected system of microtubules,Interconnected system of microtubules,
microfilaments, and intermediate filamentsmicrofilaments, and intermediate filaments
(animal only)(animal only)
• All are proteinsAll are proteins

53. CytoskeletonCytoskeleton

54. MicrofilamentsMicrofilaments
 Thinnest cytoskeletal elements (rodlike)Thinnest cytoskeletal elements (rodlike)
 Composed of the globular proteinComposed of the globular protein actinactin
 Enable cells to change shape and moveEnable cells to change shape and move

55. CytoskeletonCytoskeleton
 Intermediate filamentsIntermediate filaments

Present only in animal cells ofPresent only in animal cells of
certain tissuescertain tissues

Fibrous proteins join to form aFibrous proteins join to form a
rope-like structurerope-like structure
• Provide internal structureProvide internal structure
• Anchor organelles in place.Anchor organelles in place.

56. CytoskeletonCytoskeleton
 Microtubules – long hollowMicrotubules – long hollow
tubes made of tubulin proteinstubes made of tubulin proteins
(globular)(globular)

Anchor organelles and act asAnchor organelles and act as
tracks for organelle movementtracks for organelle movement

Move chromosomes aroundMove chromosomes around
during cell divisionduring cell division
• Used to make cilia and flagellaUsed to make cilia and flagella

57. CiliaCilia andand flagellaflagella (structures for cell motility)(structures for cell motility)

Move whole cells or materials across the cell surfaceMove whole cells or materials across the cell surface

Microtubules wrapped in an extension of the plasmaMicrotubules wrapped in an extension of the plasma
membrane (9 + 2 arrangement of MT)membrane (9 + 2 arrangement of MT)

58. Plant Cell StructuresPlant Cell Structures
 Structures found in plant, but not animalStructures found in plant, but not animal
cellscells

ChloroplastsChloroplasts

Central vacuoleCentral vacuole

Other plastids/vacuoles – chromoplast,Other plastids/vacuoles – chromoplast,
amyloplastamyloplast

Cell wallCell wall

59. ChloroplastsChloroplasts (4.14)(4.14)
 Function – site of photosynthesisFunction – site of photosynthesis
 StructureStructure

2 outer membranes2 outer membranes

Thylakoid membrane systemThylakoid membrane system
• Stacked membrane sacs called granumStacked membrane sacs called granum

Chlorophyll in granumChlorophyll in granum

StromaStroma
• Fluid part of chloroplastFluid part of chloroplast

61. Plastids/Vacuoles in PlantsPlastids/Vacuoles in Plants
 Chromoplasts – contain colored pigmentsChromoplasts – contain colored pigments
• Pigments called carotenoidsPigments called carotenoids
 Amyloplasts – store starchAmyloplasts – store starch

62. Central VacuoleCentral Vacuole
 Function – storage area for water, sugars,Function – storage area for water, sugars,
ions, amino acids, and wastesions, amino acids, and wastes

Some central vacuoles serve specializedSome central vacuoles serve specialized
functions in plant cells.functions in plant cells.
• May contain poisons to protect against predatorsMay contain poisons to protect against predators

63. Central VacuoleCentral Vacuole
 StructureStructure

Large membrane bound sacLarge membrane bound sac

Occupies the majority of the volume of theOccupies the majority of the volume of the
plant cellplant cell

Increases cell’s surface area for transport ofIncreases cell’s surface area for transport of
substancessubstances  cells can be largercells can be larger

64. Cell surfaces protect, support, and join cellsCell surfaces protect, support, and join cells

Cells interact with their environments andCells interact with their environments and
each other via their surfaceseach other via their surfaces

Many cells are protected by more than theMany cells are protected by more than the
plasma membraneplasma membrane

65. Cell WallCell Wall
 Function – provides structure and protectionFunction – provides structure and protection

Never found in animal cellsNever found in animal cells

Present in plant, bacterial, fungus, and some protistsPresent in plant, bacterial, fungus, and some protists
 StructureStructure

Wraps around the plasma membraneWraps around the plasma membrane

Made of cellulose and other polysaccharidesMade of cellulose and other polysaccharides

Connect by plasmodesmataConnect by plasmodesmata (channels through the walls)(channels through the walls)

66. Vacuole
Walls
of two
adjacent
plant cells
Plasmodesmata
Layers
of one plant
cell wall
Cytoplasm
Plasma membrane

67. Plant Cell TEMPlant Cell TEM

68. Typical Plant CellTypical Plant Cell

69. Typical Plant CellTypical Plant Cell

70. Origin of Mitochondria andOrigin of Mitochondria and
ChloroplastsChloroplasts
 Both organelles are believed to have onceBoth organelles are believed to have once
been free-living bacteria that werebeen free-living bacteria that were
engulfed by a larger cell.engulfed by a larger cell.

71. Proposed Origin of MitochondriaProposed Origin of Mitochondria
and Chloroplastsand Chloroplasts
 Evidence:Evidence:

Each have their own DNAEach have their own DNA

Their ribosomes resemble bacterialTheir ribosomes resemble bacterial
ribosomesribosomes

Each can divide on its ownEach can divide on its own

Mitochondria are same size as bacteriaMitochondria are same size as bacteria

Each have more than one membraneEach have more than one membrane

72. Cell JunctionsCell Junctions (4.18)(4.18)
 Plasma membrane proteins connectPlasma membrane proteins connect
neighboring cells - called cell junctionsneighboring cells - called cell junctions

Plant cells – plasmodesmata providePlant cells – plasmodesmata provide
channels between cellschannels between cells

73. Cell JunctionsCell Junctions (4.18)(4.18)
 3 types of cell junctions in animal cells3 types of cell junctions in animal cells
1.1. Tight junctionsTight junctions
2.2. Adchoring junctionsAdchoring junctions
3.3. Gap junctionsGap junctions

74. Cell JunctionsCell Junctions
1.1. Tight junctions – membrane proteinsTight junctions – membrane proteins
seal neighboring cells so that waterseal neighboring cells so that water
soluble substances cannot crosssoluble substances cannot cross
between thembetween them
•
See between stomach cellsSee between stomach cells

75. Cell JunctionsCell Junctions
2.2. Anchoring junctions – cytoskeleton fibersAnchoring junctions – cytoskeleton fibers
join cells in tissues that need to stretchjoin cells in tissues that need to stretch
•
See between heart, skin, and muscle cellsSee between heart, skin, and muscle cells
3.3. Gap junctions – membrane proteins onGap junctions – membrane proteins on
neighboring cells link to form channelsneighboring cells link to form channels
•
This links the cytoplasm of adjoining cellsThis links the cytoplasm of adjoining cells

76. Gap junction
Anchoring
junction
Tight junction