Cell structure

Cell Structure and Cell Structure and FunctionFunction

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

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 Hooke mid 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 existing Proposed that all cells come from existing

cellscells

Cell TheoryCell Theory

1.1. All organisms consist of 1 or more All 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-existing All cells come from pre-existing cells.cells.

Observing Cells Observing 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

Observing Cells Observing Cells (4.1)(4.1)

Electron MicroscopesElectron Microscopes Preparation needed kills the cellsPreparation needed kills the cells Images are black and white – may be Images 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

SEM

TEM

Cell StructureCell Structure

All Cells have:All Cells have: an outermost plasma membranean outermost plasma membrane genetic material in the form of DNA genetic material in the form of DNA cytoplasm with ribosomescytoplasm with ribosomes


All Cells have:All Cells have: an outermost plasma membranean outermost plasma membrane

• Structure – phospholipid bilayer with Structure – phospholipid bilayer with embedded proteinsembedded proteins

• Function – isolates cell contents, Function – isolates cell contents, controls what gets in and out of the controls what gets in and out of the cell, receives signalscell, receives signals


All Cells have:All Cells have: genetic material in the form of DNAgenetic material in the form of DNA

• Eukaryotes – DNA is within a Eukaryotes – DNA is within a membrane (nucleus)membrane (nucleus)

• Prokaryotes – no membrane around Prokaryotes – no membrane around the DNA (DNA region called nucleoid)the DNA (DNA region called nucleoid)


All Cells have:All Cells have: cytoplasm with ribosomescytoplasm with ribosomes

• Cytoplasm – fluid area inside outer Cytoplasm – fluid area inside outer plasma membrane and outside DNA plasma membrane and outside DNA regionregion

• Ribosome – site of protein synthesisRibosome – site of protein synthesis

Why Are Cells So Small? Why Are Cells So Small? (4.2)(4.2)

Cells need sufficient surface area to allow Cells need sufficient surface area to allow adequate transport of nutrients in and adequate transport of nutrients in and wastes out.wastes out.

As cell volume increases, so does the As cell volume increases, so does the need for the transporting of nutrients and need for the transporting of nutrients and wastes.wastes.

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

However, as cell volume increases the However, as cell volume increases the surface area of the cell does not expand surface area of the cell does not expand as quickly.as quickly. If the cell’s volume gets too large it cannot If 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.

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

Strategies for increasing surface Strategies 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.

Prokaryotic Cell StructureProkaryotic Cell Structure

Prokaryotic Cells are smaller and Prokaryotic Cells are smaller and simpler in structure than eukaryotic simpler 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

Prokaryotic Cell StructureProkaryotic Cell Structure

StructuresStructures Plasma membrane Plasma 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

Prokaryotic CellProkaryotic Cell

TEM Prokaryotic Cell

Eukaryotic CellsEukaryotic Cells

Structures in all eukaryotic cellsStructures in all eukaryotic cells NucleusNucleus RibosomesRibosomes Endomembrane System Endomembrane System

• Endoplasmic reticulum – smooth and roughEndoplasmic reticulum – smooth and rough• Golgi apparatusGolgi apparatus• VesiclesVesicles

MitochondriaMitochondria CytoskeletonCytoskeleton

CYTOSKELETON

MITOCHONDRION

CENTRIOLES

LYSOSOME

GOLGI BODY

SMOOTH ER

ROUGH ER

RIBOSOMES

NUCLEUS

PLASMA MEMBRANE

Fig. 4-15b, p.59

Nucleus Nucleus (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 the The RNA leaves the nucleus and directs the

synthesis of proteins in the cytoplasmsynthesis of proteins in the cytoplasm

NucleusNucleus

StructureStructure Nuclear envelopeNuclear envelope

• Two Phospholipid bilayers with protein Two Phospholipid bilayers with protein lined poreslined pores

Each pore is a ring of 8 proteins with an Each 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

Nuclear pore bilayer facing cytoplasm Nuclear envelope

bilayer facing nucleoplasm

Fig. 4-17, p.61

NucleusNucleus

DNA is arranged in chromosomesDNA is arranged in chromosomes Chromosome – fiber of DNA and the Chromosome – fiber of DNA and the

proteins attached to the DNAproteins attached to the DNA

Chromatin – all of the cell’s DNA and Chromatin – all of the cell’s DNA and the associated proteinsthe associated proteins

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

Endomembrane System Endomembrane System (4.6 – 4.9)(4.6 – 4.9)

Series of organelles responsible for:Series of organelles responsible for: Modifying protein chains into their final Modifying protein chains into their final

formform Synthesizing of lipidsSynthesizing of lipids Packaging of fully modified proteins and Packaging of fully modified proteins and

lipids into vesicles for export or use in lipids into vesicles for export or use in the cellthe cell

Endomembrane SystemEndomembrane System

Endoplasmic Reticulum (ER)Endoplasmic Reticulum (ER) Continuous with the outer membrane of Continuous with the outer membrane of

the nuclear envelope the nuclear envelope Two forms - smooth and roughTwo forms - smooth and rough

Transport vesiclesTransport vesicles Golgi apparatusGolgi apparatus

Endoplasmic ReticulumEndoplasmic Reticulum

Rough Endoplasmic Reticulum (RER)Rough Endoplasmic Reticulum (RER)• Network of flattened membrane sacs create Network of flattened membrane sacs create

a “maze”a “maze”• Ribosomes attached to the outside of the Ribosomes attached to the outside of the

RER make it appear roughRER make it appear rough

Endoplasmic ReticulumEndoplasmic Reticulum

Function RERFunction RER• Where proteins are modified and packaged Where proteins are modified and packaged

in transport vesicles for transport to the in transport vesicles for transport to the Golgi bodyGolgi body


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..)


Additional functions of the SERAdditional functions of the SER In muscle cells, the SER stores calcium ions In muscle cells, the SER stores calcium ions

and releases them during muscle contractionsand releases them during muscle contractions In liver cells, the SER detoxifies medications In liver cells, the SER detoxifies medications

and alcoholand alcohol

Golgi ApparatusGolgi Apparatus

Golgi Apparatus Golgi Apparatus Stack of flattened membrane sacsStack of flattened membrane sacs

Function Golgi apparatusFunction Golgi apparatus Completes the processing substances Completes the processing substances

received from the ERreceived from the ER Sorts, tags and packages fully processed Sorts, tags and packages fully processed

proteins and lipids in vesiclesproteins and lipids in vesicles


Golgi apparatus receives transport Golgi apparatus receives transport vesicles from the ER on one side of the vesicles from the ER on one side of the organelleorganelle Vesicle binds to the first layer of the Golgi and Vesicle binds to the first layer of the Golgi and

its contents enter the Golgiits contents enter the Golgi


The proteins and lipids are modified as they The 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 modified Molecular tags are added to the fully modified substancessubstances• These tags allow the substances to be sorted and These tags allow the substances to be sorted and

packaged appropriately.packaged appropriately.• Tags also indicate where the substance is to be Tags also indicate where the substance is to be

shipped.shipped.

Transport VesiclesTransport Vesicles

Transport VesiclesTransport Vesicles Vesicle = small membrane bound sacVesicle = small membrane bound sac Transport modified proteins and lipids from Transport modified proteins and lipids from

the ER to the Golgi apparatus (and from Golgi the ER to the Golgi apparatus (and from Golgi to final destination)to final destination)


Putting it all togetherPutting it all together DNA directs RNA synthesis DNA directs RNA synthesis RNA RNA

exits nucleus through a nuclear pore exits nucleus through a nuclear pore ribosome ribosome protein is made protein is made proteins proteins with proper code enter RER with proper code enter RER proteins proteins are modified in RER and lipids are made are modified in RER and lipids are made in SER in SER vesicles containing the vesicles containing the proteins and lipids bud off from the ERproteins and lipids bud off from the ER


Putting it all togetherPutting it all together

ER vesicles merge with Golgi body ER vesicles merge with Golgi body proteins and lipids enter Golgi proteins and lipids enter Golgi each is each is fully modified as it passes through fully modified as it passes through layers of Golgi layers of Golgi modified products are modified products are tagged, sorted and bud off in Golgi tagged, sorted and bud off in Golgi vesicles vesicles … …


Putting it all togetherPutting it all together

Golgi vesicles either merge with the Golgi vesicles either merge with the plasma membrane and release their plasma membrane and release their contents OR remain in the cell and contents OR remain in the cell and serve a purposeserve a purpose

VesiclesVesicles

Vesicles - small membrane bound sacsVesicles - small membrane bound sacs ExamplesExamples

• Golgi and ER transport vesiclesGolgi and ER transport vesicles• Peroxisome Peroxisome

Where fatty acids are metabolizedWhere fatty acids are metabolized Where hydrogen peroxide is detoxifiedWhere hydrogen peroxide is detoxified

• LysosomeLysosome

Lysosomes Lysosomes (4.10)(4.10)

The lysosome is an example of an The lysosome is an example of an organelle made at the Golgi apparatus.organelle made at the Golgi apparatus. Golgi packages digestive enzymes in a Golgi 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

Lysosomes Lysosomes (4.11)(4.11)

Tay-Sachs disease occurs when the Tay-Sachs disease occurs when the lysosome is missing the enzyme needed lysosome 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 nerve As a result the lipid accumulates and nerve

cells are damaged as the lysosome swells cells are damaged as the lysosome swells with undigested lipid.with undigested lipid.

Mitochondria Mitochondria (4.15)(4.15)

Function – synthesis of ATPFunction – synthesis of ATP 3 major pathways involved in ATP 3 major pathways involved in ATP

productionproduction1.1. GlycolysisGlycolysis

2.2. Krebs CycleKrebs Cycle

3.3. Electron transport system (ETS)Electron transport system (ETS)

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) Matrix Matrix

• DNA and ribosomes in matrixDNA and ribosomes in matrix

Mitochondria Mitochondria (4.15)(4.15)

Function – synthesis of ATPFunction – synthesis of ATP 3 major pathways involved in ATP 3 major pathways involved in ATP

productionproduction1.1. Glycolysis - cytoplasmGlycolysis - cytoplasm

2.2. Krebs Cycle - matrixKrebs Cycle - matrix

3.3. Electron transport system (ETS) - Electron transport system (ETS) - intermembrane spaceintermembrane space


TEMTEM

Vacuoles Vacuoles (4.12)(4.12)

Vacuoles are membrane sacs that are Vacuoles are membrane sacs that are generally larger than vesicles.generally larger than vesicles. Examples:Examples:

• Food vacuole - formed when protists bring food Food vacuole - formed when protists bring food into the cell by endocytosisinto the cell by endocytosis

• Contractile vacuole – collect and pump excess Contractile vacuole – collect and pump excess

water out of some freshwater protistswater out of some freshwater protists

• Central vacuole – covered laterCentral vacuole – covered later

Cytoskeleton Cytoskeleton (4.16, 4.17)(4.16, 4.17)

FunctionFunction gives cells internal organization, shape, and gives cells internal organization, shape, and

ability to moveability to move StructureStructure

Interconnected system of microtubules, Interconnected system of microtubules, microfilaments, and intermediate filaments microfilaments, and intermediate filaments (animal only)(animal only)• All are proteinsAll are proteins

CytoskeletonCytoskeleton

MicrofilamentsMicrofilaments

Thinnest cytoskeletal elements (rodlike)Thinnest cytoskeletal elements (rodlike)

Composed of the globular protein Composed of the globular protein actin actin

Enable cells to change shape and moveEnable cells to change shape and move


Intermediate filamentsIntermediate filaments Present only in animal cells of Present only in animal cells of

certain tissuescertain tissues

Fibrous proteins join to form a Fibrous proteins join to form a rope-like structurerope-like structure• Provide internal structureProvide internal structure• Anchor organelles in place.Anchor organelles in place.


Microtubules – long hollow Microtubules – long hollow tubes made of tubulin proteins tubes made of tubulin proteins (globular)(globular) Anchor organelles and act as Anchor organelles and act as

tracks for organelle movementtracks for organelle movement Move chromosomes around Move chromosomes around

during cell divisionduring cell division• Used to make cilia and flagellaUsed to make cilia and flagella

Cilia Cilia and and flagellaflagella (structures for cell motility) (structures for cell motility)

Move whole cells or materials across the cell surface Move whole cells or materials across the cell surface

Microtubules wrapped in an extension of the plasma Microtubules wrapped in an extension of the plasma membrane (9 + 2 arrangement of MT)membrane (9 + 2 arrangement of MT)

Plant Cell StructuresPlant Cell Structures

Structures found in plant, but not animal Structures found in plant, but not animal cellscells ChloroplastsChloroplasts Central vacuoleCentral vacuole Other plastids/vacuoles – chromoplast, Other plastids/vacuoles – chromoplast,

amyloplastamyloplast Cell wallCell wall

Chloroplasts Chloroplasts (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

Plastids/Vacuoles in PlantsPlastids/Vacuoles in Plants

Chromoplasts – contain colored pigmentsChromoplasts – contain colored pigments• Pigments called carotenoidsPigments called carotenoids

Amyloplasts – store starchAmyloplasts – store starch

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 specialized Some 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

Central VacuoleCentral Vacuole

StructureStructure Large membrane bound sacLarge membrane bound sac Occupies the majority of the volume of the Occupies the majority of the volume of the

plant cellplant cell Increases cell’s surface area for transport of Increases cell’s surface area for transport of

substances substances cells can be larger cells can be larger

Cell surfaces protect, support, and join cellsCell surfaces protect, support, and join cells

Cells interact with their environments and Cells interact with their environments and each other via their surfaceseach other via their surfaces

Many cells are protected by more than the Many cells are protected by more than the plasma membraneplasma membrane

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 plasmodesmata Connect by plasmodesmata (channels through the walls)(channels through the walls)

Vacuole

Wallsof twoadjacentplant cells

Plasmodesmata

Layersof one plantcell wall

Cytoplasm

Plasma membrane

Plant Cell TEMPlant Cell TEM

Typical Plant CellTypical Plant Cell

Origin of Mitochondria and Origin of Mitochondria and ChloroplastsChloroplasts

Both organelles are believed to have once Both organelles are believed to have once been free-living bacteria that were been free-living bacteria that were engulfed by a larger cell.engulfed by a larger cell.

Proposed Origin of Mitochondria Proposed Origin of Mitochondria and Chloroplasts and Chloroplasts

Evidence:Evidence: Each have their own DNAEach have their own DNA Their ribosomes resemble bacterial ribosomesTheir ribosomes resemble bacterial ribosomes 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

Cell Junctions Cell Junctions (4.18)(4.18)

Plasma membrane proteins connect Plasma membrane proteins connect neighboring cells - called cell junctionsneighboring cells - called cell junctions

Plant cells – plasmodesmata provide Plant cells – plasmodesmata provide channels between cellschannels between cells

Cell Junctions Cell Junctions (4.18)(4.18)

3 types of cell junctions in animal cells3 types of cell junctions in animal cells1.1. Tight junctionsTight junctions

2.2. Adchoring junctionsAdchoring junctions

3.3. Gap junctionsGap junctions

Cell JunctionsCell Junctions

1.1. Tight junctions – membrane proteins seal Tight junctions – membrane proteins seal neighboring cells so that water soluble neighboring cells so that water soluble substances cannot cross between themsubstances cannot cross between them

• See between stomach cellsSee between stomach cells

Cell JunctionsCell Junctions

2.2. Anchoring junctions – cytoskeleton fibers Anchoring 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 on Gap 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

Gap junction

Anchoring junction

Tight junction

Cell structure

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