Chapter 7Chapter 7

Cell Structure: A Tour of the CellCell Structure: A Tour of the Cell

Cell:Cell: A basic unit of living matter separated from A basic unit of living matter separated from

its environment by a plasma membrane. its environment by a plasma membrane. The smallest structural unit of life. The smallest structural unit of life.

Cell Theory:Cell Theory: Developed in late 1800s. Developed in late 1800s.1. All living organisms are made up of one or 1. All living organisms are made up of one or

more cells.more cells.2. The smallest living organisms are single 2. The smallest living organisms are single

cells, and cells are the functional units of cells, and cells are the functional units of multicellular organisms.multicellular organisms.

3. All cells arise from preexisting cells.3. All cells arise from preexisting cells.

Microscope FeaturesMicroscope FeaturesMagnificationMagnification:: Increase in apparent size of an object. Increase in apparent size of an object. Ratio of image size to specimen size.Ratio of image size to specimen size.

Resolving powerResolving power: Measures clarity of image.: Measures clarity of image. Ability to see fine detail.Ability to see fine detail. Ability to distinguish two objects as separate.Ability to distinguish two objects as separate. Minimum distance between 2 points at which Minimum distance between 2 points at which

they can be distinguished as separate and they can be distinguished as separate and distinct.distinct.

MicroscopesMicroscopes Light Microscopes:Light Microscopes: Earliest microscopes Earliest microscopes

used. used. Lenses pass Lenses pass visiblevisible light through a specimen. light through a specimen. MagnificationMagnification: Highest possible from 1000 X to : Highest possible from 1000 X to

2000 X.2000 X. Resolving powerResolving power: Up to 0.2 : Up to 0.2 m (1 m (1 m = 1/1000 m = 1/1000

mm). mm).

Types of MicroscopeTypes of Microscope

Electron Microscopes:Electron Microscopes: Developed in 1950s. Developed in 1950s. Electron beamElectron beam passes through specimen. passes through specimen. MagnificationMagnification: Up to 200,000 X.: Up to 200,000 X. Resolving powerResolving power: Up to 0.2 nm (1nm = : Up to 0.2 nm (1nm =

1/1’000,000 mm). 1/1’000,000 mm). Two types of electron microscopes:Two types of electron microscopes:1. Scanning Electron Microscope:1. Scanning Electron Microscope: Used to study Used to study

cell or virus surfaces.cell or virus surfaces.2. Transmission Electron Microscope:2. Transmission Electron Microscope: Used to Used to

study internal cell structures.study internal cell structures.

Components of All Cells:Components of All Cells:

1. 1. Plasma membranePlasma membrane:: Separates cell contents Separates cell contents from outside environment. Made up of from outside environment. Made up of phospholipid bilayers and proteins.phospholipid bilayers and proteins.

2. 2. CytoplasmCytoplasm: Liquid, jelly-like material inside : Liquid, jelly-like material inside cell.cell.

3. 3. RibosomesRibosomes: Necessary for protein synthesis.: Necessary for protein synthesis.

Procaryotic versus Eucaryotic CellsFeature Procaryotic Eucaryotic

Organisms Bacteria All others (animals, plants,fungi, and protozoa)

Nucleus Absent Present

DNA One chromosome Multiple chromosomes

Size Small (1-10 um) Large (10 or more um)

Membrane Absent Present (mitochondria,Bound golgi, chloroplasts, etc.)Organelles

Division Rapid process Complex process(Binary fission) (Mitosis)

Relative Sizes of StructuresRelative Sizes of Structures

1 nanometer (101 nanometer (10-9 -9 m) m) water moleculewater molecule

10 nanomters (1010 nanomters (10-8 -8 m) m) small proteinsmall protein

100 nanometers (10100 nanometers (10-7 -7 m) m) HIV virusHIV virus

1 micron (101 micron (10-6 -6 m) m) cell vacuolecell vacuole

10 microns (1010 microns (10-5 -5 m) m) bacteriumbacterium

100 microns (10100 microns (10-4 -4 m) m) large plant celllarge plant cell

1 millimeter (101 millimeter (10-3 -3 m) m) single cell embryosingle cell embryo

Relative Sizes of Procaryotic and Eucaryotic Cells and Viruses

Relative Sizes of Cells and Other Objects

Prokaryotic CellsProkaryotic Cells

BacteriaBacteria and blue-green algae. and blue-green algae. Small sizeSmall size: Range from 1- 10 micrometers in length. : Range from 1- 10 micrometers in length.

About one tenth of eukaryotic cell.About one tenth of eukaryotic cell. No nucleusNo nucleus: DNA in cytoplasm or nucleoid region.: DNA in cytoplasm or nucleoid region. RibosomesRibosomes are used to make proteins are used to make proteins Cell wallCell wall: Hard shell around membrane: Hard shell around membrane Other structures that Other structures that maymay be present: be present:

• CapsuleCapsule: Protective, outer sticky layer. May be used for : Protective, outer sticky layer. May be used for attachment or to evade immune system.attachment or to evade immune system.

• PiliPili: : Hair-like projections (attachment)Hair-like projections (attachment)

• FlagellumFlagellum: Longer whip-like projection (movement): Longer whip-like projection (movement)

Procaryotic Cells: Lack a Nucleus and other Membrane Bound Organelles

Eucaryotic CellsEucaryotic Cells

Include protist, fungi, plant, and animal cells.Include protist, fungi, plant, and animal cells. NucleusNucleus: : Protects and houses DNAProtects and houses DNA Membrane-bound OrganellesMembrane-bound Organelles:: Internal Internal

structures with specific functions.structures with specific functions. Separate and store compoundsSeparate and store compounds Store energyStore energy Work surfacesWork surfaces Maintain concentration gradientsMaintain concentration gradients

Membrane-Bound Organelles of Eucaryotic Membrane-Bound Organelles of Eucaryotic CellsCells

NucleusNucleus Rough Endoplasmic Reticulum (RER)Rough Endoplasmic Reticulum (RER) Smooth Endoplasmic Reticulum (SER)Smooth Endoplasmic Reticulum (SER) Golgi ApparatusGolgi Apparatus LysosomesLysosomes VacuolesVacuoles ChloroplastsChloroplasts MitochondriaMitochondria

Eucaryotic Cells: Typical Animal Cell

Eucaryotic Cells: Typical Plant Cell

NucleusNucleusStructureStructure

Double nuclear membrane (Double nuclear membrane (envelopeenvelope)) Large nuclear Large nuclear porespores DNADNA (genetic material) is combined with histones (genetic material) is combined with histones

and exists in two forms:and exists in two forms:• Chromatin (Chromatin (Loose, threadlike DNALoose, threadlike DNA, most of cell life), most of cell life)• Chromosomes (Chromosomes (Tightly packaged DNATightly packaged DNA. Found only . Found only

during cell division)during cell division) NucleolusNucleolus: Dense region where ribosomes are made: Dense region where ribosomes are made

FunctionsFunctions

House and protect cell’s genetic information (DNA) House and protect cell’s genetic information (DNA) Ribosome synthesisRibosome synthesis

Structure of Cell Nucleus

Endoplasmic Reticulum (ER)Endoplasmic Reticulum (ER)

““Network within the cell”Network within the cell” Extensive maze of membranes that branches Extensive maze of membranes that branches

throughout cytoplasm.throughout cytoplasm. ER is continuous with plasma membrane and ER is continuous with plasma membrane and

outer nucleus membrane.outer nucleus membrane. Two types of ER:Two types of ER:

Rough Endoplasmic Reticulum (RER)Rough Endoplasmic Reticulum (RER)Smooth Endoplasmic Reticulum (SER)Smooth Endoplasmic Reticulum (SER)

Rough Endoplasmic Reticulum (RER)Rough Endoplasmic Reticulum (RER) Flat, interconnected, rough membrane sacsFlat, interconnected, rough membrane sacs ““Rough”Rough”: Outer walls are covered with : Outer walls are covered with

ribosomes.ribosomes.

RibosomesRibosomes: Protein making “machines”. : Protein making “machines”. May exist free in cytoplasm or attached to ER.May exist free in cytoplasm or attached to ER. RER FunctionsRER Functions::

Synthesis of cell and organelle Synthesis of cell and organelle membranesmembranes.. Synthesis and modification of Synthesis and modification of proteinsproteins.. Packaging, and transport of Packaging, and transport of proteinsproteins that are that are

secretedsecreted from the cell. from the cell. • Example: AntibodiesExample: Antibodies

Rough Endoplasmic Reticulum (RER)

Smooth Endoplasmic Reticulum (SER)Smooth Endoplasmic Reticulum (SER)

Network of interconnected tubular smooth Network of interconnected tubular smooth membranes.membranes.

““Smooth”Smooth”: No ribosomes: No ribosomes SER FunctionsSER Functions::

Synthesis of phospholipids, fatty acids, and Synthesis of phospholipids, fatty acids, and steroids (sex hormones).steroids (sex hormones).

Breakdown of toxic compounds (drugs, alcohol, Breakdown of toxic compounds (drugs, alcohol, amphetamines, sedatives, antibiotics, etc.).amphetamines, sedatives, antibiotics, etc.).

Helps develop tolerance to drugs and alcohol.Helps develop tolerance to drugs and alcohol. Regulates levels of sugar released from liver into Regulates levels of sugar released from liver into

the bloodthe blood Calcium storage for cell and muscle contraction.Calcium storage for cell and muscle contraction.

Smooth Endoplasmic Reticulum (SER)

Golgi ApparatusGolgi Apparatus Stacks of flattened membrane sacs that may be Stacks of flattened membrane sacs that may be

distended in certain regions. Sacs are not distended in certain regions. Sacs are not interconnected.interconnected.

First described in 1898 by Camillo Golgi (Italy).First described in 1898 by Camillo Golgi (Italy). Works closely with the ER to secrete proteins.Works closely with the ER to secrete proteins. Golgi FunctionsGolgi Functions::

Receiving sideReceiving side receives proteins in transport vesicles receives proteins in transport vesicles from ER.from ER.

ModifiesModifies proteins into final shape, sorts, and labels proteins into final shape, sorts, and labels proteins for proper transport.proteins for proper transport.

Shipping sideShipping side packages and sends proteins to cell packages and sends proteins to cell membrane for export or to other parts of the cell.membrane for export or to other parts of the cell.

Packages digestive enzymes in Packages digestive enzymes in lysosomeslysosomes..

The Golgi Apparatus: Receiving, Processing, and Shipping of Proteins

LysosomesLysosomes Small vesicles released from Golgi containing at Small vesicles released from Golgi containing at

least 40 different least 40 different digestive enzymesdigestive enzymes, which can , which can break down carbohydrates, proteins, lipids, and break down carbohydrates, proteins, lipids, and nucleic acids.nucleic acids.

Optimal pH for enzymes is about 5Optimal pH for enzymes is about 5 Found mainly in animal cells.Found mainly in animal cells. Lysosome FunctionsLysosome Functions::

Molecular garbage dump and Molecular garbage dump and recyclerrecycler of of macromolecules (e.g.: proteins).macromolecules (e.g.: proteins).

DestructionDestruction of foreign material, bacteria, viruses, of foreign material, bacteria, viruses, and old or damaged cell components.and old or damaged cell components.

DigestionDigestion of food particles taken in by cell. of food particles taken in by cell. After cell dies, lysosomal membrane breaks down, After cell dies, lysosomal membrane breaks down,

causing rapid causing rapid self-destructionself-destruction..

Lysosomes: Intracellular Digestion

Lysosomes, Aging, and DiseaseLysosomes, Aging, and Disease As we get older, our lysosomes become leaky, As we get older, our lysosomes become leaky,

releasing enzymes which cause tissue damage and releasing enzymes which cause tissue damage and inflammation.inflammation. Example: Cartilage damage in Example: Cartilage damage in arthritis.arthritis.

Steroids or cortisone-like anti-inflammatory agents Steroids or cortisone-like anti-inflammatory agents stabilize lysosomal membranes, but have other stabilize lysosomal membranes, but have other undesirable effects (affect immune function).undesirable effects (affect immune function).

Diseases from “Diseases from “mutantmutant” lysosome enzymes are ” lysosome enzymes are usually fatal:usually fatal: Pompe’s diseasePompe’s disease: Defective glycogen breakdown in liver.: Defective glycogen breakdown in liver. Tay-Sachs diseaseTay-Sachs disease:: Defective lipid breakdown in brain. Defective lipid breakdown in brain.

Common genetic disorder among Jewish people.Common genetic disorder among Jewish people.

VacuolesVacuoles

Membrane bound sac.Membrane bound sac. Different sizes, shapes, and functions:Different sizes, shapes, and functions:

Central vacuoleCentral vacuole:: In plant cells. Store starch, water, In plant cells. Store starch, water, pigments, poisons, and wastes. May occupy up to pigments, poisons, and wastes. May occupy up to 90% of cell volume.90% of cell volume.

Contractile vacuoleContractile vacuole:: Regulate water balance, by Regulate water balance, by removing excess water from cell. Found in many removing excess water from cell. Found in many aquatic protists.aquatic protists.

Food or Digestion VacuoleFood or Digestion Vacuole: Engulf nutrients in : Engulf nutrients in many protozoa (protists). Fuse with lysosomes to many protozoa (protists). Fuse with lysosomes to digest food particles.digest food particles.

Central Vacuole in a Plant Cell

Interactions Between Membrane Bound Organelles of Eucaryotic Cells

ChloroplastsChloroplasts Site of Site of photosynthesisphotosynthesis in plants and algae. in plants and algae.

COCO22 + H + H22O + Sun Light -----> Sugar + OO + Sun Light -----> Sugar + O22 Number may range from 1 to over 100 per Number may range from 1 to over 100 per

cell.cell. Disc shaped structure with three different Disc shaped structure with three different

membrane systems:membrane systems:1. Outer membrane1. Outer membrane: Covers chloroplast surface.: Covers chloroplast surface.2. Inner membrane2. Inner membrane: Contains enzymes needed to : Contains enzymes needed to

make make glucoseglucose during photosynthesis. Encloses during photosynthesis. Encloses stromastroma (liquid) and (liquid) and thylakoidthylakoid membranes. membranes.

3. Thylakoid membranes: 3. Thylakoid membranes: Contain chlorophyll, Contain chlorophyll, green pigment that traps solar energy. Organized green pigment that traps solar energy. Organized in stacks called in stacks called granagrana..

Chloroplasts Trap Solar Energy and Convert it to Chemical Energy

ChloroplastsChloroplasts Contain their own DNA, ribosomes, and Contain their own DNA, ribosomes, and

make some proteins. make some proteins. Can divide to form daughter chloroplasts.Can divide to form daughter chloroplasts. Type of Type of plastidplastid: Organelle that produces and : Organelle that produces and

stores food in plant and algae cells.stores food in plant and algae cells.Other plastids include:Other plastids include: LeukoplastsLeukoplasts: Store starch.: Store starch. ChromoplastsChromoplasts: Store other pigments that give : Store other pigments that give

plants and flowers color.plants and flowers color.

Mitochondria (Sing. Mitochondrion)Mitochondria (Sing. Mitochondrion) Site of Site of cellular respiration:cellular respiration:

Food (sugar) + OFood (sugar) + O22 -----> CO -----> CO22 + H + H22O + ATP O + ATP Change chemical energy of molecules into the Change chemical energy of molecules into the

useable energy of the useable energy of the ATPATP molecule. molecule. Oval or sausage shaped.Oval or sausage shaped. Contain their own DNA, ribosomes, and Contain their own DNA, ribosomes, and

make some proteins. make some proteins. Can divide to form daughter mitochondria.Can divide to form daughter mitochondria. Structure:Structure:

Inner and outer membranes.Inner and outer membranes. Intermembrane spaceIntermembrane space CristaeCristae (inner membrane extensions) (inner membrane extensions) MatrixMatrix (inner liquid) (inner liquid)

Mitochondria Harvest Chemical Energy From Food

Origin of Eucaryotic Cells Endosymbiont TheoryEndosymbiont Theory: Belief that : Belief that

chloroplasts and mitochondria were at one chloroplasts and mitochondria were at one point point independentindependent cellscells that entered and that entered and remained inside a larger cell.remained inside a larger cell. Both organelles contain their own DNABoth organelles contain their own DNA Have their own ribosomes and make their own Have their own ribosomes and make their own

proteins.proteins. Replicate independently from cell, by binary Replicate independently from cell, by binary

fission.fission. Symbiotic relationshipSymbiotic relationship

Larger cell obtains energy or nutrientsLarger cell obtains energy or nutrients Smaller cell is protected by larger cell.Smaller cell is protected by larger cell.

The CytoskeletonThe Cytoskeleton Complex network of thread-like and tube-Complex network of thread-like and tube-

like structures.like structures.Functions: Functions: Movement, structure, and structural Movement, structure, and structural

support.support.Three Cytoskeleton Components:Three Cytoskeleton Components:

1. Microfilaments1. Microfilaments: : Smallest cytoskeleton fibers. Smallest cytoskeleton fibers. Important for:Important for: Muscle contractionMuscle contraction: Actin & myosin fibers in : Actin & myosin fibers in

muscle cellsmuscle cells ““Amoeboid motionAmoeboid motion” of white blood cells” of white blood cells

Components of the Cytoskeleton are Important for Structure and Movement

Three Cytoskeleton Components:Three Cytoskeleton Components:

2. Intermediate filaments2. Intermediate filaments:: Medium sized fibersMedium sized fibers Anchor organelles (nucleus) and hold cytoskeleton Anchor organelles (nucleus) and hold cytoskeleton

in place.in place. Abundant in cells with high mechanical stress.Abundant in cells with high mechanical stress.

3. Microtubules3. Microtubules: : Largest cytoskeleton fibers. Largest cytoskeleton fibers. Found in:Found in: CentriolesCentrioles: A pair of structures that help move : A pair of structures that help move

chromosomes during cell division (mitosis and chromosomes during cell division (mitosis and meiosis).meiosis).

Found in animal cells, but not plant cells.Found in animal cells, but not plant cells. Movement of Movement of flagellaflagella and and ciliacilia..

Typical Animal CellTypical Animal Cell

Cilia and Flagella Projections used for Projections used for locomotionlocomotion or to or to movemove

substances along cell surface. substances along cell surface. Enclosed by plasma membrane and contain Enclosed by plasma membrane and contain

cytoplasm.cytoplasm. Consist of 9 pairs of Consist of 9 pairs of microtubulesmicrotubules surrounding two surrounding two

single microtubules (9 + 2 arrangement).single microtubules (9 + 2 arrangement).

Flagella:Flagella: Large whip-like projections.Large whip-like projections. Move in wavelike manner, used for locomotion.Move in wavelike manner, used for locomotion.

Example: Sperm cellExample: Sperm cell

Cilia:Cilia: Short hair-like projections.Short hair-like projections. Example: Human respiratory system uses cilia to remove Example: Human respiratory system uses cilia to remove

harmful objects from bronchial tubes and trachea.harmful objects from bronchial tubes and trachea.

Structure of Eucaryotic Flagellum

Cell SurfacesA. A. Cell wall:Cell wall: Much thicker than cell membrane, Much thicker than cell membrane,(10 to 100 X thicker).(10 to 100 X thicker).

Provides support and protects cell from lysis.Provides support and protects cell from lysis. PlantPlant and and algaealgae cell wall: Cellulose cell wall: Cellulose FungiFungi and and bacteriabacteria have other polysaccharides. have other polysaccharides. Not presentNot present in in animalanimal cells or cells or protozoaprotozoa..

Plasmodesmata:Plasmodesmata: Channels between adjacent plant Channels between adjacent plant cells form a circulatory and communication system cells form a circulatory and communication system between cells.between cells. Sharing of nutrients, water, and chemical messages.Sharing of nutrients, water, and chemical messages.

Plasmodesmata: Communication Between Adjacent Plant Cells

Cell Surfaces B.B. Extracellular matrix:Extracellular matrix: Sticky layer of glycoproteins Sticky layer of glycoproteins

found in found in animalanimal cells. cells. Important for attachment, support, protection, and Important for attachment, support, protection, and response to environmental stimuli.response to environmental stimuli.Junctions Between Animal Cells:Junctions Between Animal Cells: Tight JunctionsTight Junctions: Bind cells tightly, forming a leakproof : Bind cells tightly, forming a leakproof

sheet. Example: Between epithelial cells in stomach lining.sheet. Example: Between epithelial cells in stomach lining. Anchoring JunctionsAnchoring Junctions: Rivet cells together, but still allow : Rivet cells together, but still allow

material to pass through spaces between cells.material to pass through spaces between cells. Communicating JunctionsCommunicating Junctions: Similar to plasmodesmata in : Similar to plasmodesmata in

plants. Allow water and other small molecules to flow plants. Allow water and other small molecules to flow between neighboring cells. between neighboring cells.

Different Animal Cell Junctions

Important Differences Between Plant and Animal Cells

Plant cells Animal cellsCell wall None (Extracellular matrix)

Chloroplasts No chloroplasts

Large central vacuole No central vacuole

Flagella rare Flagella more usual

No Lysosomes Lysosomes present

No Centrioles Centrioles present

Differences Between Plant and Animal Cells

Animal Cell

Plant Cell

Typical Plant CellTypical Plant Cell

Summary of Eucaryotic Organelles Function: ManufactureFunction: Manufacture

NucleusNucleus RibosomesRibosomes Rough ERRough ER Smooth ERSmooth ER Golgi ApparatusGolgi Apparatus

Function: BreakdownFunction: Breakdown LysosomesLysosomes VacuolesVacuoles

Summary of Eucaryotic Organelles Function: Energy ProcessingFunction: Energy Processing

Chloroplasts (Plants and algae)Chloroplasts (Plants and algae) MitochondriaMitochondria

Function: Support, Movement, CommunicationFunction: Support, Movement, Communication Cytoskeleton (Cilia, flagella, and centrioles)Cytoskeleton (Cilia, flagella, and centrioles) Cell walls (Plants, fungi, bacteria, and some Cell walls (Plants, fungi, bacteria, and some

protists)protists) Extracellular matrix (Animals)Extracellular matrix (Animals) Cell junctionsCell junctions

The Cell Membrane and Cell The Cell Membrane and Cell TransportTransport

Functions of Cell Membranes Functions of Cell Membranes 1.1. SeparateSeparate cell from nonliving environment. Form cell from nonliving environment. Form

most organelles and partition cell into discrete most organelles and partition cell into discrete compartments.compartments.

2.2. Regulate passageRegulate passage of materials in and out of the cell of materials in and out of the cell and organelles. Membrane is and organelles. Membrane is selectively permeable.selectively permeable.

3.3. ReceiveReceive information that permits cell to sense and information that permits cell to sense and respond to environmental changes.respond to environmental changes.

HormonesHormones Growth factorsGrowth factors NeurotransmittersNeurotransmitters

4.4. CommunicationCommunication with other cells and the organism as with other cells and the organism as a whole. Surface proteins allow cells to recognize a whole. Surface proteins allow cells to recognize each other, adhere, and exchange materials.each other, adhere, and exchange materials.

I. I. Fluid Mosaic Model Fluid Mosaic Model of the Membraneof the Membrane1. Phospholipid bilayer1. Phospholipid bilayer: : Major component Major component

is a phospholipid bilayer.is a phospholipid bilayer.Hydrophobic tails face inwardHydrophobic tails face inwardHydrophilic heads face waterHydrophilic heads face water

2. Mosaic of proteins2. Mosaic of proteins: : Proteins “float” in the Proteins “float” in the phospholipid bilayer.phospholipid bilayer.

3. Cholesterol:3. Cholesterol: Maintains proper Maintains proper membrane fluidity.membrane fluidity.

The outer and inner membrane surfaces The outer and inner membrane surfaces are are differentdifferent..

MembranePhospholipidsForm aBilayer

The Membrane is a Fluid Mosaic of Phospholipids and Proteins

Notice that inner and outer surfaces are different

A. A. Fluid Quality of Plasma Fluid Quality of Plasma MembranesMembranes

In a living cell, membrane has same fluidity as salad In a living cell, membrane has same fluidity as salad oil.oil. Unsaturated hydrocarbonUnsaturated hydrocarbon tails tails INCREASEINCREASE

membrane fluiditymembrane fluidity Phospholipids and proteins drift laterally.Phospholipids and proteins drift laterally.

Phospholipids move very rapidly Phospholipids move very rapidly Proteins drift in membrane more slowlyProteins drift in membrane more slowly

CholesterolCholesterol: Alters fluidity of the membrane: Alters fluidity of the membrane Decreases fluidity at warmer temperatures (> Decreases fluidity at warmer temperatures (>

3737ooC)C) Increases fluidity at lower temperatures (< 37Increases fluidity at lower temperatures (< 37ooC)C)

B. B. Membranes Contain Two Types of Membranes Contain Two Types of ProteinsProteins

1. Integral membrane proteins1. Integral membrane proteins:: Inserted into the membrane. Inserted into the membrane. Hydrophobic region is adjacent to hydrocarbon tails.Hydrophobic region is adjacent to hydrocarbon tails.2. Peripheral membrane proteins2. Peripheral membrane proteins::

Attached to either the inner or outer membrane surface.Attached to either the inner or outer membrane surface.

Functions of Membrane Proteins:Functions of Membrane Proteins:1. Transport of materials across membrane1. Transport of materials across membrane2. Enzymes2. Enzymes3. Receptors of chemical messengers3. Receptors of chemical messengers4. Identification: Cell-cell recognition4. Identification: Cell-cell recognition5. Attachment:5. Attachment:

Membrane to cytoskeletonMembrane to cytoskeleton Intercellular junctionsIntercellular junctions

Membrane Proteins Have Diverse Functions

C. C. Membrane Carbohydrates and Cell-Cell Membrane Carbohydrates and Cell-Cell RecognitionRecognition

Found on Found on outsideoutside surface of membrane. surface of membrane. Important forImportant for Cell-cell recognitionCell-cell recognition:: Ability of one cell to Ability of one cell to

“recognize” other cells.“recognize” other cells. Allows immune system to recognize self/non-selfAllows immune system to recognize self/non-self IncludeInclude::

• Glycolipids: Lipids with sugarsGlycolipids: Lipids with sugars• Glycoproteins: Proteins with sugarsGlycoproteins: Proteins with sugars• Major histocompatibility proteinsMajor histocompatibility proteins (MHC or(MHC or

transplantationtransplantation antigensantigens).). Vary greatly among individuals and species.Vary greatly among individuals and species. Organ transplants require matching of cell markers Organ transplants require matching of cell markers

and/or immune suppression.and/or immune suppression.

The cell plasma membrane isThe cell plasma membrane is Selectively Selectively PermeablePermeable

A.A. Permeability of the Lipid Bilayer Permeability of the Lipid Bilayer1. 1. Non-polar (Hydrophobic) MoleculesNon-polar (Hydrophobic) Molecules

• Dissolve into the membrane and cross with easeDissolve into the membrane and cross with ease• The smaller the molecule, the easier it can crossThe smaller the molecule, the easier it can cross• Examples: OExamples: O22 , hydrocarbons, steroids , hydrocarbons, steroids

2. 2. Polar (Hydrophilic) MoleculesPolar (Hydrophilic) Molecules• Small polar uncharged molecules can pass through Small polar uncharged molecules can pass through

easily (e.g.: Heasily (e.g.: H22O , COO , CO22))

• Large polar uncharged molecules pass with difficulty Large polar uncharged molecules pass with difficulty (e.g.: glucose)(e.g.: glucose)

3. 3. Ionic (Hydrophilic) MoleculesIonic (Hydrophilic) Molecules• ChargedCharged ions or particles ions or particles cannotcannot get through get through

(e.g.: ions such as Na(e.g.: ions such as Na++ , K , K++ , Cl , Cl-- ) )

Transport Proteins in the membraneTransport Proteins in the membrane: : Integral Integral membrane proteins that allow for the membrane proteins that allow for the transport of specific molecules across the transport of specific molecules across the phospholipid bilayer of the plasma phospholipid bilayer of the plasma membrane.membrane.How do they work?How do they work?May provide a “hydrophilic tunnel” May provide a “hydrophilic tunnel”

(channel)(channel)May bind to molecule and physically move May bind to molecule and physically move

ititAre specific for the atom/molecule Are specific for the atom/molecule

transportedtransported

III. III. Passive transport:Passive transport: Diffusion of Diffusion of molecules across the plasma membranemolecules across the plasma membraneA.A. Diffusion Diffusion:: The net movement of a The net movement of a

substance from an area of substance from an area of highhigh concentration to area of concentration to area of lowlow concentration.concentration.Does not require energy. Does not require energy.

B.B. Passive transport Passive transport:: The The diffusiondiffusion of of substance across a biological membrane.substance across a biological membrane.Only substances which can cross bilayer Only substances which can cross bilayer

by themselves or with the aid of a proteinby themselves or with the aid of a proteinDoes not require the cell’s energyDoes not require the cell’s energy

Passive Transport: Diffusion Across a Membrane Does Not Require Energy

IV.IV. OsmosisOsmosis::

The The diffusiondiffusion of of waterwater across a semi- across a semi-permeable membrane. permeable membrane.

Through osmosis water will move from an Through osmosis water will move from an area with higher water concentrationarea with higher water concentration to to an area with lower water concentration.an area with lower water concentration.

SolutesSolutes can’t move across the semi- can’t move across the semi-permeable membrane.permeable membrane.

Osmotic PressureOsmotic Pressure:: Ability of a solution to take up water through Ability of a solution to take up water through osmosis.osmosis.

Example: The cytoplasm of a cell has a certain osmotic pressure Example: The cytoplasm of a cell has a certain osmotic pressure caused by the solutes it contains.caused by the solutes it contains.

There are three different types of solution when compared to the There are three different types of solution when compared to the interior (cytoplasm) of a cell:interior (cytoplasm) of a cell:

1. Hypertonic solution1. Hypertonic solution: : HigherHigher osmotic pressure than cell due to: osmotic pressure than cell due to:HigherHigher solute concentration than cell or solute concentration than cell or LowerLower water concentration than cell. water concentration than cell.

2. Hypotonic solution2. Hypotonic solution: : LowerLower osmotic pressure than cell due to: osmotic pressure than cell due to:LowerLower solute concentration than cell or solute concentration than cell or HigherHigher water concentration than cell. water concentration than cell.

3. Isotonic solution3. Isotonic solution: : SameSame osmotic pressure than cell. osmotic pressure than cell. Equal concentration of solute(s) and water than cell.Equal concentration of solute(s) and water than cell.

V. Cells depend on proper water V. Cells depend on proper water balancebalanceAnimal Cells:Animal Cells:Do best in Do best in isotonicisotonic solutions. solutions. Examples:Examples:

0.9% NaCl (Saline)0.9% NaCl (Saline) 5% Glucose5% Glucose

If solution is not isotonic, cell will be affected:If solution is not isotonic, cell will be affected: Hypertonic solutionHypertonic solution: : Cell undergoes crenation. Cell Cell undergoes crenation. Cell

“shrivels” or shrinks.“shrivels” or shrinks. Example: 5% NaCl or 10% glucoseExample: 5% NaCl or 10% glucose

Hypotonic solution:Hypotonic solution: Cell undergoes lysis. Cell swells Cell undergoes lysis. Cell swells and eventually bursts.and eventually bursts. Example: Pure water.Example: Pure water.

V. Cells depend on proper water V. Cells depend on proper water balancebalancePlant CellsPlant Cells:: Do best in hypotonic solutions, because the Do best in hypotonic solutions, because the

cell wall protects from excessive uptake of water.cell wall protects from excessive uptake of water. Hypertonic solution:Hypertonic solution: Cell undergoes plasmolysis.Cell undergoes plasmolysis. Cell Cell

membrane shrivels inside cell wall.membrane shrivels inside cell wall. Isotonic solution:Isotonic solution: Cell becomes flaccid or wilts. Cell becomes flaccid or wilts. Hypotonic solution:Hypotonic solution: Turgor. Increased firmness of Turgor. Increased firmness of

cells due to osmotic pressure.cells due to osmotic pressure. This is the reason why supermarkets spray fruits This is the reason why supermarkets spray fruits

and vegetables with pure water, making them look and vegetables with pure water, making them look firm and fresh. firm and fresh.

VI. VI. Facilitated Diffusion:Facilitated Diffusion: Some substances cannot cross the membrane Some substances cannot cross the membrane by themselves due to their size or charge.by themselves due to their size or charge.Membrane proteins facilitate the transport of Membrane proteins facilitate the transport of solutes down their concentration gradient. solutes down their concentration gradient. No cell energy is required.No cell energy is required.

Transport ProteinsTransport Proteins Specific Specific : : Only transport very specific Only transport very specific

molecules (binding site)molecules (binding site)GlucoseGlucoseSpecific ions (NaSpecific ions (Na++, K, K++, Cl, Cl-- ) )

Facilitated Diffusion Uses a Membrane Transport Protein

VI. VI. Active TransportActive Transport:: Proteins use energy from ATP to actively Proteins use energy from ATP to actively

“pump” solutes across the membrane“pump” solutes across the membrane Solutes are moved Solutes are moved againstagainst a concentration a concentration

gradient.gradient. Energy is required.Energy is required.

ExampleExample: : The The NaNa++-K-K++ ATPase pump: ATPase pump: Energy of ATP hydrolysis is used to Energy of ATP hydrolysis is used to

move Namove Na++ out of the cell and K out of the cell and K+ + into into the cell the cell

EndocytosisEndocytosis:: Moving materials into cell with Moving materials into cell with vesiclesvesicles..Requires use of cell energy.Requires use of cell energy.

1. 1. PinocytosisPinocytosis (“Cell drinking”): Small droplets of liquid (“Cell drinking”): Small droplets of liquid are taken into the cell through tiny vesicles.are taken into the cell through tiny vesicles.

Not a specific process, all solutes in droplets are taken in.Not a specific process, all solutes in droplets are taken in.

2. 2. PhagocytosisPhagocytosis (“Cell eating”): Large solid particles are (“Cell eating”): Large solid particles are taken in by cell.taken in by cell.

Example:Example: Amoebas take in food particles by surrounding Amoebas take in food particles by surrounding them with cytoplasmic extensions called pseudopods.them with cytoplasmic extensions called pseudopods.

Particles are surrounded by a vacuole.Particles are surrounded by a vacuole.

Vacuole later fuses with the lysosome and contents are Vacuole later fuses with the lysosome and contents are digested.digested.

Endocytosis Uses Vesicles to Move Substances into the Cell

EndocytosisEndocytosis:: 3.3. Receptor mediated endocytosis Receptor mediated endocytosis: Highly specific. : Highly specific.

Materials moved into cell must bind to specific Materials moved into cell must bind to specific receptorsreceptors first.first.Example: Low density lipoproteins (LDL)Example: Low density lipoproteins (LDL): : Main form of cholesterol in blood. Main form of cholesterol in blood. Globule of cholesterol surrounded by single layer of Globule of cholesterol surrounded by single layer of

phospholipids with embedded proteins. phospholipids with embedded proteins. Liver cell receptors bind to LDL proteins and remove Liver cell receptors bind to LDL proteins and remove

LDLs from blood through receptor mediated LDLs from blood through receptor mediated endocytosis.endocytosis.

Familial hypercholesterolemiaFamilial hypercholesterolemia: Genetic disorder in : Genetic disorder in which gene for the LDL receptor is mutated. which gene for the LDL receptor is mutated. Disorder found in 1 in 500 human babies worldwide. Disorder found in 1 in 500 human babies worldwide. Results in unusually high levels of blood cholesterol.Results in unusually high levels of blood cholesterol.

Blood Cholesterol is Taken Up by Liver Cells through Receptor Mediated Endocytosis

ExocytosisExocytosis: : Used to Used to exportexport materials out of cell. materials out of cell. Materials in Materials in vesiclesvesicles fuse with cell membrane and are fuse with cell membrane and are released to outside.released to outside.

Tear glands export salty solution.Tear glands export salty solution. Pancreas uses exocytosis to secrete insulin.Pancreas uses exocytosis to secrete insulin.