Anatomy and PhysiologyAnatomy and Physiology

Chapter 3: The CellChapter 3: The Cell

Cell TheoryCell Theory

Cells are the building blocks of all plants and Cells are the building blocks of all plants and animals.animals.

Cells are produced by the division of pre-existing Cells are produced by the division of pre-existing cells.cells.

Cells are the smallest units that perform all vital Cells are the smallest units that perform all vital physiological functions.physiological functions.

Each cell maintains homeostasis at the cellular Each cell maintains homeostasis at the cellular level.level.

Homeostasis at the tissue, organ, system, and Homeostasis at the tissue, organ, system, and organism levels reflect the combined and organism levels reflect the combined and coordinated actions of many cells.coordinated actions of many cells.

CellsCells

Basic structural and functional unit of living Basic structural and functional unit of living organisms.organisms.

Cytology – study of cell structure and Cytology – study of cell structure and function.function.

Classes of Cells:Classes of Cells:– Sex cells – sperm and oocytes (eggs)Sex cells – sperm and oocytes (eggs)– Somatic cells – body cellsSomatic cells – body cells

Plasma MembranePlasma Membrane

Defines the extent of the cell and acts as a Defines the extent of the cell and acts as a fragile barrier between the inside and fragile barrier between the inside and outside of the cell.outside of the cell.

Exceedingly thin, but stable, structure Exceedingly thin, but stable, structure composed of a phospholipid bilayer with composed of a phospholipid bilayer with protein molecules dispersed throughout.protein molecules dispersed throughout.

Impermeable to water soluble molecules – Impermeable to water soluble molecules – semi-permeable.semi-permeable.

Phospholipid BilayerPhospholipid Bilayer

Polar, phospholipid heads are hydrophilic.Polar, phospholipid heads are hydrophilic.– Form inner and outer portions of the membrane Form inner and outer portions of the membrane

that comes in contact with the external cell that comes in contact with the external cell environment and the cytoplasm of the cell.environment and the cytoplasm of the cell.

Non-polar, fatty acid tails are hydrophobic.Non-polar, fatty acid tails are hydrophobic.– Form the inner portion of the membrane, Form the inner portion of the membrane,

between two layers of polar phospholipid heads; between two layers of polar phospholipid heads; doesn’t come in contact with any water at all.doesn’t come in contact with any water at all.

Glycoproteins serve as cell surface markers.Glycoproteins serve as cell surface markers.

Membrane ProteinsMembrane Proteins

IntegralIntegral– firmly inserted into the lipid membrane.firmly inserted into the lipid membrane.– Act as receptors for hormones and other Act as receptors for hormones and other

chemical messengers.chemical messengers.– Act as transmembrane proteins which have Act as transmembrane proteins which have

transport functions such as ion channels / pores transport functions such as ion channels / pores or carrier molecules.or carrier molecules.

– Consist of a hydrophobic and hydrophilic region Consist of a hydrophobic and hydrophilic region also.also.

Membrane ProteinsMembrane Proteins

PeripheralPeripheral– Not embedded in the membrane, but are Not embedded in the membrane, but are

attached to integral proteins exposed to the attached to integral proteins exposed to the surface.surface.

– Some are enzymes.Some are enzymes.– Some lead to cell shape changes associated Some lead to cell shape changes associated

with cell division.with cell division.– Some are responsible for muscle cell Some are responsible for muscle cell

contraction.contraction.

Membrane Protein FunctionsMembrane Protein Functions

Transport of molecules as carrier proteins Transport of molecules as carrier proteins and channels.and channels.

Two types of channels:Two types of channels:– ““Leaky” – water and ions move through all the Leaky” – water and ions move through all the

time.time.– Gated – open and close to regulate ion Gated – open and close to regulate ion

passage.passage.

Membrane Protein FunctionsMembrane Protein Functions

EnzymesEnzymes Receptor CellsReceptor Cells Cell adhesion – anchor cell to structure or Cell adhesion – anchor cell to structure or

other cells.other cells. Attachment to cytoskeleton – holds plasma Attachment to cytoskeleton – holds plasma

membrane to internal proteins; gives cell a membrane to internal proteins; gives cell a shape.shape.

Recognition – allows body to recognize Recognition – allows body to recognize foreign invaders (glycolipids)foreign invaders (glycolipids)

GlycocalyxGlycocalyx

““Sticky” carbohydrate rich area of the cell Sticky” carbohydrate rich area of the cell plasma membrane.plasma membrane.

Also contains glycoproteinsAlso contains glycoproteins Binds adjacent cells together.Binds adjacent cells together. Lubricates and protects cell membrane.Lubricates and protects cell membrane. Locomotion of specialized cells – white Locomotion of specialized cells – white

blood cells.blood cells.

Plasma Membrane FunctionsPlasma Membrane Functions

IsolationIsolation Sensitivity to changes in cellular Sensitivity to changes in cellular

environment.environment. Structural support.Structural support. Regulation of exchange with environment Regulation of exchange with environment

(semipermeable / selectivity permeable)(semipermeable / selectivity permeable)

Factors that Effect Factors that Effect Membrane PermeabilityMembrane Permeability

Size of ParticleSize of Particle Electrical Charge of ParticleElectrical Charge of Particle Shape of ParticleShape of Particle Lipid SolubilityLipid Solubility

Passive Transport Passive Transport

No net energy expended.No net energy expended. Occurs down a concentration Occurs down a concentration

gradient from an area of high gradient from an area of high concentration to an area of low concentration to an area of low concentration without using concentration without using ATP.ATP.

DiffusionDiffusion– Simple Diffusion – implies no Simple Diffusion – implies no

barrier to movement; occurs barrier to movement; occurs because of molecular collisions.because of molecular collisions.

Oxygen and carbon dioxide Oxygen and carbon dioxide exchangeexchange

Water and other small Water and other small molecules (glucose)molecules (glucose)

– Filtration Diffusion – under Filtration Diffusion – under pressure; hydrostatic pressure pressure; hydrostatic pressure forces water across a forces water across a membrane, transporting small membrane, transporting small molecules with it.molecules with it.

– Facilitated Diffusion – Facilitated Diffusion – substance coupled to a carrier substance coupled to a carrier molecule; may be an integral molecule; may be an integral membrane protein.membrane protein.

Carriers are highly specificCarriers are highly specific Saturation limits amount of Saturation limits amount of

molecules that can be movedmolecules that can be moved May be regulated by the May be regulated by the

binding of cofactors and binding of cofactors and coenzymes.coenzymes.

– Example – glucose + insulin – Example – glucose + insulin – uptake occurs 7-10X faster.uptake occurs 7-10X faster.

Factors Affecting DiffusionFactors Affecting Diffusion

Distance – the larger the distance between the Distance – the larger the distance between the molecule and the cell membrane, the longer molecule and the cell membrane, the longer diffusion takes.diffusion takes.

Size of Gradient – the larger the concentration Size of Gradient – the larger the concentration factor, the faster diffusion occurs.factor, the faster diffusion occurs.

Molecular Size – smaller molecules diffuse faster.Molecular Size – smaller molecules diffuse faster. Temperature – increasing temperature increases Temperature – increasing temperature increases

diffusion rates.diffusion rates. Electrical Forces – like charges repel each other, Electrical Forces – like charges repel each other,

while opposite charges attract each other.while opposite charges attract each other.

TonicityTonicity

Ability of a solution to change the tone or shape of Ability of a solution to change the tone or shape of cells by altering their internal water volume.cells by altering their internal water volume.– Isotonic Isotonic solute in = solute out; no NET movement of solute in = solute out; no NET movement of

water.water.– Hypertonic Hypertonic number of solute particles is larger number of solute particles is larger

outside the cell than inside the cell; net movement of outside the cell than inside the cell; net movement of water is out; cause cell to crenate.water is out; cause cell to crenate.

– Hypotonic Hypotonic number of solute particles is smaller number of solute particles is smaller outside the cell than inside the cell; net movement is outside the cell than inside the cell; net movement is into the cell; causes the cell to burst.into the cell; causes the cell to burst.

Passive TransportPassive Transport

Osmosis – diffusion of water through a Osmosis – diffusion of water through a semipermeable membrane from an area of semipermeable membrane from an area of high water content to an area of low water high water content to an area of low water concentration.concentration.

Osmotic Pressure – indication of force of Osmotic Pressure – indication of force of water movement into a solution as a result water movement into a solution as a result of solute concentration.of solute concentration.

Active Transport ProcessesActive Transport Processes

Movement of particles using energy (ATP); Movement of particles using energy (ATP); not concentration dependent.not concentration dependent.– Solute / Ion Pumps Solute / Ion Pumps

proteins in the plasma membrane that move ions proteins in the plasma membrane that move ions selectively in or out of the cellselectively in or out of the cell

creates a polarized membranecreates a polarized membrane Sodium – Potassium PumpSodium – Potassium Pump

– Sodium ions and potassium ions must be recaptured and Sodium ions and potassium ions must be recaptured and moved back to their original starting points. Each ATP used moved back to their original starting points. Each ATP used moves 3 sodium and 2 potassium back.moves 3 sodium and 2 potassium back.

Active Transport ProcessesActive Transport Processes

Bulk Transport – movement of large particles by Bulk Transport – movement of large particles by means of vesicles.means of vesicles.– Method:Method:

Molecule comes in contact with the membraneMolecule comes in contact with the membrane Membrane surrounds molecule and takes it into the cell.Membrane surrounds molecule and takes it into the cell. Membrane pinches off, freeing the vesicle.Membrane pinches off, freeing the vesicle.

– Three Types:Three Types: Phagocytosis – large particles inPhagocytosis – large particles in Pinocytosis – liquid particles inPinocytosis – liquid particles in Exocytosis – Moving material out of the cellExocytosis – Moving material out of the cell

Membrane SpecializationsMembrane Specializations

Microvilli – minute, finger-like extensions of Microvilli – minute, finger-like extensions of the plasma membrane that increases the the plasma membrane that increases the cell surface area; contains a core of actin cell surface area; contains a core of actin (protein).(protein).

Cilia – hair-like projections that move Cilia – hair-like projections that move substances along the surface of the cell.substances along the surface of the cell.

Membrane JunctionsMembrane Junctions

Tight Junctions – protein molecules fuse Tight Junctions – protein molecules fuse together; forming impermeable junctions.together; forming impermeable junctions.

GlycocalyxGlycocalyx ““Tongue in groove” fit of adjacent plasma Tongue in groove” fit of adjacent plasma

membranes.membranes. Gap Junctions – allow direct passage of Gap Junctions – allow direct passage of

chemicals between adjacent cells through chemicals between adjacent cells through hollow cylinders.hollow cylinders.