Cell TheoryCell Theory

The cell is the basic structural and functional The cell is the basic structural and functional unit of lifeunit of life

Organismal activity depends on individual and Organismal activity depends on individual and collective activity of cellscollective activity of cells

Biochemical activities of cells are dictated by Biochemical activities of cells are dictated by subcellular structuresubcellular structure

Continuity of life has a cellular basisContinuity of life has a cellular basis

Figure 3.2

Secretion being releasedfrom cell by exocytosis

Peroxisome

Ribosomes

Roughendoplasmicreticulum

NucleusNuclear envelopeChromatin

Golgi apparatus

Nucleolus

Smooth endoplasmicreticulum

Cytosol

Lysosome

Mitochondrion

Centrioles

Centrosomematrix

Microtubule

Microvilli

Microfilament

Intermediate filaments

Plasmamembrane

Plasma MembranePlasma Membrane

Separates intracellular fluids from extracellular Separates intracellular fluids from extracellular fluidsfluids

Plays a dynamic role in cellular activityPlays a dynamic role in cellular activity Glycocalyx is a glycoprotein area abutting the Glycocalyx is a glycoprotein area abutting the

cell that provides highly specific biological cell that provides highly specific biological markers by which cells recognize one anothermarkers by which cells recognize one another

Fluid Mosaic ModelFluid Mosaic Model

Double bilayer of lipids with imbedded, Double bilayer of lipids with imbedded, dispersed proteinsdispersed proteins

Bilayer consists of phospholipids, cholesterol, Bilayer consists of phospholipids, cholesterol, and glycolipidsand glycolipids Glycolipids are lipids with bound carbohydrateGlycolipids are lipids with bound carbohydrate Phospholipids have hydrophobic and hydrophilic Phospholipids have hydrophobic and hydrophilic

bipolesbipoles

PLAYPLAY Membrane Structure

Fluid Mosaic ModelFluid Mosaic Model

Figure 3.3

Functions of Membrane ProteinsFunctions of Membrane Proteins

TransportTransport

Enzymatic activityEnzymatic activity

Receptors for signal Receptors for signal transductiontransduction

Figure 3.4.1

Functions of Membrane ProteinsFunctions of Membrane Proteins

Intercellular adhesionIntercellular adhesion Cell-cell recognitionCell-cell recognition Attachment to Attachment to

cytoskeleton and cytoskeleton and extracellular matrixextracellular matrix

Figure 3.4.2

PLAYPLAY Structural Proteins

Plasma Membrane SurfacesPlasma Membrane Surfaces

Differ in the kind and amount of lipids they Differ in the kind and amount of lipids they containcontain

Glycolipids are found only in the outer Glycolipids are found only in the outer membrane surfacemembrane surface

20% of all membrane lipid is cholesterol20% of all membrane lipid is cholesterol

Lipid RaftsLipid Rafts

Make up 20% of the outer membrane surfaceMake up 20% of the outer membrane surface Composed of sphingolipids and cholesterolComposed of sphingolipids and cholesterol Are concentrating platforms for cell-signaling Are concentrating platforms for cell-signaling

moleculesmolecules

Membrane JunctionsMembrane Junctions

Tight junction – impermeable junction that Tight junction – impermeable junction that encircles the cell encircles the cell

Desmosome – anchoring junction scattered Desmosome – anchoring junction scattered along the sides of cellsalong the sides of cells

Gap junction – a nexus that allows chemical Gap junction – a nexus that allows chemical substances to pass between cellssubstances to pass between cells

Membrane Junctions: Tight Membrane Junctions: Tight JunctionJunction

Figure 3.5a

Membrane Junctions: Membrane Junctions: DesmosomeDesmosome

Figure 3.5b

Membrane Junctions: Gap Membrane Junctions: Gap JunctionJunction

Figure 3.5c

Passive Membrane Transport: Passive Membrane Transport: DiffusionDiffusion

Simple diffusion – nonpolar and lipid-soluble Simple diffusion – nonpolar and lipid-soluble substances substances Diffuse directly through the lipid bilayerDiffuse directly through the lipid bilayer Diffuse through channel proteinsDiffuse through channel proteins

PLAYPLAY Diffusion

Passive Membrane Transport: Passive Membrane Transport: DiffusionDiffusion

Facilitated diffusion Facilitated diffusion Transport of glucose, amino acids, and ionsTransport of glucose, amino acids, and ions Transported substances bind carrier proteins or Transported substances bind carrier proteins or

pass through protein channelspass through protein channels

Carrier ProteinsCarrier Proteins

Are integral transmembrane proteinsAre integral transmembrane proteins Show specificity for certain polar molecules Show specificity for certain polar molecules

including sugars and amino acids including sugars and amino acids

Diffusion Through the Plasma Diffusion Through the Plasma MembraneMembrane

Figure 3.7

Extracellular fluid

Cytoplasm

Lipid-solublesolutes

Lipidbilayer

Lipid-insolublesolutes

Watermolecules

Small lipid-insolublesolutes

(a) Simple diffusion directly through the phospholipid bilayer

(c) Channel-mediated facilitated diffusion through a channel protein; mostly ions selected on basis of size and charge

(b) Carrier-mediated facilitated diffusion via protein carrier specific for one chemical; binding of substrate causes shape change in transport protein

(d) Osmosis, diffusion through a specific channel protein (aquaporin) or through the lipid bilayer

Passive Membrane Transport: Passive Membrane Transport: OsmosisOsmosis

Occurs when the concentration of a solvent is Occurs when the concentration of a solvent is different on opposite sides of a membrane different on opposite sides of a membrane

Diffusion of water across a semipermeable Diffusion of water across a semipermeable membranemembrane

Osmolarity – total concentration of solute Osmolarity – total concentration of solute particles in a solutionparticles in a solution

Tonicity – how a solution affects cell volumeTonicity – how a solution affects cell volume

PLAYPLAY Osmosis

Effect of Membrane Permeability Effect of Membrane Permeability on Diffusion and Osmosison Diffusion and Osmosis

Figure 3.8a

Effect of Membrane Permeability Effect of Membrane Permeability on Diffusion and Osmosison Diffusion and Osmosis

Figure 3.8b

Passive Membrane Transport: Passive Membrane Transport: FiltrationFiltration

The passage of water and solutes through a The passage of water and solutes through a membrane by hydrostatic pressuremembrane by hydrostatic pressure

Pressure gradient pushes solute-containing Pressure gradient pushes solute-containing fluid from a higher-pressure area to a lower-fluid from a higher-pressure area to a lower-pressure areapressure area

Effects of Solutions of Varying Effects of Solutions of Varying TonicityTonicity

Isotonic – solutions with the same solute Isotonic – solutions with the same solute concentration as that of the cytosolconcentration as that of the cytosol

Hypertonic – solutions having greater solute Hypertonic – solutions having greater solute concentration than that of the cytosolconcentration than that of the cytosol

Hypotonic – solutions having lesser solute Hypotonic – solutions having lesser solute concentration than that of the cytosolconcentration than that of the cytosol

Figure 3.10

Cytoplasm

Extracellular fluidK+ is released andNa+ sites are ready tobind Na+ again; thecycle repeats.

Cell ADP

Phosphorylationcauses theprotein tochange its shape.

Concentration gradientsof K+ and Na+

The shape change expels Na+ to the outside, and extracellular K+ binds.

Loss of phosphaterestores the originalconformation of thepump protein.

K+ binding triggersrelease of thephosphate group.

Binding of cytoplasmic Na+ to the pump proteinstimulates phosphorylationby ATP.Na+

Na+

Na+

Na+Na+

K+K+

K+

K+

Na+

Na+

Na+

ATPP

P

Na+

Na+Na+

K+

K+

P

Pi

K+

K+