Cellular Level of Organization

CellsThere are approximately 200 different

types of cells that make up the basic structures of the human body.

Cell division creates new cells. A “parent” cell divides into two new “daughter” cells.

Different types of cells carry out different functions in the body.

Parts of a CellPlasma membraneCytoplasmCytosolOrganellesNucleusChromosomesGenes

3 main parts of a cellPlasma membrane – the cells flexible outer

surface.Cytoplasm – all the cellular contents

between the plasma membrane and the nucleus.

Nucleus – a large organelle that houses most of the cell’s DNA. Chromosomes and genes are contained here.

Typical Structures

Plasma MembraneA flexible, yet sturdy barrier that surrounds

and contains the cytoplasm of a cell.Fluid mosaic model.Lipid BilayerMembrane proteinsMembrane Permeability – Selective

Plasma Membrane continued…Gradients

ConcentrationElectrochemical

OsmosisDiffusionActive Transport

Lipid BilayerPhospholipids – 2 layersAmphipathic – polar and nonpolarHydrophilicHydrophobic

Membrane ProteinsIntegral Proteins – extend into or through

the lipid bilayer.Transmembrane proteins

Peripheral Proteins – attached to either the inside or outside of the membrane.

Functions of Membrane ProteinsIon channelTransporterReceptorEnzymeCell Identity MarkerLinker

Membrane PermeabilitySelectively PermeablePermeable to nonpolar, uncharged

molecules, such as oxygen, carbon dioxide, & steroids.

Impermeable to ions and charged or polar molecules, such as glucose.

Slightly permeable to water and urea.

GradientsConcentration Gradient – A difference in

the concentration of a chemical from one place to another.

Electrochemical Gradient – The combination of the effects of the concentration gradient and the membrane potential.

Transport Across the MembranePassive Transport – does not require

cellular energy.Substances move down their concentration

or electrochemical gradients using only their own kinetic energy.

Active Transport – requires cellular energy in the form of ATP.

3 Types of Passive TransportDiffusion through the lipid bilayer.Diffusion through membrane channels.Facilitated diffusion.

Endocytosis

Material enters the cell in vesicles.

Exocytosis

Material leaves the cell in vesicles.

DiffusionMaterials diffuse from areas of high

concentration to areas of low concentration. They move down their concentration gradient.

Equilibrium – molecules are mixed uniformly throughout the solution.

Factors Influencing DiffusionSteepness of the concentration gradient.Temperature.Mass of the diffusing substance.Surface Area.Diffusion distance.

OsmosisThe net movement of a solvent (water)

across a selectively permeable membrane.Water moves from an area of higher water

concentration to an area of lower water concentration.

Osmotic PressureA solution containing solute particles that

cannot cross the membrane exerts a force called osmotic pressure.

The greater the number of solute particles the greater the pressure.

TonicityA solution’s tonicity measures the

solution’s ability to change the volume of cells by altering their water content.

Isotonic – cell maintains shapeHypotonic – cell swells and burstsHypertonic – cell shrinks - crenation

Cytoplasm2 components

Cytosol – fluid portion that surrounds organelles.55% of total cell volumeWater with dissolved and suspended components

Ions, glucose, amino acids, fatty acids, proteins, lipids, ATP, and waste products.

Organelles – specialized structuresSpecific shapesSpecific functions

CytoskeletonNetwork of protein filaments.Structural framework for the cell.3 Types of filaments

Microvilli – small – increase surface areaIntermediate filamentsMicrotubules – largest – in cilia and flagella –

participate in cell division.

CentrosomeLocated near the nucleusPlays a critical role in cell division

Cilia and FlagellaComprised of microtubules.Cilia – short, hairlike projections that

extend from the surface of the cell.Line respiratory tractMovement is paralyzed by nicotine

Flagella – longer than ciliaUsually move an entire cellSperm’s tail

RibosomesSites of protein synthesisFree Ribosomes – located in cytosolAttached to nuclear membrane and ERIn mitochondria

Endoplasmic Reticulum ERPlasmic = cytoplasm; reticulum = networkNetwork of folded membranesTransports substances throughout cellRough ER – ribosomes attached –

synthesizes proteinsSmooth ER – synthesizes fatty acids and

steroids

Rough ER

Smooth ER

Golgi ComplexConsists of 3 – 20 golgi cisternae

(membranous sacs)Modifies, sorts, and packages proteins for

distributionProteins leave through secretory vesicles,

membrane vesicles, or transport vesicles.

LysosomesLyso = dissolving; somes = bodiesContain powerful digestive enzymes and

hydrolytic enzymesLysosomal enzymes can destroy their own

cell – autolysis (due to pathology)

Lysosome

MitochondriaGenerate ATP – “powerhouses” of the cell

Mitochondrian with Matrix

Mitochondria

NucleusSpherical or oval shapedMost prominent feature in the cellMost structures have a single nucleus,

although mature RBCs have noneContain genes arranged in chromosomesGenome – total genetic information for an

organism

Nucleus

Nucleus

Cell DivisionSomatic Cell Division – replaces dead or

injured cells and adds new ones for growth.MitosisProduces 2 identical daughter cells

Reproductive Cell Division – produces gametes – sperm and oocytes.meiosis

Cell Cycle2 major phases

Interphase – the cell is not dividingMitotic phase – the cell is dividing

InterphaseThe cell replicates its DNA during this

phase.Produces additional organelles and

cytosolic components.

Mitotic PhaseNuclear Division – MitosisCytoplasmic Division - Cytokinesis

MitosisProphase

Chromatin fibers condense and shorten.Metaphase

The microtubules align the centromeres of the chromatid pairs.

AnaphaseThe centromeres split separating the two

members of each chromatid pair.Telophase

Identical chromosomes uncoil and a nuclear envelope forms around each mass.

CytokinesisDivision of the parent cell’s cytoplasm and

organelles into two daughter cells.

Cellular DiversityThe body of an average human adult is

composed of nearly 100 trillion cells.Approximately 200 different types.The largest cell is the oocyte