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