Cells

CellsChapter 3

Generalized View of the CellThere are three main parts to a cell and each part has a very specific function.Read pages 49-50 to discover them on your own.

The Plasma Membrane

Sturdy barrier; made mainly of proteins and lipidsLipid bilayer made of three types of lipid molecules: Phospholipids (lipids that contain phosphorus), cholesterol , glycoproteins (lipids that contain carbohydrates)Two types of proteins:Intergral protein extend through(2) Peripheral loosely attached to interior/exterior example: glycoproteins proteins attached to carbohydratesSelectively permeable--controls what in/out; to water, most nonpolar lipid soluble molecules: fatty acids, fat-soluble vitamins, steroids, oxygen, carbon dioxideImpermeable to: ions (cross through ion channels), charged or polar molecules: glucose, amino acids (these cross through integral protein assist, channels; transporters change shape from one side to other)Receptors (integral proteins) recognize & bind to specific molecules; i.e. hormonesEnzymes (integral and peripheral proteins)Membrane glycoproteins and glycolipids = cell identity markers id same cell tissue or foreign cells (danger)3CytoplasmCytoplasm consists of fluid inside plasma membrane and membrane-bound organelles except the nucleusCytosol consists of fluid inside plasma membrane but excludes nucleus and membrane-bound organelles

4Transport Across the Plasma MembraneFluids in average body = ~60%ICF -- inside the cell (cytosol)ECF outside the cellInterstitial fluid (between cells of tissues)Plasma (blood vessels)Lymph (lymphatic vessels)Cerebrospinal fluid (within and around brain/spinal cord)Materials dissolve into these body fluids; direction of movement dependent upon concentration (amount of solute in solution)

5Concentration GradientsDifferences between ICF and ECF in solute concentration

3% salt solution 5% salt solution ??? Water ??? Water

Passive ActiveHigh to low Low to highNo energy needed Energy needed

Would this be passive or active6Concentration GradientsDifferences between ICF and ECF in solute concentration

3% salt solution 5% salt solution 97% Water 95% Water

Passive High to low until dynamic equilibrium reachedDown concentration gradient No energy needed

Do Practice Problem7Passive ProcessesDoes not require the use of energyDiffusion defined:Substance moves due to kinetic energyMovement from high concentration to low concentrationMovement of more molecules in one direction is called net diffusionMovement down the concentration gradientContinues until equilibrium is reached

Two types of diffusionSimple diffusion: lipid-soluble substances, simple cross membrane down the gradientFacilitated diffusion: ions, through pores of ion channels of integral proteins

NO ENERGY NEEDEDSimple: oxygen, carbon dioxide, nitrogen gases; fatty acids, steroids, fat-soluble vitamins (A, D, E, and K), glycerol, small alcohol and ammonia, water, (polar) and urea (polar)SIMPLE DIFFUSION ALLOWS GAS EXCHANGES BETWEEN BODY AND BLOOD CELLS AND BLOOD AND AIR WITHIN THE LUNGSALLOWS WASTE TO LEAVE THE BODY

Facilitated through pores: ions of potassium, chloride, sodium, calcium through gatedFacilitated: through integral protein assist; substance binds to specific transporter, transporter changes shape, release substance on other side (hormone directed process) glucose, fructose, galactose, urea, and some vitamins 9Osmosis Net movement of water down the gradient; lower solute concentration to higher solute concentration through Lipid bilayerIntegral proteins

20% sucrose80% waterDO PRACTICEBook problem and packet, sac permeable to water not sucrose; filled with solution is 20% sucrose & 80% water placed in 100% waterMine one side 20 sucrose 80 water, mine moves from high water concentration to low, levels go up because water moves in but sucrose cannot move out, pressure forces some water back out thus maintaining equilibrium, movement equal back and forthDo practice problem in packetWILL LEVELS CONTINUE TO GO UP UNTIL =???? YES!!!! YOUR LEVELS CONTINUE TO GO UP UNTIL EQUILIBRIM IS REACHED10Osmotic PressurePressure exerted on plasma membrane due to a solution containing solute particles that cannot pass through membraneHigher solute concentration = higher osmotic pressureLower solute concentration = lower osmotic pressure11Osmotic SolutionsIsotonic solution: cells maintain normal shape and volume; concentration of solutes equal on both sides of membraneHypotonic solution: higher concentration of water outside; higher concentration of solutes than cytosol inside cellWater molecules will enter cell faster than they leave it = cell will swell, eventually burstBursting of red blood cells referred to as hemolysisHypertonic solution: higher concentration of water inside; lower concentration of solutes than cytosol inside cellWater molecules will leave cell faster than they enter it = cell will shrinkShrinkage of red blood cells referred to as crenation

12Cell TonicityTonicityis a measure of the effectiveosmotic pressuregradient (as defined by the water potential of the two solutions) of twosolutions separated by asemi-permeable membrane.relative concentration of the solutions determines the direction and extent ofdiffusionUnlike osmotic pressure, tonicity is influenced only bysolutesthat cannot cross the membrane.solutes able to freely cross the membrane do not affect tonicity because they will always be in equal concentrations on both sides of the membraneThere are three classifications of tonicityHypertonic (hypertonicity)Hypotonic (hypotonicity)Isotonic (isotonicity)

Hypertonicity refers to a greater concentration. In biology, a hypertonic solution is one with a higher concentration of solutes outside the cell than inside the cell. When a cell is immersed into a hypertonic solution, the tendency is for water to flow out of the cell in order to balance the concentration of the solutes. Likewise, the cytosol of the cell is conversely categorized as hypotonic, opposite of the outer solution.Hypotonicity refers to a lesser concentration. In biology, a hypotonic solution has a lower concentration of solutes outside the cell than inside the cell. In an attempt to balance the concentrations of solutes inside and outside the cell, water will rush into the cell, and can cause it to burst.An isotonic solution is one in which its effectiveosmoleconcentration is the same as the solute concentration of a cell. In this case the cell neither swells nor shrinks because there is no concentration gradient for water across the cell membrane. Water molecules diffuse through the plasma membrane in both directions, and as the rate of water diffusion is the same in each direction that cell will neither gain nor lose water. An ISO-osmolar solution can be hypotonic if the solute is able to penetrate the cell membrane. For example an ISO-osmolar urea solution is hypotonic to red blood cells causing their lysis. This is due to urea entering the cell down its concentration gradient followed by water. For example, the osmolarity ofnormal saline, 9 grams NaCl dissolved in water to a total volume of one litre, is a close approximation to the osmolarity of NaCl in blood (about 290mOsm/L). Thus, normal saline is almost isotonic to blood plasma. Both sodium and chloride ions cannot freely pass through the plasma membrane as opposed tourea.13Short Video Reviewhttp://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.htmlhttps://www.youtube.com/watch?v=l33rQYic5ro

14Passive or Active?Have I been talking about passive, active, or passive and active transport?

Active TransportFrom low to high concentration; up the concentration gradientRequires the use of energyComes from splitting of ATP moleculeChanges shape of transporter protein, called a pumpTransports ions: Na+, K+, H+, Ca+2, I-, Cl-Example: sodium-potassium pump40% of a cells ATP expended on active transportDrugs like cyanide can turn off ATP production--FATALSodium-potassium pump expels sodium (3) from cell and brings in potassium (2) and acts as an enzyme to split ATPAlso extremely important because it maintains osmotic balance of fluids out v. inside the cell by constantly regulating sodium and potassium that easily leaks into and out of a cell; osmotic balance is needed for the ability of cells to generate electrical signals for action potentials16Cyanide Cyanide can be a colorless gas, such as hydrogen cyanide (HCN) or cyanogen chloride (CNCl), or a crystal form such as sodium cyanide (NaCN) or potassium cyanide (KCN).Cyanide sometimes is described as having a bitter almond smell, but it does not always give off an odor, and not everyone can detect this odor.You could be exposed to cyanide by breathing air, drinking water, eating food, or touching soil that contains cyanide.Cyanide enters water, soil, or air as a result of both natural processes and industrial activities. When present in air, it is usually in the form of gaseous hydrogen cyanide.Smoking cigarettes is probably one of the major sources of cyanide exposure for people who do not work in cyanide-related industries.

Transport in VesiclesVesicles small sacs formed by budding off of membranesTransport substances within the cell from one structure to anotherEnergy source again is ATPTake in substances from ECF and transport substances out to ECFEndocytosis: materials moved into cellPhagocytosis to eat - solidsBulk-phase endocytosis(pinocytosis) liquidsExocytosis: materials moved out of cellEndocytosis Endocytosis: capturing substance or particle from outside the cell by engulfing it within membrane folds from the cell membrane and releasing it into cytosol. There are two main kinds of endocytosis:PhagocytosisBulk-phase endocytosis (pinocytosis)

19PhagocytosisPhagocytosis cellular eating Particles bind to plasma membrane receptorsProjections called pseudopods extend surround particles and portions of the membrane fuse to form a vesicle Extensions of the plasma membrane and cytoplasmPseudopods vesicle formed called a phagosomePhagosome enters the cell, fuses with lysosomesLysosome enzymes break down phagosomes contentsAny undigested content remains in the phagosome, now called a residual body

Occurs only in phagocytes (certain white blood cells and macrophages), cells specialized to engulf and destroy bacteria, viruses, aged dying cells, and foreign matters protecting body from disease

Bulk-phase endocytosis (pinocytosis)Bulk-phase endocytosis (pinocytosis) cellular drinking Plasma membrane folds inward, forming a vesicle allowing tiny droplets of extracellular fluid that contain dissolved substances to be surroundedVesicle detaches or pinches off of the plasma membrane and enters the cytosolLiquid is encircled within a pinocytic vesicleVesicle fuses with a lysosome, enzymes degrade engulfed solutesDegraded solutes; like amino acids and fatty acids leave the lysosome to be used elsewhere in the cell

ExocytosisExocytosis: process of vesicles fusing with the plasma membrane and secretes their contents to the outside of the cell. All cells do exocytosis process, but most important in:Secretory cells Release digestive enzymes, hormones, mucus, and other secretionsNerve cellsRelease neurotransmitters

22CytoplasmConsists of all the cellular contents between the plasma membrane and the nucleus and includes both cytosol and organelles.

23CytosolCytosol is the liquid portion of the cytoplasm that surrounds the organelles and makes up about 55% of the cells volume.75%-90% of cytosol is water, the rest is composed of dissolved solutes and suspended particles.Examples: ions, glucose, amino acids, fatty acids, proteins, lipids, ATP, and waste.Site of many chemical reactions Maintain cell structure and enable cell growth

CytoskeletonExtends throughout cytosolNetwork of three different types of protein filaments:MicrofilamentsIntermediate filamentsMicrotubules

MicrofilamentsContribute to cell strength and shapeFunction: Provide mechanical support and help generate movementAnchor cytoskeleton to integral proteins Provide support for microvilli

MicrovilliFingerlike projections of the plasma membraneIncrease cell surface areaFound mostly in areas with great absorption needs like the small intestinesHelp cells attach to one another or extracellular materialsInvolved in muscle contractions, cell division, and cell locomotionMigration of embryonic cellsInvasion of tissues by white blood cells (WBCs) to fight diseaseMigration of skin cells in wound healing

Intermediate Filaments & MicrotubulesIntermediate FilamentsFound in parts of cells subjected to tension (stretching)Hold organelles in placeAttach cells to one anotherMicrotubulesLong, hollow tubesHelp determine cell shapeFunction as transport system forOrganelle movementSecretory vesiclesMigration of chromosomesCreate movement of cilia and flagella

OrganellesFunctions and identification of the organelles are your responsibility since this a total biology review areaInformation found on pages 58-62 of your textbookAssign for homework, then do lysosomes, peroxisomes, and proteasomes slides and assign functions of the rest for homework 28Lysosomes Membrane-enclosed vesiclesMay contain up to 60 different digestive enzymesFuse with other vesicles during endocytosisRecycle the cells own structures (worn-out organelles) autophagyMay destroy own cell autolysisThis cause tissue deterioration after deathFaulty lysosomes can contribute to certain diseases, i.e. Tay-Sachs disease

Page 13 of packet. Tay-sachs children jewish nerve cells accumulate glycolipid ganglioside causes muscle rigidity leads to blindness, dementia, lose of coordination die by age 529Peroxisomes Smaller than lysosomesContain enzymes called oxidases that oxide (remove hydrogen atoms from) various substancesCreating a by-product of hydrogen peroxide H2O2Potentially toxic compound associated with free radical superoxidesBUT peroxisomes also contain catalase which breaks down H2O2Oxidize toxic substances Abundant in liver

Proteasomes Tiny, barrel-like structureDestroys unneeded, damaged, or faulty proteins from the cytosolContain enzyme called proteaseCuts proteins into small peptidesSo other enzymes can break them down to amino acids from which new proteins can be built

Remind them to do rest on their own31NucleusOn your own, this is also a biology review topicLabel the diagram on page 14 of your packetList the functions of the nucleus alsoInformation found on page 62 of your textbook

32Gene Action: Protein SynthesisOn your own, this is also a biology review topicInformation found on pages 64-65 of your textbook.Show next slide and briefly refresh them on synthesis process33Protein Synthesis

DNA transcribed in nucleus to mRNA, leaves nucleus goes to ribosome there translated into amino acids, peptide bonds form between amino acids and polypeptide chain grows.34Somatic Cell DivisionDamaged, diseased, or worn out cells are replacedTwo types of cell division:Reproductive cell division-meiosisWill be discussed in later chaptersSomatic cell division-mitosisDivision into two identical cellsDivision occurs through a sequence of changes called the cell cycleTwo major parts to cell cycleInterphase: when cell is not dividingMitotic phase: when cell is dividingSomatic cell replacement replaces dead and injured cells and adds ones for tissue growth35Interphase1st step is DNA replicationThen production of new organelles and cytoplasmic components for the new cellHigh metabolic activityA lot of cell growth

Mitotic PhaseMitosis followed by Cytokinesis (splitting of the cytoplasm)Chromosomes are visible during this phase under a microscope

Can you identify this phase? CLICKprophaseCan you identify this phase? CLICKanaphase

37Nuclear Division: MitosisFour stages:ProphaseChromatin condenses into visible chromosomesCentrioles migrate to opposite polesMitotic spindles form attach to centromeres of chromatidsNuclear envelop breaks downMetaphaseChromatids line up at equator (metaphase plate)AnaphaseCentromeres split chromatids into chromosomesChromosomes dragged towards the polesTelophaseChromosomes uncoil into chromatinNuclear envelops reformsNucleolus reappearMitotic spindles break down

Cytoplasmic Division: CytokinesisDivision of cytoplasm and organelles between two new cellsBegins with formation of a cleavage furrow in plasma membrane that pinches inward Cells return to Interphase

Complete Process of Somatic Cell Division

Cellular DiversityAverage humans has about 100 trillion cells of varying sizesCell size is measured in micrometers (m)1 micrometer = 1 one-millionth of a meterLargest cell in human body is an oocyte with a diameter of 140 mAverage hair strands is ~100 m in diameterCells can be round, oval, flat, cube-shaped, column-shaped, elongated, star-shaped, cylindrical, or disc-shapedShape is related to functionRound: oocyte Oval: Liver Flat: Squamous

Cube-shaped: Cubiodal Column-shaped: Collumnar

Elongated: Collagen Star-shaped: Natural Killer Cells

Cylindrical: Skeletal Disc-shaped: RBCs

Round =female eggOval = liver cellFlat = epithelial; connective tissueCube= epithelial; connective tissueColumn = muscleElongated = Star-shaped = Cylindrical = skeletal muscle cellsDisc-shaped = red blood cells42Aging and CellsAs we age our cells ability to divide is diminished.DNA sequences that code for cell division break down.Free radical control becomes limited.Autoimmune responses slow down.