Cells. Cell consists of nucleus and cytoplasm. In cytoplasm - organelles (“little organs”)
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Transcript of Cells. Cell consists of nucleus and cytoplasm. In cytoplasm - organelles (“little organs”)
Cells
• Cell consists of nucleus and cytoplasm.
• In cytoplasm - organelles (“little organs”)
• Cell membrane – boundary of cell.
• Membrane thin but selectively permeable (allows certain materials to pass through but not others).
http://www.geosciences.unl.edu/~dbennett/images/Cell_membrane.gif
• Membrane has receptors that help receive messages (i.e. hormones)
• Called phospholipid bilayer (composed of phospholipids); also various proteins in membrane.
http://en.wikipedia.org/wiki/Cell_membrane
• 1Endoplasmic Reticulum – increased surface area for reactions to take place.
• ARough ER – Makes proteins (holds ribosomes)
• BSmooth ER – Makes lipids.
http://micro.magnet.fsu.edu/cells/endoplasmicreticulum/images/endoplasmicreticulumfigure1.jpg
• 2Ribosomes – some attached to rough ER (bound); some scattered throughout cytoplasm (free).
• Function - protein synthesis.
http://www.brown.edu/Courses/BI0105_Miller/read/ribosomes/ribosomes.jpg
• 3Golgi apparatus – proteins modified and packaged, then sent into cytoplasm.
http://web.mit.edu/esgbio/www/cb/org/golgi.gif
Modified protein
• 4Mitochondria – cellular respiration.
• Transform glucose into form of energy cell can use.
http://micro.magnet.fsu.edu/cells/mitochondria/images/mitochondriafigure1.jpg
• 5Lysosomes – contain enzymes that break down molecules of foreign particles (“garbage cans” of cell)
http://micro.magnet.fsu.edu/cells/lysosomes/images/lysosomesfigure1.jpg
• 6Centrosome – consists of 2 hollow cylinders (centrioles) - function in reproduction by separating chromosomes to new cells.
http://www.nicerweb.com/doc/class/bio1151/Locked/media/ch06/06_22CentrosomeStructur.jpg
• 7Cilia and 8flagella – extensions of cells; used for cell movement.
• Flagella - longer and fewer.• Cilia - smaller and more
numerous.
http://pediatrics.med.unc.edu/div/infectdi/pcd/images/cilia.jpg
Respiratory cilia
http://discover.edventures.com/images/termlib/f/flagella/support.gif
• 9Vacuoles – vesicles found in cell that have various functions.
• AFood vacuole – breakdown of food.
• BCentral vacuole – storage of waste.
• CContractile vacuole – removal of water (osmoregulation).
http://micro.magnet.fsu.edu/cells/plants/images/plantvacuolesfigure1.jpg
• 10Microfilaments and microtubules – responsible for movement within cell (also responsible for structure)
http://www.puc.edu/Faculty/Gilbert_Muth/art0053.jpg
• 11Nucleus – center of cell.• Covered by nuclear envelope
with pores to allow substances to pass through.
• Contains 12nucleolus (ribosome production) and chromatin (loose DNA).
http://micro.magnet.fsu.edu/cells/nucleus/images/nucleusfigure1.jpg
Membrane Structure
• Plasma membrane of cell selectively permeable (allows some substances to cross more easily than others)
• Made mostly of proteins and lipids (phospholipids).
• Phospholipids and proteins create unique physical environment (fluid mosaic model)
Phospholipid
• Membrane - bilayer - hydrophilic (water loving) heads pointing outwards, hydrophobic (water fearing) tails pointing inwards.
• Proteins help membrane to stick to water.
• Fluid because lipids and proteins can move laterally.
• As temperatures drop, liquid membrane can solidify.
• Saturated fatty acid tails - more solid than unsaturated fatty acid tails.
• Cholesterol found in membrane helps with fluidity of membrane.
• Membranes need to be fluid to work properly - systems in place to help keep it fluid.
• Two different types of proteins are found in membrane.
• 1Peripheral proteins not in membrane, bound to surface of protein.
• 2Integral proteins in membrane often spanning entire membrane.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/MembraneProteins.gif
• Membrane helps keep cell’s shape.
• Also aids in cell-to-cell recognition (ability of a cell to distinguish one type of neighboring cell from another)
• Some substances move steadily across membrane (sugars, ions, and wastes like CO2)
• Hydrophobic molecules (i.e. hydrocarbons, CO2, and O2) can dissolve in lipid bilayer and cross easily.
• Charged particles and polar molecules have more difficulty passing.
• Specific ions and polar molecules can cross lipid bilayer by passing through transport proteins that span membrane.
• Diffusion - tendency for substance to spread out in open area.
• Permeable membrane separating a solution with dye molecules from pure water, dye molecules will cross barrier randomly.
http://epswww.unm.edu/coursinf/eps462/graphics/diffusion.gif
• No force acting upon it - substance will tend to move down it’s concentration gradient from where it is more concentrated to less concentrated (passive transport).
• Diffusion of molecules with limited permeability through lipid bilayer may be assisted by transport proteins (facilitated diffusion)
http://w3.uokhsc.edu/human_physiology/presentation/facildiffani.gif
• Difference in concentration - ions move from one area to other.
• Solution with higher [ ] solutes - hypertonic.
• Solution with lower [ ] solutes -hypotonic.
• [ ] equal - isotonic.
http://www.biologycorner.com/resources/hypertonic.gif
http://www.biologycorner.com/resources/isotonic.gif
http://www.biologycorner.com/resources/hypotonic.gif
• Solution hypertonic - higher solute [ ] but lower H2O [ ].
• H2O moves into solution and solute moves out.
• Movement of H2O across selectively permeable membrane - osmosis.
• 2 solutions isotonic, H2O molecules move at equal rates from one to the other, (no net osmosis)
• Cell placed in hypertonic solution – H20 rushes out of cell (cell shrinks).
• Cell placed in hypotonic solution – H2O rushes into cell (cell swells).
• Filtration –molecules forced through membranes (result of blood pressure)
• Organism does not have rigid walls must have ability to osmoregulate and maintain internal environment.
• Plant cells expand when watered causing pressure to be exerted against cell wall.
• Allows plant to stand up against gravity (turgid cell); not watered, plant will begin to wilt (flaccid cell).
• Plant loses enough water, plasma membrane will pull away from cell (plasmolysis).
http://faculty.southwest.tn.edu/jiwilliams/plasmolysis.gif
• Charged particles that cannot pass through membrane - proteins to pass through (facilitated diffusion - diffusion of substance down it’s [ ] gradient with help of transport protein)
• Some channel proteins (gated channels) open/close depending on presence/absence of physical or chemical stimulus.
In this case, the protein actually rotates to dump the materials to the inside of the cell.
• Sometimes materials need to be moved against [ ] gradient (active transport)
• Active transport requires energy of cell to move substances from an area of low [ ] to an area of high [ ] (i.e. sodium-potassium pump in animal cells)
http://www.sp.uconn.edu/~terry/images/anim/antiport.gif
• Sodium-potassium pump actively maintains gradient of sodium (Na+) and potassium ions (K+) across membrane.
• Sodium-potassium pump uses energy of 1 ATP to pump 3 Na+ ions out and 2 K+ ions in.
• Cells maintain voltage across plasma membranes.
• Cytoplasm negative compared to opposite side of membrane (membrane potential - ranges from -50 to -200 millivolts)
http://bioweb.wku.edu/courses/Biol131/images/neuronions.GIF
• Membrane potential favors passive transport of cations (positive ions) into cell and anions (negative ions) out of cell.
• Creates an electrochemical gradient across membrane.
• Some organisms have proton pumps that actively pump H+ out of cell (i.e. plants, bacteria, and fungi)
• Materials leave membrane through lipid bilayer or through transport proteins.
• Exocytosis - transport vesicle buds from Golgi apparatus - moved by cytoskeleton to plasma membrane.
• When membranes meet - fuse - material is let out to outside of cell.
• Endocytosis - cell brings in macromolecules and matter by forming new vesicles from plasma membrane.
• Membrane is inwardly pinched off and vesicle carries material to inside of cell.
http://www.kscience.co.uk/as/module1/pictures/endoexo.jpg
• 1Phagocytosis (“cell eating”) - cell engulfs particle by extending pseudopodia around it, packaging it in a large vacuole.
• Contents of vacuole are digested when vacuole fuses with lysosome.
• 2Pinocytosis (cell drinking) - cell creates vesicle around droplet of extracellular fluid.
• 3Receptor-mediated endocytosis - specific in transported substances.
• Extracellular materials bind ligands (receptors) - causes vesicle to form.
• Allows materials to be engulfed in bulk (i.e. cholesterol in humans)
http://www.biologie.uni-hamburg.de/b-online/library/biology107/bi107vc/fa99/terry/images/PhagoAnA.gif
The Cell Cycle
• Cell division - process cells reproduce; necessary to living things.
• Cell division due to cell cycle (life of cell from origin in division of parent cell until own division into 2)
• Unicellular organisms - results in many new members.
• Multicellular organisms - division helps in development of organism and repair and renew preexisting cells
• Requires distribution of identical genetic material (DNA) to 2 daughter cells.
• Genome - cell’s genetic information packaged as DNA.
• DNA molecules packaged into chromosomes.
• Body cells - somatic cells; sex cells - gametes.
• DNA has proteins – maintains structure; helps control gene activity.
• Duplicated chromosome - 2 sister chromatids (identical copies of chromosome’s DNA)
• Region where strands connect shrinks to narrow area (centromere)
• Processes continue every day to replace dead and damaged cells.
• Produce clones - cells with same genetic information.
http://www.s8int.com/images2/cloned.jpg
Cloned cells
• Mitotic (M) phase of cell cycle alternates with much longer interphase.
• M phase includes mitosis, cytokinesis.
• Interphase - 90% of cell cycle.
• Interphase - cell grows by producing proteins and cytoplasmic organelles, copies chromosomes, prepares for cell division; 3 subphases.
• 1G1 phase (“first gap”) - growth. • 2S phase (“synthesis”) -chromosomes
copied. • 3G2 phase (“second gap”) - cell
completes preparations for cell division.
http://www.fhcrc.org/science/labs/fero/RL_gifs/cycle.jpg
• Mitosis – 5 subphases.• End interphase - centrosomes
duplicated, begin to organize microtubules into aster (“star”).
• 1Prophase - chromosomes tightly coiled, with sister chromatids joined together.
• Nucleoli disappear; mitotic spindle forms, appears to push centrosomes away toward opposite ends (poles) of cell.
• 2Prometaphase - nuclear envelope fragments and microtubules from spindle interact with chromosomes.
• Microtubules from 1 pole attach to 1 of 2 kinetochores (special regions of centromere), microtubules from other pole attach to other kinetochore.
• 3Metaphase - spindle fibers push sister chromatids until all arranged at metaphase plate (imaginary plane equidistant between poles)
• 4Anaphase - centromeres divide, separating sister chromatids.
• Each pulled toward pole to which it is attached by spindle fibers.
• 2 poles have equivalent collections of chromosomes.
• 5Telophase - cell elongates; free spindle fibers from each centrosome push off each other.
• 2 nuclei form, surrounded by fragments of parent’s nuclear envelope.
• Cytokinesis (division of cytoplasm) begins.
• Animals - cytokinesis (cleavage) - appearance of cleavage furrow in cell surface near old metaphase plate.
• Cytoplasmic side of cleavage furrow contractile ring of actin microfilaments and motor protein myosin form.
• Contraction of ring pinches cell in 2.
• Plants, cytokinesis - cell plate between dividing cells.
• Plate enlarges until membranes fuse with plasma membrane at perimeter; contents vesicles forming new wall material in between.
Bacteria• Prokaryotes - binary fission.• DNA of bacteria coiled, highly
packed. • Binary fission - chromosome
replication begins at 1 point in circular chromosome, (origin of replication).
• Copied regions move to opposite ends of cell.
• As chromosome replicates and copied regions move to opposite ends of cell, bacterium grows until it reaches 2x original size.
• Cell division involves inward growth of plasma membrane, dividing parent cell into 2 daughter cells with complete genome.
Regulation of cell cycle
• Some cells divide frequently in life (skin cells), others can divide (reserve - liver cells) mature nerve, muscle cells do not divide at all.
• Some control over when cells divide/how often they divide in lifetime.
http://www.ii.bham.ac.uk/webs/shuttleworth/bbsrc1.jpg
• Cycle driven by specific chemical signals in cytoplasm.
• Events of cell cycle directed by cell cycle control system.
• Checkpoint in cell cycle is critical control point where stop/go signals regulate cycle.
• 3 major checkpoints found in G1, G2, and M phases.
• G1 checkpoint (most important), cell either get go ahead to finish cycle and divide, or receive stop signal.
• If stop signal - goes into G0 phase (remains in limbo waiting to start).
• Most human cells in this mode.
http://www.microscopy-uk.org.uk/mag/imgaug99/01.jpg
• Proteins, kinases, can activate/deactivate other proteins.
• Kinases always present in cell; need cyclins (protein) to activate.
• Complex of kinases and cyclin - cyclin-dependent kinases (Cdks).
http://www.mie.utoronto.ca/labs/lcdlab/biopic/fig/9.5.jpg
• MPF (“maturation-promoting factor”) triggers cell’s passage past G2 checkpoint to M phase.
• G1 checkpoint regulated by at least 3 Cdk proteins and several cyclins.
http://www.uic.edu/classes/bios/bios100/summer2002/cdk02.gif
• M phase checkpoint makes sure chromosomes are attached to spindle so each cell ends up with right amount of chromosomes.
• Cell division influenced by growth factors, proteins released by 1 group of cells that stimulate other cells to divide.
http://www.fhcrc.org/science/education/courses/cancer_course/basic/img/growth_factors.gif
• Platelet growth driven by growth factors.
• Presence of injury - released to stimulate division of platelet cells to seal wound.
• Density of cells too high - cell division inhibited.
Cancer
• Cancer cells divide out of control - no regulation.
• Can either produce own growth factors or have problem in signaling pathway.
• Can divide indefinitely if they have continual supply of nutrients.
http://www.sandia.gov/news/resources/releases/2005/images/mitopic.jpg
• Starts when single cell undergoes transformation to change it into cancer cell.
• If immune system does not destroy, can form tumor (gathering of cells).
• If tumor does not invade other areas - benign.
• If it does - malignant.• If cells get into blood stream,
travel throughout body (metastasis).
http://www.livercancer.com/images/metastasis.gif
• http://www.teachersdomain.org/resources/tdc02/sci/life/stru/dnadivide/index.html
http://www.sirinet.net/~jgjohnso/endocytosissmall.jpg