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