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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.
Modified protein
http://web.mit.edu/esgbio/www/cb/org/golgi.gif
• 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. sodiumpotassium 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 - cyclindependent 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/t
dc02/sci/life/stru/dnadivide/index.html
http://www.sirinet.net/~jgjohnso/endocytosissmall.jpg