Cells & Organelles
A Dr. Production
Two Basic Types of Cells
• Pro karyotes:– prounounced: pro-carry-oats
• Eu karyotes– Proun: you-carry-oats
A. ProkaryotesSmall, simple cells (relative to eukaryotes)Size: about 1 µm (1 micron)No internal membrane-bounded organellesNo nucleusSimple cell divisionSingle linear chromosome
Contain the domains; 1. True (Eu)bacteria &
2. Archaebacteria
1. True Bacteria = Eubacteria
• Majority of bacteria
• Examples include: E. coli, Lactobacillus (yogurt), Lyme disease
Eubacteria•Peptido glycan cell walls (carbos & AA)
•Separated into Gram + and - forms
Gram negative
Gram positive
Bacteria in the Environment
A) An acid hot spring in Yellowstone is rich in iron and sulfur. B) A black smoker chimney in the deep sea emits iron sulfides at very high temperatures (270 to 380 degrees C).
example: Iron utilizing Baceria
A B
2. Archaebacteria
• Live in extreme environments: high salt, high temps
• Different cell wall• Very different
membrane lipids• Unusual nucleic acid
sequence
Archaea types: Based on their physiology, Archae can be organized into three types:
• Methanogens (prokaryotes that produce methane); • Extreme halophiles (prokaryotes that live at very
high concentrations of salt (NaCl); • Extreme (hyper) thermophiles (prokaryotes that
live at very high temperatures).
All archaea have features that distinguish them from Bacteria (i.e., no murein in cell wall, ether-linked membrane lipids, etc.). And, these prokaryotes exhibit unique structural or biochemical attributes which adapt them to their particular habitats.
B. Eukaryotes• Bigger cells: 10-100 µm• True nucleus• Membrane-bounded
structures inside. Called organelles
• Divide by a complex, well-organized mitotic process
Liver Cell 9,400x
Eukaryotes• Larger more complex
cells that make up most familiar life forms: plants, animals, fungi, protists
• Surrounded by a cell membrane made of lipids
The Cell Theory
• Cells first observed by R. Hooke 1665• Named for the Monk prayer cells• Cell Theory states that;
1. All life is composed of cells2. Cells are the basic units of life
3. Cells arise from already existing cells
Cells are typically Small
Typical cell size
Why are Cells Small?• Cells must exchange gases & other
molecules with environment…• Nutrients in, Wastes out• As size increases, the rate of diffusion
exchange slows down….• This is due to the ratio of surface area to
volume
Surface Area to Volume• Cell surface area is important in taking in
nutrients• Surface area increases as the square of cell
diameter• But… entire cell volume needs to be fed• And, cell volume increases as the cube of cell
diameter
Consider 2 Cells...
Surface Area to Volume Cell Radius (R)
5 µm 50 µm Surface Area
(4πr2) 314 µm2
31,400 µm2
Volume (4/ 3πr3)
524 µm3
524,000 µm3
Surf ace Area to Volume Ratio
0.6
0.06
The Eukaryotic Cell: Components
• Outer cell membrane composed of lipids and proteins
• Cytosol: interior region. Composed of water & dissolved chemicals…a gel
• Numerous organelles….
Organelles• Specialized structures
within eukaryotic cells that perform different functions...
• Analogous to small plastic bags within a larger plastic bag.
• Perform functions such as :– protein production
(insulin, lactase…)– Carbohydrates,
lipids…
Organelles of Note:The Nucleus
• Contains the genetic material (DNA), controls protein synthesis.
DNA --> RNA --> Protein• Surrounded by a double
membrane with pores• Contains the chromosomes =
fibers of coiled DNA & protein in the form of chromatin
Chromosomes
All Chromosomes from a single cell
One chromosome Pulled apart
A single chromosomeShowing the amount of DNA within
Mitochondria• Generate cellular energy in the
form of ATP molecules• ATP is generated by the
systematic breakdown of glucose = cell respiration
• Also, surrounded by 2 membrane layers
• Contain their own DNA!• A typical liver cell may have
1,700 mitoch.• All your mitoch. come from
your mother..
PlastidsSynthesize
carbohydrates• Leucoplasts: white
in roots and tubers• Chromoplasts:
rainbow accessory pigments
• Chloroplasts: green in leaves and stems
Chloroplasts• Found in plants and some
protists. Responsible for capturing sunlight and converting it to food = photosynthesis.
• Surrounded by 2 membranes
• And…contain DNA
Ribosomes• Size ~20nm• Made of two subunits
(large and small)• Composed of RNA and
over 30 proteins• Come in two sizes…80S
(40s + 60s) and 70S (30s + 50s)
• S units = Sedimentation speed
Ribosomes• DNA --> RNA --> Protein• The RNA to Protein step
(termed translation) is done on cytoplasmic protein/RNA particles termed ribosomes.
• Contain the protein synthesis machinery
• Ribosomes bind to RNA and produce protein.
Endoplasmic Reticulum = ER
• Cytoplasm is packed w. membrane system which move molecules about the cell and to outside
• Outer surface of ER may be smooth (SER): synthesizes secretes, stores, carbs, lipids and non pps
• Or Rough (RER): synthesizes pp for excretion
• ER functions in lipid and protein synthesis and transport
Golgi Complex• Stacks of
membranes…• Involved in modifying
proteins and lipids into final form…– Adds the sugars to
make glyco-proteins and glyco-lipids
• Also, makes vesicles to release stuff from cell
ER to Golgi network/Endo membrane system
Membrane Flow through Golgi
Lysosomes • important in breaking down
bacteria and old cell components• contains many digestive
enzymes• The ‘garbage disposal’ or
‘recycling unit’ of a cell• Malfunctioning lysosomes result
in some diseases (Tay-Sachs disease)
• Or may self-destruct cell such as in apoptosis
Vacuoles
• Formed by the pinching of the cell membrane
• Very little or no inner structure
• Stores various items
Peroxisomes/Microbodies
• Large vesicles containing oxidative enzymes which transfer H from substrates to O
• Contains catalase that changes H2O2 to H2O
• In plants responsible for photorespiration and converting fat to sugar during germination
Cytoskeleton• Composed of 3 filamentous
proteins:Microtubules
MicrofilamentsIntermediate filaments
• All produce a complex network of structural fibers within cell
The specimen is human lung cell double-stained to expose microtubules and actin microfilaments using a mixture of FITC and rhodamine-phalloidin. Photo taken with an Olympus microscope.
Microtubules
Function in:Function in:- division of cells - division of cells (formation of spindle (formation of spindle fibers)fibers)- some aspects of shape - some aspects of shape - many cell movements - many cell movements (flagella and cilia)(flagella and cilia)- “transport” system - “transport” system within cellwithin cell
Microtubules• Universal in eukaryotes• Involved in cell shape,
mitosis, flagellar movement, organelle movement
• Long, rigid, hollow tubes ~25nm wide
• Composed of and ß tubulin (small globular proteins)
• 9+2 vs 9x3 arrangement
Protist Movement Protist Movement
Microfilaments• Thin filaments (7nm
diam.) made of the globular protein actin.
• Actin filaments form a helical structure
• Involved in cell movement (contraction, crawling, cell extensions)
Intermediate filaments• Fibers ~10nm diam.• Very stable,
heterogeneous group• Examples:Lamins: hold nucleus shapeKeratin: in epithelial cells Vimentin: gives structure to
connective tissueNeurofilaments: in nerve
cells
Image of Lamins which reside in the nucleus just under the nuclear envelope
Cell Motility:Flagella & Cilia
• Both cilia & flagella are constructed the same
• In cross section: 9+2 arrangement of microtubules (MT)
• MTs slide against each other to produce movement
Flagella (flagellum)• Motile structure of many eukaryotic cells; Motile structure of many eukaryotic cells; long, long,
hair-like projectionhair-like projection- e.g., tail of sperm- e.g., tail of sperm
• Core composed of 9 + 2 array of microtubules Core composed of 9 + 2 array of microtubules that arise from a basal body apparatusthat arise from a basal body apparatus– Flagellated Flagellated E. coliE. coli
Cilia (cilium)• Motile or sensory structure in Motile or sensory structure in
eukaryotes composed of 9 + 2 eukaryotes composed of 9 + 2 array of microtubulesarray of microtubules
• Usually numerous short, hair-Usually numerous short, hair-like projections along outside like projections along outside of cellof cell
• Found in many Protista and in Found in many Protista and in lining of lungslining of lungs– StentorStentor feeding feeding– ParameciumParamecium rotating rotating
Possible Origins of Eukaryotic Cells
Endosymbiosis• Theory that eukaryotic
cells arose from an early prokaryote (1) engulfing a second, smaller prokaryote (2)
• The internalized #2 was not digested but became a symbiote.
• Today’s mitochondria & chloroplasts may have arisen this way
Support for this Theory:• Eg. of this type of symbiosis are found today. Sponges harbor photosyn.
algae within their tissues, allowing them to photosynthesize.• The organelles (chloroplasts and mitochondria) resemble bacteria in size
and structure.• These organelles each contain a small amount of DNA but lack a nuclear
membrane.• Each has the capability of self-replication. They reproduce by binary
fission.• They make their own proteins.• During protein synthesis, these organelles use the same control codes and
initial amino acid as prokaryotes.• They contain and make their own ribosomes, which resemble prokaryote’s. • The enzymes that replicate DNA and RNA (polymerases) of the organelles
are similar to those in prokaryotes but different from those of eukaryotes. • The organelles have a double membrane that might be derived from a
prokaryote’s plasma membrane and the membrane of a vesicle.
Resources • Rediscovering Biology Animation Guide• Cell Signaling and Cell Cycle Animations