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Chapter4.docx
Learning Objectives:
· identify basic cell structures and explain the function of each organelle.
· list the organizational levels from atoms to ecosystems.
· compare the structure of a prokaryotic and eukaryotic cell.
· list 4 evidences for the endosymbiotic theory.
I. Introduction
a. All cells are small so most cells can only be observed under a microscope.
i. Robert Hooke (1665) – coined the term ______ with respect to biology after looking at slices of cork beneath the microscope.
ii. Anton van Leeuwenhoek (1600’s) - discovered “wee beasties” in pond water and other sources.
b. Cells Are Fundamentally Important
i. Matthias Schleiden (botanist) Theodor Schwann (zoologist) in 1838-1839 independently concluded that all living things are made of cells.
ii. Virchow (1855) witnessed cell division and concluded that cells come from pre-existing cells.
iii. This research led to the __________________which states that the cell is the basic unit of structure, function, and reproduction in living things.
iv. Improved microscopy revealed two main cell types:
1. _________________ – no internal membranes including the nuclear envelope; includes Archaea and bacteria
2. ___________________– have membrane-bound organelles including a nucleus; includes all cells other than Archaea and bacteria
II. Limits to Cell Size
a. Why must organisms be subdivided into such small cells?
b. Metric units – How are cells measured?
i. meter (m) – basic unit of length
ii. millimeter (mm) – 1/1000 m (~diameter of a pencil lead)
iii. micrometer (µm) – 1/1000 mm – main unit used to measure cells (prokaryotic cells – 1-10 µm; eukaryotic 10-100 µm)
iv. nanometer (nm) – 1/1000 µm
c. Why Cells Are So Small
i. Cells are not all the same size, but most cells are small because larger cells do not function as efficiently. Larger cells are more difficult to control because of the distance between the command center at the core and the peripheral regions. Organisms that are comprised of many, small cells are at an efficiency advantage over organisms comprised of few, larger cells.
ii. The main limit on cell size is __________________________. As a cell increases in size, the amount of surface area decreases in relationship to volume. Cells must have enough surface area to interact with their environment – to take in and export substances. Some cells have folds in their membranes to increase surface area.
III. Visualizing Cells
a. Most cells are too small to be viewed by the naked eye, which has limited resolution.
i. ______________________ refers to the minimum distance that two points can be apart and still be distinguished as two separated points. The limit of resolution of the human eye is about 100 micrometers.
ii. One way to increase resolution is to use a microscope.
1. Different types of microscopes are used to increase magnification for viewing:
a. Compound light microscopes use sets of magnifying lenses to resolve structures that are separated by more than 200 nanometers.
b. Electron microscopes have 1000 times the resolving power of light microscopes and can resolve objects as close as 0.2 nanometers apart.
i. Transmission electron microscope (abbreviated T.E.M.): Electrons are passed through a specimen and then they are focused by a set of magnetic lenses. An image is formed on a fluorescent screen similar to a TV screen. The image is then photographed.
ii. Scanning electron microscope (abbreviated S.E.M.) The specimen is sprayed with a thin coat of ______________. Then an electron beam is scanned across the surface of the specimen. The surface metal emits secondary electrons. The emitted electrons are detected and focused by magnetic lenses. A 3-dimensional image is formed on a fluorescent screen similar to a TV screen. Image is then photographed.
IV. Prokaryotic cells
a. Lack a membrane bound nucleus and are structurally smaller and simpler than ________ _______, which do have a true nucleus.
b. Prokaryotic cells are placed into two taxonomic domains:
1. Bacteria/Eubacteria: Cause diseases but are also environmentally important as decomposers; can be useful in manufacturing products and drugs
2. Archaea: live in extreme habitats
c. Prokaryotes are extremely small, 1-1.5µm and 2-6µm long, usually occur in three shapes:
1. spherical (coccus, cocci)
2. ii. rod-shaped (bacillus, bacilli)
3. spiral (flexible spirillum or rigid spirochete)
d. Cell envelope contains:
1. plasma membrane (lipid bilayer with embedded and peripheral proteins that can mesosomes (internal pouches that increase surface area)
2. cell wall to maintain the shape of the cell and is strengthened by peptisoglycan
3. glycocalyx, a layer of polysaccharides exterior to the cell wall on SOME bacteria
e. ________________ – a semifluid solution encased by the plasma membrane; contains water, inorganic and organic molecules, and enzymes
f. ________________ – region that contain a single, circular DNA model
g. ______________ -- small extrachromsomal rings of DNA
h. ______________ -- tiny structures in the cytoplasm where proteins
are made
i. External structures
1. flagella (for motility)
2. fimbriae (for attachment)
3. conjugation _________ (for passing DNA from cell to cell)
V. Introduction to eukaryotic cells
a. Eukaryotic cells contain:
i. Membrane-bound nucleus that houses DNA
ii. Specialized organelles
iii. Plasma membrane which separates cell contents from environment, regulates passage of materials in and out; is composed of a phospholipid bilayer with embedded proteins (Note: ALL cells have a plasma membrane.)
b. Eukaryotic cells are larger than prokaryotic cells.
c. Eukaryotic cells are compartmentalized, since they contain small structures called organelles to perform specific functions, isolating reactions from other reactions. There are two classes of organelles:
i. ________________________ system (organelles that communicate with one another via membrane channels and small vesicles
ii. Energy-related organelles that are independent and self-sufficient
1. mitochondria
2. chloroplasts
VI. Cell Boundaries (cell membrane and cell wall)
a. All cells have a cell (plasma) membrane as their outermost living boundary. The plasma membrane is conceptualized by the _______________________.
i. __________________________ – maintained by hydrophobic and hydrophilic interactions
ii. ______________________ (not in prokaryotes)
b. Structure of the plasma membrane
i. Phospholipids
1. A phospholipid has a ____________ head and two ___________ tails. The polar region contains a phosphate chemical group and is _____________________. The non-polar region is comprised of fatty acids and is ________________________. A lipid bilayer forms spontaneously.
ii. Proteins
1. ___________________ – completely span the membrane; provide passageways
2. _____________________ – found just inside the membrane (may be enzymes or attachment sites for the cytoskeleton).
3. _____________and________________ - on outside of membrane; purposes:
a. adhesion to other cells
b. recognition markers (identifies “self’
c. receptor sites
Note: internal membranes of the cell have the same structures as the cell membrane.
c. Function of the Cell Membrane
i. Regulates passage of substances in/out of the cell.
ii. Proteins are embedded within the lipid bilayer
d. Cell Wall
i. Many cells secrete a nonliving _________________ outside of the cell membrane
ii. Structure of the Cell Wall
1. Composition varies in different organisms:
a. Bacteria – made of peptidoglycan (where penicillin works)
b. Algae – varies; may be cellulose, silica, or CaCO3
c. Fungi – made of _______________
d. Plants – primary cell wall of cellulose; may have a secondary wall for extra strength
e. Animals -- none
iii. Function of the Cell Wall
1. Supports the cell and gives it shape
2. Prevents the cell from bursting due to excess water
VI. Nucleus -- “Control center of the cell”
a. Only in eukaryotic cells
b. Structure of the Nucleus
iv. Surrounded by a double membrane called the __________________ envelope has small openings called ______________________.
v. Linear___________________ made of DNA and ________________ are found inside the nucleus. The chromosomes are normally in a very relaxed state called __________________ which gives the nucleus a grainy appearance.
vi. One or more _______________ (sing. nucleolus) are visible in the nucleus. A nucleolus is where ribosomal subunits are made.
e. Function of the Nucleus
i. Contains hereditary information (DNA)
ii. Controls all activities of the cell
Note: Although prokaryotic cells do not have nuclei, they do have DNA. The chromosome of a prokaryotic cell is a loop of naked DNA (no histone protein coating).
VII. Organelles -- Structures within the cell with specialized functions; found in the _____________________ which is the fluid-filled space between the nuclear envelope and the cell membrane.
a. Ribosomes --“Protein factories”
i. Site of protein synthesis in both prokaryotes and eukaryotes
ii. Composed of 2 subunits which differ in size between prokaryotes and eukaryotes
Note: Some antibiotics such as tetracycline, streptomycin, erythromycin and chromamphenicol work by blocking protein synthesis only in 70s ribosome.
iii. In eukaryotic cells, ribosomes may also be described by their position.
1. ___________________ are found in the cytoplasm and synthesize housekeeping proteins used within the cell; attach to cytoskeleton when functioning
2. ___________________ are found on the rough endoplasmic reticulum and usually produce proteins for transport or use in the cell membrane.
b. Endoplasmic Reticulum (ER) -- “Communications network”
i. 3-D network of interconnecting tubes/channels extending from the nucleus to the cell membrane
ii. Only in eukaryotic cells
iii. Function in transport and some processing of molecules
iv. 2 types:
1. ________________ - without ribosomes; transports primarily lipids
2. ________________- with ribosomes; transports proteins
Note: Molecules transported by the ER may ultimately be packaged into small sacs called vesicles and shipped to the Golgi complex.
b. ____________________-“Warehouse of the cell”
i. Structure - a set of flattened membranous sacs and ____________
ii. Only in eukaryotic cells
iii. Function - accepts vesicles from the ER, modifies the contents, repackages the molecules into vesicles to be sent elsewhere in the cell or out of the cell.
The Endomembrane System: the ER and Golgi complex function together as a transport system in the cell.
c. __________________ -- “Recycling center” (a.k.a. “suicide sacs”)
i. Membrane bound structures packaged by the Golgi and full of digestive enzymes
ii. Only in eukaryotic cells
iii. Functions
1. ____________________ - phagocytosis in protists, white blood cells and in recycling of cell parts
2. ______________________ (apoptosis) - developmentally directed destruction of cells such as when a tadpole resorbs its tail as it is metamorphosing into a frog; also in human embryonic development
d. Peroxisomes: specialized organelles containing enzymes that catalyze specific reactions, including breakdown of ethanol by liver/kidney. Contain ________________ which catalyzes the breakdown of toxic hydrogen peroxide produced by reactions carried out by peroxisome enzymes
i. Only in eukaryotic cells
e. __________________--“Storage sacs”
i. Membrane-bound, fluid-filled sacs used for storage of salts, vitamins, wastes, etc.
ii. Only in eukaryotic
iii. Different types
1. central vacuole of plant cells - very large, provides turgid support
2. contractile vacuole of freshwater protozoans - used to rid cell of excess water
3. food vacuole of protozoans - used to hold and digest food
f. ________________--“Powerhouse of the cell”
i. Structure:
1. Label the outer membrane, inner membrane (cristae), intermembrane space, and matrix
ii. Function – production of ATP (energy currency of the cell)
iii. Only in eukaryotic cells
g. Chloroplasts--“Food factories of the cell”
i. Site of photosynthesis
ii. Only in eukaryotic photosynthetic cells
iii. Structure (label outer membrane, inner membrane, thylakoid, granum, stroma)
Note: Chloroplast are one type of organelle in plants called plastids. Other plastids are: leucoplasts – store starch, chromoplasts – contain pigments such as carotene and xanthophyll
iv. The theory of ____________________ : states that some organelles evolved from a symbiosis in which one cell of a prokaryotic species was engulfed by and lived inside of a cell of another species of prokaryote that was a precursor to eukaryotes. The engulfed species provided their hosts with advantages because of special metabolic activities. The modern organelles of mitochondria and chloroplasts are believed to be found in the eukaryotic descendants of these endosymbiotic prokaryotes. In addition to the double membranes and circular DNA found in mitochondria and chloroplasts, there is a lot of other evidence supporting endosymbiotic theory mitochondria are about the same size as modern bacteria the cristae in mitochondria resemble folded membranes in modern bacteria mitochondrial ribosomes are similar to modern, bacterial ribosomes in size and structure mitochondria divide by fission, just like modern bacteria
h. Cytoskeleton --highly dynamic network of protein fibers found throughout the cytoplasm. Only in eukaryotic cells.
i. Components
1. microtubules - long cylinders of globular proteins
2. microfilaments (actin filaments) - twisted chains of the protein actin
3. intermediate filaments - a variety of fibrous proteins
ii. Functions:
1. Cell division
a. microtubules - form spindle fibers in all eukaryotic cells as well as ______________ in animal cells.
b. microfilaments (actin) - pinch animal/protozoan cells apart during cell division
2. Cyclosis (cytoplasmic streaming) -- microfilaments (actin) create channels through which cytoplasm circulates
3. Muscle cell contractions – involves actin
4. Support --involves intermediate filaments such as fibers of keratin/collagen
5. Amoeboid movement -- involves microfilaments (actin)
i. Flagella and cilia – microtubules within an extension of the cell membrane [Note: Prokaryotic flagella are structurally much simpler – naked stands of flagellin (protein) outside of the cell membrane and cell wall.] Additional notes on centrioles, cilia, and flagella: ______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
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