CELLS
Cell Theory, Microscopy, Prokaryotes
CELL THEORY1. All living things are composed of
cells and cell products.2. New cells are formed only by the
division of existing cells.3. The cell contains inherited
information (genes) that are used as instructions for growth, functioning and development.
CELL THEORY, continued
4. The cell is the functioning unit of life; the chemical reactions of life take place within cells.
Possible Exceptions to the Cell Theory
The structure of skeletal muscle
Muscle
Bundle ofmuscle fibers
Single muscle fiber(cell)
Plasma membrane
Myofibril
Lightband Dark band
Z line
Sarcomere
TEM 0.5 mI band A band I band
M line
Thickfilaments(myosin)
Thinfilaments(actin)
H zoneSarcomere
Z lineZ line
Nuclei
•Muscle consists of bundles of long cells called fibers.
•Each fiber has a membrane around the outside like a single cell
•But each fiber has hundreds of nuclei.
Figure 31.2: Structure of a multicellular fungus
Hyphae. The mushroom and its
subterranean mycelium are a
continuous network of hyphae.
Reproductive structure.
The mushroom produces
tiny cells called spores.
Spore-producing
structures
20 m
Mycelium
Figure 31.3: Structure of fungal hyphae
Nuclei
Cell wall
Septum
Pore
(a) Septate hypha (b) Coenocytic hypha
Cell wall
Nuclei
SOME (but not most!) biologists consider unicellular organisms to be acellular.
• Examples: Amoeba and Acetabularia
– instead of separate cells for separate functions, cytoplasm must carry out all vital functions
– usually much larger than typical cells
Acetabularia > 7 cm in length
Amoeba proteus ~ 700 -800 µm
The animal cell
The plant cell
Cell differentiation
www.cellsalive.com
www.brianpop.com
Task • Look at the diagram
and list similarities and differences between the two cells.
Prokaryotic Cells
Prokaryotic Cells
• Pro – before
• Karyon – nucleus
• Comprise domains Bacteria and Archaea (Archaebacteria)
Electron microscope views of prokaryotic cells
Functions of the parts of a prokaryotic cell• Cell wall – forms protective outer
layer which prevents damage from outside and bursting if internal pressure is high
• Plasma membrane – controls entry and exit of substances, pumping some in by active transport
Functions of the parts of a prokaryotic cell, cont’d.• Mesosome – increases the area of
membrane for ATP production; may move DNA to poles during cell division
• Cytoplasm – contains enzymes that catalyze chemical reactions of metabolism; also contains cell’s DNA, in region known as nucleoid
Functions of the parts of a prokaryotic cell, cont’d.• Ribosomes – synthesize proteins
by translating mRNA; some proteins remain in cell and others are exported
• Naked DNA – stores genetic information that controls cell and is passed onto daughter cells.
Metabolic activities in prokaryotes• Photosynthesis – carried out by
Cyanobacteria (sometimes called blue-green “algae”)
Metabolic activities in prokaryotes, cont’d.• Nitrogen fixation – nitrogen fixing
bacteria convert nitrogen gas from the air into nitrogen compounds–some are free-living bacteria–some live in symbiosis with
plants, such as Rhizobium, forming root nodules on legumes
Metabolic activities in prokaryotes, cont’d.• Fermentation - process by which an
sugar is broken and energy released.
–occurs during times of low oxygen supply and is therefore known as a type of anaerobic respiration