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NOTES: 7.2 –
CELL STRUCTURES &
FUNCTIONS
Comparing the cell to a factory:
● each cell part (“organelle”) can be
compared to a specialized machine in a
factory;
● each part performs a specific “job” or
function towards the functioning of the
cell as a whole…
Cell Organization:
● each eukaryotic cell can be divided into
2 major parts:
1) Cytoplasm
2) Nucleus
CYTOPLASM:
● CYTOPLASM: the portion of the cell
outside the nucleus; mostly water; all
other organelles suspended in
cytoplasm
NUCLEUS:
● NUCLEUS: contains nearly all of the
cell’s DNA (the coded instructions for
making all of the cell’s proteins);
● considered the “control center” of the
cell;
● nucleus is surrounded by a nuclear
envelope
NUCLEAR ENVELOPE
● double membrane which encloses the
nucleus;
● includes many nuclear pores (holes)
which allow material to move in and out
of the nucleus
CHROMATIN
● threadlike complex of
DNA bound to
proteins; it makes up
chromosomes in
eukaryotic cells
CHROMOSOMES
● compacted, coiled up
chromatin;
● human cells have 46
chromosomes (23 pairs)
NUCLEOLUS
● dense, spherical region in the nucleus
-ribosome assembly begins here
Organelles that Store, Clean
Up, and Support:
● vacuoles & vesicles
● lysosomes
● cytoskeleton
VACUOLE: ● used for storage (of
water, salts, proteins,
carbs);
● in animal cells,
vacuoles are smaller
than in plant cells
PLANT VACUOLES…
● may contain soluble pigments in some cells
(red and blue pigments in flowers);
PLANT VACUOLES…
● help protect from predators by storing waste
products that may also be poisonous
compounds
● contractile vacuole:
specialized vacuole that
pumps excess water
out of cell.
VESICLES:
● VESICLES: small, membrane-enclosed
structures that store and move materials
between cell organelles, or to and from
cell surface
LYSOSOMES:
● the cell’s “clean-up crew”!
● contain digestive enzymes
that break down
macromolecules into
smaller subunits;
● recycle the cell’s own
organic material;
● can destroy cells by
breaking open all at once
and digesting the cell from
within
CYTOSKELETON:
● CYTOSKELETON: provides shape &
internal organization; also involved in
transport of materials within the cell, as
well as whole-cell movement
● includes protein filaments:
-microfilaments
-microtubules
MICROTUBULES & MICROFILAMENTS
● make up the cytoskeleton
● structural support to cell;
maintain shape
● involved in cell movement
Microfilaments:
● threadlike structures;
● made up of protein: ACTIN
● stabilize cell shape
● microfilament assembly & disassembly allow
amoebas & other cells to “crawl” along
surfaces
Yellow: nucleus
Green: microfilaments throughout
cytoplasm
Microtubules:
● thin, hollow cylinders made of
protein: TUBULIN
● maintain cell shape;
● can serve as “tracks” to
guide organelle movement;
● involved in separation of
chromosomes in cell division;
make up SPINDLE FIBERS /
CENTRIOLES (in animal cells)
Microtubules (cont.)…
● responsible for movement of flagella &
cilia
FLAGELLA and CILIA:
● FLAGELLA: longer
usually single
extensions; used to
propel a cell
● CILIA: shorter and
more numerous than
flagella; wavelike
motion used to
sweep extracellular
material over/away
from cell
Organelles that Build,
Modify, and Transport
Proteins:
● ribosomes
● endoplasmic reticulum
● Golgi Apparatus
RIBOSOMES:
● site of protein synthesis
-small particles of RNA & protein
-follow coded instructions from DNA
-made in the nucleolus
-cells especially active in protein synthesis
often contain large #s of ribosomes
-may be free (in cytoplasm) or attached to
the ER
ENDOPLASMIC RETICULUM (ER):
● extensive network of internal membranes
● used to transport and/or modify proteins;
● can be ROUGH (ribosomes) or SMOOTH
(no ribosomes)
Rough ER:
● rough appearance due to ribosomes on
outer surface;
● newly made proteins leave the ribosomes
and are “dropped off” into the rough ER;
● modifies and transports proteins;
Smooth ER:
● synthesizes lipids, phospholipids,
steroids
● detoxifies drugs and poisons
GOLGI APPARATUS:
● stacked, flattened membranes
● finishes, sorts, packages and ships many
cell products (a.k.a. the “post office” of the
cell)
Organelles that Capture and
Release Energy:
● chloroplasts
● mitochondria
CHLOROPLASTS: (“the
organelles that feed the world”)
● contain chlorophyll;
● site of photosynthesis
(convert light energy
into “food”, or chemical
energy)
MITOCHONDRIA:
● sites of cellular respiration
● convert the chemical energy stored in
food into usable energy packets for the
cell
● the # in cells varies and is related to the
cell’s metabolic activity (i.e. if a cell uses
more energy, it will have more
mitochondria!)
Cellular Boundaries:
● cell wall
● cell membrane
Cellular Boundaries:
● CELL WALL:
- semi-rigid structure outside of cell membrane
of PLANT CELLS & most prokaryotes;
- in plants, consists of CELLULOSE fibers;
- provides support, limits cell’s volume, and
protects against fungi and/or microorganism
infection;
- most cell walls are porous enough to allow
water, oxygen, carbon dioxide, etc. to pass
through.
CELL WALL:
CELL MEMBRANE:
What must a
membrane do?
● let some things leave /
enter cell
● keep stuff inside or
outside of cell
● be flexible as cell
changes shape
● cell membranes form a LIPID BILAYER that is
flexible & can regulate what enters & exits the
cell;
● The cell membrane is composed of molecules
called PHOSPHOLIPIDS.
PHOSPHOLIPIDS:
-one end is strongly nonpolar (hydrophobic);
-one end is extremely polar (hydrophilic)
● the nonpolar lipid “tails” are repelled by
polar water molecules; the polar “heads”
of the molecules form hydrogen bonds
with water molecules.
● So, every phospholipid
molecule orients so that
its polar “head” faces
water and its nonpolar
“tails” face away... two
layers are formed with
the tails facing each
other...the result is
called a LIPID
BILAYER.
Lipid bilayer membranes are:
● PERMEABLE to:
– lipids
– nonpolar molecules: O2, CO2
– small polar molecules: H2O
● IMPERMEABLE to:
– ions (Na+, K+, Cl-)
– large polar molecules: sugars, proteins
3 Main Types of Cell Membrane
PROTEINS…
1) Channels
2) Receptor proteins
3) Cell surface
markers
1. CHANNELS:
● a channel will transport only certain
kinds of molecules...which gives the cell
membrane its selectively permeable
nature
2. RECEPTOR PROTEINS:
● collect & transmit information from the
cell’s environment
3. CELL SURFACE MARKERS:
● identify your body‘s cells as belonging to
you (useful in cell-cell recognition)