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The Discovery of Cells
 Microscope observations! General Cell &
Organelle Discovery
 1600s
 Observations made by scientists using more
powerful microscopes in the 1800s led to the
formation of the cell theory.
 All substances that enter or leave a cell must
cross the surface of the cell THE CELL
MEMBRANE.
 A cell’s ability to move substances across its
membrane can be estimated by finding its surface
area-to-volume ratio.
 Cells with greater surface area-to-volume ratios
can exchange substances more efficiently.
Eukaryotic Cells
A eukaryote is an organism made up of one or more
eukaryotic cells.
**All multicellular organisms are made of eukaryotic
cells.**
DNA is in an internal compartment: nucleus.
Organelles have membranes (are
compartmentalized).
Organelle:
Small structure in the
cytoplasm that carries out
specific activities inside the
cell.
Each organelle in a
eukaryotic cell performs
distinct functions.
***The complex
organization of eukaryotic
cells enables them to carry
out more specialized
functions than prokaryotic
cells.
Cell Membrane
Outer layer
Acts as a barrier
Made of:
- phospholipids,
- proteins
- carbohydrates
Cytoplasm
Region of the cell inside
the cell membrane.
**Includes the fluid
inside the cell called the
cytosol and holds all the
organelles**
“Jelly-like” substance
within a cell
Ribosomes: makes proteins
Ribosomes: makes
proteins
Attached RibosomesMake proteins for
EXPORT
Free Ribosomes-Make
proteins for use within
that cell.
Remember
DNARNAProteins
Directing Cellular Activity
 DNA contains instructions for making proteins which
control most of the activity of the cell.
 The DNA of eukaryotic cells is stored in the nucleus.
 DNA instructions are copied as RNA messages,
which leave the nucleus.
 DNA NEVER LEAVES THE NUCLEUS
 In the cytoplasm, ribosomes use the RNA messages to
assemble proteins.
Nucleus
Surrounded by nuclear membrane: it is a double
membrane.
Nuclear pores: located in the nuclear envelope act as
channels (holes/tunnels) to allow certain molecules
to move in and out of the nucleus.
Nucleolus: structure within the nucleus where
ribosome parts are made.
These ribosome parts are transported out of the nucleus
into the cytoplasm where they are assembled to form a
complete ribosome.
The Nucleus
Ribosomes
Each ribosome in a cell is made of RNA and many
different proteins.
“Free” Ribosomes: are suspended in the cytosol
~Make proteins that remain inside the cell.
“Bound/Attached” Ribosomes: are attached to the
membrane of another organelle are called
Endoplasmic Reticulum (ER).
~make proteins that are exported from the cell.
Ribosomes can switch between being bound or free,
depending on what proteins the cell needs to make.
Protein Processing
Proteins that are sent outside the cell are packaged
in vesicles: small, membrane-bound sacs that
enclose the proteins and keep them separate from
the rest of the cytoplasm.
***The Endoplasmic Reticulum and Golgi
Apparatus are organelles involved in preparing
proteins for extracellular export.
Endoplasmic Reticulum
An extensive system of internal membranes that
moves proteins and other substances through
the cell.
The membranes of the ER are connected to the outer
membrane of the nuclear envelope.
The endoplasmic reticulum is divided into two
portions:
Rough ER and Smooth ER.
Endoplasmic Reticulum (ER)
ER with attached ribosomes: Rough ER
It has a rough appearance when viewed with an
electron microscope.
Ribosomes on the rough ER make proteins that are
packaged into vesicles & exported
 ER with NO attached ribosomes: Smooth ER
it has a smooth appearance when viewed with an
electron microscope.
 Enzymes of the smooth ER make lipids and break
down toxic substances.
Protein Processing
Golgi Apparatus
Set of flattened, membrane-bound sacs.
Helps modify, sort, and package cell products for
distribution.
Golgi apparatus
Protein Processing, continued
Making and Exporting Proteins
 The ribosomes located on the rough ER make proteins
which then cross into the membranes of the ER. The
ER membrane then pinches off and forms a vesicle
around the proteins.
 Vesicles transport the proteins from the rough ER to
the Golgi apparatus, where they are modified by
enzymes and repackaged in new vesicles.
 These new vesicles transport the modified proteins to
the cell membrane to be released outside the cell.
Storage and Maintenance
Lysosomes
 Vesicles help maintain homeostasis by storing and
releasing a variety of substances as the cell needs
them.
 A lysosome is a vesicle produced by the Golgi
apparatus that contains enzymes that break down
large molecules.
 Lysosomes recycle old or damaged organelles and
digest food particles to provide nutrients for the cell.
Storage and Maintenance, continued
Vacuoles
 A vacuole is a fluid-filled vesicle found in the
cytoplasm of many plant cells.
 Plant cells contain a large compartment called the
central vacuole, which stores water, ions, nutrients,
and wastes.
 When water fills the central vacuole, the cell becomes
rigid, allowing the plant to stand up. When the
vacuole loses water, the cell shrinks, and the plant
wilts.
Storage and Maintenance, continued
Other Vacuoles
 Some protists have contractile vacuoles which
pump excess water out of the cell in order to
control the concentration of salts and other
substances.
 A food vacuole is another type of vacuole. It is
formed when the cell membrane surrounds food
particles outside the cell and pinches off to form a
vesicle inside the cell.
Energy Production, continued
Chloroplasts
Organelle found in plant and algae cells that uses
light energy to make carbohydrates from carbon
dioxide and water.
Surrounded by two membranes and have several
stacks of flattened sacs (thylakoids) where energy
production takes place.
 Plant cells may have several chloroplasts.
Energy Production, continued
Mitochondria
Organelles that use energy from organic compounds to
make ATP.
 Most of the ATP needed by a cell is produced inside
mitochondria. *Both animal and plant cells contain
mitochondria*.
 A smooth outer membrane and a folded inner
membrane surround a mitochondrion. ATP is
produced by enzymes on the folds of the inner
membrane.
Mitochondrion