Cells
Two Types of Cells
There is another basic cell structure that is present in many but not all living cells: the nucleus. The
nucleus of a cell is a structure in the cytoplasm that is surrounded by a membrane (the nuclear membrane)
and contains, and protects, most of the cell's DNA. Based on whether they have a nucleus, there are two
basic types of cells: prokaryotic cells and eukaryotic cells.
Prokaryotic Cells
Prokaryotic cells are cells without a nucleus. The DNA in prokaryotic cells is in the cytoplasm rather
than enclosed within a nuclear membrane. Prokaryotic cells are found in single-celled organisms, such as
bacteria. Organisms with prokaryotic cells are called prokaryotes. They were the first type of organisms
to evolve and are still the most common organisms today.
Eukaryotic Cells
Eukaryotic cells are cells that contain a nucleus. Eukaryotic cells are usually larger than
prokaryotic cells, and they are found mainly in multicellular organisms. Organisms with eukaryotic cells
are called eukaryotes, and they range from fungi to people.
Eukaryotic cells also contain other organelles besides the nucleus. An organelle is a structure
within the cytoplasm that performs a specific job in the cell. Organelles called mitochondria, for example,
provide energy to the cell, and organelles called vacuoles store substances in the cell. Organelles allow
eukaryotic cells to carry out more functions than prokaryotic cells can. This allows eukaryotic cells to
have greater cell specificity than prokaryotic cells. Ribosomes, the organelle where proteins are made, are
the only organelles in prokaryotic cells.
In some ways, a cell resembles a
plastic bag full of Jell-O. Its basic
structure is a plasma membrane
filled with cytoplasm. Like Jell-O
containing mixed fruit, the
cytoplasm of the cell also contains
various structures, such as a
nucleus and other organelles.
Does a cell have its own ER?
Yes, but in this case, the ER is not just for emergencies. True, there might be times when the cell responds
to emergency conditions and the functions of the ER may be needed, but usually the cell's ER is involved
in normal functions. Proteins are also made on the outside of the ER, and this starts a whole process of
protein transport, both around the inside of the cell and to the cell membrane and out.
Other Organelles
In addition to the nucleus, eukaryotic cells have many other organelles, including the endoplasmic
reticulum, Golgi apparatus, vesicles, vacuoles, and centrioles.
Endoplasmic Reticulum
The endoplasmic reticulum (ER) is a network of phospholipid membranes that form hollow tubes,
flattened sheets, and round sacs. The ER has two major functions:
 Transport: Molecules, such as proteins, can move from place to place inside the ER, much like on
an intracellular highway.
 Synthesis: Ribosomes that are attached to ER, similar to unattached ribosomes, make proteins.
Lipids are also produced in the ER.
Golgi Apparatus
The Golgi apparatus is a large organelle that is usually made up of five to eight cup-shaped, membranecovered discs called cisternae. The Golgi apparatus modifies, sorts, and packages different substances for
secretion out of the cell, or for use within the cell. The Golgi apparatus is found close to the nucleus of the
cell, where it modifies proteins that have been delivered in transport vesicles from the RER. It is also
involved in the transport of lipids around the cell. Pieces of the Golgi membrane pinch off to form
vesicles that transport molecules around the cell. The Golgi apparatus can be thought of as similar to a
post office; it packages and labels "items" and then sends them to different parts of the cell. Both plant
and animal cells have a Golgi apparatus.
Vesicles
A vesicle is a small, spherical compartment that is separated from the cytosol by at least one lipid bilayer.
Vesicles are basic tools of the cell for organizing metabolism, transport, and storage of molecules.
Vesicles are also used as chemical reaction chambers. They can be classified by their contents and
function.
Lysosomes are vesicles that are formed by the Golgi apparatus. They contain powerful enzymes that
could break down (digest) the cell. Lysosomes break down harmful cell products, waste materials, and
cellular debris and then force them out of the cell. They also digest invading organisms such as bacteria.
Lysosomes also break down cells that are ready to die, a process called autolysis.
Vacuoles
Vacuoles are membrane-bound organelles that can have secretory, excretory, and storage functions. Many
organisms will use vacuoles as storage areas and some plant cells have very large vacuoles.
Centrioles
Centrioles are rod-like structures made of short microtubules. Centrioles are very important in cellular
division, where they arrange the mitotic spindles that pull the chromosome apart during mitosis.
Instructions:
Define bold faced words, answer questions, and write summary
1. What are the 2 types of cells?
2. List each organelle and its function.
Cells
Two Types of Cells
There is another basic cell structure that is present in many but not all living cells:
the nucleus. The nucleus of a cell is a structure in the cytoplasm that is surrounded
by a membrane (the nuclear membrane) and contains, and protects, most of the
cell's DNA. Based on whether they have a nucleus, there are two basic types of
cells: prokaryotic cells and eukaryotic cells.
Prokaryotic Cells
Prokaryotic cells are cells without a nucleus. The DNA in prokaryotic cells is in
the cytoplasm rather than enclosed within a nuclear membrane. Prokaryotic cells
are found in single-celled organisms, such as bacteria. Organisms with prokaryotic
cells are called prokaryotes. They were the first type of organisms to evolve and
are still the most common organisms today.
Eukaryotic Cells
Eukaryotic cells are cells that contain a nucleus. Eukaryotic cells are
usually larger than prokaryotic cells, and they are found mainly in multicellular
organisms. Organisms with eukaryotic cells are called eukaryotes, and they range
from fungi to people.
Eukaryotic cells also contain other organelles besides the nucleus. An
organelle is a structure within the cytoplasm that performs a specific job in the
cell. Organelles called mitochondria, for example, provide energy to the cell, and
organelles called vacuoles store substances in the cell. Organelles allow eukaryotic
cells to carry out more functions than prokaryotic cells can. This allows eukaryotic
cells to have greater cell specificity than prokaryotic cells. Ribosomes, the
organelle where proteins are made, are the only organelles in prokaryotic cells.
In some ways, a cell resembles a
plastic bag full of Jell-O. Its basic
structure is a plasma membrane
filled with cytoplasm. Like Jell-O
containing mixed fruit, the
cytoplasm of the cell also contains
various structures, such as a
nucleus and other organelles.
Does a cell have its own ER?
Yes, but in this case, the ER is not just for emergencies. True, there might be times
when the cell responds to emergency conditions and the functions of the ER may
be needed, but usually the cell's ER is involved in normal functions. Proteins are
also made on the outside of the ER, and this starts a whole process of protein
transport, both around the inside of the cell and to the cell membrane and out.
Other Organelles
In addition to the nucleus, eukaryotic cells have many other organelles, including
the endoplasmic reticulum, Golgi apparatus, vesicles, vacuoles, and centrioles.
Instructions:
Define bold faced words, answer questions, and write a summary.
1. What are the two types of cells?
2. How is a cell like jello?
3. List 4 organelles of the cell.