Science review: Cells
Vocabulary
Cell- basic unit of all forms of life
Cell theory- fundamental concept of biology that states that all living things are
composed of cells; that cells are the basic units of structure and function in living things;
and that new cells are produced from existing cells
Cell membrane- thin, flexible barrier that surrounds all cells; regulates what enters and
leaves the cell
Nucleus- structure that contains the cell’s genetic material in the form of DNA
Eukaryote- organism whose cells contain a nucleus
Prokaryote- unicellular organism that lacks a nucleus
Cytoplasm- fluid portion of the cell outside the nucleus
Organelle- specialized structure that performs important cellular functions within a
eukaryotic cell
Vacuole- cell organelle that stores materials such as water, salts, protein, and
carbohydrates
Lysosome- cell organelle that breaks down lipids, carbohydrates, and proteins into small
molecules that can be used by the rest of the cell
Cytoskeleton- network of protein filaments in a eukaryotic cell that gives the cell its
shape and internal organization and is involved in movement
Centriole- structure in an animal cell that helps to organize cell division
Ribosome- cell organelle consisting of RNA and protein found throughout the cytoplasm
in a cell; the site of protein synthesis
Endoplasmic reticulum- internal membrane system found in eukaryotic cells; place
where lipid components of the cell membrane are assembled
Golgi apparatus- organelle in cells that modifies, sorts, and packages proteins and other
materials from the endoplasmic reticulum for storage in the cell or release outside the
cell
Chloroplast- organelle found in cells of plants and some other organisms that captures
the energy from sunlight and converts it into chemical energy
Mitochondrion- cell organelle that converts the chemical energy stored in food into
compounds that are more convenient for the cell to use
Cell wall- strong, supporting layer around the cell membrane in some cells
Yamaris Rodriguez 1
Lipid bilayer- flexible double-layered sheet that makes up the cell membrane and forms
a barrier between the cell and its surrounding
Selectively permeable- property of biological membranes that allows some substances
to pass across it while others cannot; also called semipermeable membrane
Life is Cellular
In 1500s eyeglass makers in Europe discovered that using different glass lenses in
combination could magnify the smallest objects to make them easy to see. They built
the first true microscope and opened the door to the study of biology.
1665- Robert Hooke used an early compound microscope to look at a thin slice of cork
Hooke discovered tiny empty chambers and called them cells.
In Holland Anton van Leeuwenhoek used a single-lens microscope and discovered
bacteria.
In 1838, German botanist Matthias Schleiden concluded that all plants are made of
cells.
In 1855, German physician Rudolf Virchow concluded that new cells can be produced
by the division of existing cells.
These discoveries are summarized in the cell theory, a fundamental concept of biology.
Most microscopes use lenses to magnify the image of an object by focusing light or
electron.
A typical light microscope allows light to pass through a specimen and uses two lenses
to from an image. The first lens is the objective lens, it enlarges the image of the
specimen. The second lens is the ocular lens it magnifies the image still further.
The problem with this microscope is that the light limits the detail, resolution. Another
problem is that most living cells are nearly transparent. Using dyes can usually solve
this problem.
Light microscopes can be used to see cells and cell structures as small as 1 millionth of
a meter.
Another type of microscope is the electron microscope. Instead of using light it uses
beams of electrons that are focused by magnetic fields. They offer higher resolution,
some can be used to study cellular structures that are 1 billionth of a meter in size.
Two types of electron microscopes are: transmission and scanning.
Transmission electron microscope make it possible to explore cell structure and enlarge
protein molecules.
Yamaris Rodriguez 2
The scanning electron microscope produces stunning three-dimensional images of the
specimen’s surface.
The colors in light micrographs come from the cells themselves or from the stains and
dyes used to highlight them. Electron micrographs are black and white; electrons don’t
come in light. So scientists often use computer techniques to add “false color” to make
structures stand out.
All cells at some point contain DNA, molecule that carries biological information.
All cells are surrounded by a cell membrane, which sometimes is called plasma
membrane because many cells in the body are in direct contact with fluid portion of the
blood.
Cells fall in two different categories that depend on if they have a nucleus or not.
They are: eukaryote (cells have DNA in the nucleus) and prokaryote (don’t have DNA in
the nucleus).
Differences between the prokaryote and eukaryote cells:
-prokaryote: smaller and simpler, don’t separate their genetic material within a nucleus,
they grow, reproduce, respond to the environment, some cases they glide along
surfaces or swim through liquids, bacteria are prokaryote.
-eukaryote: larger and complex, contain dozens of structures and internal membrane,
the nucleus separates the genetic material from the rest of the cell, they display variety:
protists live solitary lives as unicellular organisms and others form large multicellular
organisms like plants, animals, and fungi.
Cell structure
It’s easy to divide each cell into two major parts: the nucleus and the cytoplasm.
Prokaryotic cells have cataplasms even though they don’t have a nucleus.
Organelles are called “little organs”.
Comparing the cell to a factory: the different organelles of the cell can be compared to
the specialized machines and assembly lines of the factory. Cell like factories follow
instructions and produce products.
The nucleus is the main office of the cell because is the control center of the cell. The
nucleus contains nearly all the cell’s DNA and the coded instructions for making
proteins and other important molecules.
The nucleus is surrounded by a nuclear envelope composed of two membranes. The
nuclear envelope is dotted with thousands of nuclear pores, which allow material to
move into and out of the nucleus (like messages, instructions, and blueprints moving in
and out of the factory’s main office).
Yamaris Rodriguez 3
Chromosomes carry the cell’s genetic information are also in the nucleus. The
threadlike chromosomes are spread throughout the nucleus in the form of chromatin (a
complex of DNA bound to proteins).
Most nuclei contain a small dense region known as the nucleolus (where the assembly
of ribosomes begins).
Vacuoles are the place where you store things. They store materials like water, salts,
proteins, and carbohydrates. In many plant cells there is a single, large central vacuole
filled with liquid. Vacuoles are also found in some unicellular organisms and in some
animals.
Contractile vacuole pumps excess water out of the cell. Nearly all eukaryotic cells
contain smaller membrane-enclosed structures called vesicles. They store and move
materials between cell organelles, as well as to and from the cell surface.
The lysosomes are the cleanup crew. Lysosomes break down lipids, carbohydrates, and
proteins into small molecules that can be used by the rest of the cell. They are also
involved in breaking down organelles that have outlived their usefulness. A number of
human diseases can be traced to lysosomes that fail to function properly. They are found
in animal and plant cells.
Cytoskeleton is the steel or cement beams and by columns that hold up its walls and
roof in the factory. The cytoskeleton helps the cell maintain its shape and is also involved
in movement. It’s made up of two principal protein filaments, microfilaments and
microtubules.
Microfilaments are threadlike structures made up of a protein called actin. They form
extensive networks in some cells and produce a tough flexible framework that supports
the cell. It helps the cell move.
Microtubules are hollow structures made up of proteins know as tubulins. They play
critical roles in maintaining the cell shape. They are important in cell division, where they
form a structure known as the mitotic spindle, which helps to separate chromosomes. In
animal cell the centrioles (located near the nucleus) are also formed from tubulins.
Microtubules help build projections from the cell surface known as cilia and flagella that
enable cells to swim rapidly through liquid.
Yamaris Rodriguez 4
Proteins are assembled on ribosomes. They produce proteins by following coded
instructions that come from DNA.
The endoplasmic reticulum is where lipid components of the cell membrane are
assembled, along with proteins and other materials that are exported from the cell.
The portion of the endoplasmic reticulum involved in the synthesis of proteins is the rough
endoplasmic reticulum, the name is given because of the ribosomes found on its
surface. Proteins made on the rough ER include those that will be released from the cell
as well as many membrane proteins and proteins destined for lysosomes and other
specialized locations within the cell.
The other portion of the ER is the smooth endoplasmic reticulum, because ribosomes
are not found on its surface. It contains collections of enzymes that perform specialized
tasks, including the synthesis of membrane lipids and the detoxification of drugs.
In eukaryotic cells protein produced in the rough ER move next into the Golgi apparatus.
It modifies, sorts, and packages proteins and other materials from the endoplasmic
reticulum for storage in the cell or release outside the cell. From the Golgi apparatus
proteins are shipped to their final destination inside or outside the cell.
Chloroplast capture the energy from sunlight and convert it into food that contains
chemical energy in a process called photosynthesis. Two membranes surround the
chloroplast. Inside it there are large stacks of membranes, which contain the green
pigment chlorophyll.
Mitochondria convert the chemical energy stored in food into compounds that are more
convenient for the cell to use.
Mitochondria and chloroplasts contain their own genetic information in the form of small
DNA molecules.
Cell walls support, shape and protect the cell. Most cell walls are porous enough to
allow water, oxygen and carbon dioxide. They provide the strength needed for plants to
stand against the force of gravity.
All cells have cell membranes, which almost always are made up of a double-layered
sheet called a lipid bilayer. The cell membrane regulates what enters and leaves the
cell and also protects and supports the cell.
Yamaris Rodriguez 5
Yamaris Rodriguez 6
Cells remained out of sight until the invention of the...
Microscope
How did the first true microscope come to be?
Eyeglass makers in Europe discovered that using several glass
lenses in combination could magnify small objects
Robert Hooke
Used a compound microscope to examine cork. It seemed to
be made of thousands of tiny chambers. He called them cells.
Anton van Leeuwenhoek
Used a single-lens microscope to observe pond water and it
revealed tiny organisms that were found everywhere, today we
call them bacteria
Cells
The basic units of life
Matthias Schleiden
Concluded all plants are made of cells
Theodor Schwann
Stated all animals are made of cells
Rudolf Virchow
Concluded that new cells can be produced from the division of
existing cells
Cell Theory
The fundamental concept of biology. It states: 1) all living
things are made up of cells. 2) Cells are the basic units of
structure and function in living things. 3) New cells are
produced from existing cells.
Most Microscopes use lenses to magnify the image of an
object by _____________.
Focusing light or electrons.
Compound Light Microscope
Is a typical light microscope that allows light to pass through
a specimen and uses two lenses to form an image.
Objective lens
The first lens located just above the specimen
Ocular lens
The second lens that magnifies the image still further.
Yamaris Rodriguez 7
Light microscopes produce clear images of objects only to a
magnification of
1000 times
Using chemical stains solves the problem of
The fact that most living cells are transparent (fluorescence)
Electron microscopes
Use beam of electrons that are focused by magnetic fields.
They offer much higher resolution than light microscopes.
Two major types of electron microscopes:
Transmission and scanning.
Transmission electron microscopes
Make it possible to explore cell structures and large protein
molecules. Beams of electrons can only pass through thin
samples making images 2 dimensional
Scanning electron microscopes
A pencil like beam of electrons is scanned over the surface of
the specimen. They produce three dimensional images
To prevent electrons from scattering in the air,
Samples must be placed in a vacuum and chemically preserved
since they have to be nonliving cells and tissues
Cell membrane
A thin flexible barrier that surrounds a cell.
Nucleus
A large membrane-enclosed structure that contains genetic
material in the form of DNA.
Eukaryotes
Cells that enclose their DNA in nuclei.
Prokaryotes
Cells that do not enclose their DNA in nuclei.
Prokaryotic Cells are generally _____ and ________ than
eukaryotic cells.
Smaller and simpler
One example of prokaryotes
Bacteria
Eukaryotic Cells are generally _____ and ________ than
prokaryotic cells.
Yamaris Rodriguez 8
Larger and more complex
Eukaryotic cells contain
A nucleus and many specialized structures
Cytoplasm
Is the portion of a cell outside the nucleus.
Organelles
Are structures that have specialized functions in eukaryotic
cells
The nucleus contains...and controls...
DNA; the activity of a cell
Vacuoles
Membrane-enclosed saclike structures that store water, salts,
and organic molecules
Lysosomes
Small organelles filled with enzymes that break down large
molecules and organelles that are no longer useful
The cytoskeleton
A network of protein filaments; it helps that cell maintain its
shape and is involved in movement
Centrioles
Organelles made form tubulins; they help organize cell
division in animal cells
Three kinds of organelles work with the nucleus to make and
distribute proteins
Ribosomes, endoplasmic reticulum (ER), Golgi apparatus
Ribosome
Small particles of RNA and protein found throughout the
cytoplasm in all cells; they produce proteins by following
coded instructions from DNA
The endoplasmic reticulum (ER):
An internal membrane system where lipid components of the
cell membrane are assembled, along with proteins and other
materials
Golgi apparatus:
Yamaris Rodriguez 9
An organelle that appears as a stack of flattened membranes;
it modifies, sorts, and packages proteins and other materials
form the ER for storage in the cell or release outside the cell
Two types of organelles act as power plants of the cells.
Chloroplasts
Mitochondria
Both types are surrounded by two membranes
Chloroplasts
Capture the energy from sunlight and convert it into food that
contains chemical energy in a process called photosynthesis.
Cells
of
plants
and
some
other
organisms
contain
chloroplasts, which contain chlorophyll
Mitochondria
Are found in nearly all eukaryotic cells; they convert the
chemical energy stored in food to a usable form
Cellular Boundaries
All cells are surrounded by a cell membrane. Many cells also
have a cell wall. Both cell membranes and cell walls separate
cells from the environment and provide support.
Cell walls
Support, shape, and protect the cell. Most prokaryotes and
many eukaryotes have them. Animals do not have cell walls.
Cell walls lie outside the cell membrane. Most cell walls allow
materials to pass through them.
Lipid bilayer
What
a
cell
membrane
consists
of.
It is a strong but flexible barrier between the cell and its
surroundings. They cell membrane regulates what enters and
leaves the cell and also protects and supports the cell. Most
biological membranes are selectively permeable, allowing
some substances, but not others, to pass across them.
Selectively permeable
Allowing some substances, but not others, to pass across
them.
Describe the relationship between the cytoplasm and the
nucleus of a cell
Yamaris Rodriguez 10
The nucleus of a cell is found in the cytoplasm, but is not part
of the cytoplasm. The nucleus and cytoplasm work together to
keep a cell alive
What does the term organelle mean literally?
Little organ
In the visual analogy of a cell is a factory, what two functions
of the nucleus are represented? How are these functions
illustrated?
The nucleus act as the office, or control center, as illustrated
by the people at the desk. The nucleus is the source of
messages, instructions, and blue prints as illustrated by the
two workers helping the chain (of RNA) leave the nucleus.
Which feature of the nucleus is not clearly shown by the
visual analogy?
The chromatin is not shown
What is another possible analogy that could be compared
with the structure and function of a cell?
The structure and function of an airport control tower could
be compared to the structure and function of a cell
What are vacuoles?
Vacuoles are membrane-enclosed saclike structures that store
materials such as water, salts, proteins, and carbohydrates.
What are the two roles of the central vacuole in plant cells?
Storage of materials and support of the cell
How are contractile vacuoles different from other types of
vacuoles?
Contractile vacuoles pump excess water out of the cell, while
other types of vacuoles hold materials inside of cells
What is the role of lysosomes in the cell? Why is this a vital
role?
Lysosomes breakdown large molecules and waste without
them clutter could accumulate in the cell, which has been
linked to serious human diseases
Which structures of the cytoskeleton are found in animal
cells but not in plant cells?
Centrioles
Yamaris Rodriguez 11
What other structures of the cytoskeleton would show the
same pattern of microtubules as a flagellum?
Cilia
What are ribosomes? What do they do?
Ribosomes are small particles of RNA and protein found
throughout the cytoplasm. They are involved in synthesis of
proteins.
In which organelle are the lipid components of the cell
membrane assembled?
Endoplasmic reticulum
What is the difference between rough ER and smooth ER?
Ribosomes are found on the surface of rough ER. Smooth ER
has no ribosomes on its surface.
Using the cell as a factory analogy, describe the role of the
Golgi apparatus in cells.
The Golgi apparatus is like a customization shop in a factory.
It puts the finishing touches on proteins before they leave the
factory.
Suppose a cell's Golgi apparatus does not function properly.
How might this problem affect other cells?
If the cell manufactures proteins that are normally released to
travel to other cells. Those cells would not receive the proteins.
The loss of these proteins might cause the "receiver" cells to
function poorly.
Chloroplasts are....found in animal cells
Never
...chloroplasts, mitochondria are surrounded by a double
membrane
Like
Nearly all of the ....in your cells were inherited from your
mother
Mitochondria
Both chloroplasts and mitochondria... genetic information in
the form of DNA
Contain
Yamaris Rodriguez 12
Most cell...are porous to water and other materials but
strong enough to support and protect cells
Walls
Nearly all of the plant tissue called...is make up of cell walls
Wood
Besides
supporting
and
protecting
a
cell,
the
cell
membrane...what enters and leaves the cell.
Regulates
What is the function of vesicles in the synthesis of proteins
and the release of those proteins outside the cell?
Vesicles transport newly synthesized proteins to the Golgi
apparatus. After the Golgi apparatus modifies the proteins,
vesicles transport the modified proteins to the cell membrane,
where they are released.
Yamaris Rodriguez 13