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CHAPTER 4, STRUCTURE AND FUNCTION OF THE CELL
Both Living and Nonliving Things are composed of molecules made from chemical elements
such as carbon, hydrogen, oxygen, and nitrogen. The organization of these molecules into Cells
is one feature that distinguishes Living Things from all other matter. The CELL is the smallest
unit of matter that CAN Carry on ALL the PROCESSES OF LIFE.
OBJECTIVES: Outline the discoveries that led to the development of the Cell Theory. State
the cell theory. Identify a limiting factor on the size of cells. Describe the relationship between
cell shape and cell function. Distinguish between prokaryotes and eukaryotes.
1. Every living thing-from the tiniest bacterium to the largest whale-are made of one or more
cells.
2. Before the seventeenth century, no one knew that Cells existed.
3. Most Cells are too small to be seen with the unaided eye.
4. Cells were not discovered until after the invention of the microscope in the early seventeenth
century.
5. One of the First Microscopes was made by the Dutch drapery store owner Anton von
Leewenhoek. With his hand-held microscope, Leewenhoek became the FIRST person to
OBSERVE and DESCRIBE MICROSCOPIC ORGANISMS and LIVING CELLS.
6. In 1665, the English Scientist Robert Hooke used a microscope to examine a thin slice of cork
and described it as consisting of "a great many little boxes". It was after his observation that
Hook called what he saw "Cells". They looked like "little boxes" and reminded him of the small
rooms in which monks lived, so he called the "Cells".
7. In 1838, German Botanist Matthias Schleiden studied a variety of PLANTS and concluded
that all PLANTS "ARE COMPOSED OF CELLS".
8. The next year, German Zoologist Theodor Schwann reported that ANIMALS are also made of
CELLS and proposed a cellular basis for all life.
9. In 1855, German Physician Rudolf Virchow induced that "THE ANIMAL ARISES ONLY
FROM AN ANIMAL AND THE PLANT ONLY FROM A PLANT" OR " THAT CELLS
ONLY COME FROM OTHER CELLS".
10. His statement contradicted the idea that life could arise from Nonliving Matter. "Theory of
Spontaneous Generation" The process by which life begins when ethers enter nonliving things.
11. The COMBINE Work of Schleiden, Schwann, and Virchow make up what is now known as
the modern CELL THEORY.
12. The Cell Theory consist of THREE Principles:
A. All living things are composed of one or more cells.
B. Cells are the basic units of structure and function in an organism.
C. Cells come only from reproduction of existing cells.
CELL DIVERSITY
1. Not all cells are alike. Even cells within the same organism show Enormous Diversity in Size,
Shape, and Internal Organization. Your Body contains at least 200 Different Cell Types.
CELL SIZE
1. A few types of cells are large enough to be seen by the unaided eye. The Female Egg is the
largest cell in the body, and can be seen without the aid of a microscope.
2. Most cells are visible only with a microscope.
3. MOST CELLS ARE SMALL FOR TWO REASONS:
A. Cells are limited in size by the RATIO between their Outer Surface Area and Their
Volume. A SMALL CELL HAS MORE SURFACE AREA THAN A LARGE CELL FOR A
GIVEN VOLUME OF CYTOPLASM. This is important because the nutrients, oxygen, and
other materials a cell requires must enter through it surface. As a cell grows larger at some point
its surface area becomes too Small to allow these materials to enter the cell quickly enough to
meet the cell's need.
B. THE CELL'S NUCLEUS (THE BRAIN) CAN ONLY CONTROL A CERTAIN
AMOUNT OF LIVING, ACTIVE CYTOPLASM.
CELL SHAPE
1. Cells come in a variety of Shapes.
2. Notice the neurons on the wall, the basic cell of our Nervous System. This diversity of form
reflects a diversity of function.
3. Most Cells have a Specific Shape.
4. THE SHAPE OF A CELL DEPENDS ON IT'S FUNCTION.
5. Cells of the Nervous System that carry information from your toes to your brain are long and
threadlike.
6. Blood Cells are shaped like round disk that can squeeze through tiny blood vessels.
INTERNAL ORGANIZATION
1. Cells contain a variety of Internal Structures called ORGANELLES.
2. An organelle is a Cell Component that PERFORMS SPECIFIC FUNCTIONS FOR THE
CELL.
3. Just as the organs of a multicellular organism carry out the organism's life functions, the
Organelles of a cell Maintain the Life of the Cell.
4. There are many different cells; however, there are certain features common to all, or most
Cells.
5. The entire cell is Surrounded by A THIN MEMBRANE, called the CELL MEMBRANE.
6. Inside the Cell are a Variety of Organelles, most of which are surrounded by their own
Membrane.
7. A Large Organelle near the Center of the Cell is the NUCLEUS. IT CONTAINS THE
CELL'S GENETIC INFORMATION AND CONTROLS THE ACTIVITIES OF THE CELL.
8. The PRESENCE OR ABSENCE of a NUCLEUS is important for Classifying Cells.
9. ORGANISMS WHOSE CELL CONTAIN A NUCLEUS AND OTHER MEMBRANEBOUND ORGANELLES ARE CALLED EUKARYOTES.
10. ORGANISMS WHOSE CELLS NEVER CONTAIN (OR LACK) A NUCLEUS AND
OTHER MEMBRANE-BOUND ORGANELLES ARE CALLED PROKARYOTES.
11. UNICELLULAR ORGANISMS such as bacteria and their relatives are Prokaryotes.
12. All other organisms are Eukaryotes; plants, fish, mammals, insects and humans.
13. The difference between Prokaryotes and Eukaryotes is such an important distinction that
Prokaryotes are placed in Two Kingdoms, Separate from Eukaryotes.
SECTION 4-2, PARTS OF THE EUKARYOTIC CELL
The structures that make up a Eukaryotic Cell are determined by the specific functions carried
out by the cell. Thus, there is N0 Typical Eukaryotic Cell. Nevertheless, Eukaryotic Cells
generally have THREE Main Components: A Cell Membrane, A Nucleus, and other Organelles.
OBJECTIVES: Describe the structures, composition, and function of the cell membrane.
Name the major organelles found in a Eukaryotic cell, and describe their function. Describe the
structure and function of the nucleus. Describe three structures characteristic of plant cells.
THE CELL MEMBRANE
1. A Cell cannot survive if it is totally isolated from its environment. The Cell Membrane is a
complex barrier separating the cell from it's external environment.
2. This "Selectively Permeable" Membrane regulates what passes into and out of the cell.
3. All cells, from all organisms, are surrounded by a CELL MEMBRANE.
4. The Cell Membrane is a thin layer of Lipid and Protein that separates the cell's content from
the world around it.
5. The Cell Membrane Functions like a GATE, Controlling what ENTERS and LEAVES the
Cell.
6. The Cell Membrane CONTROLS the ease with which substances pass into and out of the
cell-some substances easily cross the membrane, while others cannot cross at all. For this
reason, the Cell Membrane is said to be SELECTIVELY PERMEABLE.
7. Cell Membranes are made mostly of PHOSPHOLIPID MOLECULES. Phosphate + Lipid.
8. Lipid is a simple form of FAT.
9. Phospholipids are a kind of Lipid that consists of TWO FATTY ACIDS (TAILS), and
PHOSPHATE GROUP (HEADS).
10. A Phospholipid Molecule has a POLAR "Head" and Two NONPOLAR "Tails".
11. POLAR - The two ends of the Phospholipid Molecule have different properties in Water.
12. The Phosphate Head is HYDROPHILIC meaning "WATER LOVING". Because of its
hydrophilic nature, the head of a Phospholipid will orient itself so that it is as close as possible to
water molecules.
13. The Lipid Tails are HYDROPHOBIC meaning "WATER-FEARING", the Hydrophobic
tails will tend to orient themselves away from water.
14. When dropped in WATER, PHOSPHOLIPIDS line up on the surface with their Phosphate
Heads Sticking into the Water and Lipid Tails pointing up from the surface.
15. Cells are bathed in aqueous, or watery, environment. Since the inside of a cell is also an
aqueous environment, both sides of the Cell Membrane are surrounded by Water Molecules.
These Water Molecules cause the Phospholipids of the Cell Membrane to form TWO LAYERS.
16. Cell Membranes CONSIST of TWO Phospholipid LAYERS Called a LIPID BILAYER.
17. Heads face the watery fluids inside and outside the cell.
18. Lipid Tails are sandwich inside the Bilayer.
19. The Cell Membrane is constantly being formed and broken down in living cells.
MEMBRANE PROTEINS (Refer to Figure 4-5)
1. A Variety of PROTEIN MOLECULES are EMBEDDED in the Lipid Bilayer.
2. Some Proteins are Attached to the surface of the cell membrane, these are called
PERIPHERAL PROTEINS, and are located on both the Internal and External Surface.
3. The Proteins that are Embedded in the Lipid Bilayer are called INTEGRAL PROTEINS.
4. Some Integral Proteins extend across the entire Cell Membrane and are exposed to both the
inside of the cell and the exterior environment. Others extend only to the inside or only to the
exterior surface.
5. There are many kinds of Proteins in membranes; they HELP to MOVE Material INTO and
OUT of the Cell.
6. Some Integral Proteins form Channels or Pores through which certain substances can pass.
7. Other Proteins bind to a substance on one side of the Membrane and carry it to the other side
of the Membrane.
8. Integral Proteins exposed to the Cell's External environment often have Carbohydrates
attached to them serve as identification badges that allow cells to recognize each other and may
act as Site where viruses or chemical messengers such as hormones can attach.
FLUID MOSAIC MODEL OF CELL MEMBRANES
1. Membranes are FLUID and have the consistency of vegetable oil.
2. The Lipids and Proteins of the Cell Membrane are always in motion.
3. Phospholipids are able to drift across the membrane, changing places with their neighbor.
4. Proteins in and on the membrane Form PATTERNS, or MOSAICS.
5. Because the Membrane is FLUID with a MOSAIC of Proteins, scientists call the modern
view of Membrane Structure THE FLUID MOSAIC MODEL.
6. The Pattern, or "Mosaic" of Lipids and Proteins in the Cell Membrane is Constantly
Changing.
ORGANELLES
CYTOPLASM (SIET-oh-PLAZ-uhm)
1. EVERYTHING BETWEEN THE CELL MEMBRANE AND THE NUCLEUS IS THE
CELL'S CYTOPLASM.
2. CYTOPLASM consists of TWO MAIN COMPONENTS: CYTOSOL and
ORGANELLES.
3. CYTOSOL is a jellylike mixture that consists MOSTLY OF WATER, along with
PROTEINS,
CARBOHYDRATES, SALTS, MINERALS and ORGANIC MOLECULES.
4. Suspended in the Cytosol are tiny ORGANELLES (ORGANS).
5. ORGANELLES ARE STRUCTURES THAT WORK LIKE MINIATURE ORGANS,
THEY CARRY OUT SPECIFIC FUNCTIONS IN THE CELL.
6. The ORGANELLES PLUS THE CYTOSOL makes up the CYTOPLASM.
7. In Eukaryotic Cells, most Organelles are surrounded by a MEMBRANE.
8. Prokaryotic Cells have NO MEMBRANE-BOUND Organelles.
MITOCHONDRIA (MET-oh-KAHN-dree-uh)
1. Mitochondria are found scattered throughout the Cytosol, and are relatively Large Organelles.
2. Mitochondria are the sites of Chemical Reactions that transfer Energy from Organic
Compounds to ATP. Energy contain in food is released. Converted to ATP. ATP is the
molecule that most Cells use as their main Energy Currency.
3. THE "POWERHOUSE" OF THE CELL.
4. Mitochondria are Usually more numerous in Cells that have a High Energy Requirement Your muscle cells contain a large number of mitochondria.
5. Mitochondria is surrounded by TWO Membranes.
A. The smooth outer membrane serves as a boundary between the mitochondria and the
cytosol.
B. The inner membrane has many long folds, known as CRISTAE (KRIS-tee). The Cristae
greatly increases the surface area of the inner membrane, providing more space for the Chemical
Reactions to occur.
6. Mitochondria have their own DNA, and new mitochondria arise only when existing ones
Grow and divide.
7. ATP Production is called CELLULAR RESPIRATION.
RIBOSOMES (RIE-buh-SOHMZ)
1. Unlike most other organelles, Ribosomes Are Not Surrounded by a membrane.
2. Ribosomes are the site of PROTEIN SYNTHESIS (Production or Construction) in a cell.
3. They are Most Numerous Organelles in almost all cells.
4. Some are free in the Cytoplasm; others line the membranes of ROUGH ENDOPLASMIC
RETICULUM.
ENDOPLASMIC RETICULUM (ER) (EN-doh-PLAZ-mik ri-TIK-yuh-luhm)
1. The ER is a system of membranous tubules and sacs.
2. The ER functions Primarily as an Intracellular Highway, a path along which molecules move
from one part of the cell to another.
3. The amount of ER inside a cell fluctuates, depending on the Cell's Activity.
4. Poisons, waste, and other toxic chemicals are made harmless.
5. ER is an extensive network of membranes that connect the Nuclear Envelope to the Cell
Membrane.
6. Transports materials through the cell.
7. Can be ROUGH OR SMOOTH.
A. ROUGH ER is studded with RIBOSOMES and processes PROTEINS to be exported
from the cell.
B. SMOOTH ER IS NOT Covered with RIBOSOMES and processes LIPIDS and
CARBOHYDRATES. The Smooth ER is involved in the synthesis of steroids in gland cells, the
regulation of calcium levels in muscle cells, and the breakdown of toxic substances by liver cells.
GOLGI APPARATUS (GOHL-jee)
1. The Golgi Apparatus is the Processing, Packaging and Secreting Organelle of the Cell.
2. The Golgi Apparatus is a system of membranes. Made of Flattened SAC like Structures called
CISTERNAE.
3. It works Closely with the ER, the Golgi Apparatus modifies proteins for export by the cell.
LYSOSOMES (LIE-suh-sohmez)
1. Lysosomes are small spherical organelles that enclose hydrolytic enzymes within a single
membrane.
2. Lysosomes are the Site of Food Digestion in the Cell.
3. Lysosomes are formed from pieces of the GOLGI APPARATUS that break off.
4. Lysosomes are common in the Cells of Animals, Fungi, and Protists, But Rare in Plant Cells.
CYTOSKELETON
1. Just as your body depends on your skeleton to maintain its shape and size, so a Cell needs
structures to maintain its shape and size.
2. In Animal Cells, an internal framework called CYTOSKELETON maintains the Shape of the
Cell.
3. THE CYTOSKELETON MAINTAINS THE THREE-DIMENSIONAL STRUCTURE OF
THE CELL, PARTICIPATES IN THE MOVEMENT OF ORGANELLES WITHIN THE
CYTOSOL, AND HELPS THE CELL MOVE.
4. The Cytoskeleton is a network of long protein strands located in the Cytosol, that are Not
surrounded by a membrane.
3. The CYTOSKELETON consists of TWO Types of structures: MICROFILAMENTS AND
MICROTUBULES.
MICROFILAMENTS
1. MICROFILAMENTS are NOT HALLOW and have a structure that resembles ROPE made of
TWO TWISTED CHAINS OF PROTEIN called ACTIN.
2. MICROFILAMENTS can CONTRACT, causing movement.
3. Muscle Cells have many microfilaments.
MICROTUBULES
1. Microtubules are HALLOW TUBES like plumbing pipes. They are the Largest Strands of the
Cytoskeleton.
2. Microtubules are made of a PROTEIN called TUBULIN.
3. Microtubules have THREE FUNCTIONS:
A. To maintain the shape of the cell.
B. To serve as tracks for organelles to move along within the cell.
C. When the Cell is about to divide, bundles of Microtubules known as SPINDLE FIBERS
come together and extend across the cell to assist in the movement of Chromosomes during Cell
Division.
CILIA AND FLAGELLA
1. Cilia and Flagella are Hairlike Organelles that extend from the surface of the cell, where they
assist in movement.
2. Microtubules are sometimes bundled into structures called CILIA AND FLAGELLA.
3. CILIA ARE SHORT HAIRLIKE PROJECTIONS.
4. FLAGELLA ARE LONG WHIPLIKE PROJECTIONS.
5. The Cilia and Flagella of all Eukaryotes consist of ONE PAIR OF MICROTUBULES
SURROUNDED BY NINE MORE PAIRS.
6. CILIA ARE OFTEN NUMEROUS.
7. FLAGELLA ARE OFTEN SINGULAR.
8. Unicellular organisms such as Paramecium and Euglena use Cilia and Flagella to move
through water.
9. Sperm use flagella to swim to the egg.
10. In Humans, beating Cilia line parts of the respiratory system, moving dust particles and
bacteria away from the lungs.
THE NUCLEUS (plural, Nuclei)
1. The Nucleus is often the most Prominent Structure within a Eukaryotic Cell.
2. It maintains its shape with the help of a Protein skeleton known as the NUCLEAR MATRIX.
3. The Nucleus is the CONTROL CENTER (BRAIN) of the Cell.
4. Most Cells have a Single Nucleus some cells have more than one.
5. The nucleus is surrounded by a Double Layer Membrane called the NUCLEAR
ENVELOPE.
6. The Nuclear Envelope is covered with many small pores through which PROTEINS and
CHEMICAL MESSAGES from the Nucleus can pass. Golf Ball like dimples (pores).
7. The Nucleus contains DNA, the HEREDITARY MATERIAL OF CELLS.
8. The DNA is in the form of a long Strand called CHROMATIN.
9. During Cell Division, Chromatin strands COIL and CONDENSES into thick structures called
CHROMOSOMES.
10. The Chromosomes in the nucleus contain coded "BLUEPRINTS" that control all cellular
activity.
11. Most Nuclei contain at least ONE NUCLEOLUS (plural, Nucleoli) (Figure 4.14).
12. The NUCLEOLUS MAKES (syntheisizes) RIBOSOMES, WHICH IN TURN, BUILD
PROTEINS.
13. When a Cell prepares to Reproduce, the NUCLEOLUS DISAPPEARS.
PLANT CELLS
1. Most of the Organelles and other parts of the cell are common in ALL Eukaryotic Cells. Cell
from different organisms have even greater difference in structure.
2. Plant Cells have Three Additional Structures Not found in animals cells - CELL
WALLS, VACUOLES, AND PLASTIDS that are extremely important to Plant Function.
3. In addition to their unique structures, Plant Cells have: MITOCHONDRIA, RIBOSOMES,
AND the other organelles.
CELL WALL
1. One of the most important differences between Plant and Animal CELLS is the Presence of a
CELL WALL IN PLANT CELLS.
2. Fungi such as Mushrooms and Yeast also have Cell Walls. Cell Walls of Fungi are made of
CHITIN.
3. A Cell Wall DOES NOT REPLACE the Cell Membrane; Cells with WALLS also have a
CELL MEMBRANE. Plant Cells are covered by a Rigid Cell Wall that lies Outside the Cell
Membrane.
4. The Rigidity of Cell Walls Helps SUPPORT and PROTECT the Plant.
5. Cell Walls of Plants contain POLYSACCHARIDE (long chains) CELLULOSE a complex
carbohydrate.
6. CELL WALLS ARE OF TWO TYPES: (Figure 4-15)
A. PRIMARY CELL WALL - While a Plant cell is being formed, a primary cell wall
develops just outside the cell membrane. As the cell expands in length, cellulose and other
molecules are added, enlarging the cell wall. When the cell reaches full size, a Secondary Cell
Wall MAY Form.
B. SECONDARY CELL WALL - The secondary cell walls forms Between the Primary Cell
Wall and the Cell Membrane. The Secondary Cell Wall is Tough and Woody, in fact the
Secondary Cell Wall is what we call WOOD. One a Secondary Cell Wall forms, a plant cell can
Grow NO Further. The Cells are Dead.
VACUOLES
1. The SECOND prominent structure in Plant Cells is the large VACUOLE.
2. The VACUOLE is a large membrane-bound sac that takes up a large amount of space in
most Plant Cells.
3. The VACUOLE serves as a STORAGE AREA, and may contain stored PROTEINS, IONS,
WASTE, OR OTHER CELL PRODUCTS.
4. VACUOLES of some plants contain Poison that discourages animals from eating the plant's
leaves.
5. Cells of Animals and other organisms also MAY contain VACUOLES, but they are much
smaller and are usually involved in FOOD DIGESTION.
PLASTIDS
1. A THIRD distinguishing feature of PLANT CELLS is the presence of STRUCTURES
CALLED PLASTIDS THAT MAKE OR STORE FOOD.
2. A common kind of PLASTID is the CHLOROPLAST, (figure 4-17) an organelle that
converts SUNLIGHT, CARBON DIOXIDE, AND WATER INTO SUGARS. This process is
called PHOTOSYNTHESIS.
3. Each Chloroplast encloses a system of Flattened, Membranous Sacs called THYLAKOIDS.
It is in the Thylakoids that Photosynthesis occurs.
4. Chloroplasts are GREEN because they contain CHLOROPHYLL, a PIGMENT that
ABSORBS ENERGY IN SUNLIGHT. THEY ARE FOUND ONLY IN ALGAE, SUCH AS
SEAWEED, AND IN GREEN PLANTS.
5. Other PLASTIDS store reddish-orange pigments that color fruits, vegetables, flowers, and
autumn leaves.