Download CELLS Section 1: Introduction to Cells Key Ideas How were cells

CELLS
Section 1: Introduction to Cells
Key Ideas
How were cells discovered?
Why does cell shape vary?
What enables eukaryotes to perform more specialized functions than prokaryotes?
The Discovery of Cells
Microscope observations of organisms led to the discovery of the basic
characteristics common to all living things.
Scientists first discovered cells in the 1600s using crude microscopes.
Observations made by scientists using more powerful microscopes in the 1800s
led to the formation of the cell theory.
Looking at Cells
Cells vary greatly in their size and shape.
A cell’s shape reflects its function. Cell size is limited by a cell’s surface area-tovolume ratio.
Cells can be branched, flat, round, or rectangular.
All substances that enter or leave a cell must cross the surface of the cell.
A cell’s ability to move substances across its surface can be estimated by finding
its surface area-to-volume ratio.
Cells with greater surface area-to-volume ratios can exchange substances more
efficiently.
When comparing cells of the same shape, small cells have greater surface area-tovolume ratios than large cells.
So, small cells function more efficiently than large cells.
Cell Features
All cells share common structural features, including a cell membrane, cytoplasm,
ribosomes, and DNA.
The cell membrane is the outer layer that covers a cell’s surface and acts as a
barrier between the outside environment and the inside of the cell.
The cytoplasm is the region of the cell within the cell membrane. The cytoplasm
includes the fluid inside the cell called the cytosol.
A ribosome is a cellular structure that makes proteins.
The DNA of a cell provides instructions for making proteins, regulates cellular
activities, and enables cells to reproduce.
Features of Prokaryotic Cells
A prokaryote is an organism made of a single prokaryotic cell.
Prokaryotic cells do not have a nucleus or other internal compartments. The
genetic material of a prokaryotic cell is a single loop of DNA.
For millions of years, prokaryotes were the only organisms on Earth.
Features of Eukaryotic Cells
A eukaryote is an organism made up of one or more eukaryotic cells. All
multicellular organisms are made of eukaryotic cells.
The DNA of a eukaryotic cell is found in an internal compartment of the cell called
the nucleus.
All eukaryotic cells have membrane-bound organelles. An organelle is a small
structure found 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.
Summary
Microscope observations of organisms led to the discovery of the basic
characteristics common to all living things.
A cell’s shape reflects its function. Cell size is limited by a cell’s surface area-tovolume ratio.
The complex organization of eukaryotic cells enable them to carry out more
specialized functions than prokaryotic cells.
Section 2: Inside the Eukaryotic Cell
Key Ideas
What does the cytoskeleton do?
How does DNA direct activity in the cytoplasm?
What organelles are involved in protein production?
What are vesicles and vacuoles?
How does the cell get energy?
The Framework of the Cell
Eukaryotic cells have an intricate network of protein fibers called the cytoskeleton
which provides the interior framework of the cell.
The cytoskeleton helps the cell move, keep its shape, and organize its parts.
There are three different kinds of cytoskeleton fibers: microfilaments, microtubules,
and intermediate fibers.
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. In the
cytoplasm, ribosomes use the RNA messages to assemble proteins.
Nucleus
A double membrane called the nuclear envelope surrounds the nucleus.
Nuclear pores located on the nuclear envelope act as channels to allow certain
molecules to move in and out of the nucleus.
The nucleolus is a 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.
Ribosomes
Each ribosome in a cell is made of RNA and many different proteins.
Ribosomes that are suspended in the cytosol are called “free” ribosomes.
Free ribosomes make proteins that remain inside the cell.
Ribosomes that are attached to the membrane of another organelle are called
“bound” ribosomes.
Bound ribosomes 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
Some proteins that a cell manufactures are needed outside the cell that makes
them.
Proteins that are sent outside the cell are packaged in vesicles. Vesicles are 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
The endoplasmic reticulum, or ER, is 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.
The portion of the ER with attached ribosomes is called rough ER because it has a
rough appearance when viewed with an electron microscope.
The portion of the ER with no attached ribosomes is called smooth ER because it
has a smooth appearance when viewed with an electron microscope.
The ribosomes on the rough ER make proteins that are packaged into vesicles.
Enzymes of the smooth ER make lipids and break down toxic substances.
Golgi Apparatus
The Golgi apparatus is a set of flattened, membrane-bound sacs.
The Golgi apparatus helps modify, sort, and package cell products for distribution.
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.
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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.
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.
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.
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
Cells need a constant source of energy.
The energy for cellular functions is produced by chemical reactions that occur in
the mitochondria and chloroplasts.
In both organelles, chemical reactions produce adenosine triphosphate (ATP), the
form of energy that fuels almost all cell processes.
Chloroplasts
A chloroplast is an organelle found in plant and algae cells that uses light energy to
make carbohydrates from carbon dioxide and water.
Chloroplasts are surrounded by two membranes and have several stacks of
flattened sacs where energy production takes place.
Plant cells may have several chloroplasts.
Mitochondria
Mitochondria are cell 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.
Summary
The cytoskeleton helps the cell move, keep its shape, and organize its parts
DNA instructions are copied as RNA messages, which leave the nucleus. In the
cytoplasm, ribosomes use the RNA messages to assemble proteins.
The endoplasmic reticulum and Golgi apparatus are organelles involved in
preparing proteins for extracellular export.
Vesicles help maintain homeostasis by storing and releasing a variety of
substances as the cell needs them.
The energy for cellular functions is produced by chemical reactions that occur in
the mitochondria and chloroplasts.
Section 3: From Cell to Organism
Key Ideas
What makes cells and organisms different?
How are cells organized in a complex multicellular organism?
What makes an organism truly multicellular?
Diversity in Cells
Both prokaryotic and eukaryotic cells can have a variety of shapes and structures.
The function of a cell is determined by its shape and the organelles found in the
cell.
The different organelles and features of cells enable organisms to function in
unique ways in different environments.
Diversity in Prokaryotes
Prokaryotes can vary in shape, the way they obtain and use energy, and their
ability to move.
Many prokaryotes have a flagellum, a long, hair-like structure that grows out of the
cell and enables the cell to move through its environment.
Prokaryotes may also have pili, short outgrowths that allow the cell to attach to
surfaces or other cells.
Eukaryotic Cell Specialization
Eukaryotic cells can vary in shape and external features.
Depending on their function, eukaryotic cells can also vary in their internal
organelles. For example, muscle cells, which use large amounts of energy, contain
many mitochondria.
Animal and plant cells are two types of eukaryotic cells. Both have many of the
same organelles, but plant cells also have chloroplasts, a large central vacuole,
and a cell wall.
Levels of Organization
Plants and animals have many highly specialized cells that are arranged into
tissues, organs, and organ systems.
A tissue is a distinct group of similar cells that perform a common function.
An organ is a collection of tissues that work together to form a structure which
performs a specific function.
An organ system is composed of a group of organs that work together to perform
major body functions.
Body Types
Unicellular organisms can thrive independently or live together in groups.
Cells that are permanently associated but do not work together or integrate cell
activities are called colonial organisms.
A multicellular organism is composed of many individual, permanently associated
cells that coordinate their activities with each other. True multicellularity occurs
only in eukaryotes.
In a multicellular body, cells are interdependent. Distinct types of cells have
specialized functions to help the organism survive.
The individual cells in a multicellular organism cannot survive alone and are
dependent on the other cells of the organism.
Must multicellular organisms begin as a single cell, which divides to form more
cells. These cells then grow and become specialized in a process called
differentiation.
Summary
The different organelles and features of cells enable organisms to function in
unique ways in different environments.
Plants and animals have many highly specialized cells that are arranged into
tissues, organs, and organ systems.
A multicellular organism is composed of many individual, permanently associated
cells that coordinate their activities with each other.