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Cell Specialization and Differentiation
What is Cell Differentiation?
Living organisms can be made of a single
cell, such as bacteria and protists, or they
can be multicellular like plants, animals, and
fungi. Unicellular organisms, like bacteria,
are able to perform all life functions within
one single cell. They can transport
molecules, metabolize nutrients, and
reproduce within this one cell. Organisms
made of more than one cell need many
different types of cells to carry out the same
life processes. Each of these special types of
cells has a different structure that helps it
perform a specific function. Humans have
many different types of cells with different
jobs, such as blood cells that carry oxygen
and nerve cells that transmit signals to all
parts of the body. Cell differentiation is the process by which cells become specialized in order to perform
different functions.
Even multicellular organisms begin as just a single cell. Getting from one single cell to billions of specialized
cells that perform different functions is a process that happens with the regulation of DNA and RNA. It can also
be influenced by factors in the environment.
Roles of DNA and RNA in Cell Differentiation
Dexoyribonucleic Acid, or DNA, is the molecule that controls the way cells
function. It also holds the key to determine what type of specialized cells
will be made. Stem cells are cells that have the ability to become any type
of specialized cell in the body. After an egg cell and sperm cell unite to
begin forming a new organism, all of the DNA in each cell of that organism
will be virtually identical. If every part of the DNA in each cell is the same,
then how does it end up with different types of cells? Let’s look more
closely at the DNA to find out.
DNA is wound tightly into chromosomes. There are different regions of the
chromosome code for every different function and cell type. Not all
sections of a chromosome are turned on, or expressed, at the same time.
Only the regions that are needed to perform a specific function are
expressed in each cell. These regions are often depicted as bands or stripes
on a drawing of a chromosome. These bands are called genes, and whether
or not a gene is expressed determines what type of cell it will become. For example, genes that are expressed, or
turned on, in a nerve cell are different from the genes that are expressed in a muscle cell. Both cells have the
same DNA but expressing specific genes determines what type of cell it will become. This is known as gene
expression.
Ribonucleic Acid, or RNA, is involved in
making proteins that the cell needs to function.
Since RNA translates and transcribes the DNA
code, it can also influence cell differentiation.
Specialized Plant Cells
Now that you know how living organisms get from a single cell to many differentiated cells, let’s discuss some
of the specialized cells that are made as a result of this process. In plants, cells are specialized for the role they
play in the plant’s survival. Three of the many specialized cell types in plants include the cells of the
roots, stems, and leaves.
Root Cells
Root cells are specialized plant cells that absorb dissolved minerals and water from the ground. Root cells
grow in long lengths called root hairs, in order to increase the surface area of the root system. This also helps
anchor the plant. Since root cells grow underground, you would not expect to find chloroplasts in these cells
since the purpose of chloroplasts is to absorb energy from the sun. The tip of the root also has specialized
cells and is called the root cap. These cells discharge a slippery substance that allows them to burrow down
into the soil more easily.
Cells of Plant Stems
Not to be confused with the type of embryonic stem cells that can differentiate, the stem cells of plants are
specialized cells that transport water, nutrients, and the products of photosynthesis throughout the plant.
They connect the photosynthesis factories in the leaves with the storage site in the roots. Xylem cells
transport water from the roots in the upward direction. Phloem cells transport nutrients in both directions to
reach all parts of the plant. Some plants have specialized stem cells that form the wood to support the plant.
Leaf Cells
The cells found in the leaves of plants are highly specialized and there are many different types. Palisade
cells are column-shaped and are found near the surface of the leaf. They are full of chloroplasts ready to
capture radiant energy from the sun and turn it into chemical energy. Along the bottom of the leaf, guard
cells open and close to allow the transfer of gases with the atmosphere as well as the transpiration of water.
These cells can help protect the plant from drying out.
Specialized Animal Cells
As you learned in the previous section about gene expression, animals require many different specialized cells
in order to function. Some cells must be able to move, like sperm cells, while other cells need to contract, like
muscle cells. Look at the three types of specialized cells below found in many animals, including humans.
Red Blood Cells
Red blood cells are specialized cells found in animals that transport oxygen throughout the body. Since
transport is their primary function, they do not need a nucleus. The lack of a nucleus leaves more space in
the cell for hemoglobin, the protein that binds to oxygen. This also gives red blood cells their unique shape.
Unlike most cells, red blood cells do not reproduce through mitosis; they are created in the marrow found in
the bones.
Muscle Cells
Muscle cells are long, fibrous cells that have the ability to contract. They allow animals to move and allow
their organs to function in circulation as well as digestion. Muscle cells are made up of two special types of
proteins called actin and myosin. Because of the actin and myosin, muscle strands are able to slide past each
other. This sliding action allows the muscle cell to contract. Since a lot of energy is needed in your muscle
cells, you will find more mitochondria than is found in most cells.
Epithelial Cells
Epithelial cells are the cells that line the outside, as well as the inside, of your body. They are the cells that
make up your skin. Skin epithelium is actually located just below the surface of your skin. They are
responsible for making new cells. They also produce the pigment melanin, which protects us from the sun’s
harmful rays. Epithelium also lines the inside of your digestive tract as well as your respiratory system. They
come in many shapes and sizes depending on their function.