Organelles, Cycles and Division, Signaling & Techniques
As a sub-discipline of biology, cell biology is
concerned with the study of the structure and function of cells. As such, it
can explain the structure of different types of cells, types of cell
components, the metabolic processes of a cell, cell life cycle and signaling
pathways to name a few. Here, we shall look at some of the major areas of cell
biology including some of the tools used.
Cell Theory is a basic principle in biology
that was formulated by Thodor Schwann, Matthias Schleiden and Rudolph Virchow.
According to the Cell Theory:
All the living things
(organisms) are made up of cells
The cell is the basic unit
Living cells come from
Recently, the theory was modified to include the
Energy flow takes place
Heredity information passes
from one cell to another
All cells have the same
basic chemical composition
Cell Biology - The Cell
A cell is a basic unit of life. This simply
means that a cell is the smallest unit of a living thing. While some organisms
are only made up of a single cell (bacteria, yeast etc) others are
multicellular organisms made up of many
While there is a clear difference between unicellular and multicellular
organisms, some organisms may transition from unicellular organisms to
multicellular organisms under certain conditions.
A good example of this is
slime mold that tends to transition to a multicellular organism under stressful
conditions. However, they are simply described as being partially
multicellular. Therefore, the cell is the basic building block of any given organism.
For a multicellular organism, cells are specialized, which means that they have
differentiated to carry out given functions.
The following are examples of specialized
Sperm Cells - Sperm cells serve to fertilize the female egg
to form the embryo.
Red Blood Cells - Red cells contain a
protein molecule known as hemoglobin and serve to transport oxygen to all parts
of the body and expel carbon dioxide from the body.
White Blood Cells - There are different
types of white blood cells that serve to protect the body from disease causing
Cardiomyocytes - These are cardiac muscle cells that make up
the heart muscle.
Nerve Cells (neurons) - These are cells of the
nervous system that transmit information to and from different parts of the body
(information is transmitted as electric and chemical signals). See also Sensory Cells.
The cell wall is a complex, highly organized structure that defines the shape of a plant cell (it is also found in bacteria, fungi, algae, and archaea). In addition to defining the shape of plant cells, a cell wall has a few other functions that include maintaining the structural integrity of a cell, acting as a line of defense against a variety of external factors as well as hosting various channels, pores and receptors that regulate various functions of a cell. As such, it is a multifunctional structure in plant cells that also contributes to plant growth.
Also known as the plasma membrane, the cell
membrane is a bi-lipid membrane layer (it is a double membranous structure)
that is also composed of proteins and carbohydrates. This fluid like structure
encircles the cell thereby containing the contents of a cell.
selectively permeable, which means that it only allows certain materials
(nutrients and minerals etc) to pass through to sustain the cell. The cell
membrane also functions to protect the cell and ensure stability.
The nucleus may be described as the largest
organelle of a cell. The nucleus is itself surrounded by a double membrane
(nuclear envelope) and contains genetic information (genes) making it the
control center of a cell. As such, it controls such activities cell metabolism
The cytoplasm is the fluid matrix (jelly-like)
found inside the cell (outside the nucleus). Various types of
organelles and minerals (salts) are suspended in this constantly streaming
fluid. Apart from containing all the cell organelles, the cytoplasm also helps
maintain the shape of a cell.
Cell organelles may be described as cell
subunits specialized to carry out given functions within the cell. There are
different types of organelles in cells that carry out given functions.
following are some of organelles that can be found in a cell (excluding the
cell membrane, cytosol and nucleus which are mentioned above):
Mitochondria - The mitochondria are rod-shaped organelles
and sites of ATP synthesis. The mitochondria is also surrounded by a double
membrane (with the inner membrane being highly folded forming the cristae).
organelle is commonly referred to as a power- generator given that it converts
oxygen and nutrients in to a chemical energy known as ATP (adenosine triphosphate)
which provides the energy required for various activities of the cell. Apart
from being a site for ATP synthesis, the mitochondrion is also involved in the
self-destruction of a cell in a process known as apoptosis.
Ribosomes - Found in the cytoplasm and the surface of the rough endoplasmic
reticulum, ribosomes are composed of RNA and proteins. They may be described as
the "cell factories" given that they are responsible for the synthesis
of protein molecules.
Lysosomes - These are sac-like structures that are surrounded by a
membrane (a single membrane). Lysosomes contain digestive enzymes, which are
responsible for breaking down proteins, lipids and nucleic acids. In addition,
lysosomes are also involved in the removal of waste molecules as well as
recycling of molecular subunits.
Golgi body - These are flattened structures in a cell
responsible for temporary storage of protein in the cell.
Vacuoles - Vacuoles are also enclosed by a membrane and function to store
such material as food, water, minerals and waste products among others.
Cell cycle refers to a sequence in actively
dividing cells where the cells pass through several stages before ultimately
The stages of cell cycle include:
Two gap phases (G1 and G2)
The S phase (synthesis)
The M phase
At GI, the metabolic changes take place
preparing the cell for the division process. At a given point known as the
restriction point, the cell is committed to cell division and moves to the next
S - The S phase involves DNA synthesis. It is
during this phase that the replication of genetic material starts with each of
the chromosome having two chromatic sisters.
G2 - During this phase, there are metabolic
changes that assemble the necessary cytoplasmic materials for the mitosis
process and splitting of the mother cell.
M - The M phase is where nuclear division takes place
and followed by the division of the cell.
For most animals, cells may divide by mitosis or
meiosis. While the two processes result in the production of new cells, they are
different and produce different daughter cells.
Mitosis is the type of cell division that occurs
in all somatic cells. These are the types of cells that make up the body
tissues (apart from gametes/sex cells). Therefore, the primary role of mitosis
is growth and replacing worn out cells.
Essentially, mitosis results in diploid cells
from one cell. Here, the chromosome is copied followed by the separation of the
copies on different sides of the cell before the cell ultimately separates into
two. In the end, each of the new cells has a copy of the chromosome.
Interphase - Here, the DNA strand is replicated/copied to
produce what is known as a bivalent chromosome (consisting of two chromatids or
DNA strands that are replicas of each other). During the interphase stage, the
new strand is attached to the original one at a point known as the centromere.
Prophase - This is the second stage of mitosis. Here, the bivalent
chromosomes formed during interphase condense to form tight packages.
Metaphase - This is the third stage where each of the chromosome line up
at the center of the cell. The nucleus membrane has already started dissolving
with each of the mitotic spindles attaching themselves to each of the
chromatids. Here, it appears as if the chromatids are being stretched towards
either pole of the cell.
Anaphase - During anaphase, the fourth stage of mitosis, the chromatids
that had attached to the spindles are separated (the chromatids are separated
from their copies) and pulled to either side of the cell. This results in two
groups of monovalent chromosomes.
Telophase - At the end of anaphase, another stage starts where nuclear
membranes start to form around the two formed groups of chromosomes. The
spindle fibers that attached to the chromatids get disassembled. Here, the
chromosomes also condense.
Eventually, the cytoplasm divides/splits with a cell
membrane forming on each of the two daughter cells. This process is known as
cytokinesis. Each of the new cells
has 46 monovalent chromosomes and has identical genetic information as the
In mitosis, it's important that the same
genetic information is copied when forming new cells. This is because the chromosomes
have all the information concerning the function of the cell.
copying of information on to the new cells ensures that the new cell functions
properly. In the event that there is a problem, then the new cell will be unable
to perform its function as it should be. This would result in complications
depending on the function of the cell.
Unlike mitosis, meiosis produces haploid cells.
Diploid - Two new daughter cells from the original cell with the same
number of chromosomes.
Haploid - With meiosis (a reductive type of cell division) the resulting
cells will have less number of chromosomes.
Meiosis is also different from mitosis in that
there are two phases of cell division. These are meiosis I and meiosis II.
Prophase 1 - Here, the homologous chromosomes pair and exchange
DNA form recombinant chromosomes. This stage ends with the spindle fibers
starting to form to attach to the chromosomes.
Metaphase 1 - The bivalent chromosomes arranges double row
having attached to the spindle fibers.
Anaphase 1 - The homologous chromosomes (in each bivalent)
are separated and move to opposite poles of the cell.
Telophase 1 - With the separation of the chromosomes, a
nuclear membrane starts to form around the two groups of the chromosomes. This
is followed by cytokinesis where the cell splits to form two new cells. This is
again followed by meiosis II. Meiosis II follows the same process as meiosis I.
However, this halves the number of chromosomes.
* Meiosis is an important process that results in
All cells originate from a single cell (a single
fertilized egg). In cell differentiation, cells become specialized as the body
develops. Apart from the single original cell (the fertilized egg), stem
cells are also unspecialized. However, under certain conditions, they can
differentiate to become specialized cells that serve a specific function(s).
Although the differentiated somatic cells are different in that they perform
different functions, they contain the same genome. However, the different types
of cells only express some of these genes, which results in the differences morphological and physiological between
Cell Biology - Signal Transduction/Signaling
In cells, signal transductions involve the
transmission of molecular signals. This is particularly from the exterior of
the cell to its interior for appropriate cell response. Signals (biochemical
changes) may either come from the environment the cell is in or from other
cells that trigger changes.
Cells have receptors on the surface of the cell,
which receives the signal prompting a response. For a response to take place,
the signal has to be transmitted across the cell membrane.
Some of the common intracellular messengers
Cell signaling is very important given that it
helps control and maintain the normal physiological processes in the body.
Different signaling processes will result in varying responses including cell
differentiation, proliferation of cells as well as metabolism among others.
Cell Biology Techniques
Cell biology is largely concerned with the study of the structure and functions of cells (morphological and physiological). For this reason, a number of techniques have to be employed.
Cells and tissues can be cultured using
complex media. With cells and tissues from more complex organisms, the culture
media has to be more complex so as to provide the same environment as the
environment from which the cell/tissue was obtained.
As for the tissue, the
culturing process also allows for single cells to be obtained from the tissue
in question for more studies.
The culture process requires the following:
A solid media - Agar media
Growth media - This
contains nutrients such as amino acids, vitamins, salts, glucose and growth
factors among others.
Cell culture is an important technique given
that it allows for only a sample (cells or tissue) to be used to learn more
about the cells without the need to use the organism as a whole. This also
gives scientists a great opportunity to study the cells under varying
Microscopes have been used since the 1670s to observe
cells. Today, microscopes have become indispensable tools in cell biology. There are many more microscopy techniques today that have allowed for better viewing of cells.
In recent years, the world of microscopy has
experienced advancements in imaging technologies enabling increased amounts
of information for microscopic analysis.
Some of the most common techniques used in cell
Staining goes hand in hand with microscopy.
Although it may be regarded as an important part of microscopy, staining is
itself very useful in cell biology. It allows for increased contrast
which in turn allows for scientists to view different parts of a cell clearly.
Although staining is highly useful when it comes to viewing specimen under the
microscope, it cannot be used when a scientist wants to observe living cells.
Cell biology is an important discipline that has
allowed for viewing and studying of cells for decades now. It has become particularly
important to differentiate and determine different types of cells, cell
processes as well as understanding of various diseases and illnesses associated
with cell malfunctioning.
With advancements in various cell biology techniques,
it is becoming easier to learn more about cells and cell processes for
effective intervention where necessary.
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