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Running head: CELL BIOLOGY
CELL BIOLOGY
Name of the Student
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1CELL BIOLOGY
Table of Contents
Section 1....................................................................................................................................2
Cell structure.........................................................................................................................2
Comparison table for prokaryotic and eukaryotic cells........................................................4
Eukaryotic subcellular organelle...........................................................................................5
Section 2....................................................................................................................................7
Role of cell membrane..........................................................................................................7
Use of nutrients by animal cells............................................................................................8
Role of nucleic acids...........................................................................................................10
Protein synthesis..................................................................................................................11
Section 3..................................................................................................................................12
Generation of specialised tissue..........................................................................................12
Role of interphase................................................................................................................13
Retrieval of genetic information by daughter cells.............................................................15
Cancer cells vs normal cells................................................................................................16
Recommendation.....................................................................................................................17
Conclusion...............................................................................................................................17
Bibliography............................................................................................................................18

2CELL BIOLOGY
Section 1
Cell structure
The cell is the most basic functional and structural unit of any living organism. It is
also considered as the building blocks of life. There are quite a few functions or
characteristics that a living cell exhibits which include Cellular metabolism, Cellular
Reproduction or Growth, Homeostasis, Internal and External Movement of Cells and Use of
Energy in Cells (U.S. National Library of Medicine 2020).
Cellular metabolism is the most promising and significant characteristic living cell.
This process involves either the catabolism or the anabolism of the biomolecules which are
taken inside the living cells. These biomolecules are taken inside the living cell with the help
of either the active transport or passive transport. Membrane transporters have been found to
play a significant role in transporting molecules inside and out of the cells. The most
significant characteristic of a living cell which is associated with cellular metabolism is the
protein machinery which synthesizes enzymes. Enzymes are the most significant components
of all the metabolic canonical pathways. Some of the most significant metabolic processes are
glycolysis, Krebs cycle, amino acid, lipid and nucleic acid metabolism. All these metabolic
processes can only be performed by a living and viable cell. Metabolism either synthesises
energy when required by a cell or uses energy to perform works such as active transport by a
cell. Thus, it can be stated that cellular metabolism is an essential functional characteristic of
living cells. Other functional characteristics of cells include response to a specific stimuli and
grow by cell division. Cell growth will be later discussed along with mitosis and meiosis.
Cellular Reproduction or Growth is one of the most important character that cells exhibit.
The mode of reproduction the living cells follow is the cell division. By dividing one mother
cell, it becomes two daughter cells and thus the whole process continues throughout a living

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being’s life to replace the old cells in the body and also for enhancing the growth of tissue.
The two daughter cells resulted from the division of mother cell contains the same genetic
material as of the mother cell (Salazar-Roa. and Malumbres 2017).
Fig. 1: Cell Structure (Image retrieved from National Cancer Institute 2020)
Homeostasis is the second character that a cell exhibit by which the internal
environment of a cell is maintained. Cell membrane, a part of the cell helps in this process by
keeping certain substances inside the boundary and other substances outside the boundary as
required and thus keeps the cell in equilibrium. Homeostasis also regulates the water content,
pH, temperature and presence of electrolytes within the cell (Kotas and Medzhitov 2015).
Internal and External Movement is the next character that a cell shows. It is the ability
a cell has by which it can maintain the fluidity and flexibility of a cell. The internal
movement is the movement of cell constituents within the cell boundary (Strale et al. 2015).
The external movement helps the cell to stay in equilibrium during temperature change and
growth (Foldes-Papp 2015). These types of movements also aids in stabilising a cell.
Cells for performing all the functions to maintain the structure needs energy. Starting
from production of protein, proper functioning of the cell and cellular reproduction, each of
the phenomenon that takes place in the cell requires energy expenditure. The cells use

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Adenosine Triphosphate (ATP) and various types of sugar molecules as its energy source
(Garcia and Shaw 2017).
Comparison table for prokaryotic and eukaryotic cells
Difference between prokaryotic cells and eukaryotic cells include (Archibald 2015):
CHARACTER PROKARYOTIC CELL EUKARYOTIC CELL
DEFINITION Prokaryotes can be defined
as the organisms having only
one cell
Eukaryotes can be defined as
the organisms having more
than one cell
NUCLEUS Prokaryotic cells lack
nucleus.
Eukaryotic cells contain
nucleus.
CHROMOSOME NUMBER Contains one chromosome
and plasmids.
Contain more than one
chromosome and plasmids.
NUCLEUS MEMBRANE It is absent. It is absent.
Genetic Recombination Process include
unidirectional transfer of
DNA.
Process include meiosis and
gamete fusion.
CELL ORGANELLES Cell organelles are absent in
prokaryotic cells.
Cell organelles are present.
PLASMA MEMBRANE It is absent in prokaryotic
cells.
It is present in eukaryotic
cells.
CELL WALL It is present in prokaryotic
cells.
It is present in some
multicellular organisms and
others lack it.
CELL SIZE Varies from 1 μm to 10 μm. Varies from 10 μm to 100
μm.
EXAMPLES Bacteria and Archaea. Plants, Animals and Insects.
Table 1: Differences between Prokaryotic and Eukaryotic Cell
When a virus attacks a prokaryotic cell, there might be three consequences. In first
case, bacteria activate some mechanisms, and neutralizes the viral DNA and as a result
nothing would happen to the bacteria or the prokaryotic cell. In the second scenario, the viral
DNA enters the cell and synthesize necessary proteins using the machineries of the host cell
and then would break open the cell and the phage will exit the cell in huge numbers. This
process is known as Lytic infection. In the third scenario, the phage or virus DNA would
enter the cell and would integrate with the bacterial chromosome and continue growing.

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When required the virus would enter the lytic cycle and would break open the cell and exit.
This is known as Lysogeny infection (Erez et al. 2017).
When a virus attacks, a eukaryotic cell it can give rise to three consequences. In the
first case, when a virus attacks a cell, interferon is released and the adjacent cells are turned
antiviral thus preventing the spread of virus. In the second case, the viral DNA is
incorporated with the genome of the host forming virome which does not express. In the third
case, the viral DNA is incorporated with the genome of the host and expresses after a latency
(Ogilvie and Jones 2015)
Eukaryotic subcellular organelle
Fig. 2 (i): Lytic & Lysogeny Cycle (Image retrieved from Researchgate 2020)
The subcellular structure in eukaryotic cells includes plasma membrane, nuclear
membrane, cytoplasm, cell wall and different organelles. Plasma membrane is made up of
lipid bilayer and proteins embedded into it. It is the outer boundary which covers the entire
cell structure. Nuclear membrane is made up of lipid bilayers as well and it covers the genetic
material of the cell. In both the eukaryotes and prokaryotes, plasma membrane can be
identified as a covering of double lipid bilayer which can be observed a microscope.

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Cytoplasm is the viscous solution that is enveloped by the cell membrane. This organelle
holds all the other organelle on itself. In other words, all the other organelles are present as
rafts on the viscous fluid solution known as the cytoplasm. All the organelles are embedded
within this viscous solution. Cell wall is only present in plants, protists and fungi and it
encircles these cells. This provides a stable structure to the cells. In plant cells, this wall is
made up of cellulose and in fungi, cell wall is made up of chitin. There are also a few
organelles that is present within eukaryotic cells which include nucleus, ribosome,
endoplasmic reticulum, golgi complex, mitochondria and chloroplast. The nucleus is
identified as the most clear organelle located inside a living cell which is visible as a gentle
mass of chromatin fibres. These organelles have specific functions that help in the cell’s
proper functioning. The nucleus contains the genetic material of the cell. Function of
ribosome is to synthesize and produce proteins. The endoplasmic reticulum functions by
folding proteins and transporting proteins to the golgi complex. There are two types of
endoplasmic reticulum located inside a living cells. One is the smooth endoplasmic reticulum
and the other is the rough endoplasmic reticulum. Endoplasmic reticulum is visible as a sac of
membrane like structures known as the cisternae. These structures are held together at place
by the cytoskeleton. The function of golgi complex is processing lipids and proteins. Golgi
bodies has been found to be visible inside the cell as thick black stack of semi-circular bags.
A large number of vesicles can also be viewed near the proximity of this organelle making
the identification process much easier. Mitochondria is also considered as the powerhouse
present in the cell. The functions of mitochondria include digestion of various nutrients,
breakdown of the nutrient and produces energy for the cell. Chloroplast is only present in
plant cells, protists and few fungi. It absorbs the sunlight and converts into sugar molecules
for utilizing the molecules as food resource (Biazik et al. 2015).

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Fig. 3 (i): Cell Organelles (Image retrieved from Oxford University Museum of
Natural History 2020)
Section 2
Role of cell membrane
The cell membrane is the outer covering that encircles a cell. It plays the key roles of
gaining nutrients and excreting the waste product from a cell. This uptake of nutrient and
excretion of waste product takes place through the cell membrane by various mechanisms.
The cell membrane is selectively permeable in nature thus helping various ions and
biomolecules to pass through it. The processes that are mostly used include Diffusion, Active
Transport and Passive Transport. In Active Transport, various molecules tend to move from a
region of lower concentration to a region of higher concentration by using energy. In Passive
Transport, the molecules can move across cellular membrane without expending any energy.
Passive Transport is of various types which include diffusion, facilitated diffusion, osmosis
and filtration. Facilitated diffusion is the process of diffusion transport via the use of
membrane transport channels. These channels have always been found to be specific for a
type of molecule and are mainly glycoprotein in nature. Diffusion is a process in which
various substances have a tendency of moving from a high concentration to a low
concentration. Facilitated diffusion is a process in which different molecules moves through
the membrane with the help of integral transmembrane protein. Diffusion has been stated to

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move the particles down their concentration gradient. A concentration gradient is generated
due to an imbalance in the concentration and diffusion tries to balance the concentration by
distributing the molecules everywhere down the concentration gradient. This movement is
also called the downhill transport of molecules and ions by diffusion process. In simple
diffusion, it has been observed that molecules are either small or nonpolar to facilitate their
downhill movement. In Osmosis, solvent molecules move across a membrane toward a solute
of higher concentration. Filtration is a process in which movement of water and molecules
occurs across cell membrane due to hydrostatic pressure (Shahin 2016).
Fig. 4 (i): Cellular Transport (Image retrieved from Bioninja 2020)
Use of nutrients by animal cells
It is very much essential for the cells to use the nutrients taken by the organism to
facilitate movement, growth and cell division. The mechanism of utilizing these uptaken
nutrients is a complex one and is dependent on various biochemical pathways. Glucose is
broken down into simplest forms by various pathways like glycolysis and Kerb’s cycle
produce various forms of energies, which include ATP and NADH. Both glycolysis and
Kreb’s cycle has been found to be the most useful processes of metabolism which are
associated with the production of energy. Glycolysis is the process of glucose breakdown by
a series of enzymes known as hexokinase, phosphofructokinase and down to pyruvate

9CELL BIOLOGY
synthase to give rise to pyruvic acid. This acid is utilised by the tri-carboxylic acid cycle to
generate oxaloacetate release 32 ATP molecules in total after completing both the rounds of
glycolysis and Krebs cycle. Both the pathways are linked since TCA cycle is followed by
glycolysis when the cell requires energy to be produced. Gluconeogenesis has been found to
occur when the cell requires glucose as a storage material and not as an energy source. These
forms of energies are also taken up by the mitochondria which is stored for performing
various cellular functions. ATP is also produced during aerobic respiration in the
mitochondria that is used as the primary source of energy of the body. This is the reason for
mitochondria to be known as the powerhouse of the cell. This energy is also used in
facilitating various biochemical pathways, helps in the absorption of various nutrients and in
the transport of nutrients to all the cells via blood. This is how animal cells utilize the
available nutrients and provides the energy for movement, growth and cell division (Lin et al.
2016).
Fig 4 (ii): Kreb’s cycle

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Source: Lin et al. (2016)
Role of nucleic acids
Nucleic acids are built of nucleotides and collectively form the deoxyribonucleic acid
or DNA. It governs all the cellular functions. Nucleic acids are present in the nucleus, cytosol
as well as the mitochondria of the cell. The nucleic acid, which is present within the nucleus,
is generally deoxyribonucleic acids or DNA. It has the responsibility for producing various
proteins so that the cell structure and functions are optimally maintained. Nucleic acids are
not synthesised as the polymer of nucleotides which re linked together by a phosphodiester
backbone. Thus, it can be said that a nucleic acid is made up of carbon (sugar base), oxygen,
hydrogen, nitrogen (nucleoside) and phosphorus. All the essential macro elements are
contained in the nucleic acids, proving the fact that it is the most significant component for
the cell growth and development. The DNA present in the nucleus also contains all the
information about production of protein and the quantity in which it should be produced. The
nucleic acid present in the mitochondria helps in the production of energy for the proper
functioning of the entire cell activities. Proteins are synthesised from mRNA which is
transcribed from the DNA itself, the central dogma of replication, transcription and
translation. Thus, it can be stated that nucleic acids are responsible for carrying the genetic
information from one generation to the next. This condition comes to play because of the fact
that it is the nucleic acids which are exchanged in the form of chromatic fibres of
chromosomes during a crossing over during cell division. The nucleic acid present in the
cytosol is entirely different with respect to the structure with lesser methylation in the
structure than the chromosomal DNA. The function of these are maintaining the aging of cell,
providing stability to the genome and in the chromosome evolution (Decarvalho et al. 2018).

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Protein synthesis
Synthesis of proteins is an essential event that occurs within a cell. Synthesis of
proteins give rise to newer proteins that is required for proper functioning of cells and in
various other cellular and bodily activities like enzymatic activity. The process of protein
biosynthesis is very much similar in both prokaryotic cells and eukaryotic cells with minor
differences. The biosynthesis of proteins can be subdivided into two stages that are
transcription and translation. During transcription, the double stranded DNA is converted into
a messenger RNA or mRNA by the action of RNA polymerases within the nucleus. Then the
mRNA is transported to the cytosol where the process translation takes place. Ribosomes take
up this mRNA and according to the nucleotide sequence of mRNA the sequence of amino
acid are decided. The amino acids are then bonded by peptide bonds thus forming protein
molecules. Protein synthesis is occurs in the cytosol of the cell and uses mRNA, amino acid
charged tRNA and ribosomes for the completion of translation. After translation the bound
amino acids gets a partial quaternary structure which is properly folded and processed by the
golgi bodies which is also known as the post translational modification. Then it is finally
released to perform all the functions in the eukaryotic cell including forming the structure of
cell and producing enzymes for essential biochemical reactions. After this, further post
translational mechanisms take place in which the protein chains are folded to form proper
functional protein structures (Liu et al. 2018).

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Fig. 5: Protein Synthesis (Image retrieved from Molecular Biology Review 2020)
Section 3
Generation of specialised tissue
The embryonic stem cells are pluripotent in nature and upon differentiation gives
different types of cells forming the germ cells. The embryonic stem cells are formed from
embryo at the beginning of the implantation into the uterus and are totipotent in nature. These
totipotent cell divides to form blastocyst which is pluripotent in nature. The blastocyst is
embryonic stem cells which undergoes several divisions to make many copies of themselves
and have the ability to repair without further differentiation. The embryonic stem cells
contain three different germ layers which differentiate to give rise to different organs of the
body. The three layers are ectoderm which differentiate to give rise to brain and nerve cells,
spinal cord, nails and hair, skin and pigment cells and sensory cells including eyes, ears,
mouth and nose; the mesoderm or the middle layer gives rise to the heart, blood and blood
vessels, muscles and connective tissue; and the endoderm gives rise to the large organ
systems of the body that is the respiratory system consisting of lungs, urinary system
consisting of bladder, gastrointestinal system containing gut, liver, pancreas and the

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reproductive system. Thus embryonic stem cells have an unlimited property of producing
specialised and differentiated cells of the body (Stemcells.nih.gov 2020).
Fig. 6: differentiation of embryonic stem cells ( Image retrieved from Ebi.ac.uk, 2020)
Role of interphase
Interphase is the longest phase of the cell cycle and the cells remain in this phase for
about 90% of its lifetime. During this phase the cells grow, appropriate proteins that are
required are produced and duplication of chromosomes takes place. DNA replication also
occurs during interphase so that sufficient materials are available for the cell to divide
without any issues (Nagano et al. 2017). Interphase is the only phase of the cell cycle in
which DNA replication and cell growth occurs simultaneously in order to prepare the cell for
its division. Interphase can also be termed as the metabolic phase of the cell cycle which
includes synthesis of the metabolites required for the cell division process and readying the
DNA for cell division. This is because of the fact that nothing can be synthesised by the cell
during the division process and thus interphase is the pre-requisite synthesis phase of the cell
cycle. This phase is also known as the resting phase of the cell cycle. There are two types of
factors responsible for triggering cell cycle which are Internal Factors and External Factors.

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The external factors are generally released from out of the cell which can be from any other
cell or any other part of the body. The external factors include physical signals, chemical
signals and growth factors. The physical signal is the contact of two cells. The chemical
signal refers to the chemical that is released from one type of cell to facilitate growth of other
cells. The growth factors are types of proteins, which stimulate cell division. On the other
hand, internal factors are signals that is regulated inside of the cell in the form of various
proteins which include Kinases and Cyclins which also facilitates cell division. These factors
initiate a cell cycle (Dalton et al. 2015).
Fig. 7: Cell Cycle (Image retrieved from National Human Genome Research Institute
2020)
Retrieval of genetic information by daughter cells
Mitosis is followed in cell division in order to transfer the genetic information from
the mother cell to the daughter cells.
There are four stages of mitosis:

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1. Prophase- Chromosomes start to condense, mitotic spindle forms and the nucleolus
disappears from the cell.
2. Metaphase- Chromosomes align at the metaphase plate. Kinetochores of the chromosomes
must be aligned properly during this phase.
3. Anaphase-Sister chromatids are pulled towards the opposite poles of the spindle assembly.
4- Telophase- The mitotic spindle is broken down and the two nuclei, one from each of the
chromosomes are distributed to the two daughter cells and the cell prepares for cytokinesis.
The same genetic information or the DNA is passed on to each daughter cells from
the parental cells through replication and specifically semi-consrvative mode of replication
before the occurrence of cell division of the parental cell. The semi-conservative mode of
replication describes replication where each of the daughter cells receive one copy of the
parental DNA starnd and one copy of the newly synthesized strand. This model was formed
after the Messelson-Stahl experiment where the two daughter cell contains two strands of the
DNA, one strand is recievd from the parental cell and another by formation of new strand.
Each of the daughter cell contain equal amount of DNA from the parental DNA strands
which means the old genetic information is divided and conserved along with new genetic
information in the daughter cells after cell division. The newly synthesized strands are
formed by the complementary base pairing with the old strand (Snedeker et al., 2017).

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Fig. 8: Models of Replication (Image retrieved from Snedeker et al. 2017)
Cancer cells vs normal cells
Comparison between cancer cells and normal cells are given below (National Cancer
Institute 2020):
CHARACTER CANCER CELLS NORMAL CELLS
DEFINITION Cancer cells can be defined
as the cells that have lost the
ability of self-repair and
ability of halting growth.
Thus, it can be said that the
cells grow and proliferate
spontaneously due to the
effect of a mutagen or a
carcinogen.
Normal cells can be defined
as the cells with proper
functioning and growth.
They have normal
functioning cell cycle
regulators which regulates
the cell cycle to control cell
growth and division.
GROWTH Cancer cells does not have
the ability of halting growth
and a as result it keeps on
growing forming tumours.
Immortality is achieved in
Normal cells have the ability
of controlling it’s growth.

17CELL BIOLOGY
these cancer cells since their
growth is spontaneous due to
non-functioning of cell cycle
regulators and apoptosis
machinery.
FUNCTIONING Cancer cells are non-
functional.
Normal cells have the ability
of performing proper
functions in growth,
development and repair of
several body systems.
COMMUNICATION There is no communication
within two adjacent cancer
cells.
Normal cells have the ability
to communicate with each
other.
CHROMOSOME NUMBER Chromosome number of
cancer cells are abnormal and
are arranged haphazardly.
Normal cells have the
appropriate number of
chromosomes as per species.
CELL REPAIR AND
DEATH
Cancer cells lose the ability
to repair the issues in the cell
and also loses the property of
cell death known as
apoptosis.
Normal cells have the ability
of repairing themselves and
can also promote cell death
when required.
SPREADING ABILITY Cancer cells have the ability
to spread to other parts of the
body, a phenomenon named
metastasis.
Normal cells do not spread to
other parts of the body and
stay in its original position.
STICKINESS Cancer cells do not stick
together and thus spread.
Normal cells stick together
by the secretion of a
substance.
IMMUNE SYSTEM
EVASION
Cancer cells have the ability
to evade and dominate the
immune system.
Normal cells do not evade or
dominate the immune
system.
Table 2: Differences between Cancer and Normal Cell
Recommendation
There is also scope of learning various cell related structures and transport systems.
Cancer related details should also be elaborately studied.
Conclusion
Thus, to conclude the paper it can be stated that, cell is the basic structure of the body,
which has various properties that it utilizes to perform various bodily functions optimally. It

18CELL BIOLOGY
also contains transport systems for passing of various nutrients and materials through the
cells when required. The cell cycle is also very important procedure that involves cell
division. Abnormal cell division or proliferation gives rise to cancer.

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