A cell is the structural and fundamental unit of life. The study of cells from their basic structure to the functions of every cell organelle is called Cell Biology. Robert Hooke was the first Biologist who discovered cells. All organisms are made up of cells. They may be made up of a single cell (unicellular), or many cells (multicellular).  Mycoplasmas are the smallest known cells. Cells are the building blocks of all living beings. They provide structure to the body and convert the nutrients taken from the food into energy. Cells are complex and their components perform various functions in an organism. They are of different shapes and sizes, pretty much like the bricks of the buildings. Our body is made up of cells of different shapes and sizes. Cells are the lowest level of organisation in every life form. From organism to organism, the count of cells may vary. Humans have more cells compared to that bacteria. Cells comprise several cell organelles that perform specialised functions to carry out life processes. Every organelle has a specific structure. The hereditary material of the organisms is also present in the cells.

1. CELL FOR YOGA NET & JRF
By Dr Shivam Mishra
Skm Yoga International

2. Cell
■ A cell is the structural and fundamental unit of life.
■ The study of cells from their basic structure to the functions of every cell organelle is called Cell
Biology.
■ Robert Hooke was the first Biologist who discovered cells.
■ All organisms are made up of cells. They may be made up of a single cell (unicellular), or many cells
(multicellular).
■ Mycoplasmas are the smallest known cells.
■ Cells are the building blocks of all living beings. They provide structure to the body and convert the
nutrients taken from the food into energy.
■ Cells are complex and their components perform various functions in an organism. They are of different
shapes and sizes, pretty much like the bricks of the buildings. Our body is made up of cells of different
shapes and sizes.
■ Cells are the lowest level of organisation in every life form. From organism to organism, the count of
cells may vary. Humans have more cells compared to that bacteria.
■ Cells comprise several cell organelles that perform specialised functions to carry out life processes.
Every organelle has a specific structure. The hereditary material of the organisms is also present in the
cells.

3. Cell Discovery
■ Robert Hooke discovered the cell in 1665. Robert Hooke observed a piece of bottle cork under a
compound microscope and noticed minuscule structures that reminded him of small rooms.
■ Consequently, he named these “rooms” cells. However, his compound microscope had limited
magnification, and hence, he could not see any details in the structure. Owing to this limitation, Hooke
concluded that these were non-living entities.
■ Later Anton Van Leeuwenhoek observed cells under another compound microscope with higher
magnification. This time, he noted that the cells exhibited some form of movement (motility).
■ As a result, Leeuwenhoek concluded that these microscopic entities were “alive.” Eventually, after a
host of other observations, these entities were named as animalcules.
■ In 1883, Robert Brown, a Scottish botanist, provided the very first insights into the cell structure. He
was able to describe the nucleus present in the cells of orchids.

4. Characteristics of Cell
• Cells provide structure and support to the body of an organism.
• The cell interior is organised into different individual organelles surrounded by a separate membrane.
• The nucleus (major organelle) holds genetic information necessary for reproduction and cell growth.
• Every cell has one nucleus and membrane-bound organelles in the cytoplasm.
• Mitochondria, a double membrane-bound organelle is mainly responsible for the energy transactions
vital for the survival of the cell.
• Lysosomes digest unwanted materials in the cell.
• The endoplasmic reticulum plays a significant role in the internal organisation of the cell by
synthesising selective molecules and processing, directing and sorting them to their appropriate
locations.
■

5. Types of Cell
■ Cells are similar to factories with different labourers and departments that work towards a
common objective. Various types of cells perform different functions. Based on cellular structure,
there are two types of cells:
• Prokaryotes
• Eukaryotes

6. Prokaryotic cells
1. Prokaryotic cells have no nucleus. Instead, some prokaryotes such as bacteria have a region
within the cell where the genetic material is freely suspended. This region is called the nucleoid.
2. They all are single-celled microorganisms. Examples include archaea, bacteria, and
cyanobacteria.
3. The cell size ranges from 0.1 to 0.5 µm in diameter.
4. The hereditary material can either be DNA or RNA.
5. Prokaryotes generally reproduce by binary fission, a form of asexual reproduction. They are also
known to use conjugation – which is often seen as the prokaryotic equivalent to sexual
reproduction (however, it is NOT sexual reproduction).

7. Eukaryotic Cell
1. Eukaryotic cells are characterised by a true nucleus.
2. The size of the cells ranges between 10–100 µm in diameter.
3. This broad category involves plants, fungi, protozoans, and animals.
4. The plasma membrane is responsible for monitoring the transport of nutrients and electrolytes in
and out of the cells. It is also responsible for cell to cell communication.
5. They reproduce sexually as well as asexually.
6. There are some contrasting features between plant and animal cells. For eg., the plant
cell contains chloroplast, central vacuoles, and other plastids, whereas the animal cells do not.

8. cell membrane
• The cell membrane supports and protects the cell. It controls the movement of substances in and out of
the cells. It separates the cell from the external environment. The cell membrane is present in all the
cells.
• The cell membrane is the outer covering of a cell within which all other organelles, such as the
cytoplasm and nucleus, are enclosed. It is also referred to as the plasma membrane.
• By structure, it is a porous membrane (with pores) which permits the movement of selective
substances in and out of the cell. Besides this, the cell membrane also protects the cellular component
from damage and leakage.
• It forms the wall-like structure between two cells as well as between the cell and its surroundings.
• Plants are immobile, so their cell structures are well-adapted to protect them from external factors. The
cell wall helps to reinforce this function.

9. Cytoplasm
■ In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed
by the cell membrane, except for the cell nucleus.
■ The material inside the nucleus and contained within the nuclear membrane is
termed the nucleoplasm.
■ The main components of the cytoplasm are cytosol (a gel-like substance),
the organelles (the cell's internal sub-structures), and various cytoplasmic
inclusions.
■ The cytoplasm is about 80% water and is usually colourless Most cellular activities
take place within the cytoplasm, such as many metabolic
pathways including glycolysis, and processes such as cell division. The
concentrated inner area is called the endoplasm and the outer layer is called the cell
cortex or the ectoplasm.
■ Movement of calcium ions in and out of the cytoplasm is a signaling activity
for metabolic processes.
■ In plants, movement of the cytoplasm around vacuoles is known as cytoplasmic
streaming.
■ The term was introduced by Rudolf von Kölliker in 1863,

10. Mitochondria
■ A mitochondria is an organelle found in the cells of most Eukaryotes, such
as animals, plants and fungi.
■ Mitochondria have a double membrane structure and use aerobic respiration to
generate adenosine triphosphate (ATP), which is used throughout the cell as a
source of chemical energy.
■ They were discovered by Albert von Kölliker in 1857 in the voluntary muscles of
insects.
■ The term mitochondrion was coined by Carl Benda in 1898.
■ The mitochondrion is popularly nicknamed the "powerhouse of the cell", a phrase
coined by Philip Siekevitz in a 1957 article of the same name.
■ Mitochondria are commonly between 0.75 and 3 μm2 in crossection.
■ mitochondria are involved in other tasks, such as signaling, cellular differentiation,
and cell death, as well as maintaining control of the cell cycle and cell growth.

11. ■ Mitochondria may have a number of different shapes.
■ A mitochondrion contains outer and inner membranes composed of phospholipid
bilayers and proteins.
■ The two membranes have different properties. Because of this double-membraned
organization, there are five distinct parts to a mitochondrion:
1. The outer mitochondrial membrane,
2. The intermembrane space (the space between the outer and inner membranes),
3. The inner mitochondrial membrane,
4. The cristae space (formed by infoldings of the inner membrane), and
5. The matrix (space within the inner membrane), which is a fluid.
■ The most prominent roles of mitochondria are to produce the energy currency of the
cell, ATP (i.e., phosphorylation of ADP), through respiration and to regulate
cellular metabolism.
■ The central set of reactions involved in ATP production is collectively known as
the citric acid cycle, or the Krebs cycle, and oxidative phosphorylation.
■ However, the mitochondrion has many other functions in addition to the production
of ATP.
■

12. Nucleus
■ The cell nucleus is a membrane-bound organelle found in eukaryotic cells.
■ Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, and a
few others including osteoclasts have many.
■ The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle
and isolates its contents from the cellular cytoplasm; and the nuclear matrix, a network within the nucleus that adds mechanical
support.
■ The cell nucleus contains nearly all of the cell's genome.
■ Nuclear DNA is often organized into multiple chromosomes – long stands of DNA dotted with various proteins, such
as histones, that protect and organize the DNA.
■ The genes within these chromosomes are structured in such a way as to promote cell function. The nucleus maintains the
integrity of genes and controls the activities of the cell by regulating gene expression.
■ Because the nuclear envelope is impermeable to large molecules, nuclear pores are required to regulate the nuclear
transport of molecules across the envelope.
■ The pores cross both nuclear membranes, providing a channel through which larger molecules must be actively transported by
carrier proteins while allowing the free movement of small molecules and ions.
■ Movement of large molecules such as proteins and RNA through the pores is required for both gene expression and the
maintenance of chromosomes.
■ Although the interior of the nucleus does not contain any membrane-bound subcompartments, a number of nuclear
bodies exist, made up of unique proteins, RNA molecules, and particular parts of the chromosomes.
■ The best-known of these is the nucleolus, involved in the assembly of ribosomes.
■ The cell nucleus contains the majority of the cell's genetic material in the form of multiple linear DNA molecules organized into
structures called chromosomes. Each human cell contains roughly two meters of DNA. During most of the cell cycle, these are
organized in a DNA-protein complex known as chromatin, and during cell division the chromatin can be seen to form the well-
defined chromosomes familiar from a karyotype.
■ A small fraction of the cell's genes are located instead in the mitochondria

13. ■ The nucleolus is the largest of the discrete densely stained, membrane
structures known as nuclear bodies found in the nucleus.
■ It forms around tandem repeats of rDNA, DNA coding for ribosomal
RNA (rRNA). These regions are called nucleolar organizer regions (NOR).
■ The main roles of the nucleolus are to synthesize rRNA and assemble
ribosomes.
■ The structural cohesion of the nucleolus depends on its activity, as a ribosomal
assembly in the nucleolus results in the transient association of nucleolar
components, facilitating further ribosomal assembly, and hence the further
association.
■ This model is supported by observations that the inactivation of rDNA results in
an intermingling of nucleolar structures.
■ Besides the nucleolus, the nucleus contains a number of other nuclear bodies.
These include Cajal bodies, Gemini of Cajal bodies, polymorphic interphase
karyosome association (PIKA), promyelocytic leukaemia (PML)
bodies, paraspeckles, and splicing speckles.

14. Golgi apparatus
■ The Golgi apparatus also known as the Golgi complex, Golgi body, or simply
the Golgi is an organelle found in most eukaryotic cells.
■ Part of the endomembrane system in the cytoplasm packages
proteins into membrane-bound vesicles inside the cell before the vesicles are
sent to their destination.
■ It resides at the intersection of the secretory, lysosomal,
and endocytic pathways.
■ It is of particular importance in processing proteins for secretion, containing a
set of glycosylation enzymes that attach various sugar monomers to proteins as
the proteins move through the apparatus.
■ It was identified in 1897 by the Italian scientist Camillo Golgi and was named
after him in 1898.
■ Owing to its large size and distinctive structure, the Golgi apparatus was one of
the first organelles to be discovered and observed in detail.
■ It was discovered in 1898 by Italian physician Camillo Golgi during an
investigation of the nervous system.

15. ■ The Golgi apparatus is a major collection and dispatch station of protein products received
from the endoplasmic reticulum (ER).
■ Proteins synthesized in the ER are packaged into vesicles, which then fuse with the Golgi
apparatus.
■ These cargo proteins are modified and destined for secretion via exocytosis or for use in the
cell.
■ In this respect, the Golgi can be thought of as similar to a post office: it packages and labels
items which it then sends to different parts of the cell or to the extracellular space.
■ The Golgi apparatus is also involved in lipid transport and lysosome formation.
■ Various models of Transportation Cisternal progression/maturation
■ Anterograde vesicular transport between stable compartments
■ Cisternal progression/maturation with heterotypic tubular transport
■ Rapid partitioning in a mixed Golgi
■ Stable compartments as cisternal model progenitors

16. Endoplasmic Reticulum
■ The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has
many other important functions such as protein folding.
■ It is a type of organelle made up of two subunits – rough endoplasmic reticulum (RER), and smooth
endoplasmic reticulum (SER).
■ The endoplasmic reticulum is found in most eukaryotic cells and forms an interconnected network of flattened,
membrane-enclosed sacs known as cisternae (in the RER), and tubular structures in the SER.
■ The membranes of the ER are continuous with the outer nuclear membrane. The endoplasmic reticulum is
not found in red blood cells, or spermatozoa.
■ The two types of ER share many of the same proteins and engage in certain common activities such as the
synthesis of certain lipids and cholesterol.
■ Different types of cells contain different ratios of the two types of ER depending on the activities of the cell.
RER is found mainly toward the nucleus of cell and SER towards the cell membrane or plasma membrane of
cell.
■
The outer (cytosolic) face of the RER is studded with ribosomes that are the sites of protein synthesis. The
RER is especially prominent in cells such as hepatocytes.
■ The SER lacks ribosomes and functions in lipid synthesis but not metabolism, the production of steroid
hormones, and detoxification.The SER is especially abundant in mammalian liver and gonad cells.
■ The ER was observed with light microscope by Garnier in 1897, who coined the
term ergastoplasm. With electron microscopy, the lacy membranes of the endoplasmic reticulum were first
seen in 1945 by Keith R. Porter, Albert Claude, and Ernest F. Fullam.
■ Later, the word reticulum, which means "network", was applied by Porter in 1953 to describe this fabric of
membranes.

17. lysosome
■ A lysosome is a membrane-bound organelle found in many animal cells. They are spherical vesicles that
contain hydrolytic enzymes that can break down many kinds of biomolecules.
■ A lysosome has a specific composition, of both its membrane proteins, and its lumenal proteins. The lumen's pH
(~4.5–5.0) is optimal for the enzymes involved in hydrolysis, analogous to the activity of the stomach.
■ Besides the degradation of polymers, the lysosome is involved in various cellular processes, including
secretion, plasma membrane repair, apoptosis, cell signalling, and energy metabolism.
■ Lysosomes act as the waste disposal system of the cell by digesting used materials in the cytoplasm, from both
inside and outside the cell.
■ Material from outside the cell is taken up through endocytosis, while material from the inside of the cell is
digested through autophagy.
■ The sizes of the organelles vary greatly—the larger ones can be more than 10 times the size of the smaller
ones. They were discovered and named by Belgian biologist Christian de Duve, who eventually received
the Nobel Prize in Physiology or Medicine in 1974.
■ Lysosomes are known to contain more than 60 different enzymes and have more than 50 membrane
proteins. Enzymes of the lysosomes are synthesized in the rough endoplasmic reticulum and exported to
the Golgi apparatus upon recruitment by a complex composed of CLN6 and CLN8 proteins.
■ Mutations in the genes for these enzymes are responsible for more than 50 different human genetic disorders,
which are collectively known as lysosomal storage diseases.
■ These diseases result from an accumulation of specific substrates, due to the inability to break them down. These
genetic defects are related to several neurodegenerative disorders, cancers, cardiovascular diseases,
and ageing-related diseases

18. Cell Theory
■ Cell Theory was proposed by the German scientists, Theodor Schwann, Matthias Schleiden, and
Rudolf Virchow. The cell theory states that:
• All living species on Earth are composed of cells.
• A cell is the basic unit of life.
• All cells arise from pre-existing cells.
■ A modern version of the cell theory was eventually formulated, and it contains the following
postulates:
• Energy flows within the cells.
• Genetic information is passed on from one cell to the other.
• The chemical composition of all the cells is the same.

19. Function of Cell
■ A cell performs major functions essential for the growth and development of an organism. Important functions of the cell are as follows:
■ Provides Support and Structure
■ All organisms are made up of cells. They form the structural basis of all organisms. The cell wall and the cell membrane are the main components
that function to provide support and structure to the organism. For eg., the skin is made up of a large number of cells. The xylem present in
vascular plants is made of cells that provide structural support to the plants.
■ Facilitate Growth Mitosis
■ In the process of mitosis, the parent cell divides into the daughter cells. Thus, the cells multiply and facilitate the growth of an organism.
■ Allows Transport of Substances
■ Various nutrients are imported by the cells to carry out various chemical processes going on inside the cells. The waste produced by the chemical
processes is eliminated from the cells by active and passive transport. Small molecules such as oxygen, carbon dioxide, and ethanol diffuse
across the cell membrane along the concentration gradient. This is known as passive transport. The larger molecules diffuse across the cell
membrane through active transport where the cells require a lot of energy to transport the substances.
■ Energy Production
■ Cells require energy to carry out various chemical processes. This energy is produced by the cells through a process called photosynthesis in
plants and respiration in animals.
■ Aids in Reproduction
■ A cell aids in reproduction through the processes called mitosis and meiosis. Mitosis is termed as the asexual reproduction where the parent cell
divides to form daughter cells. Meiosis causes the daughter cells to be genetically different from the parent cells.

20. Final Topic of Net JRF For Yoga Net
• Cell membrane
• Cell wall
• Cell organelles
• Nucleolus
• Nuclear membrane
• Endoplasmic reticulum
• Golgi Bodies
• Ribosome
• Mitochondria
• Lysosomes
• Chloroplast
• Vacuoles
• Prokaryotic cells
• Eukaryotic cells
• Cell Theory

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