ANIMAL CELL
Prof. Amol B. Deore
Department of Physiology
MVP’S Institute of Pharmaceutical Sciences, Nashik

• The cell is the smallest structural, functional, and
biological unit of all living organisms which can capable
of biosynthesis, replication and energy transformation.
• They are often called the ‘building blocks of life’.
The cell

Cytology is the scientific
study of cellular structure
and function.
Organisms can be
classified as unicellular
(consisting of a single cell;
including bacteria) or
multicellular (including
plants and animals).
While the number of cells
in plants and animals
varies from species to
species,
Humans contain about
100 trillion (1014) cells.

All cells arise from existing cells by the process
of cell division, in which one cell divides into two
identical cells.
Different types of cells fulfil unique roles that
support homeostasis and contribute to the many
functional capabilities of the human organism.

Most plant and animal cells are visible only under the
microscope, with dimensions between 1 and 100 µm.
Animal cell contains membrane bound nucleus, it also contains
other membrane bound cellular organelles. These cellular
organelles carry out specific functions that are necessary for the
normal functioning of the cell.

PLASMA MEMBRANE
• A biological membrane that surrounds the cytoplasm of a cell. In
short, it is the outer boundary of the cell.
• It is a thin, elastic structure about 7.5 to 10 nm in thickness.
• It separates the internal environment (inside the cell) from the
external environment (outside the cell).
• The plasma membrane is made up of lipid bilayer, which contains
lipid molecules— phospholipids, cholesterol, and glycolipids.

The plasma membrane is said to be 'semi-permeable'. Semi-permeable means
that the membrane allows some materials to pass while excluding others.
Lipid soluble substances and gasses such as oxygen and carbon dioxide can
easily pass through the phospholipids.
Water soluble substances such as glucose and charged molecules such as ions,
however, are unable to pass through the lipid bilayer.
These hydrophilic molecules and ions must use transfer proteins within the
membrane to pass into or out of the cell.

Two different types of proteins that are embedded in the cell membrane are
the integral proteins and peripheral protein.
A transport protein (channel) is an example of an integral protein that
selectively allows particular materials, such as certain ions, to pass into or out
of the cell.
Another important group of integral proteins are cell recognition proteins,
which serve to mark a cell’s identity so that it can be recognized by other cells.

A receptor is a type of recognition protein that can
selectively bind a specific molecule outside the cell, and
this binding induces a chemical reaction within the cell.
Some integral membrane proteins are glycoproteins.
A glycoprotein is a protein that has carbohydrate
molecules attached, which help in cell-to-cell recognition.

FUNCTIONS
• The membrane allow the passage of different nutrients and
electrolyte ions into and out of a cell.
• The plasma membrane also plays a vital role in
communication between cells to cells.
• Plasma membranes also contain proteins that allow cells to
detect external signalling molecules such as hormones.

CYTOPLASM
• The intracellular substance in which all cell organelles are suspended
is known as cytoplasm.
• Cytoplasm is a viscous, transparent, gel like semisolid fluid containing
75-90% water, proteins, carbohydrates, lipids, organic substances
including amino acids, sugars polysaccharides and inorganic
substances such as mineral ions.

Nucleus
• The nucleus is the largest and most prominent of a cell’s organelle.
• The nucleus is generally considered the control center of the cell because
it stores all of the genetic instructions for manufacturing proteins.

The nucleus is surrounded by a double membrane
called the nuclear envelope. This envelope consists of
lipid bilayers with a thin fluid space called nuclear pore.
A nuclear pore is a tiny passageway for the passage of
proteins, RNA, and solutes between the nucleus and
the cytoplasm.

Inside the nuclear envelope is a gel-like nucleoplasm with solutes that include
the building blocks of nucleic acids. The nucleolus is a region of the nucleus that
is responsible for manufacturing the RNA necessary for production of ribosomes.
Once synthesized, newly made ribosomal subunits exit the cell’s nucleus through
the nuclear pores. The genetic instructions that are used to build and maintain an
organism are arranged in an orderly manner in strands of DNA.
Within the nucleus are threads of chromatin composed of DNA and associated
proteins.

ENDOPLASMIC RETICULUM
• The endoplasmic reticulum (ER) is an extensive network of membranous
tubules that extend from the nuclear envelope to the cell membrane.
• The ER provides passages throughout the cell for transporting,
synthesizing, and storing materials. It serves as a mini circulatory system
for the cell.
• Endoplasmic reticulum can exist in two forms: rough ER and smooth ER.
• These two types of ER perform different functions and can be found in
very different amounts depending on the type of cell.

Rough ER
• Rough ER is dotted with embedded granules called ribosomes, which are sites
of protein biosynthesis. The cavities of the rough ER work in the separation
and transport of these proteins.
Smooth ER
• Smooth ER does not contain ribosome. It performs biosynthesis of steroidal
hormones, sex hormones, digestive enzymes, fatty acids, phospholipids,
triglycerides and cholesterol.
• In addition, the smooth ER also stores and regulates the concentration of
cellular Ca+2, a function extremely important in nerve cells.
• Additionally it metabolizes some carbohydrates and carry out detoxification
certain toxins in the liver

Ribosomes
• A ribosome is the site of protein synthesis. It can be found free floating in
the cytoplasm or attached to the rough ER. It is composed of two
ribosomal RNA subunits that wrap around mRNA to start the process of
translation, a stage of protein synthesis.
• Protein synthesis consists of two main stages: transcription and
translation.
• Transcription occurs within the nucleus and is a phase of proteins
synthesis in which mRNA is copied from DNA. The mRNA leaves the
nucleus through nuclear pores and goes to the ribosome.

The ribosome then “reads” or interprets the instructions within mRNA and
uses transfer RNA (tRNA) to link amino acids in the appropriate order to
produce a protein.
Typically, a protein is synthesized within the ribosome and released inside
the channel of the rough ER, where sugars can be added to it (by a process
called glycosylation) before it is transported within a vesicle to the next
stage in the packaging and shipping process: the Golgi apparatus.

Golgi apparatus
• Golgi apparatus is a membrane-bound organelle, which is mainly
composed of a series of flattened, stacked pouches (look like
pancakes) called cisternae. It is located in the cytoplasm next to the
endoplasmic reticulum. It is primarily responsible for sorting,
modifying, packaging and transporting of proteins and lipids to
targeted areas of the cell.

(Cis face)
(Trans face)

The Golgi apparatus has two distinct ends: the cis face and the
trans face of Golgi network, each has a different function. The
cis face receives products from transport vesicles.
These products are sorted through the Golgi apparatus, and
then they are released from the trans face after being
repackaged into new secretory vesicles.

functions of Golgi apparatus
• sorting, modifying, packaging and transporting of proteins and lipids to
targeted areas of the cell and some are exported from the cell through
exocytosis.
• Proteins formed by ribosomes are stored in the secretory vesicles of
Golgi apparatus.
• The secretory vesicles of Golgi apparatus are composed of enzymatic
proteins further develop in to lysosomes.
• Synthesis of glycolipids etc

Mitochondrion
• Mitochondria are bean-shaped organelles that can be considered the
power houses of the cell, converting oxygen and nutrients into
adenosine triphosphate (ATP). The number of mitochondria present
in a cell depends upon the metabolic requirements of that cell.
• There are about 1600-2000 mitochondria present in liver cells,
muscle cells, kidney, however sperm cells contain only 20-24.
• The outer membrane and the inner membrane are made of proteins
and phospholipid layers separated by the intermembrane space.

The outer membrane covers the surface of the mitochondrion and has a large
number of special proteins known as porins. The inner membrane has
numerous folds called cristae, and this helps in increasing the surface area
inside the organelle.
The mitochondrial matrix is a viscous fluid that contains a mixture of enzymes
and proteins. It also comprises ribosomes, inorganic ions, mitochondrial DNA,
nucleotide cofactors, and organic molecules. The proteins and enzymes
present in the matrix play an important role in the synthesis of ATP molecules.

The important functions of mitochondria are
• Produce energy through the process of oxidative phosphorylation
• Regulates the metabolic activity of the cell
• Promotes the growth of new cells and cell multiplication
• Apoptosis or programmed cell death
• It is also involved in various cellular activities like cellular
differentiation, cell signalling, cell senescence, controlling the cell
cycle and also in cell growth.

The cellular respiration can be stated as follows:
Food (like glucose) + oxygen Energy + waste+ water
C6H12O6 + 6O2 ATP + 6CO2 + 6H2O
Most of the energy-producing reactions, which occur in
the mitochondria, take place on the surface of the cristae.
For this reason, the mitochondria are known as the
powerhouses of the cell.

Lysosome
• The Golgi apparatus releases secretory vesicles which further
converted into new lysosomes. A lysosome is an organelle
that contains enzymes that break down and digest unneeded
cellular components, such as a damaged cell organelle.

Lysosomes are involved with various cell processes. They
break down excess or worn-out cell parts. They may be used
to destroy invading viruses and bacteria. If the cell is
damaged beyond repair, lysosomes can help it to self-
destruct in a process called programmed cell death, or
apoptosis. Hence lysosomes are referred as suicidal bags.

THANKING YOU