Cytology (cy·​tol·​o·​gy)

Cell Biology / Cellular Biology / Cytology is a branch of Biology studying the Structure and Function of the Cell, also known as the basic unit of life.

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522006, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522006, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Course Layout...

• Unit I : Cytology I
• Definition, History, Prokaryotic and Eukaryotic Cells, Virus, Viroids & Mycoplasma
• Electron Microscopic Structure of Eukaryotic Cell
• Plasma Membrane : Different Models of Plasma membrane
• Unit II : Cytology II (Cell Organelles)
• Structure & Functions of Endoplasmic Reticulum, Golgi Apparatus, Lysosomes, Ribosomes, Mitochondria
• Nucleus
• Chromatin : Structure & Significance
• Chromosomes : Structure, Types & Functions

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Introduction...

• A cell is the smallest unit of all living organisms.
• Cells are the basic building blocks of all organisms.
• Organisms may be unicellular made of one cell (like bacteria) or multicellular made of many cells (like a human).
• In multicellular organisms, several cells of one kind interconnect with each other and perform a shared function to form tissues; several tissues combine to form an organ; several organs make up an organ system and several organ systems function together to form an organism.

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Definition...

• A Cell is defined as the smallest, basic unit of life that is responsible for all of life’s processes.”
• A branch of Biology dealing with the Structure, Function, Multiplication, Pathology, and Life history of cells is called Cytology.

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

History...

• The invention of the microscope by Zacharias Jansen in the late 16^th century led to the discovery of cells in 1665 by Robert Hooke.
• He examined very thin slices of cork using a compound microscope and observed a multitude of pores that looked like the wall compartments of a honey comb.
• He introduced the term “Cell” for each compartment and Hooke's description of these cells was published in Micrographia.

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

History...

Robert Hooke's Microscope

Robert Hook refined the design of the compound microscope around 1665 and published a book titled Micrographia which illustrated his findings using the instrument.

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Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

History...

• The cells in the cork observed by Hooke were actually dead cells giving no indication of the nucleus and other organelles and cells of living organisms could be observed only after the discovery of improved microscopes having high magnification.
• Live cells were first observed under a microscope in 1674 by Antony van Leeuwenhoek. He observed the algae Spirogyra and named the moving organisms as animalcules, meaning "little animals".

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Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

History...

• Cell Theory :
• Ludolph Christian Treviranus (1811) and Johann Jacob Paul Moldenhawer (1812) first proposed the idea that cells were separable into individual units and in 1824, Henri Dutrochet declared that "the cell is the fundamental element of organization".
• The cell theory was first formulated based on two publications in the 1800s. The first one was by Matthias Jacob Schleiden in 1838, in which he proposed that all plant tissues are made from cells. The second one was in the following year 1839 by Theodor Schwann in a publication in which he generalized the proposal to all living organisms stating that all animal tissues also are made from cells.
• These generalizations by Schleiden and Schwann after subsequent modifications were later came to be known as the Cell Theory.

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

History...

Matthias Jacob Schleiden

Theodor Schwann

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

History...

• Cell Theory :
• The theory was further extended by subsequent discoveries by Karl Wilhelm von Nägeli who showed that cells form by division of one cell into two and Karl Theodor Ernst von Siebold who extended the cell theory to protists in the 1840s.
• The third component of classical cell theory was completed by Rudolf Virchow in 1858 with his generalization that all cells come from pre-existing cells.
• Thus, Virchow along with Schleiden and Schwann are often credited together for the formulation of the classical cell theory.

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

History...

• Classical Cell Theory
• The main proposition of the classical cell theory holds that :
• All organisms are made up of one or more cells.
• Cells are the fundamental, functional and structural unit of life.
• All cells come from pre-existing cells (omni cellulae e cellula)

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

History...

• Modern Cell Theory
• The classical cell theory has been extended to formulate the modern cell theory by incorporating further discoveries. The generally accepted parts of modern cell theory include :
• All living things are made up of cells.
• The cell is the smallest fundamental unit of structure and function in living things.
• All cells come from pre-existing cells by division.
• Energy flow in the form of metabolism and biochemistry occurs within cells.
• All cells contain genetic material which is passed from cell to cell during cell division.

Cont...

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

History...

• Modern Cell Theory
6. All cells are basically the same in chemical composition and metabolic processes associated with life occur within cells.
7. Some organisms are unicellular or made up of only one cell while other organisms are multicellular or composed of many cells.
8. The activity of an organism depends on the total activity of independent cells.

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

History...

• Exceptions to the Theory :
• Some exceptions to the cell theory are :
• Viruses are not made up of cells and yet, they are considered to be alive by some.
• The first cell did not originate from a pre-existing cell according to the accepted theory of evolution.
• Mitochondria and chloroplasts have their own genetic material, and reproduce independently from the rest of the cell.

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Cell Morphology...

• A Cell is a small, membrane-bound compartment that contains all the chemicals and molecules required to sustain an organism's life.
• Cells contain organelles, or tiny membrane bound structures that carry out specific functions and cells also contain DNA (deoxyribonucleic acid) or RNA (ribonucleic acid) as the genetic material for directing cellular activities.
• Thus, a cell generally consists of three parts:
1. The plasma membrane or cell membrane which serves as a selective barrier enclosing a cell. Plant cells have cell wall outside the plasma membrane.

Cont...

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Cell Morphology...

• Thus, a cell generally consists of three parts:
2. The cytoplasm representing all the cellular contents between the plasma membrane and the nucleus including the cytosol (a jelly-like fluid), all the organelles other than the nucleus, and the cytoskeleton.
3. The nucleus containing the genetic material in the form of a fine network of threads called chromatin which condenses at the time of cell division to form chromosomes.

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Cell Sizes & Shapes...

• Cells differ remarkably in size, shape and function.
• Cells come in many different sizes. Some cells like eggs of birds are visible to the naked eye. However, most cells are microscopic and cannot be seen by the naked eye and can be observed only with the help of microscopes.
• The size of the cell is generally measured in micrometers (μm) in diameter. For example, the size of bacterial cells range from 0.2 to 0.3 μm while the size of liver cell is about 20 μm and the size of plant cells range from 30 to 40 μm.

Cont...

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Cell Sizes & Shapes...

• The smallest cell is that of Mycoplasma genitalium with a size of 0.2 μm. Regarding size, the size of human body cells are highly variable with erythrocytes of 7 microns, hepatocytes with 20 microns, sperm of 53 μm, eggs of 150 μm while some neurons are as long as one meter.
• The pollen grains of plant cells may also reach 200 to 300 μm while sizes of bird eggs may vary from 1 cm in quail to 7 cm in diameter in ostrich.

Cont...

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Cell Sizes & Shapes...

• Cells also differ variably in shapes and the shapes of cells may be fusiform (spindle shaped), stellate, prismatic, flattened, elliptical, globose or rounded, and so on.
• Some cells are also capable of changing their shape (e.g. amoebae and macrophage) while some others have typical shape (e.g. spermatozoa and epithelial cells).
• The shapes of cells have evolved to help them carry out their specific function in the body.
• Some cells have a rigid cell wall while others lack them allowing them to freely move the membrane and cytoplasmic contents as in pseudopods.

Cont...

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Classification of Cells...

• Cells can be grouped into two broad categories - prokaryotic and eukaryotic based on their complexity :
• Prokaryotes : Prokaryotic cells lack a well defined nucleus and other membrane-bound organelles. The nuclear material commonly consists of a single chromosome lying in the cytoplasm, called nucleoid. Prokaryotic cells are found in bacteria, cynobacteria (blue-green algae) and Archaea.

Cont...

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Classification of Cells...

• Cells can be grouped into two broad categories - prokaryotic and eukaryotic based on their complexity :
• Eukaryotes: Eukaryotic cells, on the other hand, have distinct nuclei bound by a nuclear membrane and other membrane-bound organelles like mitochondria, chloroplasts, lysosomes, rough and smooth endoplasmic reticulum and vacuoles. They also possess organized chromosomes which store genetic material. Eukaryotic cells include all other cells, such as protista, fungal, plant and animal cells.

Cont...

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Classification of Cells...

• All living organisms (bacteria, blue green algae, plants and animals) are made of cells and may contain one or many cells.
• Some organisms contain only one cell in their body and are called unicellular organisms (e.g., bacteria, blue green algae, some algae, Protozoa, etc.). while other organisms have many cells in their body and are called multicellular organisms (e.g., fungi, most plants and animals).
• Further, based on the kingdom into which they fall cells may be grouped as plant and animal cells.

Cont...

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Some Typical Cells...

• Some cells have typical characteristics which differ from normal cells.
• Some examples are:
• Cyanobacteria: Cyanobacteria are small, aquatic, photosynthetic and usually unicellular (though they often grow in large colonies) organisms.
• Virus: viruses are small infectious agents that can replicate only inside the living cells of organisms. They contain DNA or RNA as their genetic material and viruses infect all types of organisms, from animals and plants to bacteria and archaea.

Cont...

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Some Typical Cells...

• Some cells have typical characteristics which differ from normal cells.
• Some examples are:
• Red Blood Cells: Red blood cells are the most common type of blood cell serving as the principal means of carrying oxygen in the vertebrate body. They, however, lack organelles like nucleus and mitochondria unlike typical eukaryotic cells.

Cont...

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Functional Characteristics of Cells...

• All living cells are complex biochemical systems and many features distinguish the cells from non-living chemical systems.
• The features that distinguish cells from non-living systems are:
• Nutrition: The cells take up substances from the environment, transform the substances from one form to another, releasing energy during the process and eliminating waste products through the metabolism unlike non-living things.
• Growth and multiplication: The cells are capable of directing their own division. As a result of nutritional processes, a cell grows and divides, forming two daughter cells through cell division.
• Differentiation: Many cells can undergo changes in form or function in a process called cellular differentiation. During cell differentiates, some substances and specialized structures related to reproduction, dispersal or survival are formed that were not previously present.

Cont...

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Functional Characteristics of Cells...

• The features that distinguish cells from non-living systems are:
• Signaling: Cells respond to chemical and physical stimuli from the external environment and cells can also interact or communicate with other cells, usually by means of signals or chemical messengers such as hormones, neurotransmitters, growth factors.
• Evolution: Unlike the nonliving systems, unicellular and multicellular organisms evolve. During evolution, small heritable changes occur at low frequency in cells that may influence the adaptation of the cell and result in the selection of organisms best adapted to live in a particular environment.

Cont...

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

Conclusion...

• Cells are the unit of structure, physiology, and organization in living organisms.
• The Cell Theory provides the proof for the fact that that every living organism contains one or more cells.
• The tenets of the modern cell theory states that all known living things are made of cells, the cell is the structural and functional unit of all living things, all cells come from preexisting cells by division, cells contain hereditary information, all cells have similar chemical composition, and all energy flow (metabolism and biochemistry) of life occurs within cells.
• Although all living organism are made of cells, cell differ variably in size, shape and function across the living kingdoms.

Cont...

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43

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Thank You…

Lecture prepared by :

Ram Babu Chikkala, Department of Zoology, Tellakula Jalayya Polisetty Somasundaram College, Guntur 522004, Andhra Pradesh, India

Email ID : rbchikkala@gmail.com; Contact No. : 94 94 41 47 43