eChapters

Introduction
It is a fundamental biological process in which one cell splits into two or more daughter cells. Both unicellular and multicellular organisms rely heavily on it for growth, development, repair, and reproduction. There are two main types of cell division: mitosis and meiosis. Mitosis occurs in somatic cells and produces two genetically identical daughter cells that share the same chromosomal number as the parent cell. This process is necessary for tissue development and repair. Meiosis, on the other hand, happens in germ cells and results in the formation of gametes, which reduces the number of chromosomes by half to ensure genetic diversity in progeny. Proper regulation of cell division is vital for maintaining cellular health, and disruptions in this process can lead to disorders like cancer.
The different stages of cell division is as follows:-
1. Interphase
• Although not a component of mitosis, interphase is essential for preparing the cell for division. It is separated into three sub-phases:
• G1 phase (Gap 1): The cell expands in size while creating proteins and organelles. S phase (Synthesis): DNA replication occurs, guaranteeing that each daughter cell receives an identical copy of the genetic information.
• G2 phase (Gap 2): The cell continues to expand while new organelles are synthesised)
The cell checks for DNA replication mistakes and gets ready for mitosis.
2. Prophase
• In this phase chromatin condenses into visible chromosomes, each made up of two sister chromatids linked at the centromere.
• The nuclear membrane breaks down, allowing the spindle fibres to interact with the chromosomes.

There are a number of different cell lines derived from human and animals. With the dramatic increase in numbers of cell lines, the risk of intraspecies and interspecies cross contamination rises proportionally. It is particularly a major problem in laboratories where many different cell lines of human and animal origin are handled at a time. The purity of the primary cell or continuous cell lines and species of its origin should be checked on a regular basis to authenticate the cell line identity. In the absence of such monitoring, inter and intra species cell line contamination are likely to occur in the laboratory resulting in loss of investigator’s time effort and resources. The advantages of working with a well defined cell line free from contaminating organisms would appear obvious.

Cell Lysis Procedure

Pellet the cells in a microfuge tube: add 1.5 ml culture, centrifuge for 15 seconds at maximum speed, discard the supernatant, and then repeat the procedure. This will result in the cells from 3 ml of culture in a single tube.

Resuspend the cells in 1 ml Lysis buffer.

Take 300 µl aliquot for Bradford protein assay.

Add 50 µl lysozyme, and mix gently.

After 10-20 minutes at room temperature, microfuge for 10 minutes to pellet cell debris.

Use supernatant for LDH assay.

Plant body consists of numerous microscopic box like components called cells. The word cell has been derived from the Latin word cellula, meaning a small room. The descriptive term for this smallest living biological structure was coined by Robert Hooke in a book he published in 1665. When he compared the cork cells, he saw through his microscope to the small rooms monks lived in. The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life, which is classified as a living thing and is often called the building block of life (Maton et al., 1997). It is defined as a mass of protoplasm surrounded by a membrane- the plasma membrane- within which complicated chemical reactions are going on.

ALL LIVING ORGANISMS ARE MADE UP OF UNITS CALLED CELLS

All living creatures are made from 1 or more cells

All cells are produced from previously existing cells (no spontaneous generation)

All cells appear to be descended from the first cell which existed about 4 billion years ago

For a species to exist its reproductive cells must be potentially immortal (no aging)

Our bodies start from a single cell and contain about 100,000,000,000,000 (10^14) cells at maturity

Principle

Cell viability refers to the quantity of healthy cells in a sample, while cell proliferation is a crucial indicator for comprehending the mechanisms and pathways involved in the survival of cells or death following exposure to toxic substances. The methods used to assess viability are typically the same as those used to detect cell proliferation. Cell cytotoxicity and proliferation assays are commonly employed in drug evaluations to determine if the test compounds impact cell proliferation or exhibit direct cytotoxic effects. Cell viability can be determined by calculating the ratio of total live cells to the total number of cells (live and dead). Staining also helps to observe the general cell structure. Cell proliferation assay by MTT. Metabolically active cells reduce the yellow tetrazolium MTT (3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide) through dehydrogenase enzymes to produce NADH and NADPH. The purple formazan produced inside the cell can be dissolved and measured using spectrophotometry. The MTT Cell Proliferation Assay quantifies cell proliferation rate and detects decreases in cell viability caused by metabolic events leading to apoptosis or necrosis. The MTT Reagent produces minimal absorbance values when no cells are present.

I. WALL COMPONENTS – CHEMISTRY

The main ingredient in cell walls are polysaccharides (or complex carbohydrates or complex sugars) which are built from monosaccharides (or simple sugars). Eleven sugars are common in these polysaccharides including like glucose and galactose. Carbohydrates are good building blocks because they can produce a nearly infinite variety of structures. There are a variety of other components in the wall including protein, and lignin. Let’s look at these wall components in more detail:

A. Cellulose: β1,4-glucan (structure provided in class). Made of as many as 25,000 individual glucose molecules. Every other molecule (called residues) is “upside down”. Cellobiose (glucose-glucose disaccharide) is the basic building block. Cellulose readily forms hydrogen bonds with itself (intra-molecular H-bonds) and with other cellulose chains (inter-molecular H-bonds). A cellulose chain will form hydrogen bonds with about 36 other chains to yield a microfibril. This is somewhat analogous to the formation of a thick rope from thin fibers. Microfibrils are 5-12 nm wide and give the wall strength - they have a tensile strength equivalent to steel. Some regions of the microfibrils are highly crystalline while others are more “amorphous”.

Summary

Multicellular organisms are made up of diverse set of cells. Cells respond to the changes in the particular microenvironment by means of cellular communication. This cell-cell communication is extremely important for the development, maintenance and survival of the organism. This communication is equally important for the unicellular organisms. Cells communicate to one another and respond to the environmental changes using diverse chemical languages, as discussed in this chapter. However, in many cases like multicellular organisms, cell communication is primarily mediated by specific receptor(s) expressed on the cell membranes. These receptors bind to the extracellular signaling molecules (called ligands) and activate specific signaling pathways to bring about particular cellular responses. These different receptors, ligands and signaling pathways are briefly discussed here.

Cell mediated immune response (CMI) is the major defense mechanism against intracellular microbes and tumor cells. It is mediated mainly by T lymphocytes. T cells originate in bone marrow but the maturation of T cells occurs in thymus.

Cell mediated immune response performs different functions in protecting the immune system. When antigens are destroyed by cells, without producing antibodies, the immunity is called cell-mediated immunity (CMI) or cellular immunity. In this immunity T cells play a major role. The principal role of cell mediated immunity is to detect and eliminate the cells that have intracellular pathogens. When the antigen remains inside the cell the antibody cannot handle them. The intracellular pathogens are controlled by cell- mediated immunity. CMI is invited by the recognition of antigens by T cells. T cell lymphocytes recognize protein antigens of intracellular microbes that are displayed on the cell surface of infected cells. It is also important for elimination of cells which express foreign MHC molecules. Antigen specific and nonspecific cells can contribute to the cell-mediated immune response. The activities of both specific and non-specific components usually depend on effective local concentration of cytokines.

Cell

Cells (small, membrane-bounded structures filled with a variety of chemicals in an aqueous solution that interact to give life) are the basic unit of life. Cells are capable of acquisition and use of energy, have the capacity to reproduce and respond to the environment and are able to carry out a variety of chemical reactions. They maintain a relatively constant internal environment despite changes in the external environment. There are two types of cells, namely, prokaryotes and eukaryotes.

The prokaryotic (pro = before, karyote = nucleus) cells are the simple form of cell types which include the various types of cells of bacteria and their relatives, all belonging to kingdom Monera. They possess a cell wall constructed of peptidoglycan, a substance unique to prokaryotes. Beneath the cell wall, there is a plasma membrane that encloses a cytoplasm containing DNA, RNA, proteins and various small molecules.

This chapter describes the cells, tissues and organs responsible for immune defence. It examines lymphocytes, macrophages, dendritic cells, neutrophils, mast cells, natural killer cells and plasma cells, emphasizing their respective functions. Primary and secondary lymphoid organs—including bone marrow, thymus, bursa of Fabricius, spleen, lymph nodes and mucosa-associated lymphoid tissue—are discussed. The chapter also covers lymphocyte maturation, antigen presentation, phagocytosis, immune-cell surface markers and the organization of lymph-node regions. Positive and negative selection of T lymphocytes and the formation of memory cells are included. Together, these topics explain how immune components develop, communicate and coordinate effective responses against infectious agents.

Cells are the Working Units of Life

With the possible exception of viruses, every form of life on Earth either is a cell or composed of cells. All cells come into existence through the activity of other cells.

All Cells are either Prokaryotic or Eukaryotic

All cells can be classified as prokaryotic or eukaryotic. All plants, animals, fungi, and protists are either single eukaryotic cells or are composed of eukaryotic cells. Prokaryotic cells are either bacteria or archaea. Eukaryotic cells have most of their DNA contained in a membrane-lined nucleus, whereas prokaryotic cells do not have a nucleus. Eukaryotic cells also have more specialized structures, called organelles, than do prokaryotic cells. All prokaryotes are single-celled, whereas many eukaryotes are multi-celled.

The Eukaryotic Cell

There are five principal components to the eukaryotic animal cell: the nucleus, other organelles, the cytosol, the cytoskeleton, and the plasma membrane. Organelles are “tiny organs” within the cell that carry out specialized functions, such as energy transfer and material recycling. The cytosol is the fluid in which these organelles are immersed (The cytoplasm is the region of the cell inside the plasma membrane but outside the nucleus.) The cytoskeleton is composed of several groups of proteins that give the cell support and facilitate transportation of cellular elements. The plasma membrane is the chemically active outer boundary of the animal cell. Plant cells have a plasma membrane that has, outside of it, a cell wall.

Introduction

Robert Brown discovered the nucleus in some plant cells in 1831. After analyzing tissues from a range of animals and plants, T. Schwann (1839) declared, “All living organisms are composed of cells.”

The fundamental elements of Prokaryotic and Eukaryotic cells

The simplest cells, called prokaryotic cells, have a straightforward structural arrangement. There is only one membrane system in it. They contain rickettsia, spirochete, mycoplasma, virus, blue-green algae, and bacteriablue-green algae, or cyanobacteria are the largest and most intricate prokaryotes, where higher plant photosynthesis occurs and have changed throughout time.

Prokaryotic cells

Prokaryotic cells range in size from 1 to 10 µm. They take place in a range of formats. A bacterial cell is made up of three basic parts:

I. External layer: It is composed of the inner cell or plasma membrane, middle cell wall and outer slimy capsule.

a. Cell membrane: The thin, flexible membrane of the cell, composed of proteins and lipids, regulates the flow of chemicals throughout the cell. It carries respiratory enzymes for reactions that release energy. Respiratory enzymes are found in mesosomes, which are folded regions of the plasma membrane that are compared to the mitochondria in eukaryotic cells. Similarly, the pigments and enzyme molecules found in photosynthetic cells are linked to the in-folds of the plasma membrane known as photosynthetic lamella, which is responsible for absorbing light and converting it into chemical energy.

b. The cell wall: It is the non-living, semi-rigid layer that encloses the cell membrane, with a thickness that varies from 1.5 to 100 µm. It is chemically made up of peptidoglycans. Certain bacteria, such as mycoplasma, don’t have cell walls.

A cellular phone is also known as a mobile phone, cell phone, portable phone and a hand phone. It is a device that can make and receive telephone calls over a radio link while moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile phone operator, allowing access to the public telephone network.

The cell phone was invented by Dr. Martin Cooper who led a team of developers at Motorola and made the first cell phone call in April 3, 1973 at Motorola.

Today, cell phones are becoming capable of doing almost anything a computer is capable to do. Below, are few examples of what a phone can do?

Introduction
Embryogenesis begins with the fertilization of the oocyte by the sperm, leading to the formation of a zygote. This single cell undergoes a series of highly regulated mitotic divisions known as cleavage, forming a multicellular structure called the blastocyst. As the blastocyst implants in the uterine wall, the cells continue to divide and differentiate into the three primary germ layers: the ectoderm, mesoderm, and endoderm. Each of these layers gives rise to specific tissues and organs, controlled by genetic instructions and cellular signalling mechanisms.One of the most critical aspects of embryogenesis is the intricate interplay of cellular signalling pathways and genetic mechanisms, which regulate the precise growth and differentiation of cells into tissues and organs. Understanding these mechanisms not only helps in comprehending normal embryonic development but also in diagnosing and treating developmental disorders in veterinary practice.
Cellular Signalling in Embryonic Development
Cellular signalling is a fundamental process in embryogenesis that ensures cells communicate with each other to perform specific tasks. The coordination of cell proliferation, differentiation, migration, and apoptosis (programmed cell death) is essential for the proper formation of tissues and organs.
Types of cell signalling
1. Short range signalling: It involves communication within a cell as well as between nearby cells. This includes:
a) Paracrine signalling: where a cell releases signals that affect neighbouring cells.
b) Autocrine signalling: where a cell sends signals to itself, affecting its own behaviour.

Introduction

The smallest, most basic, most primitive organisms are known as prokaryotic (Greek: pro= primitive or prior, and karyon = nucleus). Likely, they originated around 3.5 billion years ago. Bacteria, such as Mycoplasma and Cyanobacteria, are known to contain these cells. A prokaryotic cell is a deeply organized single-enveloped system. Its constituent nuclear parts are encased in a plasma membrane, with the cytoplasmic ground substance encircling the center. Prokaryotic cells’ cytoplasm lacks distinct cytoplasmic organelles, the nuclear envelope, and any other cytoplasmic membrane.

Despite being incredibly thin and delicate structures, in Eukaryotes plasma membranes are essential to many of a cell’s most vital processes. Membranes are lipid-protein assemblages where non-covalent linkages hold the constituents in place in a thin sheet. Both integral protein and phospholipid lateral mobility are significantly impacted by the physical condition of the lipid bilayer. The plasma membrane is a selectively permeable barrier that permits solute passage via assisted diffusion, active transport, and simple diffusion via membrane channels or the lipid bilayer. A system of membrane organelles, such as the endoplasmic reticulum, Golgi complex, and lysosomes, is found in the cytoplasm of eukaryotic cells. These organelles are physically and functionally connected to the plasma membrane and one another. The cytoplasm is separated into a luminal region inside the ER membranes and a cytosolic space outside the membranes by the endoplasmic reticulum (ER), a network of tubules, cisternae, and vesicles. Additionally, the ER is where the majority of a cell’s membrane lipids are generated and transported to different locations. Proteins’ asparagine residues are added with sugars (a process known as glycosylation), which starts in the rough ER and continues in the Golgi complex.

Estimation of Cellulose in Feeds and Fodders
Principle

The feed well ground is digested with acetic acid which dissolves all other constituents like protein, disaccharides, fatty acids, etc., and cellulose and mineral contents are unaffected. The residue is made acid and alcohol free by washings. Alcohol removes water, benzene removes pigments and fat and at the end the sample is dried and ashed. The difference between the dried weight before ashing and weight after ashing gives cellulose content of the feed sample.