UNIT 2: Cellular Organization

Unit-2: Cellular Organization:

This is the second unit topics of CSIR NET Life Sciences examination syllabus. Unit name is Cellular Organization. Just navigate the links on the given topics.

Cellular Organization - CSIR NET Life sciences Unit 2

Unit 2 Syllabus
  • Membrane structure and function: Structure of model membrane, lipid bilayer and membrane protein diffusion, osmosis, ion channels, active transport, ion pumps, mechanism of sorting and regulation of intracellular transport, electrical properties of membranes.
  • Structural organization and function of intracellular organelles: Cell wall, nucleus, mitochondria, Golgi bodies, lysosomes, endoplasmic reticulum, peroxisomes, plastids, vacuoles, chloroplast, structure & function of cytoskeleton and its role in motility.
  • Organization of genes and chromosomes: Operon, interrupted genes, gene families, structure of chromatin and chromosomes, unique and repetitive DNA, heterochromatin, euchromatin, transposons.
  • Cell division and the cell cycle: Mitosis and meiosis, their regulation, steps in cell cycle, and control of cell cycle.
  • Microbial Physiology: Growth, yield, and characteristics, strategies of cell division, stress response.

Basics on Cellular Organization:

Life exhibits varying degrees of organization. Atoms are organized into molecules, molecules into organelles, and organelles into cells, and so on. According to the Cell Theory, all living things are composed of one or more cells, and the functions of a multicellular organism are a consequence of the types of cells it has. Cells fall into two broad groups: prokaryotes and eukaryotes. Prokaryotic cells are smaller (as a general rule) and lack much of the internal compartmentalization and complexity of eukaryotic cells. No matter which type of cell we are considering, all cells have certain features in common, such as a cell membrane, DNA and RNA, cytoplasm, and ribosomes. Eukaryotic cells have a great variety of organelles and structures.

Cell Size and Shape:

The shapes of cells are quite varied with some, such as neurons, being longer than they are wide and others, such as parenchyma (a common type of plant cell) and erythrocytes (red blood cells) being equal dimensional. Some cells are encased in a rigid wall, which constrains their shape, while others have a flexible cell membrane (and no rigid cell wall).

The size of cells is also related to their functions. Eggs (or to use the latin word, ova) are very large, often being the largest cells an organism produces. The large size of many eggs is related to the process of development that occurs after the egg is fertilized, when the contents of the egg (now termed a zygote) are used in a rapid series of cellular divisions, each requiring tremendous amounts of energy that is available in the zygote cells. Later in life, the energy must be acquired, but at first, a sort of inheritance/trust fund of energy is used.

Cells range in size from small bacteria to large, unfertilized eggs laid by birds and dinosaurs. The realtive size ranges of biological things is shown in Figure 1. In science we use the metric system for measuring. Here are some measurements and convesrions that will aid your understanding of biology.

  • 1 meter = 100 cm = 1,000 mm = 1,000,000 µm = 1,000,000,000 nm
  • 1 centimenter (cm) = 1/100 meter = 10 mm
  • 1 millimeter (mm) = 1/1000 meter = 1/10 cm
  • 1 micrometer (µm) = 1/1,000,000 meter = 1/10,000 cm
  • 1 nanometer (nm) = 1/1,000,000,000 meter = 1/10,000,000 cm

Repetitive DNA

The genome is the entire complement of DNA in a cell. Some of this exists as unique DNA (most genes). Other parts exist as repeated stretches – maybe 50 to 1,000 copies. Repetitive DNA was originally found by denaturing genomic DNA (making it single stranded) and then measuring the rate of renaturation. It was found […]


What are Vacuoles? Why these are called Storage Bubbles?

Vacuoles are storage bubbles found in cells. They are found in both animal and plant cells but are much larger in plant cells. Vacuoles might store food or any variety of nutrients a cell might need to survive. They can even store waste products so the rest of the cell is protected from contamination. Eventually, […]

Mitosis stages and importance

What is mitosis? Steps of Mitosis and Importance

What is Mitosis? mitosis definition is the division of the mother cell into two daughter cells genetically identical to each other. It is a nuclear division plus cytokinesis and produces two identical daughter cells during prophase, prometaphase, metaphase, anaphase, and telophase. Interphase is often included in discussions of mitosis, but interphase is technically not part of the […]



Cytoplasm of plant cell consists of discoid, oval or spherical bodies called Plastids. They are present in all plant except bacteria, fungi and blue green algae. Plastids are living. They are formed a fresh but arise from minute pre existing bodies called Protoplastids already present in embryonic cells. They multiply in number by division. On […]



In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure. Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing. However, the DNA […]

Transposons Jumping Genes at Cellular levels

Transposons: Jumping Genes at Cellular levels

Transposons are segments of DNA that can move around to different positions in the genome of a single cell. In the process, they may cause mutations increase (or decrease) the amount of DNA in the genome of the cell, and if the cell is the precursor of a gamete, in the genomes of any descendants. […]


Plastids in algae

In algae, the term leucoplast is used for all unpigmented plastids and their function differs from the leucoplasts of plants. Etioplasts, amyloplasts and chromoplasts are plant-specific and do not occur in algae.[citation needed] Plastids in algae and hornworts may also differ from plant plastids in that they contain pyrenoids. Glaucocystophytic algae contain muroplasts, which are […]

Bacterial stress response

What is Bacterial Stress Response?

Bacteria can survive under varied conditions (called as Bacterial Stress Response), and to overcome adverse conditions, the changes must be sensed by bacteria and mount reactions in protein activity and gene expression. The stress reaction in bacteria involves a system of components that behave against the stimulation. Compounds can respond simultaneously to many different stresses, and […]

Active transport Cellular Membrane Mechanism

Active transport: The Specially designed Cell Membrane Mechanism

Active transport is a cellular mechanism by which molecules cross the cell membrane against a concentration gradient, that is, from an area of low concentration to high concentration other with the consequent energy. Typical examples are the sodium-potassium pump, the pump simply calcium or glucose transport. (Check in Biochemistry Dictionary) In most cases the active […]


Meiosis: function/stages

Meiosis, or reduction division, is a process during which exchange of genetic material between the homolog chromosomes (crossing-over and recombination) takes place and such a division of the genetically material occurs the four daughter cells have received each only one set of chromosomes (they are haploid, in contrast to the mother cell which contained homolog […]


Electrical properties of a membrane

The simplest representation of a piece of nerve membrane is a simple RC– circuit as shown in Figure 1. The capacitance of a typical membrane, Cm arises due to the fact that there are layers of conductive and nonconductive (lipids) media. The capacitance of a typical patch of membrane is That is the membrane capacitance […]


What is the Basic Conditions and Types of Bacterial Growth?

Bacteria are cultivated and studied under laboratory conditions. Numerous media(singular, medium) have been developed for bacterial cultivation. Because the nutritional requirements of bacteria vary widely, there are great differences in the chemical compositions of the media used in the laboratory. Nutritional requirements: All organisms require a ‘source of energy’. Some depends on chemical compounds for […]



It contains and protects the majority of the cell’s DNA in the form of chromosomes. DNA also occurs in the mitochondria and chloroplasts. The nucleus occupies about 10% of volume of cell and typically averages 5 microns in diameter. Surrounded by nuclear envelope with pores. Nuclear pores regulate the passage of materials between the nucleus […]

Euchromatin : The Packed form of Chromatin

Euchromatin : The Packed form of Chromatin

Euchromatin is a lightly packed form of chromatin (DNA, RNA and protein) that is rich in gene concentration, and is often (but not always) under active transcription. Unlike heterochromatin, it is found in both cells with nuclei (eukaryotes) and cells without nuclei (prokaryotes). It comprises the most active portion of the genome within the cell […]

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The cytoskeleton (also CSK) is a cellular "scaffolding" or "skeleton" contained within a cell’s cytoplasm and is made out of protein. The cytoskeleton is present in all cells; it was once thought to be unique to eukaryotes, but recent research has identified the prokaryotic cytoskeleton. It has structures such as flagella, cilia and lamellipodia and […]


Membrane Protein Diffusion and Its Types

Concentration gradients by which diffusion and osmosis operate are only partially effective when all needs of the plant are considered. Some essential materials, for example, are present in small amounts in the soil but used in greater concentrations by the plant. How do the plants retain such materials as they accumulate in cells against the […]


Plastids in plants

Plastids are responsible for photosynthesis, storage of products like starch and for the synthesis of many classes of molecules such as fatty acids and terpenes which are needed as cellular building blocks and/or for the function of the plant. Depending on their morphology and function, plastids have the ability to differentiate, or redifferentiate, between these […]


Interrupted Genes

Most eukaryotic genes are interrupted by non-coding or non-translatable sequences known as introns. The coding or translatable sequences are known as exons.Such genes are called split genes/interrupted genes. Both intron and exon sequences are transcribed to produce a primary transcript/precursor RNA/pre RNA. The precursor RNA for mRNA is known as heterogenous RNA/hn RNA. Following the […]


Bacterial cell walls

Around the outside of the cell membrane is the bacterial cell wall. Bacterial cell walls are made of peptidoglycan (also called murein), which is made from polysaccharide chains cross-linked by unusual peptides containing D-amino acids. Bacterial cell walls are different from the cell walls of plants and fungi which are made of cellulose and chitin, […]


Plant cell walls

Many plant cells have walls that are strong enough to withstand the osmotic pressure from the difference in solute concentration between the cell interior and distilled water.[3] Plant cell walls vary from 1/10 to several µm thick. Layers Molecular structure of the primary cell wall in plants. Up to three strata or layers may be […]

Heterochromatin From Chromosome to Protein

Heterochromatin: From Chromosome to Protein

The definition of chromatin in eukaryotes, on the contrary of prokaryotes, the DNA is packaged in the form of a nucleoprotein complex called “Chromatin“, which carries the hereditary message. It is located in a nucleus and is organized in several separate entities, the chromosomes. The Concept of Heterochromatin : In 1928, based on histologist observations, […]



In genetics, an operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single regulatory signal or promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo trans-splicing to create monocistronic mRNAs that are translated separately, i.e. several […]

Cell Cycle : Sequential events in Cell Division

Cell Cycle : Sequential events in Cell Division

What is Cell Cycle ? The sequence of events which occurs between one cell division and the next  is called the Cell cycle. The cell cycle comprises the period between the release of a cell as one of the progeny of a division and its own subsequent division into two daughter cells. Stages of Cell […]


The Golgi complex

In 1898, camillo Golgi, an Italian cytologist, discovered that when he treated the cells with silver salts, certain peculiar bodies showed up in the cytoplasm. The “reticular apparatuses” he described had never been noticed before, and they didn’t show up with other stains. But when other workers used Golgi’s silver treatment, they found the bodies […]

Microbial growth

Microbial growth and its Basics

Microbial growth may be described as occurring in different ways under different circumstances. Microbial growth is usually studied as a population not an individual. Individual cells divide in a process called binary fission where two daughter cells arise from a single cell. The daughter cells are identical except for the occasional mutation. Bacterial Cell: Structure […]


Algal Cell Walls

Like plants, algae have cell walls. Algal cell walls contain either polysaccharides (such as cellulose (a glucan)) or a variety of glycoproteins (Volvocales) or both. The inclusion of additional polysaccharides in algal cells walls is used as a feature for algal taxonomy. Mannans: They form microfibrils in the cell walls of a number of marine […]


Cell Wall

Cell Wall – What’s it for? Cell wall diagram While cell membranes might be around every cell, cell walls made of cellulose are only found around plant cells. Cell walls are made of specialized sugars called cellulose. Cellulose provides a protected framework for a plant cell to survive. It’s like taking a water balloon and […]

cellular organization


Unit-2: Cellular Organization: This is the second unit topics of CSIR NET Life Sciences examination syllabus. Unit name is Cellular Organization. Just navigate the links on the given topics. Basics on Cellular Organization: Life exhibits varying degrees of organization. Atoms are organized into molecules, molecules into organelles, and organelles into cells, and so on. According […]


Bacterial Cell: Structure and its Composition

Bacteriology is the study of bacteria. Bacteria are minute, microscopic, simple, unicellular prokaryotic organisms occurring as saprophytes and parasites on a wide range of habitats. Structurally a bacteria cell consists of three categories of structurally namely, Structures of External side of the cell wall. Cell wall Structures of Internal side of the cell wall Bacterial […]


Plasma membrane : Basic structure and Function

All cells are enclosed by a thin, film-like membrane called the plasmalemma or more popularly as the plasma membrane Danielli and Davson (1935) proposed a “trilaminar model” according to which, the plasma membrane is formed of a bimolecular layer of phospholipids (35 Å thick) sandwitched between two layers of proteins (each 20 Å thick). The […]