Molecular Biology Tutorials

Different Forms of DNA (A-DNA, B-DNA and Z-DNA) A Comparison Table with PPT


Different Types of DNA Conformations
(A-DNA, B-DNA and Z-DNA: A Comparison Table)

DNA, the genetic information carrier molecule of the cell, is a long polymer of nucleotides and can adopt different types of structural conformations. The various types of conformations that the DNA can adopt depend on different factors such as:

1.      Hydration level
2.      Salt concentration
3.      DNA sequence
4.      Quantity and direction of super-coiling
5.      Presence of chemically modified bases
6.      Different types of metal ions and its concentrations
7.      Presence of polyamines in solution.

The most common types of structural conformations of DNA are named as:

(1).  A-DNA

(2).  B-DNA

(3).  Z-DNA

Among these three types, the most abundant type of DNA is B-DNA, commonly known as Watson-Crick Model of DNA double helix. The present post describes the structural features of A, B and Z forms of DNA in a comparative manner. We will also discuss the similarities and differences between A-DNA, B-DNA and Z-DNA.

(1). A-DNA

A-DNA is a rare type of structural conformation that a DNA can adopt under dehydrating conditions. A-DNA is a double stranded helical structure almost similar to B-DNA but with a shorter and more compact structural organization. A-DNA was discovered by Rosalind Franklin and the credit for the naming of A-DNA and B-DNA was also accounted to her. Important structural features of A-DNA are given below:

Ø  A-DNA is formed from B-DNA under dehydrating condition.

Ø  A-DNA is much wider and flatter than B-DNA.

Ø  Similar to B-DNA, the A-DNA is also a right handed helix.

Ø  The helix diameter of A-DNA is 26 Å.

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Botany lecture notes

Types of Stelar Systems and its Evolution in Pteridophytes and Higher Plants with PPT

types of steles in pteridophytes

Stelar Evolution in Vascular Plants
(Origin and Evolution of Stele in Pteridophytes and Higher Plants)

What is stele? What are the components of stele?

Ø  Stele is the central cylinder or core of vascular tissue in higher plants.

Ø  The stele consists of xylem, phloem, pericycle and medullary rays and pith if present.

Ø  The term ‘stele’ was for the first time used by Van Tieghem and Douliot in 1886 in their ‘Stelar Theory’.

What is ‘stellar theory’?

Ø  Proposed by Van Tieghem and Douliot in 1886.

Ø  Major highlights in stellar theory are:

$.  The stele is a real entity and present universally in all axis of higher plants.

$.  The primary components of stele are xylem and phloem.

$.  Tissues like pericycle, medullary rays and pith are also the components of stele.

$.  ‘Stelar theory’ also says that the cortex and the stele are the two fundamental parts of a shoot system.

$.  Both these components (stele and cortex) are separated by the endodermis.

$.  In higher vascular plants (Pteridophytes, Gymnosperms and Angiosperms), the leaf traces are large, and it appears that they play an important role in the vascular system of the axis.

$.  The whole set-up of leaf traces appears as a composite structure in these plants.

$.  Such composite structures do not remain within the limits of stellar theory of Van Tieghem and Douliot.

What are the different types of steles in plants (Pteridophytes and higher plants)?

Ø  On the basis of ontogeny and phylogeney, there are THREE broad categories of steles in vascular plants.

Ø  They are:

(1).  Protostele

(2).  Siphonostele

(3).  Solenostele

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Zoology lecture notes and study materials

Parasitic Adaptations (Platyhelminthes, Nematodes, Insects and Plants)

parasitic adaptations

Parasitic Adaptations of Plants and Animals

What is meant by Adaptation?

Adaptation definition: ‘Any feature of an organism or its part which enables it to exist under conditions of its habitat is called adaptation.’ The adaptations are mainly to withstand the adverse conditions of the environment and to use the maximum benefit of the environment.

What are Parasites?

A parasite is an organism which lives in or on another organism (called host) and benefits by deriving shelter and nutrients from them. The parasitism is a type of negative ecological / biological interaction in nature where one organism gets benefited (the parasite) and the other is harmed (the host). The parasites may be microbes such as bacteria, virus and Mycoplasma, or animals such as liver fluke, worms, nematodes, some insects and plants such as Loranthus, Cuscuta etc. All types of parasites show peculiar adaptations to survive in or on the host system and to get maximum benefit from them.

Learn more: Positive and Negative Interactions in an Ecosystem

Parasites show three level adaptations, they are

(1).     Structural Adaptations (Morphological and Anatomical Adaptations)

(2).     Physiological Adaptations

(3).     Reproductive Adaptations

(1).  Structural Adaptations (Morphological and Anatomical) Adaptations of Parasites:

Ø  Feeding organs are usually absent in endoparasites.

Ø  Fluid feeding insects such as aphids have highly specialized mouth parts for the easy absorption of cell sap from the host.

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Botany lecture notes

Receptacular vs Appendicular Theory of Inferior Ovary Development in Flowers

Origin and Evolution of Inferior ovary

Receptacular vs Appendicular Theory
(A Comparative Approach)

Based on the position of ovary there are three types of flowers- (1) Hypogynous, (2) Perigynous, and (3) Epigynous.

(1). Hypogynous Flower: The most primitive type with convex shaped Thalamus (torus). The ovary is superior and all other floral parts (calyx, corolla and androecium) arise from the base of the ovary.

(2). Perigynous Flower: An intermediate or transient type between Hypogynous and Epigynous flowers. The thalamus is more or less cup shaped and the ovary is half inferior, located at the centre of the thalamus cup. All other floral parts arise from the rim of the thalamus cup. Sometimes the thalamus cup forms a long tube like structure called hypanthium.

(3). Epigynous Flower: The most advanced type of flower. The ovary is inferior and all other floral parts arise from the above portion of the ovary.

Ovary Position Classification

(image source: cc wikipedia)

Ø  The origin and evolution of inferior ovary is a well debated question in the phylogenetics of Angiosperms.

Ø  Comparative morphological, anatomical and paleo-botanical studies suggest that the inferior ovary has evolved many times among different groups of Angiosperms in different ways and in different times in the remote past.

Ø  In order to explain the formation of inferior ovary, two theories have developed by the evolutionary biologists.

Ø  The two theories are:

(1). Appendicular Theory

(2). Receptacular (axial) Theory

Ø  Both these theories are proposed on close attention to the organization of the course of vascular bundles supply to the ovules in the flower.

Ø  The two theories also considered that the hypogynous flower is the most primitive one. Moreover, the epigynous condition evolved from a hypogynous condition through the transient perigynous state.

(1). Appendicular Theory

Ø  Proposed by Eames in 1961.

Ø  According to this theory, extensive fusion (both connation and adnation) of the outer lower portion floral whorls to one another and to the ovary wall has occurred. This result in the formation of an inferior ovary (epigynous condition).

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Biotechnology Lecture Notes

Advantages and Disadvantages of Animal Cell Culture (Short Lecture Notes)

animal cell culture advantages and limitations

Advantages and Disadvantages of Cell / Tissue Culture

Tissue culture is an aseptic in vitro culture of animal or plant cells in a precisely controlled environmental condition. The term “Tissue Culture” was for the first time coined by Thomas Burrows. Even though the in vitro culture of prokaryotes and both plant and animal cells are possible now, the term ‘Tissue Culture’ generally denotes to Animal Cell / Tissue culture. The term ‘Plant Tissue Culture’ symbolizes the in vitro culture of plant cells.

In cell culture the cells are maintained in an artificial environment consists of a suitable culture vessel containing a culture medium. The medium supplies all the nutrients, growth factors, and required gases for the growth of the cells. Moreover, the physiochemical environment of the culture system is strictly monitored most probably through automated systems. The control of the physiochemical environment in the culture system is one of the most important advantages of cell culture system. However, the tissue culture process is not always profitable and there are a plenty of difficulties in maintaining the cells in in vitro conditions. The present post describes the Advantages and Disadvantages of animal cell or tissue culture techniques.

Advantages of Animal Cell Culture:

Ø  Physio-chemical environment in the culture such as pH, temperature, osmolarity and level of dissolved gases can be precisely controlled in the in vitro system.

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