Biotechnology Eligibility Test Preparation

DBT BET JRF 2018 Original Solved Question Paper with Answer Key (Download PDF)


DBT JRF 2018 Question Paper

Original (original) Previous Year (old) Solved Question Paper of DBT BET JRF 2018 Examination (Department of Biotechnology- Biotechnology Eligibility Test – Junior Research Fellowship) with Answer Key and Explanations as PDF. DBT BET JRF aspirants can download the question paper as single PDF file for your exam preparation. Please feel free to inform the Admin if you find any mistakes in the answer key provided.

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biological chemistry

Proton Hopping in Water (Grotthuss Mechanism)


What is Proton Hopping

Proton Hopping in Water
(The Grotthuss Mechanism)

Proton Hopping is the process of diffusion of protons (H⁺ ions) through the network of hydrogen-bonded water molecules in the liquid water. Proton hopping is also called as Grotthuss mechanism, named after the discoverer Theodor Grotthuss. The net result of proton hopping is the fast movement of H⁺ ions in water than any other dissolved cations such as Na⁺ or K⁺. Let’s see how proton hopping occurs in water.

Water has a slight tendency of ionization. The H2O molecules can ionize into H⁺ and OH¯ ions as in the equation (1).

ions in water

The ionization reaction of water can be described by its equilibrium constant. The equilibrium constant (Keq) of the ionization of water at 25°C is calculated as 1.8 X 10¯16 M. The equilibrium constant and the concentration of H⁺ and OH¯ ions formed as a result of the ionization of H2O molecules are responsible for the pH of water.

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biological chemistry

How to Calculate pH and pKa of a Buffer Using Henderson-Hasselbalch Equation?


Henderson Hasselbalch Equation Sample Problems

How to Calculate pH and pKa of a Buffer using Henderson-Hasselbalch Equation?

Henderson-Hasselbalch equation is a numerical expression which relates the pH, pKa and Buffer Action of a buffer. A buffer is a solution which can resist the change in pH. Chemically, a buffer is a solution of equimolar concentration of a weak acid (such as acetic acid – CH3COOH) and its conjugate base (such as acetate ion – CH3COO¯). In the previous post, we have discussed the Titration Curve of a weak acid and the Derivation of Henderson-Hasselbalch Equation. The characteristic shape of the titration curve of a weak acid is also described by the Henderson-Hasselbalch equation. In this chapter we will discuss the methods to calculate the pH or pKa of a buffer using Henderson-Hasselbalch equation using sample problems.

Learn more: Titration Curve of a Weak Acid (Acetic Acid)

Lean more: How to Derive Henderson-Hasselbalch Equation?

Henderson-Hasselbalch Equation is given as:

Hasselbalch equation

Where,

pH – the negative logarithm of H⁺ ion concentration in the medium.

pKa – the negative logarithm of Ka of the acid (Ka is the dissociation constant)

Proton acceptor – the ionized or deprotonated acid (example – CH3COO¯).

Proton donor – intact (non-ionized) weak acid (example – CH3COOH).

Let’s see some sample problems and solutions.

Problem-1: A mixture of 0.20M acetic acid and 0.30M sodium acetate is given. Calculate the pH of the medium if the pKa of the acetic acid is 4.76.

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biological chemistry

pH and pKa – Henderson-Hasselbalch Equation Deriving


ph and pKa Relationship

Henderson–Hasselbalch Equation
How to Derive Henderson Hasselbalch Equation?

Henderson-Hasselbalch equation is a simple expression which relates the pH, pKa and the buffer action of a weak acid and its conjugate base. The Henderson-Hasselbalch equation also describes the characteristic shape of the titration curve of any weak acid such as acetic acid, phosphoric acid, or any amino acid. The titration curve of a weak acid helps to determine the buffering pH which is exhibited around the pKa of that acid. For example, in the case of acetate buffer, the pKa is 4.76. This is the best buffering pH of acetic acid. Besides, at this pH the acetic acid (CH3COOH) and acetate ions (CH3COO¯) will be at equimolar concentration in the solution. This equimolar solution of a weak acid and its conjugate base will resist the change in pH by donating or taking up the H⁺ ions. (pH is the negative logarithm of hydrogen ion concentration in a medium.The pKa is the negative logarithm of Ka. The Ka is the dissociation constant (similar to the equilibrium constant) for the ionization reaction of an acid.)

Learn more: Titration Curve of a Weak Acid (Acetic Acid)

In the present post, we will see the derivation of Henderson-Hasselbalch equation from the ionization reaction of a weak acid. We also discuss the significance of Henderson-Hasselbalch equation.

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Zoology lecture notes and study materials

Difference between Keratinized and Non-keratinized Epithelial Tissues


Keratinized vs Nonkeratinized Epithelium

Keratinized vs Non-keratinized Epithelium
Difference between Keratinized and Non-keratinized Epithelial Tissues

Epithelium constitutes the outer layer of body surfaces, linings of the alimentary canal and the walls of hollow structures. It covers the internal or external surfaces of the body. The functions epithelial tissue is to protect the underlying tissues from physical damages, infection, desiccation, UV radiation and heat loss. Based on the presence of Keratin, the epithelial tissues are categorized into Keratinized epithelium and Non-keratinized epithelial tissues. Keratins are a diverse group of structural proteins that form the intermediate filament network and they provide the structural integrity of keratinized epithelial cells.

The present post discusses the Difference between Keratinized and Non-keratinized Epithelial Cells.

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