Question
Experimental confirmation of semiconservative replication of $\text{DNA.}$
✓
Answer
$(1)$ Matthew Meselson and Franklin Stahl $(1958)$ used equilibrium – density – gradient – centrifugation technique to experimentally prove semiconservative $\text{DNA.}$ replication.
$(2)$ They cultured bacteria $E.$coli in the medium containing $^{14}N ($light nitrogen$).$ They obtained equilibrium density gradient band by using $6M \ CsCl_2.$ The position of this band is recorded.
$(3) \ E$. coli cells were then transferred to $^{15}N$ medium $($heavy isotopic nitrogen$)$ and allowed to replicate for several generations. At equilibrium point density gradient band was obtained, by using $6M \ CsCl_2.$ The position of this band is recorded.
$(4)$ The heavy $\text{DNA.} (^{15}N)$ molecule can be distinguished from normal $\text{DNA.}$ by centrifugation in a $6M$ Cesium chloride $(CsCl_2)$ density gradient. At the equilibrium point $^{15}N \text{DNA.}$ will form a band. In this both the strands of $\text{DDNA.}$ are labelled with $^{15}N.$
$(5)$ Such $E.$ coli cells were then transferred to another medium containing $^{14}N$ i.e. normal $($light$)$ nitrogen. After first generation, the density gradient band for $^{14}N ^{15}N$ was obtained and its position was recorded. After second generation, two density gradient bands were obtained – one at $^{14}N ^{15}N$ position and other at $^{14}N$ position.
$(6)$ The position of bands after two generations clearly proved that $\text{DNA.}$ replication is semiconservative.
Need a full question paper?
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.
Explore more
Similar questions
Placenta.
Give reasons:
(a) Lymphatic vessels are milky in appearance.
(b) Monocytes are called scavengers.
(c) The wall of left ventricle is thicker than the right ventricle.
(d) Valves are present in the veins.
(e) Pulmonary veins carry oxygenated blood.
(a) Lymphatic vessels are milky in appearance.
(b) Monocytes are called scavengers.
(c) The wall of left ventricle is thicker than the right ventricle.
(d) Valves are present in the veins.
(e) Pulmonary veins carry oxygenated blood.
Describe the concept of energy flow. ### In an ecosystem the flow of energy is unidirectional. Explain.
Pond as a small ecosystem.
If a desired gene is identified in an organism for some experiments, explain the process of the following:
- Cutting this desired gene at specific location.
- Synthesis of multiple copies of this desired gene.
Explain the process of replication of a retrovirus after it gains entry into human body.
Resting potential of a nerve fibre.
Why are sedimentary cycles slower than gaseous cycles? Explain giving resons.
The following table shows certain diseases, their causative organisms and symptoms. Fill the gaps.
| Name of the Disease | Causative organism | Symptoms | |
| i. | Ascariasis | Ascaris | ________ |
| ii. | ________ | Trichophyton | Appearance of dry, scaly lesions on various parts of the body. |
| iii. | Typhoid | ________ | High fever, weakness, headache, stomach pain, constipation. |
| iv. | Pneumonia | Streptococcus pneumoniae | ________ |
| v. | ________ | Rhino viruses | Nasal congestion and discharge, sorethroat, cough, headache. |
| vi. | Filariasis | ________ | Inflammation in lower limbs. |
“The energy flow in the ecosystem follows the second law of thermodynamics.” Explain.