Molecular Biology MCQ on DNA Replication (Molecular Biology MCQ-07)
(Biology / Life Sciences MCQ: Multiple Choice Questions in Molecular Biology)
(Sample/Model/Practice Questions for CSIR JRF/NET Life Science Examination, ICMR JRF Exam, DBT BET JRF Exam, GATE BT and XL Exam, ICAR JRF NE Exam, PG Entrance Exam, JAM Exam, GS Biology Exam and Medical Entrance Exam)
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:
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.
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.
The DNA molecules are not always double stranded helical structures, sometimes they occur in single stranded form called ssDNA. In 1959 Robert Sinsheimer discovered a unique bacteriophage called φX 174 (which infect Escherichia coli) with single stranded DNA as its genetic material. Even though the chemical composition of single stranded and double stranded DNA are the same, they also show some characteristic differences.
The present post describes the similarities and differences between dsDNA and ssDNA.s
Similarities between dsDNA and ssDNA
Ø Both dsDNA and ssDNA can acts as genetic material
Ø Both are polymers of nucleic acids
Ø The sugar molecule in both the case is deoxyribose
Ø Both contain purines and pyramidines
Ø Both ssDNA and dsDNA contain the nitrogen bases A, G, T and C
Similarities & Differences between DNA and RNA – A Comparison Table
We wish to suggest a structure for the salt of deoxyribose nucleic acid (DNA).
This structure has novel features which are of considerable biological interest. Watson & Crick, 1953
DNA and RNA are the two types of nucleic acids (a class of macromolecules in the cells) present in all prokaryotic and eukaryotic organisms. Both are essentially the polymers of nucleotides and have immense role in the storage and expression of genetic information in an organism. DNA and RNA allow the storage of genetic information for long period of time without any changes in the genetic constitution of the organism. The presence of two categories of nucleotides also allows the decoding of genetic information during protein synthesis by the process of transcription and translation. The current post describes the similarities and differences between DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
Similarities between DNA and RNA
Ø Both DNA and RNA can acts as genetic material.
Ø Both are polymers of nucleotides.
Ø Both DNA and RNA are linear structures with secondary and super-secondary arrangements.
Ø Both contain purines and pyrimidines.
Ø Both DNA and RNA contain pentose sugar.
Ø In DNA and RNA the adjacent nucleotides are connected by 3’-5’ phosphodiester bonds.