Giemsa Staining and G-band Formation
Giemsa staining is a technique used in cytogenetics to visualize chromosomes. To obtain G-bands (the dark and light bands seen on chromosomes), a specific enzymatic digestion step is required prior to staining.
Chromosome Digestion for G-bands
The process involves treating the prepared chromosomes with an enzyme that selectively digests certain components of the chromatin. This differential digestion creates variations in staining intensity along the chromosome arms, revealing the characteristic G-band pattern.
- The enzyme primarily used for this purpose is Trypsin.
- Trypsin is a protease that breaks down proteins. It selectively digests the non-histone proteins in the chromosome structure.
- This digestion causes the chromosome material to become partially decondensed, especially in the G-negative regions (which stain lightly).
- The remaining, more resistant chromatin (G-positive regions) stains darkly with Giemsa stain.
Therefore, Trypsin is the correct enzyme used to obtain G-bands during Giemsa staining of chromosomes.
Important Questions from Genes and chromosomes
Readers of histone modifications include:
The amino acid side chains of the four histones in the nucleosome are subjected to remarkable variety of post-translation modifications such as phosphorylation, acetylation and methylation. Which one of the following post-translational marks on histone tails is usually associated with transcriptional repression?
In context of DNA methylation, which one of the following statements is FALSE?
The nucleosome is the fundamental subunit of chromatin in eukaryotes. Following statements are made about nucleosome:
A. Generally, a typical nucleosome contains ~ 200bp of DNA and two copies of each histone (H2A, H2B, H3 and H4)
B. 146 bp length of DNA per nucleosome core particle is strictly maintained across the organisms
C. The histone octamers are not conserved during/after replication, however, H32-H42 tetramers are.
D. Variants have been identified for all core histones except histone H3
E. While wrapping around the core histones, the structure of DNA is altered at the middle of the nucleosome core particle and exhibits increased number of base pairs per turn
Which one of the following combination of statements is most appropriate?
Which one of the following statements about Short Interspersed Nuclear Elements (SINEs) is TRUE?
