Question

Satellite of chromosome is
a. Rich in RNA and Deficient in DNA
b. Rich in DNA and deficient in RNA
c. Rich in protein
d. Lacks DNA

Answer 1

Hint: Chromosome is a DNA molecule containing all the genetic material or genome of an organism. Most eukaryotic chromosomes include packaging proteins. Three-dimensional genome structure plays a significant role in transcriptional regulation.

Complete answer:
Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA) and passes from generation to generation. A chromosome consists of two identical halves, the chromatids which are held together at one point called centromere and it appears as a narrow region called primary constriction of chromosome. On the sides of the centromere, disc shaped structures are present known as kinetochores. Ends of the chromosome are called telomeres.

Depending on the position of centromere, chromosomes are divided into four types:
- Metacentric chromosome: The centromere is present at the centre.
- Sub-metacentric chromosome: The centromere is present slightly away from the centre of chromosome.
- Acrocentric chromosome: The centromere is present very close to one end of the chromosome.
- Telocentric chromosome: The centromere is present at the terminal ends of the chromosome.

Some chromosomes may have additional constrictions known as secondary constrictions or Nucleolar organizer near their ends. The part of the chromosome beyond the secondary constriction is called satellite and represents the site for nucleolus formation and RNA synthesis. Secondary constrictions are rich in heterochromatin which is a coiled and inactive form of DNA having less DNA and more RNA than euchromatin (loosely packed DNA with higher gene concentration).

Hence, The correct answer is option (A).

Note: A chromosome having a satellite is called SAT-chromosome and considered as marker chromosome as they are present at the tip of chromosomes. Euchromatin is loosely packed DNA and has high gene concentration compared to Heterochromatin which has tightly packed DNA with less gene concentration.