Chromosomes are composed primarily of DNA and protein, with DNA making up about 40% and proteins about 60% of their structure. A significant amount of RNA is also associated, as chromosomes are key sites for RNA synthesis. The DNA in a chromosome is a long, double-stranded molecule coiled tightly to fit within the nucleus. This coiling is facilitated by histone proteins, which form nucleosomes—bead-like structures where DNA wraps around histones every 200 nucleotides. This organization allows efficient packaging into a compact chromatin structure while enabling accessibility for replication and gene expression. Chromatin exists in two forms: euchromatin, which is loosely packed and transcriptionally active, and heterochromatin, which is tightly packed and mostly inactive.
What are chromosomes primarily composed of?
Chromosomes are primarily composed of DNA and proteins, with DNA making up about 40% and proteins about 60%.
What type of protein helps in the coiling of DNA in chromosomes?
Histone proteins help in the coiling of DNA in chromosomes.
What is a nucleosome?
A nucleosome is a bead-like structure formed when DNA wraps around a core of eight histone proteins, approximately every 200 nucleotides.
What are the two main forms of chromatin in chromosomes?
The two main forms of chromatin are euchromatin, which is loosely packed and transcriptionally active, and heterochromatin, which is tightly packed and mostly inactive.
Why is the coiling of DNA important in chromosomes?
The coiling of DNA is important because it allows the long DNA molecules to fit within the small space of the nucleus and facilitates its organization for processes like replication and transcription.
What is the primary composition of chromosomes?
a) Only DNA
b) DNA and protein
c) DNA, RNA, and lipids
d) Only protein
Answer: b) DNA and protein
What percentage of a chromosome is typically made up of DNA?
a) 20%
b) 40%
c) 60%
d) 80%
Answer: b) 40%
What is the basic structural unit of chromatin?
a) Nucleosome
b) Centromere
c) Chromatid
d) Histone
Answer: a) Nucleosome
What is the role of histone proteins in chromosomes?
a) Replicating DNA
b) Providing a scaffold for DNA coiling
c) Repairing DNA
d) Synthesizing RNA
Answer: b) Providing a scaffold for DNA coiling
Which of the following is transcriptionally active chromatin?
a) Heterochromatin
b) Euchromatin
c) Centromeric chromatin
d) Telomeric chromatin
Answer: b) Euchromatin