Biology · Cell: The Unit of Life · NEET
No, they are not the same. The centromere is the pinched, narrow region of the chromosome, also called the primary constriction. The kinetochores are small disc-shaped structures that sit ON the two sides of that centromere. So the centromere is the location, and the kinetochores are the protein plates built at that location. NEET loves to test this exact difference.
Spindle fibres attach to the KINETOCHORE, not directly to the centromere. This is the most common trap in NEET. NCERT says disc-shaped kinetochores are present on the sides of the centromere, and the spindle microtubules connect to these kinetochores to pull the chromatids apart. Many students wrongly pick centromere. Correct answer = kinetochore.
The centromere holds the two chromatids of a chromosome together. A duplicated chromosome has two identical sister chromatids joined at the centromere. During cell division the centromere region is where they stay linked until the spindle fibres (through the kinetochores) separate them.
The primary constriction is just another name for the centromere. It is the main narrow, pinched point on the chromosome. There is also a secondary constriction in some chromosomes, which is a different point linked to the satellite and nucleolus, but the MAIN one you must remember is: primary constriction = centromere.
No. NCERT clearly states a chromosome is visible only in DIVIDING cells. In a non-dividing cell the material stays as loose chromatin. The neat rod-shape with a centromere and kinetochores becomes visible only when the cell is dividing (during metaphase it is clearest).
Spindle fibres attach on to:
Match List-I with List-II: List I: (a) Cristae (b) Thylakoid (c) Centromere (d) Cisternae List II: (i) Primary constriction in chromosome (ii) Disc-shaped sacs in Golgi apparatus (iii) Infoldings in mitochondria (iv) Flattened membranous sacs in stroma of plastids
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes, the centromere is a special region of the chromosome's DNA. The kinetochores that sit on it are protein structures assembled on that DNA region. So centromere = DNA region, kinetochores = protein plates on top.
A duplicated chromosome (with two sister chromatids) has two kinetochores, one on each side of the centromere, so each chromatid can be pulled to an opposite pole by spindle fibres.
No. The centromere position varies. When it is in the middle the chromosome is metacentric; slightly off-middle is sub-metacentric; near one end is acrocentric; at the very tip is telocentric. This position-based classification is a separate NEET topic.
Because NCERT directly states the centromere holds the two chromatids and that kinetochores on its sides bind spindle fibres. This exact wording is asked repeatedly (2016, 2021, 2024, 2025), often as a match-the-column or 'where do spindle fibres attach' question.
