nucleus, chromosomes - basic structure, number

Nucleus

• It is called the brain of the cell as it controls all the activities of cell.
→ Composition of Nucleus

• The nucleus has a double layered covering called nuclear membrane.
• The nuclear membrane has pores which allow the transfer of material from inside the nucleus to
the cytoplasm.
• The nucleus contains chromosomes, which are visible as rod-shaped structures only when the cell
is about to divide.
→ Functions of chromosomes

• Chromosomes contain information for inheritance of features from parents to next generation in
the form of DNA (Deoxyribo Nucleic Acid) molecules. Chromosomes are composed of DNA and
protein.
• DNA molecules contain the information necessary for constructing and organising cells.
• Functional segments of DNA are called genes.
• In non-dividing cell, this DNA is present as part of chromatin material.
• Chromatin material is visible as entangled mass of thread like structures. Whenever the cell is
about to divide, the chromatin material gets organised into chromosomes and perform cell division

→ Functions of Nucleus

• The nucleus plays a central role in cellular reproduction. It is the process by which a single cell
divides and forms two new cells.
• It also plays a crucial part, along with the environment, in determining the way the cell will develop
and what form it will exhibit at maturity, by directing the chemical activities of the cell.

Nucleoid

• In some organisms like bacteria, the nuclear region of the cell may be poorly defined due to the
absence of a nuclear membrane.
• Such an undefined nuclear region containing only nucleic acids is called a nucleoid.