TOPIC 16. Cell nucleus – chromosomes, structure and replication of DNA
Eukaryotes have diploid number of chromosomes (2n)
The nucleus contains the chromosomes, which contains the genetic information of an organism in the form of DNA and associated proteins. Chromosomes contain all the genetic information of the organism and they are also the method by which hereditary information is passed on to offspring.
Chromosomes have 4 main functions:
- 1. Genetic Code Storage: Chromosome contains the genetic material that is required by the organism to develop and grow.
- 2. Sex Determination: Humans have 23 pairs of chromosomes, 22 pairs of autosomes and 1 pair of sex chromosomes. If XX– female. If XY – male with the Y chromosome from the male.
- 3. Control of Cell Division: Chromosomes check successful division of cells during the process of mitosis. The chromosomes of the parent cells ensure that the correct information is passed on to the daughter cells.
- 4. Formation of Proteins and Storage: The chromosomes direct the sequences of proteins formed in our body and maintaining the order of DNA.
The DNA is only organized into chromosomes during cell replication. Between replication DNA is stored in chromatin and wrapped around histones to form nucleosomes. Each cell contains about 2 meters of DNA coiled around histones.
The inner nuclear membrane is continuous with the nuclear lamina. The lamina is an attachment site for chromosomes and helps to stabilize the structure of the nucleus.