Cell Biology: Nucleus Structure and Chromosome Types

Nucleus Structure

• The nucleus is a membrane-bound organelle that contains the cell's genetic material.
• The nuclear envelope is a double membrane structure surrounding the nucleus.
• Nuclear pores are interruptions in the nuclear envelope that allow RNA and proteins to pass between the nucleus and the cytoplasm.
• Nucleoplasm is the fluid within the nucleus.
• The nucleolus is a spherical structure within the nucleus involved in ribosomal RNA synthesis, and is not membrane-bound.
• Chromatin is a complex of DNA and proteins that are highly extended and elaborate nucleoprotein fibers.
• Most cells have one nucleus, but some have multiple nuclei or lack nuclei.
• The number of nucleoli in a cell varies based on its protein synthesis activity.

Chromosome Types

• Metacentric chromosomes have a centromere in the middle, resulting in two equal arms.
• Submetacentric chromosomes have a centromere slightly off-center, resulting in one shorter arm and one longer arm.
• Acrocentric chromosomes have a centromere near one end, resulting in a very short arm and a very long arm.
• Telocentric chromosomes have a centromere at the very end of the chromosome, resulting in only one arm.
• The centromere is the primary constriction on a chromosome where the two chromatids are joined together.
• Kinetochores are disc-shaped structures on the sides of the centromere where spindle fibers attach during cell division.
• Chromatids are two identical copies of a chromosome formed during replication.
• Satellites are small pieces of DNA attached to some acrocentric chromosomes.
• Secondary constrictions are constricted regions on some chromosomes where the satellite is located.