Overview
This lecture introduces the concepts of chromosomes and chromatids, explaining their structure, function, and importance in cell division.
Chromosomes: Structure and Function
- Chromosomes are tightly packed DNA structures formed when a cell prepares to divide.
- During interphase (when the cell is not dividing), DNA is spread out within the nucleus for efficient functioning.
- Packing DNA into chromosomes makes it easier for the cell to divide its genetic material accurately.
Chromosome Anatomy
- Chromosomes appear as condensed, thick structures before cell division.
- Each chromosome has a central pinched region called the centromere.
- The position of the centromere can vary (middle, near the top, etc.) but always marks the chromosome's constricted area.
Chromatids and Their Relationship
- Each chromosome is composed of two identical strands called sister chromatids.
- Sister chromatids are joined at the centromere and are genetically identical.
- During cell division, sister chromatids separate so that each new cell gets an exact DNA copy.
Chromosome Duplication in Interphase
- In the S phase of interphase, DNA is duplicated, resulting in a chromosome that consists of two sister chromatids held together by a centromere.
- Biologically, "chromosome" can refer to either a single chromatid or a pair of sister chromatids depending on the cell cycle stage.
Key Terms & Definitions
- Chromosome — Condensed, tightly packed DNA formed for cell division.
- Interphase — Cell cycle phase when DNA is spread out and the cell is not dividing.
- Centromere — Pinched region on a chromosome joining two sister chromatids.
- Chromatid — One of two identical DNA strands making up a duplicated chromosome.
- Sister Chromatids — Two identical chromatids joined at the centromere.
Action Items / Next Steps
- Review this overview to understand chromosome structure before starting mitosis in the next lesson.