Cell Division, Cell Cycle, and Genetic Material: Study Notes for General Biology

Cell Division

Definition and Types

Cell division is the process by which a single (parent) cell divides or splits into two or more daughter cells. This process is fundamental for growth, development, and reproduction in all living organisms.

• Fission: A type of cell division in prokaryotes (bacteria and archaea) where the cell splits into two identical cells.

• Mitosis: Eukaryotic cell division producing somatic (body) cells. Human somatic cells are diploid (2n), meaning they have two copies of every chromosome.

• Meiosis: Eukaryotic cell division producing gametes (sex cells). Human gametes are haploid (n), having only one copy of each chromosome.

Example: Fission in prokaryotes and mitosis/meiosis in the human life cycle.

Asexual vs. Sexual Reproduction

Comparison and Definitions

All living organisms must reproduce, either asexually or sexually.

• Asexual Reproduction: Involves only one parent and produces genetically identical offspring. Example: binary fission in bacteria.

• Sexual Reproduction: Involves two parents, each contributing genetic material, resulting in genetically diverse offspring. Example: meiosis and fertilization in humans.

Example: Binary fission (asexual) vs. mitosis and meiosis (sexual).

Importance of Cell Division

Roles in Organisms

• Reproduction: Produces new life forms.

• Growth: Essential for fetal development and organismal growth.

• Tissue Repair and Renewal: Replaces damaged or dead cells, maintaining tissue health.

Example: Cell division in embryos, growing tissues, and healing wounds.

Genetic Material Organization

Genome, Chromatin, Nucleosomes, and Chromosomes

The genome is the complete set of DNA in a cell. Genetic material determines inherited traits and is organized in several levels:

• DNA associates with proteins (mainly histones) to form units called nucleosomes.

• Nucleosomes are further packed to form chromatin in non-dividing cells.

• Chromosomes are highly condensed chromatin, visible during cell division.

Example: DNA is coiled around histone proteins to form nucleosomes, which are packed into chromatin and further condensed into chromosomes during cell division.

DNA Replication and Chromatids

Process and Terminology

Before a cell divides, its DNA must be replicated (synthesized/duplicated).

• DNA Replication: Produces an exact copy of all the DNA in a cell.

• Replication converts single, unreplicated chromosomes into replicated chromosomes with two identical sister chromatids joined at a centromere.

Example: After replication, each chromosome consists of two sister chromatids attached at the centromere.

Cell Cycle

Phases and Regulation

The cell cycle is a series of events that a cell undergoes from its formation to its division.

• It is divided into two major phases:

  • Interphase: Non-dividing phase for cell growth, DNA replication, and production of organelles/enzymes. Includes G1, S, and G2 phases.

  • Mitotic (M) Phase: Division phase, including mitosis (nuclear division) and cytokinesis (cytoplasmic division).

• G0 Phase: Cells that exit the cell cycle and do not divide further (e.g., nerve cells).

Example: The cell cycle diagram showing G1, S, G2, M, and G0 phases.

Key Terms and Definitions

• Chromatin: Loosely packed DNA and proteins in non-dividing cells.

• Chromosome: Highly condensed DNA and proteins, visible during cell division.

• Nucleosome: DNA wrapped around histone proteins.

• Sister Chromatids: Two identical copies of a chromosome joined at the centromere after DNA replication.

• Centromere: Region where sister chromatids are attached.

• Genome: Complete set of genetic material in a cell.

Practice Questions (Examples)

• Which process produces genetically identical cells?

• What is the correct order of genetic material organization from smallest to largest?

• What must occur before a cell divides?

• What are sister chromatids?

• What is the function of the centromere?

Additional info:

• Equations: No specific equations are present, but the process of DNA replication can be summarized as: $\text{DNA}_{\text{parent}} \xrightarrow{\text{Replication}} 2 \times \text{DNA}_{\text{daughter}}$

• Classification Table: Organization of genetic material can be summarized as:

Level	Description
DNA	Genetic material, double helix
Nucleosome	DNA wrapped around histone proteins
Chromatin	Loosely packed nucleosomes
Chromosome	Highly condensed chromatin, visible during cell division