Cell Cycle and Cellular Reproduction

Vocabulary and Key Terms

Understanding the cell cycle and cellular reproduction requires familiarity with several essential terms. These terms form the foundation for studying how cells grow, divide, and contribute to the continuity of life.

• Chromosome: A threadlike structure composed of DNA and proteins that carries genetic information. In eukaryotes, chromosomes are found in the nucleus.

• Chromatin: The complex of DNA and proteins (mainly histones) that makes up chromosomes. Chromatin is less condensed than chromosomes and is present during interphase.

• Homologous chromosomes: Pairs of chromosomes (one from each parent) that are similar in shape, size, and genetic content but may carry different versions (alleles) of genes.

• Sister chromatids: Two identical copies of a chromosome connected by a centromere, formed during DNA replication in the S phase.

• Autosomes: Chromosomes that are not directly involved in determining the sex of an organism. Humans have 22 pairs of autosomes.

• Sex chromosomes: Chromosomes that determine the sex of an organism (e.g., X and Y in humans).

• Cell cycle: The ordered sequence of events in the life of a cell, including growth, DNA replication, and cell division.

• Interphase: The phase of the cell cycle during which the cell grows, performs its normal functions, and duplicates its DNA. Interphase consists of G1, S, and G2 phases.

• G1 phase: The first gap phase of interphase, characterized by cell growth and preparation for DNA synthesis.

• S phase: The synthesis phase of interphase, during which DNA is replicated.

• G2 phase: The second gap phase of interphase, where the cell prepares for mitosis by producing proteins and organelles.

• Mitosis (M phase): The process of nuclear division in eukaryotic cells, resulting in two genetically identical daughter nuclei.

• Prophase: The first stage of mitosis, where chromatin condenses into visible chromosomes and the mitotic spindle begins to form.

• Metaphase: The stage of mitosis where chromosomes align at the cell's equatorial plate.

• Anaphase: The stage of mitosis where sister chromatids are separated and pulled toward opposite poles of the cell.

• Telophase & Cytokinesis: Telophase is the final stage of mitosis, where chromosomes decondense and nuclear envelopes reform. Cytokinesis is the division of the cytoplasm, resulting in two separate daughter cells.

• Diploid (2n): A cell or organism with two sets of chromosomes, one from each parent. Most human cells are diploid (46 chromosomes).

• Haploid (n): A cell with a single set of chromosomes. Gametes (sperm and egg cells) are haploid (23 chromosomes in humans).

• Fertilization: The fusion of two gametes (sperm and egg), resulting in a zygote with a diploid set of chromosomes.

• Zygote: The single cell formed by fertilization, which will undergo mitosis to develop into a multicellular organism.

• Gamete: A reproductive cell (sperm or egg) that carries a haploid set of chromosomes.

Key Concepts in the Cell Cycle and Cellular Reproduction

Distinction Between Homologous Chromosomes and Sister Chromatids

It is important to differentiate between homologous chromosomes and sister chromatids, as they play distinct roles in cell division.

• Homologous chromosomes: Two chromosomes (one from each parent) that are similar in structure and gene content but may have different alleles.

• Sister chromatids: Identical copies of a single chromosome, produced during DNA replication and joined at the centromere.

• Key difference: Homologous chromosomes are not identical, while sister chromatids are exact copies.

• Example: In a human cell, chromosome 1 from the mother and chromosome 1 from the father are homologous; after DNA replication, each chromosome 1 consists of two sister chromatids.

Distinction Between Autosomes and Sex Chromosomes

Chromosomes are classified based on their role in inheritance and sex determination.

• Autosomes: Chromosomes that do not determine sex; humans have 22 pairs.

• Sex chromosomes: Chromosomes that determine the sex of an individual (XX for females, XY for males in humans).

• Example: Chromosome 1 is an autosome; the X and Y chromosomes are sex chromosomes.

Order and Function of Each Phase of Interphase

Interphase is the longest phase of the cell cycle, during which the cell grows and prepares for division.

• G1 phase (First Gap): Cell grows, synthesizes proteins, and carries out normal functions.

• S phase (Synthesis): DNA is replicated, resulting in sister chromatids for each chromosome.

• G2 phase (Second Gap): Cell continues to grow and prepares for mitosis by producing necessary proteins and organelles.

Order and Function of Each Phase of Mitosis

Mitosis is the process by which a eukaryotic cell divides its nucleus and genetic material.

• Prophase: Chromatin condenses into visible chromosomes; spindle fibers form; nuclear envelope breaks down.

• Metaphase: Chromosomes align at the metaphase plate (center of the cell).

• Anaphase: Sister chromatids are separated and pulled to opposite poles by spindle fibers.

• Telophase: Chromosomes decondense; nuclear envelopes reform around each set of chromosomes.

• Cytokinesis: Division of the cytoplasm, resulting in two genetically identical daughter cells.

Major Differences Between Meiosis and Mitosis

Meiosis and mitosis are two types of cell division with distinct outcomes and purposes.

Distinction Between, and Examples of, Diploid and Haploid Cells

Cells can be classified based on the number of chromosome sets they contain.

• Diploid (2n): Cells with two sets of chromosomes (e.g., somatic/body cells in humans).

• Haploid (n): Cells with one set of chromosomes (e.g., gametes: sperm and egg cells).

• Example: Human skin cells are diploid (46 chromosomes); human sperm and egg cells are haploid (23 chromosomes).

Role of Gametes and Fertilization in the Reproductive Life Cycle

Sexual reproduction involves the formation of gametes and their fusion during fertilization.

• Gametes: Specialized haploid cells (sperm and egg) produced by meiosis.

• Fertilization: The process by which two gametes fuse to form a diploid zygote.

• Zygote: The first cell of a new organism, which undergoes mitosis to develop into a multicellular individual.

• Life cycle: Alternates between diploid and haploid stages in sexually reproducing organisms.

Summary Table: Key Terms and Their Functions

Key Equation: Chromosome Number in Gametes and Zygotes

The relationship between diploid and haploid chromosome numbers can be expressed as:

Where n is the haploid number and 2n is the diploid number.

Additional info: In humans, n = 23 and 2n = 46. Gametes (sperm and egg) each have 23 chromosomes; after fertilization, the zygote has 46 chromosomes.