Cellular Reproduction, Gene Expression, and Regulation – Study Notes

Cellular Reproduction: Mitosis & Meiosis

Overview of Cell Division

Cellular reproduction is essential for growth, repair, and reproduction in living organisms. The two main types of cell division are mitosis and meiosis, each serving distinct biological purposes.

• Mitosis: Produces two genetically identical diploid cells for growth and repair.

• Meiosis: Produces four genetically unique haploid gametes for sexual reproduction.

Key Terms and Concepts

• Chromosome: A DNA molecule with associated proteins, carrying genetic information.

• Chromatid: One of two identical halves of a duplicated chromosome.

• Centromere: The region where sister chromatids are joined and spindle fibers attach.

• Homologous Chromosomes: Chromosome pairs with genes for the same traits, one from each parent.

• Diploid (2n): Cells with two sets of chromosomes.

• Haploid (n): Cells with one set of chromosomes (gametes).

• Cell Cycle: The sequence of growth (G1), DNA synthesis (S), preparation (G2), and division (M phase).

• Interphase: The cell grows and replicates DNA (G1, S, G2 phases).

• Prophase, Metaphase, Anaphase, Telophase: Stages of mitosis and meiosis.

• Cytokinesis: Division of the cytoplasm, forming two cells.

• Synapsis: Pairing of homologous chromosomes during meiosis I.

• Crossing-over: Exchange of genetic material between homologous chromosomes, increasing genetic diversity.

• Independent Assortment: Random distribution of homologous chromosomes during meiosis I.

Comparison of Mitosis and Meiosis

Feature	Mitosis	Meiosis
Number of Divisions	1	2
Number of Daughter Cells	2	4
Genetic Identity	Identical	Unique
Chromosome Number	Diploid (2n)	Haploid (n)
Role	Growth, repair	Gamete production

DNA Structure and Replication

DNA Structure

DNA is a double helix composed of nucleotides, each containing a phosphate group, deoxyribose sugar, and a nitrogenous base (adenine, thymine, cytosine, guanine).

• Antiparallel Strands: DNA strands run in opposite directions (5' to 3' and 3' to 5').

• Complementary Base Pairing: Adenine pairs with thymine, cytosine pairs with guanine.

DNA Replication

• Semiconservative Replication: Each new DNA molecule consists of one old and one new strand.

• Enzymes: DNA helicase unwinds the helix; DNA polymerase synthesizes new strands; ligase joins fragments.

• Leading and Lagging Strands: Leading strand synthesized continuously; lagging strand synthesized in Okazaki fragments.

Gene Expression and Regulation

Central Dogma of Molecular Biology

Genetic information flows from DNA to RNA to protein.

• Transcription: Synthesis of RNA from a DNA template.

• Translation: Synthesis of protein from an mRNA template.

Types of RNA

• mRNA (messenger RNA): Carries genetic code from DNA to ribosome.

• tRNA (transfer RNA): Brings amino acids to the ribosome during translation.

• rRNA (ribosomal RNA): Structural and catalytic component of ribosomes.

Gene Regulation

• Promoter: DNA sequence where RNA polymerase binds to initiate transcription.

• Operator: Segment of DNA that regulates gene expression in prokaryotes (e.g., lac operon).

• Repressor: Protein that binds to the operator to block transcription.

• Inducer: Molecule that inactivates the repressor, allowing gene expression.

Mutations

• Point Mutation: Change in a single nucleotide.

• Frameshift Mutation: Insertion or deletion that alters the reading frame.

• Silent, Missense, Nonsense Mutations: Types of point mutations with different effects on protein sequence.

Review Checklist

• Be able to describe and illustrate the three major RNA molecules involved in protein synthesis.

• Understand the differences between prokaryotic and eukaryotic gene regulation.

• Be able to describe the differences between mitosis and meiosis (including the role of crossing-over and independent assortment).

• Understand the structure and function of DNA and the process of DNA replication.

• Be able to describe the different types of mutations and their effects on gene function.

Additional info: The above content is expanded from the provided review terms and checklist, with academic context added for clarity and completeness.