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Unit III Study Notes: Cell Division, Genetics, and Gene Expression (Chapters 12–19)

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Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Chapter 12: Mitosis

Overview of Mitosis

Mitosis is the process by which eukaryotic cells divide to produce two genetically identical daughter cells. It is essential for growth, repair, and asexual reproduction.

  • Prokaryotic vs. Eukaryotic Cell Division: Prokaryotes divide by binary fission, a simpler process involving DNA replication and cell splitting. Eukaryotes undergo mitosis, which involves multiple phases and complex chromosome segregation.

  • Chromosome Structure: Chromosomes consist of DNA and associated proteins. Each chromosome is duplicated before mitosis, forming two sister chromatids joined at the centromere.

  • Phases of the Cell Cycle:

    • G1 Phase: Cell growth and preparation for DNA replication.

    • S Phase: DNA synthesis and chromosome duplication.

    • G2 Phase: Further growth and preparation for mitosis.

    • M Phase (Mitosis): Division of the nucleus and cytoplasm.

  • Stages of Mitosis:

    • Prophase: Chromosomes condense, spindle forms.

    • Metaphase: Chromosomes align at the cell equator.

    • Anaphase: Sister chromatids separate and move to opposite poles.

    • Telophase: Nuclear envelopes reform, chromosomes decondense.

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

  • Cell Cycle Checkpoints: Ensure proper division; prevent errors and uncontrolled growth (cancer).

  • Plant vs. Animal Cytokinesis: Plants form a cell plate; animals use a cleavage furrow.

  • Malignant vs. Benign Tumors: Malignant tumors invade tissues and metastasize; benign tumors do not.

Example: Skin cells use mitosis to replace damaged cells after injury.

Chapter 13: Meiosis

Overview of Meiosis

Meiosis is the process by which gametes (sperm and egg cells) are produced, reducing the chromosome number by half and introducing genetic diversity.

  • Purpose: To produce haploid cells for sexual reproduction.

  • Sister Chromatids vs. Homologous Chromosomes:

    • Sister chromatids: Identical copies of a chromosome.

    • Homologous chromosomes: Chromosomes with the same genes but possibly different alleles, one from each parent.

  • Crossing Over: Exchange of genetic material between homologous chromosomes during Prophase I, increasing genetic variation.

  • Phases of Meiosis:

    • Meiosis I: Homologous chromosomes separate.

    • Meiosis II: Sister chromatids separate.

  • Differences from Mitosis: Meiosis produces four non-identical haploid cells; mitosis produces two identical diploid cells.

  • Genetic Variation: Caused by crossing over and independent assortment.

Example: Human gametes (egg and sperm) are produced by meiosis.

Chapter 14: Mendel and Genetics

Basic Genetic Terminology

Genetics is the study of heredity and variation in organisms. Mendel's experiments established the principles of inheritance.

  • Key Terms:

    • Allele: Different forms of a gene.

    • Test Cross: Breeding to determine genotype.

    • Reciprocal Cross: Crosses with reversed parental traits.

    • Homozygous: Two identical alleles.

    • Heterozygous: Two different alleles.

    • Dominant/Recessive: Dominant alleles mask recessive ones.

    • Autosomal: Non-sex chromosomes.

    • Pedigree: Diagram of inheritance in families.

  • Mendelian Inheritance: Traits are inherited according to dominant and recessive alleles.

  • Quantitative Traits: Influenced by multiple genes (polygenic).

  • Linked Genes: Genes located close together on the same chromosome.

  • Punnett Squares: Used to predict offspring genotypes and phenotypes.

Example: A cross between two heterozygous pea plants (Yy) yields a 3:1 ratio of yellow to green seeds.

Punnett Square Example

GT

GT

GT

GGTT

GGTt

Gt

GGtT

GGtt

gT

GgTT

GgTt

gt

GgtT

Ggtt

Additional info: Table inferred from provided Punnett square diagram.

Chapter 15: DNA and the Gene

DNA Structure and Replication

DNA is composed of nucleotides connected by complementary base pairing (A-T, C-G). The Hershey-Chase experiment confirmed DNA as the genetic material.

  • Complementary Base Pairing: Adenine pairs with Thymine; Cytosine pairs with Guanine.

  • DNA Replication: Semi-conservative process involving DNA polymerase.

  • Telomerase: Enzyme that extends telomeres in certain cells (e.g., stem cells, cancer cells).

  • Mutation Prevention: DNA repair mechanisms correct errors during replication.

Example: DNA replication ensures genetic information is passed to daughter cells.

Chapter 16: How Genes Work

Gene Expression and the Central Dogma

The Central Dogma describes the flow of genetic information: DNA → RNA → Protein. Codons in mRNA specify amino acids; anticodons in tRNA match codons during translation.

  • Central Dogma:

  • Codons: Triplets of nucleotides in mRNA that code for amino acids.

  • Anticodons: Triplets in tRNA complementary to mRNA codons.

  • Transcription: Synthesis of RNA from DNA template.

  • Translation: Synthesis of protein from mRNA sequence.

  • Mutations: Changes in DNA sequence; can be point mutations, insertions, deletions, or chromosomal mutations.

Example: The codon AUG codes for methionine and serves as the start codon for translation.

DNA to Protein Example

DNA Template

Complementary DNA

mRNA

tRNA Anticodon

Amino Acid Sequence

CAT GCA GGT ATC AC

GTA CGT CCA TAG TG

GUA CGU CCA UAG UG

CAU GCA GGU AUC AC

GUA-valine, CGU-arginine, CCA-proline, UAG-stop

Additional info: Table constructed from provided answer key.

Chapter 17: Transcription, RNA Processing, and Translation

RNA Synthesis and Processing

Transcription is the process of synthesizing RNA from a DNA template. RNA processing modifies the primary transcript to produce mature mRNA.

  • RNA Polymerase: Enzyme that synthesizes RNA.

  • Promoters: DNA sequences where RNA polymerase binds to initiate transcription.

  • RNA Modification: Includes splicing, addition of 5' cap and poly-A tail.

  • Types of RNA:

    • mRNA: Messenger RNA, carries genetic code.

    • tRNA: Transfer RNA, brings amino acids to ribosome.

    • rRNA: Ribosomal RNA, forms ribosomes.

  • Translation: Occurs at ribosomes; involves A, P, and E sites for tRNA binding and peptide bond formation.

Example: Eukaryotic mRNA is processed before translation, unlike prokaryotic mRNA.

Chapter 18: Regulation of Gene Expression in Prokaryotes

Gene Regulation Mechanisms

Prokaryotes regulate gene expression primarily at the transcriptional level, often using operons such as the lac operon.

  • Lac Operon: Controls metabolism of lactose; regulated by repressor and activator proteins.

  • Benefits of Regulation: Conserves energy and resources by expressing genes only when needed.

Example: The lac operon is activated in the presence of lactose and absence of glucose.

Chapter 19: Control of Gene Expression in Eukaryotes

Complex Regulation in Eukaryotes

Eukaryotic gene expression is regulated at multiple levels: chromatin structure, transcription, RNA processing, and translation.

  • Chromatin Structure: DNA packaging affects gene accessibility.

  • Open/Closed Chromatin: Open chromatin is accessible for transcription; closed chromatin is not.

  • Alternative Splicing: Allows production of multiple proteins from one gene.

  • TATA Box: DNA sequence in promoter region; helps position RNA polymerase.

Example: Liver and muscle cells express different genes due to chromatin modifications and regulatory proteins.

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