BIOL 190A Final Exam Study Guide: DNA, Gene Expression, and Cell Division

Chapters 9-12 Review: Cell Cycle, Meiosis, and Genetics

Cell Cycle and Mitosis

The cell cycle is the series of events that cells go through as they grow and divide. Understanding the timing of DNA replication and chromosome configuration is essential for interpreting cell division.

• Phases: G1 (growth), S (DNA synthesis), G2 (preparation for mitosis), M (mitosis and cytokinesis).

• DNA Replication: DNA amount doubles during the S phase.

• Mitosis Stages: Prophase, Metaphase, Anaphase, Telophase.

• Chromosome Counting: Chromatids are counted as individual DNA molecules; chromosomes are counted by centromeres.

• Example: During metaphase, each chromosome consists of two sister chromatids.

Meiosis and Sexual Life Cycles

Meiosis is the process by which gametes (sperm and egg) are produced, reducing chromosome number by half to maintain species stability across generations.

• Stages: Meiosis I (homologous chromosomes separate), Meiosis II (sister chromatids separate).

• DNA Content: DNA is doubled before meiosis I, then halved after each division.

• Chromosome Configuration: Homologous pairs align in metaphase I; sister chromatids align in metaphase II.

• Role: Ensures genetic diversity and stable chromosome number in offspring.

Genetics and Mendelian Laws

Genetics explores how traits are inherited. Mendel's laws explain the patterns of inheritance observed in organisms.

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

• Monohybrid Cross: 3:1 phenotypic ratio in F2 generation.

• Dihybrid Cross: 9:3:3:1 phenotypic ratio in F2 generation.

• Mendel’s Laws: Law of Segregation and Law of Independent Assortment relate to chromosome behavior in meiosis.

• Exceptions: Incomplete dominance, codominance, multiple alleles, polygenic inheritance.

Pedigree Analysis

Pedigrees are diagrams that show inheritance patterns across generations.

• Autosomal Dominant: Trait appears in every generation.

• Autosomal Recessive: Trait can skip generations.

• X-linked Recessive: More common in males; affected males often have carrier mothers.

• Assigning Genotypes: Use patterns to deduce possible genotypes of individuals.

Chapter 13: DNA Structure, Replication, and Technology

History of DNA Discovery

The discovery of DNA's role and structure involved several key experiments and researchers.

• Griffith: Discovered transformation in bacteria.

• Chargaff: Found base pairing rules (A=T, G=C).

• Hershey & Chase: Demonstrated DNA is genetic material using bacteriophages.

• Watson & Crick: Proposed the double helix model.

• Franklin: Provided X-ray diffraction images crucial for double helix model.

• Meselson & Stahl: Showed DNA replication is semiconservative.

DNA Structure

• Double Helix: Two antiparallel strands held by hydrogen bonds between complementary bases.

• Nucleotide: Consists of a phosphate group, deoxyribose sugar, and nitrogenous base.

• Bonds: Phosphodiester bonds (backbone), hydrogen bonds (between bases).

DNA Replication

• Replication Bubble and Forks: Sites where DNA unwinds for replication.

• Leading Strand: Synthesized continuously.

• Lagging Strand: Synthesized in Okazaki fragments.

• RNA Primers: Short RNA sequences that initiate DNA synthesis.

• Enzymes: DNA polymerase, helicase, primase, ligase.

• Prokaryotic vs Eukaryotic Replication: Prokaryotes have a single origin; eukaryotes have multiple origins.

• Proofreading and Repair: DNA polymerase corrects errors; repair enzymes fix mismatches.

• End Replication Problem: Eukaryotic chromosomes shorten; telomeres and telomerase help prevent loss of genetic information.

Chromatin Organization

• Levels: DNA wraps around histones to form nucleosomes; further coiling forms chromatin fibers and chromosomes.

• Structural Proteins: Histones and scaffolding proteins maintain structure and regulate gene accessibility.

DNA Technology

• Recombinant DNA: Combining DNA from different sources using cloning vectors (e.g., plasmids).

• Transgenic Organisms: Organisms with foreign genes inserted.

• PCR (Polymerase Chain Reaction): Amplifies DNA using Taq polymerase.

• DNA Fingerprinting: Identifies individuals based on unique DNA patterns.

• DNA Sequencing: Determines the order of nucleotides in DNA.

• CRISPR: Genome editing tool (general knowledge only).

Chapter 14: Gene Expression and the Genetic Code

Central Dogma and Flow of Genetic Information

The Central Dogma describes the flow of genetic information: DNA → RNA → Protein.

• Prokaryotes: Transcription and translation occur in the cytoplasm, often simultaneously.

• Eukaryotes: Transcription occurs in the nucleus; translation in the cytoplasm.

Transcription

• Steps: Initiation, elongation, termination.

• Polarity: RNA synthesized 5' to 3' from DNA template (3' to 5').

• Types of RNA: mRNA (messenger), tRNA (transfer), rRNA (ribosomal).

• Prokaryotes vs Eukaryotes: Eukaryotes have more complex regulation and RNA processing.

RNA Processing in Eukaryotes

• 5' Cap: Modified guanine added to 5' end.

• Poly-A Tail: Adenine nucleotides added to 3' end.

• Splicing: Removal of introns (non-coding regions); exons (coding regions) joined.

Translation

• Steps: Initiation, elongation, termination.

• Ribosome Binding Sites: A (aminoacyl), P (peptidyl), E (exit).

• Polarity: Polypeptide synthesized from N-terminus (amino) to C-terminus (carboxyl).

• Protein Processing: Folding and modification occur in the cytoplasm or endoplasmic reticulum.

Properties of the Genetic Code

• Triplet Code: Three nucleotides (codon) specify one amino acid.

• Redundancy: Multiple codons can code for the same amino acid.

• Universality: Code is nearly universal among organisms.

Mutations

• Classification by Scale: Point mutations (single base), chromosomal mutations (large segments).

• By Cell Type: Somatic (non-inheritable), germline (inheritable).

• Types of Point Mutations: Silent (no change in amino acid), missense (change in amino acid), nonsense (introduces stop codon), frameshift (insertion/deletion alters reading frame).

Chapter 15: Regulation of Gene Expression

Prokaryotic Gene Regulation: Operons

Operons are clusters of genes under the control of a single promoter, allowing coordinated regulation in bacteria.

• Main Components: Promoter, operator, structural genes, regulatory gene.

• Repressible Operon (Trp Operon): Usually on; can be turned off by a repressor (tryptophan acts as corepressor).

• Inducible Operon (Lac Operon): Usually off; can be turned on by an inducer (allolactose).

• Negative Control: Repressor protein inhibits transcription.

• Positive Control: Activator protein (e.g., CAP-cAMP) enhances transcription.

Eukaryotic Gene Regulation

• Differences from Prokaryotes: More complex, involves chromatin structure and multiple regulatory elements.

• Chromatin Modification: Acetylation and methylation of histones affect gene accessibility.

• Combinatorial Control: Multiple transcription factors and regulatory sequences determine gene expression patterns.

Chapter 16: Cloning, Stem Cells, and Cancer

Types of Cloning

• Cell Cloning: Producing identical cells from a single cell.

• Gene Cloning: Making multiple copies of a gene.

• Organismal Cloning: Creating a genetically identical organism (e.g., Dolly the sheep).

• Therapeutic Cloning: Producing embryonic stem cells for medical treatment.

Types of Stem Cells

• Embryonic Stem Cells: Pluripotent; can become any cell type. Types include totipotent (can form all cell types, including placenta) and pluripotent (all body cells).

• Adult Stem Cells: Multipotent; limited to certain cell types.

• Induced Pluripotent Stem Cells (iPS): Adult cells reprogrammed to pluripotency.

Molecular Basis of Cancer

• Proto-oncogenes: Normal genes that promote cell growth; mutations can convert them to oncogenes (cancer-causing).

• Oncogenes: Mutated genes that drive uncontrolled cell division.

• Types of Mutations: Point mutations, gene amplification, chromosomal translocation.

• RAS Mutations: Lead to constant cell signaling and division.

• Tumor-Suppressor Genes: Inhibit cell division; mutations inactivate these brakes (e.g., p53 gene).

• Cumulative Effects: Multiple mutations accumulate in genes regulating cell cycle, leading to cancer (e.g., colorectal and breast cancer models).