BIOL 190A 1001 Final Exam Study Guide: Molecular Genetics, Gene Expression, and Genomics

DNA: History, Structure, and Replication

Discovery of DNA and Its Structure

The discovery of DNA as the genetic material and its structure was a pivotal moment in biology. Key experiments and scientists contributed to our understanding of DNA's role in heredity.

• Key Contributors: Chargaff, Hershey & Chase, Watson & Crick, Franklin, Meselson & Stahl

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

• Base Pairing: Adenine pairs with thymine, and cytosine pairs with guanine via hydrogen bonds.

Example: The Hershey-Chase experiment used bacteriophages to confirm that DNA, not protein, is the genetic material.

DNA Replication

DNA replication is the process by which a cell copies its DNA before cell division. It is semi-conservative, meaning each new DNA molecule contains one old and one new strand.

• Meselson and Stahl Experiment: Demonstrated the semi-conservative nature of DNA replication using isotopic labeling.

• Replication Bubble: Replication begins at origins, forming bubbles where DNA is unwound.

• Leading and Lagging Strands: DNA polymerase synthesizes the leading strand continuously and the lagging strand in Okazaki fragments.

• Key Enzymes:

  • Helicase: Unwinds DNA

  • Primase: Synthesizes RNA primers

  • DNA Polymerase: Adds nucleotides

  • Ligase: Joins Okazaki fragments

• Prokaryotic vs. Eukaryotic Replication: Eukaryotes have multiple origins of replication and more complex regulation.

Equation:

$\text{DNA}_{\text{parent}} \xrightarrow{\text{replication}} \text{DNA}_{\text{daughter}}$

Chromatin and Chromosomes

• Chromatin: DNA wrapped around histone proteins, forming nucleosomes.

• Chromosome Structure: Chromatin condenses to form chromosomes during cell division.

DNA Technology and Genomics

DNA Technology Techniques

Modern biology uses various techniques to manipulate and analyze DNA.

• PCR (Polymerase Chain Reaction): Amplifies specific DNA sequences.

• Cloning Vectors: Used to insert DNA into host cells for replication or expression.

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

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

• Genome Editing (CRISPR): Allows targeted modification of genes.

Gene Expression: From Gene to Protein

Transcription and Translation

Gene expression involves two main processes: transcription (DNA to RNA) and translation (RNA to protein).

• Transcription: Synthesis of RNA from a DNA template by RNA polymerase.

• Translation: Synthesis of a polypeptide at the ribosome, using mRNA as a template.

• Genetic Code: Triplet codons in mRNA specify amino acids.

• Prokaryotic vs. Eukaryotic Gene Expression: Eukaryotes process pre-mRNA (splicing, capping, polyadenylation); prokaryotes do not.

Equation:

$\text{DNA} \xrightarrow{\text{transcription}} \text{mRNA} \xrightarrow{\text{translation}} \text{Protein}$

Mutations

• Types: Point mutations (single nucleotide changes), insertions, deletions.

• Effects: Silent, missense, nonsense mutations; frameshifts can alter protein function.

Regulation of Gene Expression

Prokaryotic Gene Regulation

• Operons: Clusters of genes regulated together (e.g., lac operon).

• Regulatory Elements: Promoters, operators, repressors, and inducers control transcription.

• Example: The lac operon is regulated by the presence or absence of lactose and glucose.

Eukaryotic Gene Regulation

• Levels of Regulation: Chromatin structure, transcription factors, RNA processing, mRNA stability, translation, and protein modification.

• Cell Differentiation: Gene regulation leads to specialized cell types during development.

Development, Stem Cells, and Cancer

Development of Multicellular Organisms

• Cell Differentiation: Cells become specialized through gene expression changes.

• Stem Cells: Undifferentiated cells with the potential to become various cell types.

• Pattern Formation: Spatial organization of tissues and organs during development.

Cancer

• Oncogenes: Mutated genes that promote uncontrolled cell division.

• Tumor Suppressor Genes: Genes that normally inhibit cell division or cause apoptosis.

• Mutations: Accumulation of mutations in key genes can lead to cancer.

Viruses

Structure and Function

• Basic Structure: Genetic material (DNA or RNA) enclosed in a protein coat (capsid); some have envelopes.

• Replication: Viruses infect host cells and use host machinery to replicate.

• Genetic Variation: High mutation rates and recombination contribute to viral diversity.

Genomes and Their Evolution

Genomics and Bioinformatics

• Genomics: Study of whole genomes, including sequencing, mapping, and analysis.

• Bioinformatics: Use of computational tools to analyze genetic data.

• Genome Size and Diversity: Genome size and gene content vary widely among organisms.

Sample Table: Types of Mutations

Type of Mutation	Description	Effect on Protein
Silent	Change in nucleotide does not alter amino acid	No effect
Missense	Change in nucleotide alters amino acid	May affect protein function
Nonsense	Change in nucleotide creates a stop codon	Premature termination of protein
Frameshift	Insertion or deletion shifts reading frame	Usually nonfunctional protein

Additional info: These notes are based on a final exam study guide and cover core topics in molecular genetics, gene expression, genomics, and related areas as outlined in the General Biology curriculum.