General Biology: Molecular Genetics, DNA Structure, Replication, and Biotechnology Study Guide

Molecular Genetics and DNA Structure

Griffith Transformation Experiment

The Griffith experiment demonstrated the phenomenon of transformation in bacteria, providing early evidence that genetic information could be transferred between organisms.

• Transformation: Harmless R (rough) bacteria became virulent S (smooth) bacteria after exposure to material from heat-killed S cells.

• Implication: Suggested the existence of a "transforming factor" responsible for heredity.

• Example: Streptococcus pneumoniae strains in mice.

Hershey & Chase Experiment

This experiment confirmed that DNA, not protein, is the hereditary material in cells.

• Method: Used bacteriophages labeled with radioactive isotopes: sulfur-35 (protein) and phosphorus-32 (DNA).

• Result: Only DNA entered bacterial cells and carried genetic information.

Differences Between DNA and RNA

DNA and RNA are nucleic acids with distinct structural and functional properties.

• Sugar: DNA contains deoxyribose; RNA contains ribose (extra –OH group).

• Bases: DNA uses A, T, C, G; RNA uses A, U, C, G (uracil replaces thymine).

• Strands: DNA is usually double-stranded; RNA is usually single-stranded.

• Stability: DNA is more chemically stable; RNA is less stable.

• Function: DNA stores genetic information; RNA transmits and acts on that information (e.g., mRNA, rRNA, tRNA).

Base Pairing Rules

Base pairing ensures accurate replication and transcription of genetic material.

• DNA: A pairs with T; G pairs with C.

• RNA: A pairs with U; G pairs with C.

• Watson & Crick: Discovered the double helix structure and base pairing rules.

Differences in DNA and RNA Bases

DNA and RNA differ in one nitrogenous base.

• DNA: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).

• RNA: Adenine (A), Uracil (U), Cytosine (C), Guanine (G).

DNA Structure and Discovery

The double helix model of DNA was proposed by Watson and Crick, based on X-ray diffraction data.

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

• X-ray Diffraction: Rosalind Franklin's images provided key structural information.

DNA Replication

DNA replication is a semi-conservative process, producing two identical DNA molecules from one original molecule.

• Process: Parental DNA strands separate; each serves as a template for a new strand.

• Enzyme: DNA polymerase synthesizes new DNA by adding nucleotides to the 3' end.

• Proofreading: DNA polymerase has 3'→5' exonuclease activity to correct errors.

• Equation: $\text{(dNMP)}_n + dNTP \rightarrow \text{(dNMP)}_{n+1} + PP_i$

Transcription and Translation

Transcription

Transcription is the process by which RNA is synthesized from a DNA template.

• Stages: Initiation, elongation, termination.

• Enzyme: RNA polymerase.

• Product: mRNA, tRNA, or rRNA.

Translation

Translation is the synthesis of proteins from mRNA in the ribosome.

• Stages: Initiation, elongation, termination.

• Genetic Code: Triplet codons specify amino acids.

• Equation: $\text{mRNA} + \text{ribosome} + \text{tRNA} \rightarrow \text{polypeptide}$

Introns and Exons

Genes in eukaryotes contain coding (exons) and non-coding (introns) regions.

• Exon: Coding sequence retained in mature mRNA.

• Intron: Non-coding sequence removed by RNA splicing.

DNA Technology and Biotechnology

Restriction Enzymes

Restriction enzymes cut DNA at specific sequences, enabling genetic engineering.

• Recognition Site: Short, palindromic DNA sequences.

• Application: Cloning, gene mapping, DNA fingerprinting.

Polymerase Chain Reaction (PCR)

PCR is a technique to amplify specific DNA sequences exponentially.

• Steps: Denaturation, primer annealing, extension.

• Equation: $\text{DNA}_{\text{template}} + \text{primers} + \text{polymerase} \rightarrow \text{amplified DNA}$

DNA Sequencing

DNA sequencing determines the exact order of nucleotides in a DNA molecule.

• Methods: Sanger sequencing, next-generation sequencing.

• Applications: Genomics, medicine, evolutionary biology.

Genomics and the Human Genome Project

Genomics is the study of whole genomes, including gene mapping and sequencing.

• Human Genome Project: International effort to sequence the entire human genome.

• Applications: Medicine, agriculture, biotechnology.

Genetic Engineering and CRISPR

Genetic engineering involves modifying DNA using tools like CRISPR.

• CRISPR: Clustered Regularly Interspaced Short Palindromic Repeats; enables precise gene editing.

• Applications: Disease treatment, crop improvement, research.

Mutations and DNA Repair

Types of Mutations

Mutations are changes in DNA sequence that can affect gene function.

• Silent Mutation: No change in amino acid sequence.

• Missense Mutation: Changes one amino acid to another.

• Nonsense Mutation: Converts a codon to a stop codon, truncating the protein.

• Frameshift Mutation: Insertion or deletion not in multiples of three, altering downstream amino acids.

DNA Repair Mechanisms

Cells have mechanisms to correct DNA damage and maintain genetic integrity.

• Mismatch Repair: Fixes base-pair mismatches and small insertions/deletions.

• Nucleotide Excision Repair: Removes bulky lesions (e.g., thymine dimers).

Gene Expression and Regulation

Gene Regulation

Gene expression is controlled at multiple levels, including transcription, translation, and post-translational modification.

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

• Enhancers: Regulatory sequences that increase transcription rates.

• Epigenetics: Heritable changes in gene expression not involving changes in DNA sequence (e.g., DNA methylation).

Applications and Ethical Considerations

Biotechnology Applications

Biotechnology uses biological systems for practical purposes in medicine, agriculture, and research.

• Examples: Recombinant DNA, gene therapy, genetically modified organisms (GMOs).

Safety and Ethics

Biotechnology raises important safety and ethical questions.

• Concerns: Biosafety, environmental impact, labeling, consent, privacy, and risk-benefit assessment.

• Example: Gene flow to wild species, long-term health effects, ethical limits on gene editing.

HTML Table: Types of RNA and Their Functions

Type of RNA	Function
mRNA (messenger RNA)	Carries genetic information from DNA to ribosome for protein synthesis
tRNA (transfer RNA)	Brings amino acids to ribosome; matches codon with anticodon
rRNA (ribosomal RNA)	Structural and catalytic part of ribosome
snRNA (small nuclear RNA)	Involved in splicing of pre-mRNA
miRNA/siRNA (micro/small interfering RNA)	Regulate gene expression; RNA interference

HTML Table: Types of Mutations

Mutation Type	Description
Silent	No change in amino acid sequence
Missense	Changes one amino acid to another
Nonsense	Converts codon to stop codon
Frameshift	Insertion/deletion not in multiples of three

Additional info:

• Some context and definitions were expanded for clarity and completeness.

• Tables were inferred and organized for study purposes.