Study guide: Chromosomes and Molecular Biology

📋 Course Outline

1. DNA Discovery and Historical Experiments
2. Nucleotide Structure and DNA Strands
3. DNA Base Pairing and Stability
4. Semiconservative DNA Replication
5. Genetic Information Flow
6. DNA and RNA Comparison

📖 1. DNA Discovery and Historical Experiments

★ Must-know

• Friedrich Miescher first discovered DNA in 1869, isolating a phosphorus-containing material from white blood cell nuclei in pus and naming it “nuclein.”

• Griffith mixed heat-killed virulent bacteria with nonvirulent bacteria; some nonvirulent cells became virulent, and the injected mice died of pneumonia. - F. Griffith, 1928

• Hershey and Chase’s 1952 T2 bacteriophage blender experiment established that viral DNA enters bacterial cells and is required to synthesize new viral particles. - “Blender experiment”

Further detail

• In 1928, Griffith found that mice died after injection with virulent Streptococcus pneumoniae but survived injection with a nonvirulent strain. - F. Griffith

• Griffith’s transformation experiment suggested that genetic information remained in the heat-killed virulent bacteria. - F. Griffith, 1928

• Watson and Crick built a three-dimensional DNA model using Rosalind Franklin’s X-ray crystallography, Maurice Wilkins’s contributions, and Chargaff’s biochemical results.

📖 2. Nucleotide Structure and DNA Strands

🔑 Key Concepts & Definitions

• Nucleoside: Consists of a sugar and a base.

• Nucleotide: A nucleoside with one or more phosphate groups.

★ Must-know

📌 Bases can be added only to the sugar’s 3′-OH, so a DNA strand grows in the 5′-to-3′ direction.

Further detail

• Nucleotide sequences are read in the 5′-to-3′ direction, as illustrated by the sequence 5′-AGCT-3′.

• The C-O-P-O-C linkage is a covalent phosphodiester bond that can resist pH and temperature changes that may break weaker bonds.

💡 Memory Hook

A nucleoside is sugar plus base; adding phosphate makes a nucleotide.

📖 3. DNA Base Pairing and Stability

★ Must-know

• Chargaff’s rule states that DNA contains equal amounts of guanine and cytosine and equal amounts of adenine and thymine.

• Hydrogen bonds between bases on opposite DNA strands contribute to the stability of the double helix.

Further detail

• Interactions between bases on the same DNA strand result in base stacking.

📖 4. Semiconservative DNA Replication

🔑 Key Concepts & Definitions

• Mutation: An error in the installation of one or more bases during DNA replication.

★ Must-know

• In semiconservative replication, the DNA double helix unwinds and each original strand serves as a template for a new strand, producing two molecules that each contain one old and one new strand. - Meselson and Stahl, 1958

• Complementary base pairing preserves the fidelity of DNA replication.

Further detail

• DNA replication produces two new double helices that are copies of the original DNA molecule.

💡 Memory Hook

Picture each daughter helix carrying one old strand paired with one newly made strand.

📖 5. Genetic Information Flow

★ Must-know

• The central dogma describes the flow of genetic information from DNA to RNA to protein.

• Transcription uses DNA as a template to produce RNA, and translation uses RNA to produce proteins.

Further detail

• In eukaryotic cells, transcription occurs in the nucleus, and RNA is processed before entering the cytoplasm.

• In prokaryotes, transcription and translation occur more or less simultaneously.

• Certain RNA viruses use reverse transcription, allowing information to flow from RNA to DNA and then back to RNA and protein.

💡 Memory Hook

DNA → RNA → protein; some RNA viruses reverse the first arrow.

📖 6. DNA and RNA Comparison

★ Must-know

• DNA contains deoxyribose, whereas RNA contains ribose.

• DNA uses the bases adenine, thymine, cytosine, and guanine, whereas RNA uses adenine, uracil, cytosine, and guanine.

• DNA is very large and double-stranded, whereas RNA is smaller and single-stranded.

Further detail

📌 DNA has a monophosphate at its 5′ end, whereas RNA has a triphosphate at its 5′ end.

💡 Memory Hook

DNA uses thymine and deoxyribose; RNA uses uracil and ribose.

📊 Synthesis Tables

DNA and RNA Features

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Bases	A, T, C, G	A, U, C, G
5′ end	Monophosphate	Triphosphate
Size	Very large	Smaller
Strands	Double	Single