Molecular Genetics - DNA Structure, Function, and History

Question 1

DNA location, function, structure, and longevity

Answer 1

• Located in the nucleus only (except meiosis and mitosis)
• Stores genetic info
• Made of deoxyribose sugar + A, T, C, G bases
• Usually double-stranded, double helix
• Very long (10^6 base pairs)
• Very stable, can survive thousands of years

Question 2

RNA location, function, structure, and longevity

Answer 2

• Made in nucleus, used in nucleus + cytoplasm
• Transfers DNA instructions to ribosomes
• Made of ribose sugar + A, U, C, G bases
• Usually single-stranded, single helix or other shapes
• Short (100s - 10^5) nucleotides
• Very fragile, easily broken down by enzymes, only last a few hours

Question 3

Johannes Friedrich Miescher contribution

Answer 3

Isolated nucleic acids from nucleus of white blood cells (pus from patient bandages) and called it “nuclein”

Question 4

Frederick Griffith contribution

Answer 4

• Used dead S and live R strains of pneumonia (R gained protective coating)
• Couldn’t identify material involved in inheritance
• Understood that some hereditary substance passed from S to R
• Called the process transformation, factor responsible was the transforming principle (either proteins or DNA)

Question 5

Avery, Macleod, + McCarty contribution

Answer 5

• DNA was the transforming substance
• Did not reveal due to possibly incorrect results (if some protein not destroyed by enzymes)
• More precise experiments required to confirm

Question 6

Hershey + Chase contributions

Answer 6

• DNA is indeed the carrier of genetic info
• Used radioisotopes to tag protein and DNA (DNA w/ phosphorus, protein w/ sulfur)
• Radioactivity only determined in bacteria colony infected by DNA tagged virus

Question 7

Phoebus Levene contribution

Answer 7

• Each DNA molecule contains 3 components: deoxyribose sugar, phosphate groups, and nitrogenous bases
• DNA is a polymer made of nucleotide subunits (each made of nitrogenous base attached to 1 deoxyribose sugar, which is connected to a phosphate group)
• Led to bases being identified in 1949: adenine and guanine (purines), thymine and cytosine (pyrimidines)

Question 8

Erwin Chargaff contribution

Answer 8

• Bases occur in definite ratios
• Quantities of A + T and G + C match

Question 9

Franklin + Wilkins contribution

Answer 9

• Used X-ray crystallography (combination of crystals and X-rays created a pattern of a photographic plate) to study shape of DNA molecule
• Sugar-phosphate backbones face outside of molecule, not inside
• DNA is a double helix, rotates in clockwise direction
• Molecule has a diameter of 2nm and one turn is 3.4 nm in length

Question 10

Watson + Crick contribution

Answer 10

• Used information determined by other researchers
• DNA is only stable if two strands run antiparallel
• 3’ end attaches to 5’ end of other strand, other strand must wind around the other
• Nitrogenous bases connected by hydrogen bonds
• Purine and pyrimidine base pairs linked to each other (T-A by 2 bonds, G-C by 3 bonds)
• Symmetry is key to structure and ability to divide accurately + convey genetic info