DNA History, Structure, and Replication Quiz Review

T.H. Morgan (1908)

determined that DNA is the genetic material

Frederick Griffith (1928)

• demonstrated transformation

• suggested that a “transforming factor” within heat-killed bacteria could still transmit disease-causing properties

Oswald Avery, Maclyn McCarty, & Colin MacLeod (1944)

• injected purified DNA into harmless bacteria → transforming them into virulent bacteria

• while… protein had no effect

Erwin Chargaff

• determined Chargaffs rules

• base pairs exist in about the same concentrations

Alfred Hershey & Martha Chase

• Conducted the “blender” experiment

• bacteriophage labeled with radioactive sulfur (35S in protein) and phosphorus (32P in DNA)

• confirmed DNA carried viral genetic information

Rosalind Franklin & Maurice Wilkins

their photographs helped Watson and Crick develop a 3D double-helical structure of DNA

James Watson & Francis Crick

• developed the double-helical model for DNA

• The structure explained the basis of Chargaff’s rules

• Each strand serves as a template for a new strand

Meselson & Stahl

• discovered that DNA replication follows the semi-conservative model

• used heavy/light nitrogen to label new/parent nucleotides

DNA

the primary source of heritable information

RNA

a strand of genetic material that codes for protein synthesis

Specific Nucleotide Base Pairing

DNA (and sometimes RNA) exhibits specific pairing conserved through evolution: Adenine pairs with Thymine (A-T) or Uracil (A-U), and Cytosine pairs with Guanine (C-G)

Purines

• double ring structure

• Adenine (A) and Guanine (G)

Pyrimidines

• single ring structure

• Thymine (T), Uracil (U), and Cytosine (C)

Prokaryotic Chromosomes

circular chromosomes

Eukaryotic chromosomes

multiple linear chromosomes

Plasmids

Small extrachromosomal, double-stranded, circular DNA molecules found in both prokaryotes and eukaryotes

Double Helix Orientation

• anti-parallel orientation

  • one strand 5’ to 3’

  • the other 3’ to 5’

• DNA strands held together by hydrogen bonding between the nitrogenous bases

Central Dogma

• The flow of genetic information in a cell: DNA → RNA → Protein

• DNA also undergoing replication

Semiconservative Replication

one strand of the parental double helix separates and serves as the template for synthesis of a new complementary strand

Direction of Synthesis

New DNA is made from 5’ toward 3’

Helicase

• “unzips” the DNA

• Unwind the DNA strands at the replication fork

Topoisomerase

the enzyme that relaxes the supercoiling of the DNA in front of the replication fork

Primase

and enzyme that lays down a segment of RNA primer to initiate the synthesis of a new DNA strand

DNA Polymerase 3

an enzyme that “adds” the complementary base pairs to the new DNA strand

DNA Polymerase 1

an enzyme that replaces the RNA primers once neighboring base pairs are added

Leading Strand

The new strand of DNA that is synthesized toward the replication fork/3’ end

Lagging Strand

The new strand of DNA that is synthesised away from the replication fork/5’end

Okazaki Fragments

The short DNA segments synthesized on the lagging strand

DNA Ligase

an enzyme that “glues” the Okazaki fragments and replaced RNA primers to the base pair complement strands

Telomeres

• at the ends of chromosomes made of repetitive DNA sequences (junk DNA) that shorten with each cell division

• allows somatic cells to divide only 20-50 times

Telomerase

• an enzyme that extends telomeres

• present in cancer cells, allowing them to divide an infinite number of times

nucleosome