Ch. 9: Molecular structure of DNA and RNA

the central dogma

• the flow of biological information

• DNA —→ RNA —→ Protein

eukaryotic DNA

• linear and organized into chromosomes

tertiary structure

• the complex packaging of DNA (chromatin)

nucleosome

• DNA wrapped around histone proteins

primary structure

• string of nucleotides joined together by phosphodiester linages

• order of nucleotides

secondary structure

• DNA’s stable 3-D structure

DNA structure

• two complimentary and antiparallel strands that from a double helix

nucleic acids

• linear molecules made up of repeating subunits

nucleotide

• contains a phosphate, a nitrogenous base, and a ribose or deoxyribose

phosphodiester bonds

• what covalently links nucleotides together

deoxyribonucleic acid

• lacks O on the pentose sugar (only has H)

ribonucleic acid

• has O on pentose sugar (has OH)

purines

• double ringed

• adenine and guanine

pyrimidines

• single ringed

• thymine, uracil, cytosine

3

• number of bonds between G and C

2

number of bonds between A and T

hydrogen bonds

• type of bonding that occurs between base pairs

• low energy bonds

• they stabilize the molecule but can be disrupted by enzymes or with the input of energy

3’ to 5’

• since strands run in anti parallel directions, if one side runs 5’ to 3’3 the other side must run

secondary structures

• how RNA stabilizes itself

• folds on itself by finding complimentary base pairing

bulge loop

internal loop

multibranched loop

stem loop

factors contributing to tertiary structure of RNA

• base paring and base stacking within the RNA itself

• interactions with ions, small molecules and large proteins

criteria genetic material must meet to fulfill its role

• information: it must contain the information necessary to make an entire organism

• transmission: it must be passed from parent to offspring

• replication: it must be copied in order to be passed from parent to offspring

• variation: it must be capable of changes to account for the known phenotype variation in each species

principle of transformation

• discovered by Griffith in 1928

• he isolated two strains of Streptococcus pneumoniae

• One strain was virulent (disease-causing) and had polysaccharide coat that made the colonies appear smooth (IIIS)

• Virulent forms occasionally mutated into non-virulent forms and lost the polysaccharide coat and appeared to be rough (IIR)

• he injected live mice with Streptococcus pneumoniae

• Smooth (type IIIS): mouse dies

  • virulent bacteria recovered

• Rough (type IIR): mouse lives

  • no bacteria recovered

• Heat killed smooth (type IIIS): mouse lives

  • no bacteria recovered

• Heat killed Smooth (type IIIS) mixed with Rough (type IIR): mouse dies

  • virulent bacteria recovered

transforming principle

• Avery, McCloud, and McCarthy 1944

• only DNA had the ability to transform

confirmation the DNA is the genetic material

• Hershey and Chase

• Used Bacteriophage T2 (infects E. coli)

• radioactively labeling molecules us a common technique to track molecule of interest

• Hershey-Chase incorporates:

  • Radioactive P in DNA

  • Radioactive S in proteins

Chargaff’s rule

• found that amounts of the four bases varied between species but their ratios did not

• adenine = thymine

• guanine = cytosine

X-ray diffraction of DNA fibers

• Rosalind Franklin

• studies wet fibers of DNA

• a diffraction pattern is interpreted to provide information concerning the structure of molecule

three-dimensional structure of DNA

• James Watson and Francis Crick in 1953

• used existing data (including Rosalind Franklin’s) molecule models and knowledge of structural chemistry

• Watson recognized and adenine could bond with a thymine and a guanine could bond with a cytosine