Chapter 10 DNA structure and Analysis

• replicate
• store information
• express information
• allow variation by mutation

• 1940s many geneticists favored proteins
• proteins are more diverse and abundant in cells
• subject of the most active areas of genetic research, with more known about proteins than nucleic acid
• DNA was thought of as too simple to be genetic material and only four types of nucleotides compared to 20 different amino acids

• showed that avirulent strains of Diplococcus pneumoniae could be transformed to virulence
• speculated that the transforming principle could be part of the polysaccharide capsule or a compound required for capsule synthesis

• smooth colony
• virulent

• avirulent
• rough colony

demondstared that the transforming principle was DNA and not protein

• using E.coli and an infecting virus (bacteriophage T2) demonstrated DNA and not protein was genetic material
• used radioisotope 32P and 35S
• demonstrated that DNA enters the bacterial cell during infection and directs viral reproduction

• process of infection by viral DNA into bacterial cells
• proved conclusively that the viral DNA alone contains all the necessary information for production of mature viruses

• DNA and RNA absorb UV light most strongly at 260 nm and UV light is capable of inducing mutations in genetic material at 260 nm
• This provided strong indirect evidence for DNA as genetic material

• strongest direct evidence for DNA as the genetic material
• segments of eukaryotic DNA corresponding to specific genes are isolated and spliced into the bacterial DNA
• complex can be inserted into a bacterial cell and monitored

demonstrates that RNA serves as the genetic material for these viruses (some viruses have a RNA core instead of a DNA core)

replication of viral RNA

• Retroviruses replicate in this unusual way
• RNA serves as template for synthesis of complementary DNA by the RNA dependent DNA polymerase
• DNA is incorporated into the host cell genome; when transcribe, copies of the original retroviral RNA chromosomes are also produced

• building blocks of DNA
• Consist of nitrogenous base, pentose sugar, and phosphate group

• Adenine and Guanine
• Bicyclic compounds
• Both have an amine group
• Guanine has a carbonyl

• Cytosine, Thymine and Uracil
• Cytosine = one amine group and carbonyl
• Uracil = two carbonyl groups
• Thymine = two carbonyls and a methyl group

• contains the nitrogenous base and the pentose sugar
• MISSING PHOSPHATE

nucleoside with a phosphate group added

Carbon 5

• their naming system
• ex. NMPs, NDPs, NTPs

• this is how nucleotides are linked to each other
• they are linked at the carbon 5 and the OH group on the carbon 3 group

• showed that the amount of A is proportional to T and the amount of C is proportional to G
• however percentage of CG is not necessarily equal to the percentage of AT

• studies by Rosalind Frankllin
• DNA showed 3.4 angstrom periodicity
• characteristic of helical structure

• proposed that DNA is a right-handed double helix in which two strands are antiparallel and the bases are stacked
• two strands are connected by AT and GC pairing and there are 10 base pairs per helix turn

two bonds

three bonds

• slightly more compact than B DNA
• prevalent under high-salt or dehydration conditions
• doubtful that it occurs in vivo

• seen under aqueous, low-salt conditions and is believed to be the biologically significant conformation
• more compact that C DNA, D DNA, E DNA, and P DNA

forms a left-handed double helix

• messenger RNA (mRNA)
• ribosomal RNA (rRNA) makes up 80%
• transfer RNA (tRNA)

structural components of ribosomes for protein synthesis

template for protein synthesis

carry amino acids for protein synthesis

gradient centrifugation procedures

• separates by density gradient
• bouyancy

measures the velocity of sedimentation in Svedberg coefficient units

• during DNA denaturation
• used to determine the melting temperature (Tm)

method for estimating the base composition of DNA

• denaturation and renaturation of nucleic acids
• increased understanding of gene transcription
• refinements have helped advance study of molecular evolution and organization of DNA in chromosomes

• uses fluorescent probes to monitor hybridization
• can be used to identify the chromosomal location of a DNA of interest
• ex. DNA specific to the centromeres of human DNA

• analyzes rate of reassociation of complementary single DNA strand
• provides information about he size and complexity of genomic DNA from an organism

separates RNA and DNA fragments by size such that smaller fragments migrate through a gel at a faster rate than large fragments