BIO- DNA structure and Function

Fredrich Meischer

Isolated phosphate rich acidic compounds from the nuclei of leucocytes in pus hospital bandages, and called it Nuclein.

Fredrick Griffiths

Transforming Principle— Used strands of streptococcus pneumonia in rats (S and R) and injected mice with a heat-killed mixture of both, later concluding that something had transformed after recovering the S-Strain bacteria.

Oswald Avery Colin Macleod, and Maclyn McCarty

In 1944, they concluded that the Transforming Principe was most likely nucleic acids. they recovered the cell extracts of the S-Strain mice and used enzymes to degrade macromolecules. They mixed these extracts with the R-Strain and injected the mice.

Breaks lipids Down

Lipase

Breaks down Nucleic acids.

DNAse and RNAse

Breaks proteins down

Trypsin

Hershey and Chase

The Blender experiment— Injected bacteriophages with radiolabeled 25S for protein and 32P for DNA and blended the bacteria so that the phage was knocked off the host.

Erwin Chargaff

In 1950, he showed that A and T where the same amount, and C and G were also the same amount. He then concluded that DNA was comprised of four nucleotides: Adenine, Guanine, Thymine, and Cytosine.

Chargaff’s Rules

Equal % of A and T, Equal % of G and C

Structure of a nucleotide

Deoxyribose or Ribose, a nitrogenous base, and a phosphate group.

Roseland Franklin

In 1953 she concluded that DNA was a double-helix structure using a DNA diffraction patters of DNA. This discovery was later stolen from her by James Whatson and Francis Crick.

Structure of DNA

An antiparallel, double helix structure with alternating nucleotides linked by phosphodiester bonds and Hydrogen bonds. The double helix is formed by major and minor grooves used by binding proteins during transcription and replication. 

Matthew Meselson & Franklin Stahl

Proved that DNA replication is semiconservative, meaning each new DNA molecule consists of one original (parental) strand and one newly synthesized strand. They achieved this by using a heavy isotope of nitrogen 15𝑁 to label the DNA of E. coli bacteria, then transferring the bacteria to a medium with normal nitrogen 14N. After one replication cycle, the DNA was an intermediate density, supporting the semiconservative model

Conservative Strand

Original parent strand stays in tact, and a completely new strand is synthesized.

Semiconservative Strand

Parent strand breaks apart, acting as a template for the synthesizing strand.

Dispersive strand

The parent strand is broken into small pieces and incorporated into the new strand. 

Topoisomerase

Relieves additional coiling in DNA replication.

helicase

Unzips DNA in replication

single-stranded binding proteins

stabilizes the opened DNA and keeps it from re-binding during replication.

primase

Makes the DNA primer, and makes the starting point for DNA polymerase using RNA primer in DNA replication.

DNA polymerase

Synthesizes the new strand, from 3’ to 5’. Proofreads any possible errors.

Okazaki Fragment

The lagging strand of DNA replication when the DNA polymerase is on the 5’ to 3’ strand. Having to keep going backwards, resulting in fragments in the synthesized strand. 

ligase

Glues the Okazaki fragments together.

DNA Replication in Prokaryotes

Replicates their DNA in a circle, starting with the Origin point, with replication proceeding in both directions. The part where the DNA is being replicated is called 'Replication Forks' The two strands bud off each other from the 'Termination of Replication'

DNA Polymerase I

Replaces RNA primer with DNA

Mismatch Repair

The incorrect base that was added is detected after replication The mismatch repair proteins detect this and remove it from the strand using nuclease action The gap is then filled with a correct pair

Nucleotide Excision

Repairs Thymine dimers. When exposed to UV, thymie dimers lying adjacent to each other can form covalently linked thymine dimers In normal cells, these mutations are replaced

telomerase enzyme

Maintains the end of the chromosome

Elizabeth Blackborn

Discovered how telomerase works

Point Mutations

Silent, Missense, and Nonsense

Silent Mutation

no effect on protein sequence, codon swapped for another of the same amino acids.

Missense Mutation

Results in an amino acid substitutions

Nonsense

Substitutes a 'stop' codon for an amino acid.

Frameshift Mutation

Insertions or deletions may result in a shift in the reading frame or the insertion of the 'stop' codon

Chromosome Mutation

Insertions, deletions, translocations, inversions, fusions, and duplications