DNA

Chargaffs rules

Chargaffs rules

# of A = # of T, # of C = # of G

Shape of DNA

double helix , antiparallel strands (one runs 5’-3’, other is 3’-5’). sugar phosphate backbone w/ nitrogenous base interior

semiconservative DNA replication

each new strand will have one strand of DNA from the og molecule, and the other strand is built using that as a template

origins of replication

where DNA replication begins, forms a replication bubble as the two strands are seperated.

DNA in prokaryotes vs eukaryotes

prokaryotes: one single circular chromosome

eukaryotes: multiple linear chromosomes

helicase

enzymes that untwist the double helix at the replication forks, using hydrolysis to seperate base pairs

Single stranded binding proteins

bind to and stabilize single stranded DNA. prevent DNA from winding back into a double helix

topoisomerase

an enzyme that relieves the strain of twisting of the double helix by breaking, swiveling, and rejoining DNA strands

RNA primase

an enzyme that synthesizes the RNA primer for nucleotides to be added onto.

DNA polymerase III

catalyze the synthesis of new DNA at a replication fork, add nucleotides to 3’ end (can only add to DNA running 5’-3’)

leading strand

where DNA is continuously replicated, runs 5’-3’, occurs all at once.

lagging strand

DNA is replicated in segments (okazaki fragments) that are joined together by DNA ligase, runs 3’-5’

DNA ligase

joins together segments of DNA in the lagging strand via dehydration synthesis

DNA Polymerase I

an enzyme that removes RNA nucleotides from RNA primer from 5’ end and replaces them w/ DNA nucleotides added to the 3’ end.

mismatch repair

repair enzymes replace incorrectly paired nucleotides that have evaded the proofreading process

nucleotide excision repair

nuclease cuts out and replaces damaged stretches of DNA

importance of DNA mutations

source of the genetic variation upon which natural selection operates and are ultimately responsible for the appearance of new species

telomeres

postpone the erosion of genes near the ends of DNA molecules that occurs during DNA replication.

telomerase

an enzyme that catalyzes the lengthening of telomeres in germ cells to protect importat DNA

histones

proteins that are responsible for the main level of DNA packing in interphase chromatin

amino end of histone extends outwards and is involved in gene regulation.

nucleosomes

the “beads” on uncoiled chromatin. formed by wrapping DNA around a histone core.

euchromatin

Loosely packed chromatin

heterochromatin

highly condensed chromatin such as centrosomes and telomeres

James Watson and Francis Crick

Watson found X ray diffraction imagery produced by Maurice Wilkins colleague Rosalind Franklin. This showed the DNA had two strands when combined w/ their previous research, and made them realize it was a double helix. Watson also revealed that they are antiparallel. They also proved how purines and pyrimidines pair up due to their width. Explained chargaffs ratios.

Worked alongside Linus Pauling and Maurice Wilkins.

Wilkins, Watson, and Crick got nobel prizes, except rosalind who had already died

Fredrick Griffin

trying to develop vaccine against pnemonia, discovered that when he killed the pathogenic bacteria w/ heat and put them in living nonpathogenic bacteria, some of the living cells became pathogenic. he named this “transformation” (change in genotype and phenotype due to assimilation od external DNA by a cell)

T.H.Morgan

showed that genes exist as part of chromosomes. DNA and protein emerged as leading candidates for genetic material.

Oswald Avery, Maclyn McCarty, COlin MacLeod

identified the transforming subject of Griffiths experiments as DNA

bacteriophage/phages

“bacterio eater" viruses that infect bacteria.

virus

A little more than DNA or RNa enclosed by a usually protein protective coat, infects cells and take over the cells metabolic machinery to produce more viruses.

Alfred Hershey and Martha Chase

performed experiments showing that DNA was a genetic material of the T2 Phage. this infects e-coli and could somehow reprogram host cell to produce more viruses. unsure whether protein or DNA was responsible.

used radioactive sulfur isotope to tag protein in one batch of T2 and radioactive phosphorus to tag DNA. phosphorus only labeled DNa becayse most phosphorus in DNA. showed that phage DNA entered host cells from phage, but protein didnt. concluded that the DNA injected must be the genetic material to make cells produce more viral DNA.

Rosalind Franklin

said that hydrophobid nitrogenous bases in interior of DNA, sugar phosphate backbone on outside. her data indicated that the helix makes one full turn 0.34 mm along its length.

mehleson and stahl

showed that dna replicated in a semiconservative fashion instead of conservative or dispersive