Please enable JavaScript.
Coggle requires JavaScript to display documents.
chapter 16 (DNA replication how DNA is copied and how cells repair their…
chapter 16
DNA replication how DNA is copied and how cells repair their DNA
origins of replication- site of Chromosomal DNA replication, short stretches of DNA
proteins that initiate DNA replication recognize this sequence, separating two strands and opening a replication " bubble". replication proceeds in both directions until entire molecule is copied.
at the end of each replication bubble is the REPLICATION FORK- y shaped regions where parental strands of DNA are bring unwound.
Helicases- enzymes that untwist the double helix at the replication forks, separating two parental stands and making them templates strands
single strand proteins bind to unpaired dna strands, keeping them from re-pairing
Topoisomeras-enzyme that helps relieve the strain by breaking, swiveling, and rejoining strands
a Primer- initial nucleotide chain that is a short stretch of RNA, synthesized by the enzyme -primase. starts a RNA chain with a single RNA nucleotide and adds RNA nucleotide one at a time, using the parental DNA as template.-->completed primer, usually 5-10 nucleotide,is base paired to the template strand, starting from the 3' end of RNA primer.
enzyme called DNA ploymerases catalyze the synthesis of new DNA, ading nucleotids to the end of an already existing chain.
Findings of DNA evidence
James Watson figures that DNA was composed of a helix with two strands with nitrogenous bases around it, called a double helix
conformed to char gaffs rules of base equivalencies, sugar phosphate backbones were outside the DNA molecule. negative charged phosphate groups faces aqueous surroundings, while hydrophobic nitrogenous bases were hidden in the interior.
two sugar phosphate backbones are anti parallel, running in opposite directions
adenine can form two bonds with with thymine and only thymine,guanine forms three hydrogen bonds with cytosine and only cytosine, A-T, G-C
the DNA of any organism, amount A=T,G=C
more evidence from biologist erwin chargaff proved that proved the nitrogenous base adenine was present in DNA, making it a prime candidate for genetic material
created two rules, "chargaffs rules"DNA base composition varies between species, and for each species, percentages of both A and T bases are roughly equal, and G and C bases are roughly equal as well.
Herchel and Chase conducted studies on a bacteriophage that infected E coli. founc that theDNA inside the cell played a role during infection process that the DNA injected by the phage must be the molecule carrying genetic information that makes cells produce new copies.,
roved evidence that nucleic acids, rather than proteins hereditary material
conservative model.-two parental strands reassociate, acting as new templates
semi conservative model- model of DNA replication, two daughter molecules will have one old strand, from the parental molecule, and a new one is made
dispersion model- each strand of both daughter molecules contains a mixture of old and newly synthesized DNA
leading strand- DNA strand replicating in the 5'-3' direction, continuously adding nucleotides as the fork progresses
lagging strand- DNA strand elongating away from the replication fork. it is synthesized discontinually in segments called - okazaki fragments
DNA ligase joins sugar phosphate backbones of all okazaki fragments into a continuous DNA strand
a chromosome sonsists of a DNA molecule packed together with proteins.
each eukaryotic chromosome contains a single linear DNA double helix, with a realativly large amount of DNA compared to its length (1.5 x 10*8).
in the cells, eukaryotic DNA is combined with a large amount of protein, in a complex called the chromatin.
proofreading and repairing DNA
errors in a complete DNA molecule amount to only one in every 10 billion nucleotide. DNA polymerases proofread every nucleotide against its template when its covalently bonded to the growing strand, when finding an incorrectly paired nucleotide, it is removed during synthesized
mismatched nucleotides sometimes evade proofreading from a DNA polymerase, called a mismatch pair.
nuclease- enzyme that cuts out damaged strains of DNA, and fills tha gap with nucleotide. enzymes involved infilling these gaps are DNA polymerase andDNA ligase. one repair system is called nucleotide excision repair
an example of this is DNA repair enzymes in our skin cells that repair genetic damage from UV rays.by thymine dimer caused by UV radiation, would otherwise distort the DNA molecule.
telomers- nucleotide sequences at the end of chromosomal DNA molecules, protects chromosomes from being eroded away at the end of succesive rounds of DNA
two functions of telomeres- first,specific proteins prevent teh staggered ends of daughter molecules from activating the cells system for monitoring DNA damage( staggered ends can lead to cell cycle arrest or cell death). second, acts as a bufferzone that provides protection against an organisms gene shortening.