Chapter 13 Flashcards
What year was it known that chromosome consisted of DNA and proteins?
1920s
What crucial piece helped see the structure of Dna?
x -ray crystallography by rosalind franklin
results showed a spiral model}
DNA is a polymer of nucleotides:
deoxyribose, a phosphate group, and a nitrogen containing base
The bases:
Purines: Adenine and guanine
Pyrimidines: cytosine and thymine
Erwin Chargaff found what is 1950?
A=T
C=G
this is chargaffs rule
What is the dna structure?
Helical and antiparallel
what happened in 1953?
watson and crick established the general structure of DNA
What is the model of DNA?
double helix right handed antiparallel -outer edges of nitrogenous bases are exposed in the major and minor grooves - complementary base pairings
what is the direction of the strand determined by?
sugar - phosphate bonds
what is the function of DNA?
4 important functions:
- stores information
- susceptible to mutation
- precisely replicated
- expressed as a phenotype
What is the dna replication pattern?
semiconservative
what are the two steps of DNA replication?
- double helix is unwound, making two strands
2. new nucleotides are added to the new strand at the 3’ end and joined by phosphodiester linkages.
how is the sequence determined?
complementary base pairings
How does DNA replication begin?
with a short primer that is complementary to DNA template
What is the primer called?
Primase- it synthesizes DNA one nucleotide at a time
DNA polymerase III does what?
adds nucleotides to the 3’ end.
what is Dna polymers shaped like?
open right hand palm. It brings the active site and the substrates into contact.
what is the function of helicase?
uses energy from ATP hydrolysis to unzip the DNA
what do SSBs do?
keep strands from connecting back together
what is the replication fork?
the site where DNA unwinds to expose bases
where does the leading strand extend?
toward fork
where does lagging strand extend?
away from fork
what are okazaki fragments?
synthesis of the lagoon strands that occur in small discontinuous stretches
what three repair mechanism do cells have/
proofreading - as the DNA polymerase adds a nucleotide to a growing strand, it has a proofreading function - it the bases are paired incorrect, the nucleotide is removed
mismatch repair
excision repair
what does ligase do?
fills in the gaps at the end in the lagging strand.
what does polymerase III do?
adds nucleotides and extends
what does polymerase I do?
replaced primer with DNA
