Chapter Thirteen Flashcards
What is the importance of Rosalind Franklin?
Rosalind Franklin prepared crystallographs from DNA samples and this suggested a double helix with 10 nucleotides per turn
suggested that the sugar phosphate backbone must be on the outside
What was the importance of Watson and Crick?
Used model building (based on Franklin’s idea) and physical and chemical evidence to solve the DNA structure
What are the four features of DNA structure?
- DNA is a double stranded helix
- DNA is right handed
- Strands of DNA run antiparallel
- The outer edges of the bases are exposed in major and minor grooves
What is DNA made of?
DNA is made of four different nucleotides (deoxyribose, phosphate, and nitrogenous base) that are connected by phosphodiester linkages
Where is DNA found in the cell?
Usually found in the nucleus, but can be found in organelles like the chloroplast and the mitochondria
How are strands of DNA held together?
by hydrogen bonds and vanderwal’s forces
What are the purines?
they are nitrogenous bases that are two rings fused and are Adenine and Guanine
What are the pyrimidines?
they are single ringed nitrogenous bases and they include Cytosine and Thymine (and in RNA also Uracil)
What nitrogenous bases pair with each other, DNA/DNA?
the A’s and T’s go together
and the C’s and G’s go together
What nucleotides pair with each other DNA/RNA?
the C’s and the G’s still go together
but the A’s now go with the U’s
What is Chargaff’s rule?
in all DNA the amount of purines is the same as the amount of pyrimidines
What is DNA replication?
It is the process of making two identical DNA molecules originated from the original two strands
What is meant by semi conservative?
Semi conservative is a mechanism by which DNA is replicated
Each parent strand is a template, and the new molecules receive one old molecule
this conserves one old template strand
What are the two main steps of DNA replication?
- the double helix is unwound, making two template strands
- new nucleotides form complimentary base pairs with the template DNA strand and are linked by phosphodiester linkages
When does replication start?
when the pre-replication complex of proteins bind to the origin of replication
What is the origin of replication?
the ori or specific region of DNA that indicates the starting point of replication
What are replication forks?
The two points at which the two strands of DNA are separated to allow replication of each strand
V shape when the zipper starts moving outward
What is DNA helicase?
it is the enzyme that unzips the original strand into template strands and forms the replication fork
uses energy from ATP hydrolysis
What are the single stranded binding proteins?
they work with the DNA helicase to keep the separate strands from folding back
What does primase do?
it is an enzyme that synthesizes the primer
What are primers?
the primer is a short starter strand, usually RNA, that is complementary to the DNA template so the polymerase can grab onto it
What is DNA polymerase
it is the enzyme that adds nucleotides to the template strand at the three prime end of the template strand and is shaped like a right-handed palm
it can only add nucleotides in the five prime to three prime direction on the new strand
What is the leading strand?
DNA polymerase can only add nucleotides in the 5 prime to 3 prime direction
So the leading edge is at an advantage because they get to add nucleotides in the direction that the helicase is going continuously
What is the lagging strand?
Again the DNA polymerase can only add nucleotides in the 5 to 3 direction
the lagging edge is at a disadvantage because the nucleotides are added in the opposite direction of the helicase’s movement, so it becomes discontinuous
this results in the formation of Okazaki fragments
What are Okazaki fragments?
they are small discontinuous stretches of new DNA, which each require its own primer
What is DNA ligase?
it is the enzyme that catalyzes the anabolic reaction of the phosphodiester linkages on the lagging edge in order for the new strand to be complete
What are the three DNA repair mechanisms?
- Proofreading: DNA polymerase recognizes mismatched pairs and removes incorrectly paired bases
