DNA Flashcards
What is the main structure of DNA?
It has 2 backbones organized from 5’ to 3’ and crossed nucleotides in the center held together by H-bonds, matched purines to pyrimidines (A-T(U)) and (C-G). Forms a helical shape.
How is DNA organized in Eukaryotes?
Histones wrap around the DNA double helix to form chromatids organized further into chromosomes.
What are histones?
They are positively charged proteins that work like cations.
How is DNA organized in prokaryotes?
It is circular and supercoiled on itself.
What are the five different mechanisms that affect the stability of the DNA structure?
1) Temperature, 2) Cations, 3) Base pairings, 4) Length, 5) Proteins
Increasing temperature causes denaturing/melting of the DNA helix. Why does it occur more slowly in C-G pairings?
C-G pairings have 3 H-bonds compared to the 2 H-bonds in A-T(U), so it takes more energy to break them apart. Thus, denaturing occurs more slowly in strands that have more C-G pairings.
Cations affect the stability of DNA structure. How?
They help stabilize the helix by reducing the charge of repulsion of the two stands.
How do base pairings affect the stability of DNA?
If bases are mismatched, the DNA helix will be destabilized.
Are shorter or longer DNA helixes more stable?
Longer helixes are more stable.
How do proteins stabilize the DNA helix?
Histones are added which work similarly to cations; reducing charge and repulsion of the DNA strands.
What does DNA replication do?
It copies the DNA structure and can repair damaged strands throughout the cell cycle.
When does DNA replication occur?
It occurs before the cell divides in S-Phase at origins of replication in the nucleus, mitochondria, chloroplasts and even in the lab in test tubes.
Why is DNA replication special in the mitochondria and chloroplasts?
It is not usually tied to cell division.
What are the two requirements for DNA replication to occur in the cell?
It must be coordinated with the cell cycle and the accuracy (fidelity) of replication must be high. It doesn’t want mistakes/mutations.
What are the seven important materials for the replication of DNA?
1) Helicase. 2) Single-Strand binding protein. 3) Topoisomerase. 4) Primase. 5) DNA polymerase III. 6) DNA polymerase I. 7) DNA ligase.
What does helicase do in DNA replication?
Helicase unwinds the parental double helix into its 2 respective strands.
What do the single-strand binding proteins do in DNA replication?
The SS binding proteins maintain the single-strandedness of unwound DNA left by the helicase.
What does topoisomerase do in DNA replication?
Topoisomerase prevents the overwinding of DNA helix before replication (keeps DNA in place before helicase unwinds).
What does primase do in DNA replication?
Primase synthesizes the RNA primer so production of the leading/lagging strands can commense.
What does DNA polymerase III do in DNA replication?
DNA polymerase III elongates the DNA by adding to the RNA primer, creating the leading/lagging strands with help from the sliding clamp which follows behind the DNA polymerase III.
What does DNA polymerase I do in DNA replication?
DNA polymerase I removes the RNA primer from the 5’ end and replaces the primer with DNA.
What does DNA ligase do in DNA replication?
DNA ligase joins the DNA strands together; leading to leading, lagging to lagging once DNA polymerase I has removed RNA primer.
How does DNA polymerase III/I correct errors?
As it moves along, creating DNA, it corrects mispairing before proceeding like a proof-reading function. Paired bases that do not fit to its active site and do not have the right geometry of AT(U)/CG pairs are fixed.
Why does DNA polymerase III/I need a end of DNA (RNA primer) to function properly?
It needs an end of a correctly paired nucleotide to scan for errors and build the correct paired corresponding strand.
