T11 Flashcards
What does it mean to
be semi-conservative?
The two original strands of DNA split en each is used to create a new complementary DNA strand with which it will then form dsDNA (daughter molecules)
Simply put, what are the four steps in DNA Replication ?
- Separation of the strands
- RNA primer
- Use both DNA strands as templates to create the new strand.
- Replace RNA primer blocks and end
What enzymes are involved in each step of DNA replication (in order).
- Helicase (unzips) and Topoisomerase (twists the strands to relive tension, allowing for Helicase to separate them)
- Primase
- DNA polymerase
- Nuclease and DNA
Where does replication start ?
Origin of replication
What does the origin of replication do to the DNA strands?
It creates multiple bubbles of replication.
What is replication fork and thanks to what can it occur?
It is the area where DNA replication can take place. It happens thanks to the origins of replication which kick start this process.
What is reannealing ?
When DNA strands attach to each other through H-bonds.
What keeps the sDNA strands from reannealing ?
Single-strand binding protein (SSBP)
Explain the role of Helicase.
Separate the DNA strand.
Explain the role of Topoisomerase.
It removes the tension in the DNA strand by breaking phosphodiester bonds, swivelling around it and rejoining the DNA after relieving tension.
In what direction do we build DNA ?
From 5’ to 3’
Explain the function of DNA polymerase.
It copies DNA.
Why do we need primase ?
DNA polymerase cannot build a new strand from ssDNA, it can only a monomers to the 3’ end of a strand. Therefore, we need a ‘block’ (monomer) to start from.
Explain the function of primase.
It attaches to the ssDNA and creates a short primer of RNA on each strand in a 5’ to 3’ direction, moving in a 3’ to 5’ direction.
Why does primase move in a 3’ to 5’ direction ?
Because DNA polymerase cannot build going that way, it needs to go from an RNA primer to the 3’ end. And so, to have the new ssDNA reach and match all the way to the end of 5’ end of the old DNA strand, we need to build bit by bit (still from 5’ to 3’) with RNA primer going all the way to the 5’ end.
What does DNA polymerase produce ?
A complementary strand of DNA.
In which direction does it build? in which direction does it move?
Moves: Reading way –> 3’ to 5’
Builds : Inverse –> 5’ to 3’
Why do we move from 3’ to 5’ if we are building in the reverse order.
The strands are ‘opposites’ to each other, in the sense that they are complementary. Therefore, the 5’ end of the old strand needs to be matched with the 3’ end of the new strand.
Explain leading and lagging strand.
We are building in the same direction we are moving (leading)–> I build from 5 to 3 and move from 3 to 5.
We are building in the opposite direction we are moving (lagging, because we go bit by bit to build)
Explain the role nuclease.
Cuts DNA and RNA. Basically cuts the little part at the end where we couldn’t build from (3’)
Explain the role of DNA ligase.
Binds the DNA with phosphodiester bonds.
At what steps is DNA polymerase needed? If more than one, explain.
Step 3 and 4 (in 4, we remove the primers and have to fill those empty spots with DNA).
T or F : More errors are found in the completed, replicated DNA molecule than in the initial pairing.
F: During replication, DNA polymerase and other proteins ‘proof-read’ the nucleotide sequence being copied.
What happens if the DNA being copied is faulty?
Nuclease cuts the bonds and DNA polymerase replace it with ligase reforming the phosphodiester bonds.
