NAGE 2 Flashcards
What charge do histones have?
Positive charge. They interact closely with the negatively charged sugar phosphate backbone.
Around how many histones are DNA wrapped?
8
In order to open the DNA helix for DNA replication, which enzyme unravels the DNA?
Topoisomerase
Which end can DNA polymerase add nucleotides to?
The 3’ end
What are the requirements for DNA polymerase to work?
- Template strand
- Oligonucleotide primer
- Deoxynucleotide triphosphates (dNTPs)
How does DNA synthesis happen?
- DNA polymerase adds dNTPs to the 3’ end of DNA.
- DNA synthesis occurs in a 5’ to 3’ direction.
- Hydrolysis of triphosphate releases energy. Drives the process.
Free 3’ end required for DNA synthesis.
How is DNA synthesised in the lagging strand?
Discontinuous synthesis. DNA synthesised in short fragments called Okazaki fragments.
Explain the process of lagging strand DNA synthesis.
- DNA Primase (special RNA polymerase) synthesises short RNA fragment complementary to template strand. ( fragment removed later on)
- DNA polymerase adds nucleotides to 3’ end.
- Continues to synthesise Okazaki fragment until it reaches the end of the previous Okazaki fragment.
- RNA primer of previous fragment is removed and replaced by DNA.
- DNA ligase joins two adjacent fragments.
What is exonuclease activity?
Ability of enzyme to remove one nucleotide at a time from the end of the polynucleotide chain
Explain the process of joining Okazaki fragments.
- Ribonuclease removes RNA primer using 5’ to 3’ exonuclease activity.
- RNA replaced by DNA using repair DNA polymerase.
- DNA ligase joins two Okazaki fragments together.
What do Single Strand binding proteins do?
Prevents single stranded DNA from folding
What does the sliding clamp do?
Ensures DNA polymerase is in the correct place.
How is it ensured that DNA synthesis occurs in a coordinated manner?
Lagging strand forms a loop
How many origins of repli/cation do eukaryotes have
Multiple, as large linear DNA
What does each replication give?
Bi-directional replication forks.
