More biological molecules: DNA replication Flashcards
State why DNA replicates
To ensure each cell has a full amount of DNA
Outline the steps of semi-conservative replication
- DNA helicase breaks the hydrogen bonds between the complementary base pairs on the two polynucleotide DNA strand - making the helix unwind to form two single stands (like a zip)
- Each original strand acts as a template for a new strand to form
- Free floating DNA nucleotides become attracted to their complementary exposed bases (on the template strand)
*DNA polymerase catalyses the condensation reactions that join the nucleotides of the new strands together - Hydrogen bonds form between bases from the template and original strand
- MEANING each new DNA strand contains one strand from the original DNA molecule and one new strand
Describe the function of DNA helicase
DNA helicase catalyses the hydrolysis reactions between the hydrogen bonds that holds the the strands of DNA together - unwinding and separating the DNA
Describe the function of DNA polymerase
DNA polymerase catalyses the condensation reactions that join the adjacent free nucleotides of the new strands together
State how is DNA replicated
Through semi conservative replication
State what end of a DNA strand that the active site of DNA polymerase is complementary to
3’ of pentose sugar
State which two directions polynucleotide strands in a DNA can go
3’ to 5’
AND
5’ to 3’
State what direction DNA polymerase builds a new strand of polynucleotides in
5’ to 3’
What is the function of DNA primase
It catalyses the production of short RNA molecules used a primers, indicating where DNA polymerase should start synthesising a new polynucleotide chain
What is a leading strand in DNA replication
A new strand of DNA that is synthesized in the same direction that DNA helicase unwinds the two polynucleotide strands of a DNA molecule
What is a lagging strand in DNA replication
A new strand of DNA that is synthesized in the opposite direction that DNA helicase unwinds the two polynucleotide strands of a DNA molecule
What is the function of DNA ligase
DNA ligase facilitates the joining of Okazaki fragments together by condensation reactions by catalysing the formation of phosphodiester bonds on lagging strands
What are Okazaki fragments
Short sequences of DNA nucleotides synthesized on the lagging strand during DNA replication - later joined together by DNA ligase
What evidence validates the semi-conservative replication
Meselson and Stahl’s experiment
Describe the meaning of semi-conservative in terms of DNA replication
DNA replication that produces 2 copies, each containing one ORIGINAL and one NEW strand.
Compare conservative and semi-conservative replication
- Semi-conservative: Two copies each contain one original strand and one new strand
- Conservative: Two DNA copies are produced from one original DNA, which serves as a template. Out of these two, one is entirely new DNA, and the other is made of old DNA strands
Describe the meaning of conservative in terms of DNA replication
When two DNA copies are produced from one original DNA, which serves as a template. Out of these two, one is entirely new DNA, and the other is made of old DNA strands
Describe the procedure of the Meselson and Stahl experiment
- E. Coli were grown in heavy nitrogen (15N) This caused all the DNA to incorporate heavy nitrogen into their bases
- Heavy nitrogen DNA was more dense, so when it was spun in the centrifuge, it all accumulated at the bottom
- Then the cells were transferred to light nitrogen (14N) and allowed the cells to divide once (creating one new and one fused)
- DNA now has heavy and light nitrogen. When centrifuged, the DNA didn’t sink as far.
- The cells divides one more time in light N which caused 2 bands (one light and one fused)
Explain how the Meselson and Stahl experiment demonstrated semiconservative DNA replication
- Each DNA molecule separate and serves as a template for a synthesis of a new complementary strand
- So each daughter molecule comprises one “old” and one “new” strand.
