DNA Replication Flashcards
What stage of the cell cycle does DNA replication occur in?
S (synthesis) stage.
Why are DNA molecules very large?
-Can carry a vast number of genes which are confined in a small number of DNA molecules.
-More likely that all information is passed on during cell division to all generations.
What two enzymes are involved in DNA replication.
-DNA helicase.
-DNA polymerase
What does DNA helicase do in DNA replication?
-Unwinds and unzips DNA so the bases are accessible.
-Breaks hydrogen bonds so there are two separate strands and running anti-parallel to each other.
What happens after DNA helicase and before DNA polymerase?
-The new DNA is built up from 4 nucleotides that are abundant in the nucleoplasm.
-The nucleotides are attracted and attach (with hydrogen bonds) to the template strands from the parent by complementary base pairings.
What does DNA polymerase do?
-Joins the nucleotides to each other through a series of condensation reactions with strong phosphodiester bonds forming the sugar-phosphate backbone of the new DNA strand.
How do the enzymes work in replication?
-Work in opposite directions as the two strands run anti-parallel to each other.
What is DNA made up of after both enzymes have been used?
-1 new strand of DNA and 1 old strand of DNA (from the parent).
-Then reforms the helical structure.
What is the conservative hypothesis?
1 new DNA molecule is made entirely of new material and the other would be all original material.
What is the semi-conservative hypothesis?
-Half new template, half old template.
What is the correct hypothesis scientists follow today?
Semi-conservative hypothesis.
Who discovered the semi-conservative hypothesis?
Meseles and Stahl in 1958.
How as the semi-conservative hypothesis discovered?
-All organic bases contain nitrogen.
-Nitrogen has two isotopes 14N and 15N.
-Bacteria will take nitrogen from surroundings into any new DNA they make.
-They grew bacteria in the 15N and grew for one generation and then transferred the cells into 14N and grew for another generation.
-Then two bands showed when the cells were separated out 1 for 14N on top and one for 15N on the bottom.
What is the role of the single-stranded DNA strands?
Act as a template strand.
What is the role of the DNA nucleotides?
Determine the order of bases.
