2b. DNA REPLICATION Flashcards
Describe what the 3’ end of a single DNA strand is
The 3′ end (three prime end) of a strand is so named due to it terminating at the hydroxyl group of the third carbon on the pentose sugar.
Describe what the 5’ end of a single DNA strand is
The 5’ end (five prime end) of the DNA is the one with the terminal phosphate group on the 5’ carbon of the pentose sugar.
In a DNA molecule, the two DNA strands are antiparallel. Describe what this means.
One DNA strand goes in the 3’ to 5’ direction and the other strand goes in the 5’ to 3’ direction. (Run next to each other but in different directions)
Describe why DNA replication is ‘semi-conservative’
One strand is old, and one strand is new
During which other cellular process does DNA replication occur?
Mitosis
Name the two enzymes involved in DNA replication
DNA Helicase and DNA Polymerase
Describe the function of DNA Helicase
To unzip the DNA strands by catalysing the breaking of hydrogen bonds between complementary base pairs bases
Describe the function of DNA Polymerase
It catalyses the formation of phosphodiester bonds between adjacent nucleotides, forming the new strands
Which strands are continuous and discontinuous replication carried out on?
Continuous replication occurs on the leading strand. Discontinuous replication occurs on the lagging strand.
Why can continuous replication be carried out on the leading strand?
DNA polymerase has a specific shape and therefore can only bind at the 3’ end. The leading strand has an exposed 3’ end.
In continuous replication, what direction does DNA Polymerase run, and in what direction are new nucleotides added?
DNA Polymerase runs 3’ to 5’. The new nucleotides are added from 5’ to 3’
Why does discontinuous replication have to be carried out on the lagging strand?
DNA polymerase has a specific shape and can therefore only bind at the 3’ end. The lagging strand has an exposed 5’ end.
What are Okazaki fragments?
The short fragments/sequences of DNA formed on the lagging strand in discontinuous replication
What happens to Okazaki fragments at the end of DNA replication?
Okazaki fragments are joined together with an enzyme to create a complete strand
Recall the two nitrogen isotopes that can be used to form nitrogenous bases. Which is heavy and which is light?
Nitrogen -14 (light) and Nitrogen-15 (heavy)
What do we call the original DNA molecule?
Generation 0
Generation 0 was produced in N14. Generation 1 was produced in N15. Compare the densities of Gen 0 and Gen 1.
Generation 1 will have a higher density compared to Generation 0
Generation 0 was produced in N15. Generation 1 was produced in N14. Compare the densities of Gen 0 and Gen 1.
Generation 1 will have a lower density compared to Generation 0
How will you know from the centrifuge tube that the molecules have different densities?
The more dense molecules are lower down and the less dense molecules are higher up
What two things are current scientific models based on?
Experimental evidence/observations and current knowledge
What will lead scientists to accept or reject an experimental hypothesis?
Using evidence from repeatable experiments
What will lead scientists to change a scientific model or theory?
New evidence that disproves old theories and is repeatable.
Why were proteins favoured over DNA to be the molecule of inheritance?
Scientists thought that DNA was too simple and has too few components to be the molecule of inheritance. Proteins are more complex.
Name the two strains of streptococcus pneumoniae that were used by Griffith in his experiment. Describe if they were virulent or avirulent.
Smooth (virulent) and rough (avirulent)
Describe the surprising result in Griffith’s experiment with mice and streptococcus pneumoniae
When mice were injected with a heat-killed version of the smooth strain and the rough strain together, they still died.
What did Griffith name the discovery from his experiment with streptococcus pneumoniae?
The transforming principle
What is a bacteriophage? What are they made from?
Viruses that infect bacteria. They are made from a protein coat containing DNA
Describe which isotopes Hershey and Chase radiolabelled their bacteriophages with.
P32 and S35
In a centrifuge tube, what do you call the solid at the bottom, and the liquid?
solid = pellet
liquid = supernatant
In Hershey & Chase’s experiment, where were the radiolabelled proteins found?
Sulphur is found in the proteins, but not DNA so it was found in the supernatant
In Hershey & Chase’s experiment, where was the radiolabelled DNA found?
Phosphorus is found in DNA, but not protein so it was found in the pellet.
