DNA & MOLECULAR GENETICS Flashcards
1) Summarize the experiments performed by Griffith that demonstrated the phenomenon of transformation. Why were these experiments and those performed by Avery, McCarty and MacLeod important steps to showing that DNA carries the genetic information?
Griffith experiment that demonstrated transformation was he mixed living non-viral bacteria with heat inactivated viral bacteria. The mice that had the mixture died which demonstrated that non-viral one must have transformed from the viral one, so it transformed and became deadly to the mice. Avery McCarty and MacLeod experiments were Taking the heat killed s cells and treated it with something that destroys protein RNA or DNA. What they concluded from this was that once you kill the cells the DNA still remains which transformed nonvirulent into virulent. These showed that the DNA was carrying the information and then could also be transformed.
2) What were the experiments performed by Hershey and Chase that further demonstrated that DNA was the genetic material?
Hershey and Chase experiments were labeling proteins and DNA and used each to infect bacterial cells. They looked at what went into the cell and the result was that the DNA was moving into the cell, but the proteins were not. (ex. Phosphorus only in DNA moved into cell sulfur only present on proteins was not moved into the cell.)
3) What are the three basic chemical components of DNA? What are the purines and pyrimidines?
Phosphate, Sugar, and Nitrogenous base is the three basic components of DNA. A purine has two rings, and a pyrimidine has one ring. AG are purine TC are pyrimidine. DNA double helix is one purine with one pyrimidine which is why AT and GC are base pairs.
4) What were Chargaff’s rules about the chemical content of DNA?
Chargaff’s law is AT and GC are pairs and they are a 1:1 ratio to each other
5) What information about the structure of DNA was provided by Rosalind Franklin’s X-ray crystallography studies?
It showed that DNA is a double helix and that there are 10 steps per repeat
6) What are the details of Watson & Cricks model of DNA structure? How does this model integrate both Chargaff’s and Franklin’s data?
Watson and Cricks model of DNA structure is that AT GC are base pairs and that it’s in a double helix with AT connected across and GC connected across which integrates both Chargaff and franklins’ data
7) What does it mean when we say that the two sugar-phosphate backbones are antiparallel?
One is going 5-3 prime and the other is going the other direction 5-3 prime, but they are going opposite directions, so they are antiparallel backbones. Leading strands technically going 3-5 prime.
8) How does the structure proposed by Watson & Crick suggest a simple mechanism for DNA replication?
They concluded that base pairing of AT GC and constant diameter = base pairing and that a purine + pyrimidine are same length which support the double helix with the same width. Their simple mechanism for DNA replication was suggested to be that the two strands unwound and separated. Then each one acted as a template for a new DNA strand and dictated the new bases on daughter strands.
9) Describe the experiments performed by Meselson and Stahl that provided evidence for the mechanism that Watson and Crick’s suggested for DNA replication? What were the results of the experiment and how were they interpreted?
In order to test if Watson and cricks hypothesis is correct, they needed to be able to specifically label the new DNA being made then detect it. They used two relatively new technologies nucleotides with different isotopes of nitrogen and cesium-chloride density centrifugation to separate out the DNA molecules based on their density. Tested semiconservative replication, conservative replication, and dispersive replication. The results were that after one round of replication it was not conservative, after two rounds it could be concluded it is semiconservative replication
10) What was Arthur Kornberg’s contribution to our understanding of DNA replication?
Characterized DNA polymerase - a protein which is capable of catalyzing DNA synthesis. He found that it requires a primer and is only capable of catalyzing the addition of nts in a 5 to 3 prime direction.
11) When observed at a macroscopic level, how does DNA replication appear to spread through a chromosome?
DNA replication appears to start at a origin point and proceed bidirectionally all the way around the circular chromosome.
12) What is the role of DNA polymerase III, helicase, topoisomerase, primase, RNAse, DNA polymerase I and DNA ligase during the process of DNA replication?
DNA polymerase III synthesizes the leading and lagging strands. Helicase opens up the DNA strands and also it responsible for unwinding the strands. Topoisomerase has the role of providing relieve in the DNA ahead of the replication fork caused by the untwisting of the double helix. RNAse are enzymes that help remove primers. DNA polymerase I remove RNA primers and fill gaps of Okazaki fragments. Ligase connects the fragments together after the DNA is filled in.
13) Why is it not possible to have continuous synthesis of both DNA strands?
Because replication starts at the origin and goes bidirectionally one strand will be able to continuously replicate antiparallel to the parent strand while the other would be going the same direction and could not be antiparallel which is why Okazaki fragments are necessary for these lagging strands since the copied strand must be going antiparralel to the original strand.
14) Describe the process of DNA replication on the leading strand and on the lagging strand.
On the leading strand, DNA is replicated on original strand but 5-3 on this strand. The double helix opens up, primer is laid down and DNA polymerase starts to add nucleotides. This is then continued down the strand in 5-3 direction synthesizing leading strand. Lagging strand is replicated in short Okazaki fragments that are each produced in the 5 to 3 directions but are initiated further and further from origin. Multiple primers are placed in order for the lagging strand to be synthesized. After it is added all nucleotides, the primers are removed by RNAse and Polymerase I, and Polymerase I fills in the gaps and ligase connect these gaps completing synthesis of the lagging strand this is all “discontinuous synthesis”.
15) Using your answer to #14, Describe what the DNA replication process of the DNA strands looks like in a growing replication bubble.
In a growing replication bubble the leading strand goes 5-3 prime and then polymerase follows the helicase when it opens up. Lagging strand is discontinuous 5-3 prime but the difference is when helicase goes to right helicase going to the left
