Topic 17: DNA Structure and Function Flashcards
Explain the properties of the genetic material.
Properties of Genetic Material:
Carries Information
Capable of Change
Transmissible from one cell or generation to the next.
Capable of being copied
Explain the transformation experiment of Griffith(1928) and how Avery, Macleod, and McCarty showed that DNA is responsible for Griffith results(1944)
The Griffith transformation experiment was done by taking pathogenic S cells and nonpathogenic R cells and injecting mice with each sample.
S cells caused the mice to die
R cells did no harm to mice: they survived
Then they mixed both Heat killed S cells and live R cells and injected the mice: They died
This proved that transformation occurred from R cells transforming into S cells to kill the mice.
Avery and Macleod experiment proved that DNA being present caused the transformation.
In their experiment they separated the mixture of Heat-killed S cells and live R cells and placed them into two seperate test tubes.
In one they added enzyme protease - degrades proteins
In the second they added enzyme DNAse - degrades DNA
As they injected the first sample they still died.
But when they added the second sample they survived meaning that when DNA is absent genetic transformation does not occur.
Explain the Hershey Chase experiment 1952 using bacteriophage T2 and be able to predict the results if other macromolecules (not DNA) were the genetic material.
In the Hershey Chase Experiment of 1952 proved that DNA was the genetic material.
They used bacteriophage T2 viruses and grew one sample with radio labeled sulfur and the second with radio labeled phosphate.
Then they infected the bacteria cells and centrifuged them. The cell fell to the bottom of the tube and the bacteriophage capsule at the top of the tube.
The one with radiolabeled phosphate was radioactive and continued making viruses meaning it was DNA presence.
The one with the radiolabeled sulfur was not radioactive and did not continue making viruses in the cell.
Explain Chargaff’s rule and apply them.
%A = %T %G=%C
Chargaff’s rule explains that the amount of purine adenine equals the amount of pyrimidine thymine
The amount of purine guanine equals the amount of pyrimidine cytosine.
%A=%T
%G=%C
Practice an Example
Describe the Watson and Crick (1953) model of DNA structure and explain the contributions of Chargaff and Franklin.
Watson and Crick (1953) model of DNA structure determined that it is a double-helix structure.
Chargaff helped by determining that adenine and thymine always pair together and guanine and cytosine always pair together.
A purine and pyrimidine always pair to each other.
Franklin helped this process as well because she determined that DNA was a double helix through her X-ray diffraction photo.
Explain how base pairs of DNA encodes information and how they suggest a mechanism for replication
Base pairs are bonded together through hydrogen bonds. One strand of DNA holds genetic information. When bonded together they are able to hold the other strands information and vice versa. Since we know that DNA is antiparallel from a 5’ phosphate end to a 3’ sugar end or 3’ sugar end to a 5’phosphate end.
Explain how DNA encodes information
DNA encodes information by the sequencing of the bases of DNA
Explain how DNA is packed into chromosomes and describe features of human chromosomes
DNA is wrapped around histones creating nucleosomes.
The nucleosomes are then packed together creating a chromatin fiber
Then their is further condensation of the chromatin
During mitosis we can get a duplicated chromosomes
Features of human chromosomes are
