Chapter 16 BIO
Make a detailed list of the steps that occur in the synthesis of a new strand of DNA.
1. Helicase unwinds double helix. 2. SSBP stabilizes. 3. Leading strand synthesizes in 5' to 3' direction by DNA pol III. 4. Primase synthesizes RNA primer for okazaki fragments. 5. DNA nucleotides added to RNA primer on okazaki fragments. 6. DNA pol I removes RNA primar and adds DNA. 7. DNA ligase bonds okazaki fragments.
What enzyme untwists and separates strands?
Helicases
Distinguish between heterochromatin and eucromatin.
In heterochromatin it is more compact and in irregular clumps. In euchromatin, it is more dispersed and can be expressed.
Distinguish between the leading and lagging strands.
Leading strand continuously elongates. Laggin strand has to wait a little, then work backwords because DNA nucleotides can only be added in the 5' to 3' direction and because the DNA is antiparrelel.
How was "Heave" DNA created in Meselson and Stahl's experiment?
Marking with N15.
Who performed the experiments that elucidated the correct mechanism of DNA replication?
Meselson and Stahl
What enzyme holds DNA strands apart?
Single stranded binding protein
Define the origins of replication.
Site where replication of DNA begins and consists of specific nucleotide sequences.
What are the components of the backbone?
Sugar and phosphate
How did Watson and Crick's model explain the basis for Chargaff's rules?
The model showed that for the DNA double helix structure to work, A must pair with T, and C must pair with G.
How does a bacteriophage destroy a bacteria cell?
The phage attaches to the cell, inserts its DNA, takes over cellular machinery, and goes through lytic cycle to break / destroy the cell.
What does antiparallel mean?
The subunits of the sugar-phosphate backbones run in opposite directions of each other.
Explain the base pairing rule. A forms 2 hydrogen bonds with T. G forms 3 hydrogen bonds with C. Pyrimodines always bind to purines.
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What is the distance between nucleotides?
.34nm
What are Chargaff's rules?
A pairs with T, C pairs with G. He arrived at this when he noticed specific ratios in same species.
What is the role of DNA polymerase in proofreading and repair?
Adds new nucleotides.
Explain Oswal Avery's approach.
Avery extracted cellular contents and those cells with DNA extracted did not transform.
What enzyme removes RNA primer and replaces with DNA
DNA pol I
What enzyme adds DNA nucleotides to new strands of DNA?
DNA pol III
How did Hershey and Chase label viral DNA and viral protein so that they could be distinguished?
DNA was labeled with radioactive phosphorus. Proteins were labeled with radioactive sulfer. DNA did not have sulfer, and the majority of the phosphorus in the phage was in the DNA.
What is the semiconservative model?
Double strands separate and new DNA forms from old strands as templates
Describe by which Hershey and Chase established that only the DNA of a phage enters and E. coli cell.
E. coli were infected by the phage, and there was more radioactive phosphorus that entered. They concluded that DNA carried the genetic information to produce DNA and proteins.
What is the role of nuclease in proofreading and repair?
Exices damaged area of DNA
What is the distance across a DNA molecule?
1nm
What is the distance between respective turns?
3.4nm
Explain what is meant by 5' to 3'
5' refers to the 5' carbon which is close to the phosphate group. 3' refers to the carbon at -OH group.
What is the direction of synthesis of the new strand?
5'to 3'
Define transformation.
Change in genotype and phenotype due to assimilation of external DNA.
What is a thymine dimer? How might it occur? How is it repaired?
Covalent linking of thymine is a thymine dimer. It is repaired by nucleotide exicion repair. It can occur by exposure of Ultraviolet rays of the sun.
What did Oswald Avery determine to be the transforming factor?
DNA
What are the two chemical components of chromosomes?
DNA and proteins.
What enzyme joins DNA fragments together?
DNA ligase
List the three components of a nucleotide.
Nitrogenous base, sugar, phosphate group.
What are the components of the rungs?
Nitrogoneous base
What enzyme synthesizes RNA primer?
Primase
Why did researchers originally think that protein was the genetic material?
Proteins had specific functions with great heterogeneity.
Adenine
Purine, B
Guanine
Purine, B
Cytosine
Pyrimodine, B
Thymine
Pyrimodine, D
Uracil
Pyrimodine, R
Distinguish between the structure of pyrimidines and purines.
Pyrimodines have 1 organic ring, purines have 2 organic rings.
What are the role of Repair enzymes?
Repair genetic damage (like from UV light)
What is the role of Ligase in proofreading and repair?
Seals free ends of DNA
What are Okazaki fragments? How are they welded together?
Segments of the lagging strand synthesized discontinuously. DNA ligase welds them together
What was the purpose of Griffith's studies?
To see why mice with the dead virulent strain + live non virulent strain were still dying.
What enzyme relieves strain cause by unwinding?
Topoisomerase
Who built the first model of DNA and shared the 1962 Nobel Prize for discovery of its structure?
Watson and Crick.
What was the role of Rosalind Franklin in the discovery of the double helix?
X-Ray Crystolography.