Chapter 16 - The Molecular Basis Of Inheritance Flashcards
Who performed an experiment using Streptococcus pneumonia that proved DNA could transform bacteria?
Frederick Griffith, in 1928
What were the 2 strains Griffith used?
- S strain - pathogenic
* R strain - non-pathogenic
What are bacteriophages?
“Bacteria-eaters” : viruses that only affect bacteria
Why are viruses simpler than cells?
They are DNA (or RNA) enclosed by a protective coat (protein)
What is a phage composed of?
- protein coat
* encapsulated DNA or RNA
Which phage infects E. coli?
T2
DNA
What did Hershey & Chase’s experiment consist of?
They used radioactive sulphur and phosphorus to trace the fates of protein and DNA of T2 phages that infected bacterial cells.
What results did Hershey and Chase obtain?
When proteins were labelled, radioactivity remained outside the cells. When DNA was labelled, radioactivity was found inside the cells. Bacterial cells with radioactive phage DNA released new phages with some radioactive phosphorus.
Conclusion- Phage DNA entered bacterial cells but phage proteins do not. Hershey & Chase concludes that DNA, not protein, functions as the genetic material of phage 2.
What is Chargaff’s rule?
Adenine => Thymine
Cytosine => Guanine
___ took an X-ray diffraction photo of DNA resulting in the deduction of a double-helical structure of DNA by ____ & ____
- Rosalind Franklin
- J. Watson
- F. Crick
How does the double strand assemble in DNA?
- 1 is assembled in 5’ to 3’
- the other runs anti-parallel, from 3’ to 5’
What links 2 bases of the nucleotide ?
Hydrogen bonds
How many HBs between A & T?
2
How many HBs between C & G?
3
True/False:
At higher temperatures, a species with 4 million G-C and 2 million A-T will live longer than a species with 2 million G-C and 4 million A-T
True
What serves as a template strand for DNA replication?
Each strand of the parental molecule (which abs 2 complementary strands of DNA)
What does DNA replication result in?
2 daughter DNA double strands that are identical.
The Meselson-Stahl experiment showed that DNA replication was ___. What does this mean?
Semiconservative
The parental molecule unwinds, and each strand serves as a template for the synthesis of a new strand according to base-pairing rules.
How many bands in the semiconservative model after :
- 1 replication
- 2 replications
- 1
- 2
Where does DNA replication begin?
At origins of replication (short stretches of DNA with specific sequence of nucleotides)
What is the difference between bacterial (prokaryotes) and eukaryotic DNA replication?
Eukaryotic chromosomes may have hundreds or even a few thousand replication origin (-> multiple replication bubbles)
Prokaryotes have a single origin.
How many phosphates are released during the incorporation of a nucleotide into a DNA strand?
2
The nucleoside tri phosphate is added to the __ end of a growing DNA strand.
3’
Which strand is synthesized in short Okazaki fragments, later joined by DNA ligase?
Lagging strand
Which strand is continuously synthesized by DNA pol 3
Leading strand
__ synthesized a short RNA primer
Primase
True/False
DNA polymerase a can add nucleotides only to the free 3’ end of a primer or growing DNA strand, never to the 5’ end.
True
In which direction does the new DNA stand elongate?
5’—-> 3’
Which strand is synthesized continuously?
Leading
How are Okazaki fragments joined together?
DNA ligase
The presence of ___, repetitive sequences at the ends of linear DNA molecules, postpones the erosion of genes.
Telomeres
80-90% cancer cells express high amounts of ___.
Telomerase
Short telomeres means that you ___
There is a gradual decline of __ cells when we age.
Age
Somatic
Less compact chromatin
Euchromatin
Highly condensed chromatin
Heterochromatin
Which chromatin is accessible for transcription of genes?
Euchromatin
What signals the chromatin to condense or loosen up?
Histone tails
